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'[EE] Using a high current MOSFET as a variable res'
2011\04\14@105858 by V G

picon face
Hey all, instead of using a wire wound resistor for testing battery drain,
I'm thinking of using a heat sink bound MOSFET and control the drain-source
current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance
between drain and source. Is this possible

2011\04\14@111652 by Sergey Dryga

flavicon
face
V G <x.solarwind.x <at> gmail.com> writes:

>
> Hey all, instead of using a wire wound resistor for testing battery drain,
> I'm thinking of using a heat sink bound MOSFET and control the drain-source
> current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance
> between drain and source. Is this possible?

It is possible.  I have not done it myself, but there schematics on the web to
do just that.  Usually one is more interested in not just a resistance, but
drain current for the battery discharge.  You can put a small current sense
resistor between source and ground and control g-s voltage to achieve desired
current draw.
Sergey Dryga

http://beaglerobotics.com

2011\04\14@112543 by Sean Breheny

face picon face
It is possible, but it will be difficult to get much power-handling
ability this way. A TO-220 type package will be limited to around 20
Watts absolute maximum continuous dissipation regardless of how big
the heatsink is.

One way I've done this before is to have two power resistors: one
which is the minimum resistance (call this Rmin) desired and a second
which is the difference between the max resistance and the min
resistance (call thisRb). I put these two resistors in series and put
a transistor (FET or BJT) across resistor B. By using this transistor
to shunt current around resistor Rb, to a varying degree, I could vary
the effective resistance from the min to the max and the maximum power
the transistor needs to handle is around one quarter of what it would
need to handle if it were the only dissipating element.

Another way is to use a switching regulator. Let's say your battery
voltage ranges from 10 to 20V. If you made a buck converter which took
10 to 20V in and gave, say, 2 to 8V out, then you could put a fixed
resistor on the output of the converter and vary the voltage setpoint
to vary the power drawn from the battery.

Sean


On Thu, Apr 14, 2011 at 10:58 AM, V G <spam_OUTx.solarwind.xTakeThisOuTspamgmail.com> wrote:
> Hey all, instead of using a wire wound resistor for testing battery drain,
> I'm thinking of using a heat sink bound MOSFET and control the drain-source
> current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance
> between drain and source. Is this possible?
>

2011\04\14@113354 by Michael Watterson

face picon face
On 14/04/2011 15:58, V G wrote:
> Hey all, instead of using a wire wound resistor for testing battery drain,
> I'm thinking of using a heat sink bound MOSFET and control the drain-source
> current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance
> between drain and source. Is this possible?

yes, but measure the source current with a 0.01 to 0.5 Ohm resistor as the "resistance" will increase as it warms. This is why FETs can be paralleled, unlike bipolar which give INCREASE in current with temperature.

2011\04\14@120459 by Harold Hallikainen

face
flavicon
face

{Quote hidden}

This reminds me of a technique I used in a battery monitor for an electric
vehicle. We wanted to prevent overcharging of some batteries in the series
string, so if the voltage went above some threshhold, we'd increase the
duty cycle on a "bypass resistor." The bypass resistor went from the
battery positive to the drain of an N channel FET. The FET was pulse width
modulated to give the desired battery voltage (increased duty cycle
increased current, decreasing the battery voltage).

In the "programmable load" situation, a 1 ohm resistor could be made to
look like anything between 1 ohm and infinity by varying the duty cycle of
when the resistor is in circuit. The instantaneous current, of course,
will be higher than the average current, but if the instantaneous current
is not excessive, this may be a way of providing a variable load to the
battery.

Harold


-- FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available

2011\04\14@121853 by Spehro Pefhany

picon face
At 10:58 AM 14/04/2011, you wrote:
>Hey all, instead of using a wire wound resistor for testing battery drain,
>I'm thinking of using a heat sink bound MOSFET and control the drain-source
>current with the gate. I'm looking to get around a 0.5 - 2 ohm resistance
>between drain and source. Is this possible?

Sure. That's how many electronic loads work. You can actively control
the gate voltage to give constant current, constant wattage or
constant resistance if you like. Having an electronic load in a box
is a great convenience if you do a lot of work with batteries and
supplies. Not generally absolutely necessary, but a good use of $$ IMHO.

Watch the power dissipation and safe operating area of the transistor..
anecdotally.. they don't always do what you might hope from reading the
data sheet- they're not typically used in linear mode. If you have
a minimum resistance that you'd ever need in mind, putting most of
that external to the MOSFET(s) will make things easier. A resistor
can run a lot hotter than a semiconductor, so it's easier to get
rid of the heat. 0.5 ohm on a 12V battery is almost 300W -- so maybe
half a dozen TO-247 or TO-220 units if no external resistor is used.

Of course you'll want a fuse too, as semis generally fail shorted,
and shorting batteries can be expensive and unpleasant.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\14@131248 by Olin Lathrop

face picon face
V G wrote:
> Hey all, instead of using a wire wound resistor for testing battery
> drain, I'm thinking of using a heat sink bound MOSFET and control the
> drain-source current with the gate. I'm looking to get around a 0.5 -
> 2 ohm resistance between drain and source. Is this possible?

Sure it's possible, but will require active control and feedback else you'll
have no idea what is actually going on.  The easiest is probably a low side
current sense resistor with a opamp driving the gate to keep the voltage
accross the resistor at the desired level.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000

2011\04\14@133933 by Spehro Pefhany

picon face
At 01:13 PM 14/04/2011, you wrote:
>V G wrote:
> > Hey all, instead of using a wire wound resistor for testing battery
> > drain, I'm thinking of using a heat sink bound MOSFET and control the
> > drain-source current with the gate. I'm looking to get around a 0.5 -
> > 2 ohm resistance between drain and source. Is this possible?
>
>Sure it's possible, but will require active control and feedback else you'll
>have no idea what is actually going on.  The easiest is probably a low side
>current sense resistor with a opamp driving the gate to keep the voltage
>accross the resistor at the desired level.

If he wants to simulate a resistor rather than a constant current sink
he'll need to adjust the voltage across the sense resistor in proportion
to the battery voltage. Eg. control Vs = Vbat/k where k is a constant

I = Vs/Rsense
Req = Vbat/I = Vbat*Rsense/Vs = Vbat*Rsense*k/Vbat
     = Rsense * k

Since the battery voltage shouldn't be changing very fast with a
steady load, a PIC could be used to do this rather than an analog
multiplier. Perhaps by deriving the ADC reference from the battery..
So, an inner analog loop that sinks a current proportional to input
voltage and an outer digital loop that commands that current.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speffspamKILLspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\14@134133 by Oli Glaser

flavicon
face
On 14/04/2011 18:13, Olin Lathrop wrote:
> V G wrote:
>> Hey all, instead of using a wire wound resistor for testing battery
>> drain, I'm thinking of using a heat sink bound MOSFET and control the
>> drain-source current with the gate. I'm looking to get around a 0.5 -
>> 2 ohm resistance between drain and source. Is this possible?
> Sure it's possible, but will require active control and feedback else you'll
> have no idea what is actually going on.  The easiest is probably a low side
> current sense resistor with a opamp driving the gate to keep the voltage
> accross the resistor at the desired level.
>

Plenty of examples out there for this type of circuit - there is a reasonable video on making the above on EEVBlog:
http://bit.ly/dmxNQ5
Do remember that (as Spehro mentioned) many MOSFETs are not designed for linear mode - check the datasheet and look at the Safe Operating Area graph - it should have various pulse widths down to (hopefully) DC, pick one that has the curves you need for DC, preferably with ample headroom. Also remember to calculate thermal resistance correctly and use the right heatsink - as it happens there is another tutorial on EEVBlog about this:
http://bit.ly/b3EOck

2011\04\14@135216 by RussellMc

face picon face
> This reminds me of a technique I used in a battery monitor for an electric
> vehicle. We wanted to prevent overcharging of some batteries in the series
> string, so if the voltage went above some threshhold, we'd increase the
> duty cycle on a "bypass resistor." The bypass resistor went from the
> battery positive to the drain of an N channel FET. The FET was pulse width
> modulated to give the desired battery voltage (increased duty cycle
> increased current, decreasing the battery voltage).

> In the "programmable load" situation, a 1 ohm resistor could be made to
> look like anything between 1 ohm and infinity by varying the duty cycle of
> when the resistor is in circuit. The instantaneous current, of course,
> will be higher than the average current, but if the instantaneous current
> is not excessive, this may be a way of providing a variable load to the
> battery.

This works well, provided that your supply can tolerate the high
current/no current approximation to a constant value resistor.
I used this for an exercise cycle load with dissipation varying
between 0 - 500 Watts depending on load and speed.

If you add a series inductor and a catch diode this becomes a buck
regulator based variable resistor.
Sounds remarkably like my Peltier supply solution :-).
Inductor must be suitably dimensioned to avoid saturation. Air core
may be a good idea for  large currents.
Low (and not so low) frequency radio transmitters can happen this way :-).


                   Russell


.

2011\04\14@140142 by Spehro Pefhany

picon face
At 01:41 PM 14/04/2011, you wrote:
>..
>Also remember to calculate thermal resistance correctly and use the
>right heatsink - as it happens there is another tutorial on EEVBlog
>about this:

Hopefully Dave will be able to continue with his popular vblog
despite the (over) sea-changes at his erstwhile employer.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam.....interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\14@143456 by Mark Rages

face picon face
On Thu, Apr 14, 2011 at 1:05 PM, Spehro Pefhany <EraseMEspeffspam_OUTspamTakeThisOuTinterlog.com> wrote:
> At 01:41 PM 14/04/2011, you wrote:
>>..
>>Also remember to calculate thermal resistance correctly and use the
>>right heatsink - as it happens there is another tutorial on EEVBlog
>>about this:
>
> Hopefully Dave will be able to continue with his popular vblog
> despite the (over) sea-changes at his erstwhile employer.

In fact, he is a full-time blogger now, thanks to said changes.

Regards,
Mark
markrages@gmail
-- Mark Rages, Engineer
Midwest Telecine LLC
markragesspamspam_OUTmidwesttelecine.co

2011\04\14@153915 by Fred Langley

flavicon
face

This is slightly off the original question, but what is better for this sort
of application, a MOSFET, or a bipolar transistor. Since as mentioned, FET's
are designed more for fast switching and often to stay out of the linear
area, would a big transistor be a better choice since they were probably
designed to be in the linear region of operation? I have a bag full of TO-3
cased units from old linear power supplies for instance. Would they be
better?

2011\04\14@160917 by Spehro Pefhany

picon face
At 03:39 PM 14/04/2011, you wrote:

>This is slightly off the original question, but what is better for this sort
>of application, a MOSFET, or a bipolar transistor. Since as mentioned, FET's
>are designed more for fast switching and often to stay out of the linear
>area, would a big transistor be a better choice since they were probably
>designed to be in the linear region of operation? I have a bag full of TO-3
>cased units from old linear power supplies for instance. Would they be
>better?

Might well be.. you can probably get away with a couple devices
in parallel (with some care to make sure they share nicely- I'd
tend to control them individually with (say) 1/2 the current each.
You can reliably run real (metal) TO3s at least 25'C-50'C hotter
than most plastic packages.

One approach would be to make a sort of hybrid darlington with a
smallish n-channel MOSFET and an PNP BJT, which means that the
collector/drain current of the hybrid device equals almost exactly
the emitter current.

>Best regards.

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
@spam@speffKILLspamspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\14@161042 by V G

picon face
On Thu, Apr 14, 2011 at 3:39 PM, Fred Langley <KILLspampiclistKILLspamspamplatinum.ca> wrote:

>
> This is slightly off the original question, but what is better for this
> sort
> of application, a MOSFET, or a bipolar transistor. Since as mentioned,
> FET's
> are designed more for fast switching and often to stay out of the linear
> area, would a big transistor be a better choice since they were probably
> designed to be in the linear region of operation? I have a bag full of TO-3
> cased units from old linear power supplies for instance. Would they be
> better?
>
>
I was wondering that too actually

2011\04\14@161142 by V G

picon face
On Thu, Apr 14, 2011 at 1:51 PM, RussellMc <RemoveMEapptechnzTakeThisOuTspamgmail.com> wrote:

>  This works well, provided that your supply can tolerate the high
> current/no current approximation to a constant value resistor.
> I used this for an exercise cycle load with dissipation varying
> between 0 - 500 Watts depending on load and speed.
>
> If you add a series inductor and a catch diode this becomes a buck
> regulator based variable resistor.
> Sounds remarkably like my Peltier supply solution :-).
> Inductor must be suitably dimensioned to avoid saturation. Air core
> may be a good idea for  large currents.
> Low (and not so low) frequency radio transmitters can happen this way :-)..
>

I'd break that bicycle. I think I sustained a kilowatt of power output at
one point for a short time with my legs

2011\04\14@164538 by Spehro Pefhany

picon face
At 04:12 PM 14/04/2011, you wrote:


>PNP BJT
^^^^^
Gremlins must have flipped a couple of bits. "NPN BJT" that should be.
Mixed devices would be more of a hybrid Sziklai pair.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spamBeGonespeffspamBeGonespaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\14@180053 by IVP

face picon face
> In the "programmable load" situation, a 1 ohm resistor could be
> made to look like anything between 1 ohm and infinity by varying
> the duty cycle of when the resistor is in circuit

A synthesiser I built many years ago used that technique in the
voltage controlled section (filters, amps etc). No high current of
course, CMOS, with 4066 / 4416 gates as the switched FETs

Jo

2011\04\14@190529 by Sean Breheny

face picon face
Do watch out here - it is true that MOSFETs have a positive
temperature coefficient of the "on resistance" when in the OHMIC
region (close to being fully ON), but in the LINEAR region (where Vdg
is less than the threshold voltage), the temperature coefficient of
CURRENT is positive. SO, MOSFETs can be paralleled as long as the
LINEAR region power dissipation is kept to a minimum, but if you have
multiple MOSFETs in a partially-on state, they cannot be paralleled
without ballast resistors (just like a BJT).

In other words, for a given gate-source voltage, there is a current
threshold, call it I1. Below I1, the current is linearly proportional
to the applied voltage (Vds), hence the OHMIC region. If the current
goes above I1, it becomes independent of Vds (LINEAR region, called
LINEAR because this is the region of operation typically for linear
amplifiers). Paralleling FETs is OK if they stay within the OHMIC
region, but requires extra caution if they dissipate any significant
power in the LINEAR region. I've even seen this become an issue for
FETs in switching applications where the switching losses were
comparable to the I2R losses in the FET.

Sean


On Thu, Apr 14, 2011 at 11:33 AM, Michael Watterson <TakeThisOuTmikeEraseMEspamspam_OUTradioway.org> wrote:
{Quote hidden}

>

2011\04\15@030129 by Michael Watterson

face picon face
On 15/04/2011 00:05, Sean Breheny wrote:
> it is true that MOSFETs have a positive
> temperature coefficient of the "on resistance" when in the OHMIC
> region (close to being fully ON), but in the LINEAR region (where Vdg
> is less than the threshold voltage), the temperature coefficient of
> CURRENT is positive. SO, MOSFETs can be paralleled as long as the
> LINEAR region power dissipation is kept to a minimum, but if you have
> multiple MOSFETs in a partially-on state, they cannot be paralleled
> without ballast resistors (just like a BJT).

References?

I have seen many RF linear amp designs using parallel FETs, none with BJT type "ballast" resistors.
Your explanation doesn't make sense to me either.

2011\04\15@101921 by RussellMc

face picon face
> >  This works well, provided that your supply can tolerate the high
> > current/no current approximation to a constant value resistor.
> > I used this for an exercise cycle load with dissipation varying
> > between 0 - 500 Watts depending on load and speed.

> I'd break that bicycle. I think I sustained a kilowatt of power output at
> one point for a short time with my legs.

No.
Getting more than 500 Watts out of it was a challenge.
Given enough speed you could do so as it asymptoted to about constant
torque, but I think 1000 Watts was probably beyond it.

I could do 500 Watts plus for maybe 10 seconds, after which I and my
legs turn to Jelly and I can't do anything much for a while.
100 Watts continuously is annoyingly heavy but doable.
50 Watts a really fit person can do all day.
To fly the English Channel (Gossamer Condor / Albatross) you need to
produce a horsepower plus continuously.

The annoying ones were the kids who set the load to zero and then
pedalled at astoundingly high speeds. Thgis would push the bus voltage
over the ;level sustainable by my load FET. I added software to load
the system down if people truied this. It worked.


                      R

2011\04\15@102328 by Sean Breheny

face picon face
Hi Michael,

I've never been able to find a general reference which states that
this is always the case for MOSFETs, but have a look at this
datasheet:

http://www.irf.com/product-info/datasheets/data/irfs4310.pdf

Specifically, see fig 1 versus fig 2. The lowest curve is for Vgs=4.5
Volts. At Vds=1 volt, the 25 deg C curve is about 1.5 Amps. the 175
deg C curve is about 22 Amps.

Compare with figure 4 which shows that Rds ON also increases with temperature.

Sean


On Fri, Apr 15, 2011 at 3:00 AM, Michael Watterson <RemoveMEmikespamTakeThisOuTradioway.org> wrote:
{Quote hidden}

>

2011\04\15@102838 by Sean Breheny

face picon face
I think that the limitation here is aerobic respiration. Your heart
and lungs can only get so much oxygen to your muscles. For a very
quick burst, you can use the reserves in the blood in your legs and
you can also dip into anaerobic respiration (lactic acid generation),
but this cannot be sustained for more than a few seconds. So, you can
sprint up a couple of flights of stairs (which for a 100 kg person
going up a 10 meter flight of stairs in 5 seconds is about 2kW or 3
Horsepower), but you cannot sprint up 10 flights of stairs.

There may also be a thermal dissipation problem in your leg muscles.

I wonder if an ultra-fit marathon runner or cyclist could sustain >500
Watts for minutes?

Sean


On Fri, Apr 15, 2011 at 10:18 AM, RussellMc <apptechnzEraseMEspam.....gmail.com> wrote:
{Quote hidden}

>

2011\04\15@103302 by V G

picon face
On Fri, Apr 15, 2011 at 10:18 AM, RussellMc <EraseMEapptechnzspamgmail.com> wrote:

> No.
> Getting more than 500 Watts out of it was a challenge.
> Given enough speed you could do so as it asymptoted to about constant
> torque, but I think 1000 Watts was probably beyond it.
>
> I could do 500 Watts plus for maybe 10 seconds, after which I and my
> legs turn to Jelly and I can't do anything much for a while.
> 100 Watts continuously is annoyingly heavy but doable.
> 50 Watts a really fit person can do all day.
> To fly the English Channel (Gossamer Condor / Albatross) you need to
> produce a horsepower plus continuously.
>
> The annoying ones were the kids who set the load to zero and then
> pedalled at astoundingly high speeds. Thgis would push the bus voltage
> over the ;level sustainable by my load FET. I added software to load
> the system down if people truied this. It worked.
>
>
Are you for sereal?

I can do a kilowatt for probaly 20-30 seconds last time I tried, no problem..
I regularly go to the gym and watch my power output (in Watts) that the new
bicycles display. I'm training for biking across Canada...

I do 200 Watts continuously, regularly. It's part of my workout

2011\04\15@103755 by V G

picon face
On Fri, Apr 15, 2011 at 10:28 AM, Sean Breheny <RemoveMEshb7EraseMEspamEraseMEcornell.edu> wrote:

> I think that the limitation here is aerobic respiration. Your heart
> and lungs can only get so much oxygen to your muscles. For a very
> quick burst, you can use the reserves in the blood in your legs and
> you can also dip into anaerobic respiration (lactic acid generation),
> but this cannot be sustained for more than a few seconds. So, you can
> sprint up a couple of flights of stairs (which for a 100 kg person
> going up a 10 meter flight of stairs in 5 seconds is about 2kW or 3
> Horsepower), but you cannot sprint up 10 flights of stairs.
>
> There may also be a thermal dissipation problem in your leg muscles.
>
> I wonder if an ultra-fit marathon runner or cyclist could sustain >500
> Watts for minutes?
>
> Sean


They can. A trained athlete can sustain 1 kW for a short time, maybe a few
minutes

2011\04\15@110711 by k c

picon face
Sean Breheny wrote:
>
> I wonder if an ultra-fit marathon runner or cyclist could sustain >500
> Watts for minutes?
>

"ultra-fit marathon runner" shouldn't, a sprinter would

2011\04\15@111742 by Sean Breheny

face picon face
Interesting. I didn't realize that there would be a difference in the
"fitness". Are there different kinds of cardio-respiratory fitness? In
other words, if I train so that my heart and lungs are good at
sustaining high throughput over hours, is that different from training
my heart and lungs to achieve a high throughput over minutes? I can
understand that a sprinter would have differences in his leg muscles
versus a marathoner, but I didn't think that their heart and lungs
would be very different.

Sean


On Fri, Apr 15, 2011 at 11:07 AM, k c <RemoveMEkaikoura.canyonspam_OUTspamKILLspamgmail.com> wrote:
> Sean Breheny wrote:
>>
>> I wonder if an ultra-fit marathon runner or cyclist could sustain >500
>> Watts for minutes?
>>
>
> "ultra-fit marathon runner" shouldn't, a sprinter would.
>

2011\04\15@112159 by Michael Watterson

face picon face
On 15/04/2011 15:23, Sean Breheny wrote:
> I've never been able to find a general reference which states that
> this is always the case for MOSFETs, but have a look at this
> datasheet:
>
> http://www.irf.com/product-info/datasheets/data/irfs4310.pdf
>
> Specifically, see fig 1 versus fig 2. The lowest curve is for Vgs=4.5
> Volts. At Vds=1 volt, the 25 deg C curve is about 1.5 Amps. the 175
> deg C curve is about 22 Amps.
>
> Compare with figure 4 which shows that Rds ON also increases with temperature.
>
Yes, RDS on *INCREASES* with temperature, thus they can be safely paralleled without BJT thermal runaway and without source "ballast" resistors.

2011\04\15@113901 by RussellMc

face picon face
> Are you for sereal?

?
Ultrahigh speed no load use was abuse of system. Curtailing the kids'
'fun' rather than smoking the load control FET was liable to meet with
owner approval.
It doesn't take much load to bring speed into the safe region.

> I can do a kilowatt for probaly 20-30 seconds last time I tried, no problem.
> I regularly go to the gym and watch my power output (in Watts) that the new
> bicycles display. I'm training for biking across Canada...
>
> I do 200 Watts continuously, regularly. It's part of my workout.

I can probably do 200 Watts "for a while" - but I'm also several times
older than you and not a paragon of fitness.

My "100 Watts continuously" was the sort of figures that a reasonably
fit person could maintain for an hour say.
I'd be far more comfortable at 50 Watts and even that would be
annoying after an hour.

As I noted, keeping airborne requires substantial power.
Gossamer Albatross took 2 hours 49 minutes to cross the English
Channel. 300 Watts in still air - rather more with turbulence

    http://en.wikipedia.org/wiki/Gossamer_Albatross

" ...The aircraft is of unusual "canard" configuration, using a large
horizontal stabilizer forward of the wing in a manner similar to the
Wright brothers' successful "Flyer" aircraft. The Gossamer Albatross
was constructed using a carbon fiber frame, with the ribs of the wings
made with expanded polystyrene; the entire structure was then wrapped
in a thin, transparent plastic (mylar aka PET film). The empty mass of
the structure was only 32 kg (71 lb), although the gross mass for the
Channel flight was almost 100 kg (220 lb). To maintain the craft in
the air it was designed with very long tapering wings (high aspect
ratio), like those of a glider, allowing the flight to be undertaken
with a minimum of power. In still air the required power was of the
order of 0.4 horsepower (300 W), though even mild turbulence made this
figure rise rapidly. The Albatross I is on display at the Smithsonian
Institution's Udvar-Hazy Center."

Little brother

    http://en.wikipedia.org/wiki/Gossamer_Condor

http://www.google.co.nz/search?q=gossamer+albatross&hl=en&pwst=1&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=IGSoTcLqIYq4sAOw5pj5DA&ved=0CD0QsAQ&biw=1920&bih=1115

2011\04\15@114447 by V G

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On Fri, Apr 15, 2011 at 11:38 AM, RussellMc <RemoveMEapptechnzTakeThisOuTspamspamgmail.com> wrote:

>
> I can probably do 200 Watts "for a while" - but I'm also several times
> older than you and not a paragon of fitness.
>

Oh yeah, I keep forgetting about the age difference on this list

2011\04\15@132836 by William \Chops\ Westfield

face picon face

On Apr 15, 2011, at 7:28 AM, Sean Breheny wrote:

> (which for a 100 kg person going up a 10 meter flight of stairs in 5  
> seconds is about 2kW or Horsepower)

An average flight of stairs is closer to 3 meters...
10 meters of stairs in 5 seconds would be pretty impressive.

I dunno if I'd trust a "Watts output" from an exercise machine to be  technically accurate, or even consistent between different vendors...

A human is supposed to be "about 100W" at normal (in)activity levels.

BillW

2011\04\15@133616 by Olin Lathrop

face picon face
'William Chops" Westfield ' <EraseMEwestfwspamspamspamBeGonemac.com wrote:
> A human is supposed to be "about 100W" at normal (in)activity levels.

I thought it was more like 30W.  I remember seeing various human activities
rated in terms of Kcal/hour.  Just sitting around was rated at 25 Kcal/h,
which is about 30W.


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(978) 742-9014.  Gold level PIC consultants since 2000

2011\04\15@134852 by Sean Breheny

face picon face
Sorry, I was not clear enough in my explanation. I was _contrasting_
fig 4 with figs 2 and 1. Rds only applies in the fully-on state, and
fig 4 does indicate that Rds INCREASES with temperature. However, in
the LINEAR region (i.e., partially-on), CURRENT increases with
temperature (as figs 1 and 2 show).

Sean


On Fri, Apr 15, 2011 at 11:21 AM, Michael Watterson <RemoveMEmikeKILLspamspamradioway.org> wrote:
{Quote hidden}

>

2011\04\15@135143 by Oli Glaser

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face
On 15/04/2011 18:27, William "Chops" Westfield wrote:
> I dunno if I'd trust a "Watts output" from an exercise machine to be
> technically accurate, or even consistent between different vendors...

Me neither, without knowing a little about how it was calculated. I would only use it as a rough guide of how I was improving (if you use the same machine/settings)
For instance, it may be done indirectly using other readings.
I have managed to attain ridiculous speeds on some gym exercise bikes, which unless I was riding behind a shield on a suitable racing surface, I would have no chance of achieving in "real life".

2011\04\15@135600 by M.L.

flavicon
face
On Fri, Apr 15, 2011 at 1:27 PM, William "Chops" Westfield
<westfwSTOPspamspamspam_OUTmac.com>wrote:

>
> On Apr 15, 2011, at 7:28 AM, Sean Breheny wrote:
>
> > (which for a 100 kg person going up a 10 meter flight of stairs in 5
> > seconds is about 2kW or Horsepower)
>
> An average flight of stairs is closer to 3 meters...
> 10 meters of stairs in 5 seconds would be pretty impressive.
>
> I dunno if I'd trust a "Watts output" from an exercise machine to be
> technically accurate, or even consistent between different vendors...
>
> A human is supposed to be "about 100W" at normal (in)activity levels.
>
> BillW
>
>
Professional cyclists use power meters integral to their rear hub for
training. It measure torque from the chain and speed (angular velocity.) So
it's not impossible to know what the body can really put out.

2kW seems pretty high, I've never seen that number thrown around. 1kW seems
likely for very short amounts of time, and many people can sustain 500W for
a short time.

-- Martin K

2011\04\15@140817 by Herbert Graf

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On Fri, 2011-04-15 at 13:36 -0400, Olin Lathrop wrote:
> 'William Chops" Westfield ' <spamBeGonewestfwSTOPspamspamEraseMEmac.com wrote:
> > A human is supposed to be "about 100W" at normal (in)activity levels.
>
> I thought it was more like 30W.  I remember seeing various human activities
> rated in terms of Kcal/hour.  Just sitting around was rated at 25 Kcal/h,
> which is about 30W.

WAY off. Try: http://www.bmi-calculator.net/bmr-calculator/

For a 5'8" 40 year old male that weighs 120lbs (VERY light for that
height) the base rate is 1405kcal/day=58kcal/hr.

For a more "typical" North American you gotta increase the weight, say
to 170lbs, and you get 1716kcal/day.

For a short light woman (5'2", 100lbs, 40years old) you still get
1193kcal/day.

Google is your friend Olin, might try using it before wasting the lists
time.

TTYL

2011\04\15@141828 by Mark Rages

face picon face
On Fri, Apr 15, 2011 at 9:37 AM, V G <KILLspamx.solarwind.xspamBeGonespamgmail.com> wrote:
{Quote hidden}

This spreadsheet on this page gives watts/kg for different classes of athletes:

http://home.trainingpeaks.com/articles/cycling/power-profiling.aspx

If you can do 1kW for more than a minute, you are better than most
professional athletes.

(I work for a company that makes bicycle power meters.  1kW is hard!
I can reach it for about one second.  That puts my W/kg somewhere
below the "untrained" figure in the chart...)

Regards,
Mark
markrages@gmail
-- Mark Rages, Engineer
Midwest Telecine LLC
@spam@markrages@spam@spamspam_OUTmidwesttelecine.co

2011\04\15@142953 by M.L.

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face
On Fri, Apr 15, 2011 at 2:08 PM, Herbert Graf <spamBeGonehkgrafspamKILLspamgmail.com> wrote:

> Google is your friend Olin, might try using it before wasting the lists
> time.
>


Your assumption being that reading other random speculative/hearsay posts on
how much power a human can sustain is /not/ wasting time?

-- Martin K

2011\04\15@164542 by Olin Lathrop

face picon face
Herbert Graf ranted:
>>> A human is supposed to be "about 100W" at normal (in)activity
>>> levels.
>>
>> I thought it was more like 30W.  I remember seeing various human
>> activities rated in terms of Kcal/hour.  Just sitting around was
>> rated at 25 Kcal/h, which is about 30W.
>
> WAY off.

I did say I *thought* it was 30W, which was based on Kcal/hour numbers I saw
many years ago.

> Google is your friend Olin, might try using it before wasting the
> lists time.

Oh get over yourself.  Apparently you need to try this yourself too.  Don't
worry, nobody will look while you wipe that egg off your face.

I did just now look around on the net, and it's amazing how widely calorie
estimates vary for different activities.  I found one for sleeping to be as
high as 50Kcal/hour (58W) while another claimed sitting and watching TV was
only 34 Kcal/hour (40W).  So my 30W recollection appears to be low, but
probably still closer to reality than the 100W figure.  Best guess at this
point is that the truth is somewhere in the middle.


********************************************************************
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(978) 742-9014.  Gold level PIC consultants since 2000

2011\04\15@180726 by V G

picon face
On Fri, Apr 15, 2011 at 4:46 PM, Olin Lathrop <.....olin_piclistspam_OUTspamembedinc.com>wrote:

> I did just now look around on the net, and it's amazing how widely calorie
> estimates vary for different activities.  I found one for sleeping to be as
> high as 50Kcal/hour (58W) while another claimed sitting and watching TV was
> only 34 Kcal/hour (40W).  So my 30W recollection appears to be low, but
> probably still closer to reality than the 100W figure.  Best guess at this
> point is that the truth is somewhere in the middle.
>

Apparently, someone needs to put various animals (including humans) into a
calorimeter and see how much energy is given off during various activities

2011\04\15@190210 by Oli Glaser

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On 15/04/2011 18:55, M.L. wrote:
> 2kW seems pretty high, I've never seen that number thrown around. 1kW seems
> likely for very short amounts of time, and many people can sustain 500W for
> a short time.
>

This page seems to think 2kW is possible as an "instantaneous maximum":
en.wikipedia.org/wiki/Human-powered_transport

2011\04\15@202734 by William \Chops\ Westfield

face picon face

On Apr 15, 2011, at 3:07 PM, V G wrote:

> someone needs to put various animals (including humans) into a
> calorimeter and see how much energy is given off during various  
> activities.

IIRC, The 100W figure I was throwing around provides the rough guess  for how much airconditioning you need for a party having N people, if  you don't want the room to get unbearably warm.

It would be interesting/amusing if gyms used a different number :-)

BillW

2011\04\16@100140 by RussellMc

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> Apparently, someone needs to put various animals (including humans) into a
> calorimeter and see how much energy is given off during various activities.

It will definitely have been done many times already.

Putting Olin and Herbert in a calorimeter together is liable to be a
more effective energy source than any thing achieved by eg  cold
fusion to date.


           Russell


[   :-)

2011\04\16@102750 by RussellMc

face picon face
> An average flight of stairs is closer to 3 meters...
> 10 meters of stairs in 5 seconds would be pretty impressive.

Watts = N.m/s = kg.g.m/s ~= 10 x kg x m / s

For an 80 kg body

   Watts = 10 x 80 kg x 10 m / 5 seconds = 1600 Watts.

Definitely impressive.
And, that's the actual work done in lifting the "body".
Actual power required would be somewhat more - say 2 to 3 kW.
Even VGSW would have jelly legs after that :-).


> I dunno if I'd trust a "Watts output" from an exercise machine to be
> technically accurate, or even consistent between different vendors...

To be taken seriously exercise machines need to be certified to comply
with relevant standards relating to accuracy.
Figures escape me now (quite some years since ...) but there was a
rating above and below 50 Watts for exercise bikes and elliptical
trainers. May have been 5% below 50 and 10% above (or the opposite or
something else) ... .

Any equipment being used in a gym has a high likelihood of needing to
meet such standards.

Getting adequately accurate results using an electronically controlled
load was "annoying" at least. Use of a torque arm and speed
measurement would have made life easier but the client didn't want to
pay what that would cost. Use of alternator current and voltage and
speed was a poor substitute due to temperature effects on alternator
windings,  magnetic saturation with current and speed and airgap and
...., and more. Much tearing of hair needed to meet standards. Doing it
again - and I certinly never wish to if avoidable -  I'd really try to
be able to use true torque.

Mark Rages may have some good things to say about this.

_______

Re the load control discussion. I'd personally try very hard to use a
FET as they are beautifully easy to control and manage in this context
compared to a BJT. Low side current sense and drive power become non
issues.
There are enough very cheap FETs available (MJ?3055's if you want to
feel linked to the past)("3055" is burned forever into my brain)(along
with eg '26 BNE')  that having to parallel a suitable number is not  a
great problem. As noted, load sharing is easy, and if desired the cost
of an opamp and sense resistor per FET is not going to be cost
prohibitive in most applications.

Use of a modulated resistor (as per my and others' previous posts)
with a FET as switch would serve many needs.
Placing a largish capacitor (onl of Olins N mFs would do well) at the
hot end of the load resistor would allow peak currents to be largely
carried only by the R with the source largely feeding the capacitor.
RC time constant need sto be "somewhat" greater than switching
frequency. Watch ripple current ratings.

eg a 1 ohm resistor plus (FET) switch can be made to look like 1 ohm
on up. If the source was say 15 volts max power = 200+ Watts. At say
30 Watts mean source current is 2A but switch current is either 15A or
0 A.
For a 1 mF filter cap the time constant = RC = 1 x 0.001 or 1 mS. PWM
at say 10 kHz or above would do a fair job of letting the source see
an effective 7.5 ohm mean load (at 2 A ) and 50 kHz + would be very
fine.

1 ohm 250 Watt wire (or ribbon) wound resistors are liable to be
available from surplus outlets for about $0. In this example a 15A +
FET also approaches $0 compared to time to build etc.

Nobody is liable to send you free samples of 1 ohm 250 Watt resistors
:-). [ YMMV ].



                 Russel

2011\04\16@120404 by k c

picon face
RussellMc wrote:
>> An average flight of stairs is closer to 3 meters...
>> 10 meters of stairs in 5 seconds would be pretty impressive.
>
> Watts = N.m/s = kg.g.m/s ~= 10 x kg x m / s
>
> For an 80 kg body
>
>    Watts = 10 x 80 kg x 10 m / 5 seconds = 1600 Watts.
>
> Definitely impressive.
> And, that's the actual work done in lifting the "body".
> Actual power required would be somewhat more - say 2 to 3 kW.

How about weightlifters that do 200kg * 2m plus their body (200kg *
1m) in about one second?

2011\04\16@121337 by k c

picon face
Sean Breheny wrote:
> Interesting. I didn't realize that there would be a difference in the
> "fitness". Are there different kinds of cardio-respiratory fitness? In
> other words, if I train so that my heart and lungs are good at
> sustaining high throughput over hours, is that different from training
> my heart and lungs to achieve a high throughput over minutes? I can
> understand that a sprinter would have differences in his leg muscles
> versus a marathoner, but I didn't think that their heart and lungs
> would be very different.
>

This discussion is under [EE] tag, admins won't be happy with it

2011\04\17@195944 by Gerhard Fiedler

picon face
k c wrote:

> RussellMc wrote:
>>> An average flight of stairs is closer to 3 meters...
>>> 10 meters of stairs in 5 seconds would be pretty impressive.
>>
>> Watts = N.m/s = kg.g.m/s ~= 10 x kg x m / s
>>
>> For an 80 kg body
>>
>>    Watts = 10 x 80 kg x 10 m / 5 seconds = 1600 Watts.
>>
>> Definitely impressive.
>> And, that's the actual work done in lifting the "body".
>> Actual power required would be somewhat more - say 2 to 3 kW.
>
> How about weightlifters that do 200kg * 2m plus their body (200kg *
> 1m) in about one second?

I don't think there are many -- if any -- that lift 200kg in one second.
It usually takes them a few seconds, and typically three (sometimes two)
steps. With around 3 seconds this gets them into the kW range where
other athletes also are.
Regarding the body... they typically start out (almost) standing, and
end up standing. The time they go down in between they trade energy
between the body and the weight. There's some lifting of the body, but
it's probably less than 200kg and less than 1m.

Gerhard

2011\04\18@074928 by Oli Glaser

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On 18/04/2011 00:59, Gerhard Fiedler wrote:
{Quote hidden}

I dunno - you have dead lifters doing nearly 500kg in around 1 second, which is a "pure" lift. This has to be around the maximum for human instantaneous power.
This got me wondering in the case of power measurement with other things, is the momentum taken into account in the case of e.g. a spinning disc in cycles, is it averaged over a certain time, or is it only the power added at that instant (i.e. sufficiently short time) that is measured?

2011\04\18@131202 by V G

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On Mon, Apr 18, 2011 at 7:48 AM, Oli Glaser <TakeThisOuToli.glaser.....spamTakeThisOuTtalktalk.net> wrote:

> I dunno - you have dead lifters doing nearly 500kg in around 1 second,
> which is a "pure" lift. This has to be around the maximum for human
> instantaneous power.
> This got me wondering in the case of power measurement with other
> things, is the momentum taken into account in the case of e.g. a
> spinning disc in cycles, is it averaged over a certain time, or is it
> only the power added at that instant (i.e. sufficiently short time) that
> is measured?
>
>
Well, if E = mgh, then doesn't matter how he got the mass in in the air, the
fact is, he got a certain mass m against a gravity g to a height h in a
certain time t. So he must have given the object a certain amount of energy
to reach that height. Average it over some amount of time and you get
energy. But maybe the power output isn't linear over that time. Maybe the
power output was maximum at the first millisecond and decreased for the rest
of the second

2011\04\18@132200 by RussellMc

face picon face
> > This got me wondering in the case of power measurement with other
> > things, is the momentum taken into account in the case of e.g. a
> > spinning disc in cycles, is it averaged over a certain time, or is it
> > only the power added at that instant (i.e. sufficiently short time) that
> > is measured?

> Well, if E = mgh, then doesn't matter how he got the mass in in the air, the
> fact is, he got a certain mass m against a gravity g to a height h in a
> certain time t. So he must have given the object a certain amount of energy
> to reach that height. Average it over some amount of time and you get
> energy. But maybe the power output isn't linear over that time. Maybe the
> power output was maximum at the first millisecond and decreased for the rest
> of the second.

Oli was asking about the case where you have equipment that stores energy.
On the system I designed power is considered to be torque x speed
(although torque was inferred via a proxy) so it's the instantaneous
power that the system as a whole is delivering. If your user suddenly
stops pedalling the power reported will be the stored power being
delivered by flywheel or whatever. However, in many cases power is
averaged over a number of seconds with the display being updated
periodically, so short term variations are smoothed out.


2011\04\18@140230 by Oli Glaser

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On 18/04/2011 18:11, V G wrote:
> But maybe the power output isn't linear over that time. Maybe the
> power output was maximum at the first millisecond and decreased for the rest
> of the second.

This was my point - I'm wondering how accurately they measure the instantaneous power.
For instance, if the power was 10kW for a millisecond then drops to 100W for 999ms, but you were only averaging the power over every second then you will have a reading of ~110W, and never know about the 10kW peak.
Also, I think it does matter about how he gets the mass in the air, and how long it takes, from the point of view of athletic achievement (and interest) For example, almost anyone could lift 500kg using a pulley, jack or lever - the same energy is expended but over a longer period/distance. Or a weightlifter could lift in very small increments, taking a rest in between each one. As Gehard also pointed out, with other types of lift one usually uses the weight of the body and trades energy with the weight to be lifted, making it harder to calculate the instantaneous power.
I'm just curious to know how quickly/accurately the readings are taken, and also whether they account for the current momentum of whatever is involved. "They" is sports equipment manufacturers or anyone who may be involved in similar research.

2011\04\18@142107 by V G

picon face
On Mon, Apr 18, 2011 at 2:02 PM, Oli Glaser <TakeThisOuToli.glaserKILLspamspamspamtalktalk.net> wrote:

> For example, almost anyone could lift 500kg using a pulley,
> jack or lever - the same energy is expended but over a longer
> period/distance. Or a weightlifter could lift in very small increments,
> taking a rest in between each one.
>

But in that case, the average power output would be much lower. I agree with
what you're saying, but the average power calculations do show who is
"stronger", I guess

2011\04\18@143000 by Olin Lathrop

face picon face
V G wrote:
> So he must have given the object a
> certain amount of energy to reach that height. Average it over some
> amount of time and you get energy.

No, you get power.

energy / time = power


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(978) 742-9014.  Gold level PIC consultants since 2000

2011\04\18@143419 by Oli Glaser

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face
On 18/04/2011 18:21, RussellMc wrote:
> Oli was asking about the case where you have equipment that stores energy..
> On the system I designed power is considered to be torque x speed
> (although torque was inferred via a proxy) so it's the instantaneous
> power that the system as a whole is delivering. If your user suddenly
> stops pedalling the power reported will be the stored power being
> delivered by flywheel or whatever. However, in many cases power is
> averaged over a number of seconds with the display being updated
> periodically, so short term variations are smoothed out.

Yes - specifically stuff like the above, was exactly what I was wondering about.
So in this case the 10kW for a millisecond example I gave in my other mail would not be "noticed". Is this the case in most gym equipment though? I would have thought that measuring the delta would be more accurate, as with the momentum of the flywheel you have the possibility of over estimating the maximum (instantaneous) output. At least having an option to set readings this way might be good.
I just got on my exercise bike here (I avoid it like the plague usually, but in the name of science..) It doesn't have a power reading but I noticed the speed and calories took around 2 or 3 seconds to drop to zero after I stopped pedalling. I could still hear the flywheel going round though, so it can't be reading directly/only from that. It looks like the display updates every second or so, and very short bursts seem to make little difference (although hard to test his empirically). It's one of the magnetic resistance ones, FWIW.

2011\04\18@154220 by RussellMc

face picon face
> > However, in many cases power is
> > averaged over a number of seconds with the display being updated
> > periodically, so short term variations are smoothed out.

> Yes - specifically stuff like the above, was exactly what I was
> wondering about.

> So in this case the 10kW for a millisecond example I gave in my other
> mail would not be "noticed".

It would be noticed as a contribution to mean energy in.

Reading too finely can cause problems.
When pedalling a bike the power is delivered in two surges per crank cycle.
If you track this power variation and display it, a digital display
would be a constant mess of changing figures. Even reading an analog
display would be difficult if it tracked power surges.

At one stage I had a certain update rate - maybe once per second, and
customers asked for a much slower update rate.

>Is this the case in most gym equipment
> though?

I think so.

> I would have thought that measuring the delta would be more
> accurate, as with the momentum of the flywheel you have the possibility
> of over estimating the maximum (instantaneous) output. At least having
> an option to set readings this way might be good.

1. How would you read the  delta?
2. As long as you can accurately measure the fluwheel energy
contribution you are liable to get a smoother system energy level.
Refusal of the flywheel to peak read the 10 kW / 1 mS spike would seem
to STOP it over reading.

> to make little difference (although hard to test his empirically). It's
> one of the magnetic resistance ones, FWIW.

MR is very good if done well.
What brand?
'Mine' were sold mainly as "Infiniti" - but also badged with other
labels by other people.



R

2011\04\18@163434 by Oli Glaser

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On 18/04/2011 20:41, RussellMc wrote:
>>> However, in many cases power is
>>> averaged over a number of seconds with the display being updated
>>> periodically, so short term variations are smoothed out.
>> Yes - specifically stuff like the above, was exactly what I was
>> wondering about.
>> So in this case the 10kW for a millisecond example I gave in my other
>> mail would not be "noticed".
> It would be noticed as a contribution to mean energy in.

Yes - that's why I put the noticed in brackets :-)
I meant that peak specifically would not be noticed, although of course it's energy will contribute to the reading.

> Reading too finely can cause problems.
> When pedalling a bike the power is delivered in two surges per crank cycle.
> If you track this power variation and display it, a digital display
> would be a constant mess of changing figures. Even reading an analog
> display would be difficult if it tracked power surges.
>
> At one stage I had a certain update rate - maybe once per second, and
> customers asked for a much slower update rate.

I was thinking more along the lines of a setting to choose how the information is gathered. I guess normally people will want to know the average power over a while, so the slow update/sampling will not be an issue. If you want to know peak instantaneous power it is though, so maybe you could read at a higher rate, but display at a slower rate, while retaining things like maximum peak power/speed attained.
You could even have a graph of power over time in more advanced machines.

>> Is this the case in most gym equipment
>> though?
> I think so.
>
>> I would have thought that measuring the delta would be more
>> accurate, as with the momentum of the flywheel you have the possibility
>> of over estimating the maximum (instantaneous) output. At least having
>> an option to set readings this way might be good.
> 1. How would you read the  delta?

With difficulty I imagine, it would require knowing about the flywheel/friction, and figure out how much energy is required to keep it at whatever speed it's at. Then you can (begin to) work out the energy input to the system.
Either that or do something like read the force directly on the pedals with a strain gauge.

> 2. As long as you can accurately measure the fluwheel energy
> contribution you are liable to get a smoother system energy level.
> Refusal of the flywheel to peak read the 10 kW / 1 mS spike would seem
> to STOP it over reading.
>

Why? If it misses a *valid* 10kW power surge (I know 10kW is very unlikely but it's arbitrary), but then reads, say 2kW when the actual power added to the system by the user is only 1kW, how is this more accurate?
I agree for most situations people are probably only interested in power over a reasonable period of time, but I am talking about the situation where people want to know the peak power delivered instantaneously (or as near as) plus how reliable that information is (does it include momentum of flywheels etc)
I would think the best system would be the one that can sample as fast as possible - you can do what you like with the data afterwards, but the detail is there if you need it.

>> to make little difference (although hard to test his empirically). It's
>> one of the magnetic resistance ones, FWIW.
> MR is very good if done well.
> What brand?

Reebok - an "i.bike"

> 'Mine' were sold mainly as "Infiniti" - but also badged with other
> labels by other people.
>
>
>
> R
>

2011\04\18@171446 by Spehro Pefhany

picon face
At 04:34 PM 18/04/2011, you wrote:
{Quote hidden}

I would average the power over an integral number of rotations of the
crank, with a minimum and maybe maximum update rate. You _know_ it's
going to vary cyclically, and the update rate does not have to be fixed,
so why not take advantage of this degree of freedom?

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffspamRemoveMEinterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2011\04\18@173511 by V G

picon face
On Mon, Apr 18, 2011 at 2:30 PM, Olin Lathrop <RemoveMEolin_piclistspamspamBeGoneembedinc.com>wrote:

>  No, you get power.
>
> energy / time = power
>
>
Obviously a typo

2011\04\23@000724 by Gerhard Fiedler

picon face
Oli Glaser wrote:

> On 18/04/2011 18:11, V G wrote:
>> But maybe the power output isn't linear over that time. Maybe the
>> power output was maximum at the first millisecond and decreased for the rest
>> of the second.
>
> This was my point - I'm wondering how accurately they measure the
> instantaneous power.
> For instance, if the power was 10kW for a millisecond then drops to 100W
> for 999ms, but you were only averaging the power over every second then
> you will have a reading of ~110W, and never know about the 10kW peak.

That's sort of basic measurement theory. The stronger the filter, the
more stable the reading but you also get less data -- which is the
objective :) If you want to see 1 ms peaks, you can't use a 1 s filter
-- but you'd have to be prepared for the much higher data rate.

> Or a weightlifter could lift in very small increments, taking a rest
> in between each one. As Gehard also pointed out, with other types of
> lift one usually uses the weight of the body and trades energy with
> the weight to be lifted, making it harder to calculate the
> instantaneous power.

We're only talking about simple, abstract mechanical power here. While
holding 500 kg at a height of 1 m doesn't cost any abstract mechanical
power, we probably can agree that most of us would have to expend more
"biological power" than we have at our disposal in doing so for longer
than a few milliseconds.

The actual energy expended is something else, higher, and the
relationship between the energy expended and the effect would be an
interesting figure.

Gerhar

2011\04\23@005632 by Oli Glaser

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On 23/04/2011 05:07, Gerhard Fiedler wrote:
>> This was my point - I'm wondering how accurately they measure the
>> >  instantaneous power.
>> >  For instance, if the power was 10kW for a millisecond then drops to 100W
>> >  for 999ms, but you were only averaging the power over every second then
>> >  you will have a reading of ~110W, and never know about the 10kW peak.
> That's sort of basic measurement theory. The stronger the filter, the
> more stable the reading but you also get less data -- which is the
> objective:)  If you want to see 1 ms peaks, you can't use a 1 s filter
> -- but you'd have to be prepared for the much higher data rate.
>

Yes, it's a very basic point I was trying to make, about just what you mention - getting *less* data. This is not always the objective.
If your concern is about excessive data rates, your have cheap PICs with up to 1Msps ADC capabilities, more than enough for very accurate peaks.
My point is simply what if someone wants to know their maximum instantaneous power attained? For some sports I imagine this may be important/useful to know and it might be good for sports equipment to sample it accurately. For this reason I imagine sampling at a higher rate would be better as it is more flexible - then you can keep the peaks for the true maximums and also average the data in firmware over a longer period. If you filter first the peak data is lost forever.

2011\04\23@015629 by RussellMc

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> For some sports I imagine this may be
> important/useful to know and it might be good for sports equipment to
> sample it accurately. For this reason I imagine sampling at a higher
> rate would be better as it is more flexible - then you can keep the
> peaks for the true maximums and also average the data in firmware over a
> longer period. If you filter first the peak data is lost forever.
>
>
>
>

2011\04\23@115629 by Sergey Dryga

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Oli Glaser <oli.glaser <at> talktalk.net> writes:

>
> On 23/04/2011 05:07, Gerhard Fiedler wrote:
> >> This was my point - I'm wondering how accurately they measure the
> >> >  instantaneous power.
> >> >  For instance, if the power was 10kW for a millisecond then drops to 100W
> >> >  for 999ms, but you were only averaging the power over every second then

<SNIP>

{Quote hidden}

What about a pulse of 0.1 ms, or 0.1 ps?  If the objective is to detect peak
power, along with average use, one can use a peak detector.  This will give you
that information without a significant increase in the data rate, although at
the cost of a second ADC channel.  
Sergey Dryga
http://beaglerobotics.com

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