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PICList Thread
'[EE] Watercooler - revisited'
2006\03\19@192423 by Robert Ammerman

picon face
Some of you may remember a thread that I started a month or two ago about
finding a potable water pump for a TEC based water cooler I wanted to build.
I  received many useful and interesting replies. Those, of course, are two
overlapping, distinct, subsets of all the replies :-)


Well, I have progressed in my thinking and want to expose my current
thoughts for comment. See the section after the line "******" for specific
areas where I am looking for ideas.

As currently designed, my system would consist of three primary components:

1: A cold water reservoir. This is fed by the output of the water filter, at
house mains water pressure, and the output is to the separate "good water"
tap at the sink.

2: A cooling loop. This consists of a water-to-water heat exchanger within
the cold water reservoir (just a coil of copper tubing), a small pump, and a
waterblock mounted to the TEC for extraction of heat from the system.

3: A heat sink. This would consist of a large container of water thermally
connected to the hot side of the TEC.

I expect to fabricate the cold water reservoir from a vertical section of
large diameter PVC pipe. This is both pressure-safe and safe for drinking
water. The reservoir will have two ports: (a) at the top, via a simple
diffuser that forces the water to spread out horizontally for the incoming
water, and (b) at the bottom for the cold water draw off to be sent to the
tap at the sink. I need to complicate things a little bit, though, because I
have to run a loop back from the tap which returns to the top port. This
allows me to keep the water in the loop at the cold reservoir temperature so
that it is immediately available at the tap. (Otherwise I'd have a problem
similar to waiting forever for the hot water when at a distance from the
heater and waste a lot of my cold water just filling the tubing)

The cooling loop is a separate closed loop for several reasons:
1: Its components do not have to be safe for drinking water.
2: It can operate at atmospheric instead of house mains pressure.
3: Its cooling liquid can contain additions to inhibit bacteria, mold and
corrosion as necessary.
4: Its cooling liquid can run below 0 C to provide more efficient heat
transfer to the reservoir

My heat sink will just be a large container of room temperature water (in
the basement in my case) thermally connected to the hot side of the TEC. I
can make a lot of cold water before the heat sink will get too hot, and if
it does the controller can just shut the system down, or refill the heatsink
with new tap water :-)

To maximize efficiency, the cooling loop (not including the pump motor of
course), the cold water reservoir, and the loop to the tap (about 2 m long)
would all be 'hyperinsulated'. Most of it would be inside several inches of
foil-faced polyisocyanurate foam (best R for given thickness, easy to work
with) sealed with foil tape. Both the up and down runs of tubing for the
loop to tap would be enclosed at the center of a single assembly of two or
three layers of standard foam pipe insulation wrapped with foil and sealed
with foil tape. With this construction, my computations show that I can
limit loses to 1 or 2 Watts or so, not counting whatever loss I get by
reverse conduction through the unpumped liquid in the loop from the heat
sink when the TEC is off.

Just a couple of numbers from my thinking:

Desired dispense temperature: 5 C
Recovery rate: 2L per hour assuming incoming feed at 20 C
Heat flow required for recovery above: 35 Watts
Reservoir capacity: 4L
Reservoir size: about 50 cm of  4" PVC pipe (sorry for the mixed units but I
really know nothing about metric pipe sizes).

********

So finally, questions/requests:

1: Any general comments, including criticisms please (if couched politely).

2: I need a way to get the water in the reservoir and the loop to the tap to
recirculate for two reasons: (a) to keep cold water at the top of the loop
near the tap, and (b) to mix the water in the reservoir so that it is all
cooled by the heat exchanger. I don't know if natural convection can do it
for me, but I don't think so without allowing for more heat loss to set up a
bigger temperature differential and I don't want that. Any good ideas here?
I don't want or need a real pump here, just something to keep the water
drifting along. Also this is something that I don't want to have in action
when I am in a drawdown state (i.e.: water has been used and I haven't yet
recovered from it), because I am hoping that the water will remain
stratified in the reservoir (warm on top where it comes in and cold on the
bottom where it is drawn). Note, by the way, that a checkvalve must be
included between the loop return and the top of the reservoir to prevent
the tap from trying to draw from the top instead of the bottom of the
reservoir. The recirculation could be driven in the tap loop, or in the
reservoir itself. Perhaps something magnetically coupled. Lack of wear
points would be great.

3: Any good insulation ideas. Especially those that would allow for easy
access for rework, repairs, etc.

4: Any good way to thermally isolate the heatsink / TEC from the cooling
loop when the TEC is not running to avoid thermal loss. (One of my prime
goals here is to make the 'idle efficiency' of this thing ridiculously
good - just for the challenge of it. The construction here is currently
planned as follows: (a) Large container with thermal 'slug'
bolted/soldered/epoxied/welded to it, (b) Slug/TEC/waterblock stack bolted
together, (c) waterblock plumbed into cooling loop. For details on the
waterblock I have see:
http://www.polarflo.com/index.asp?PageAction=VIEWPROD&ProdID=125&HS=1

5: I need cheap, simple temperature sensors to connect to PIC. Working
temperature range from 0 C to 30 C or so. Accuracy not as important as
precision, although it would be nice if they 'tracked' each other very well.
Response time doesn't have to be particularly fast. Linearity is not a big
deal if the correction function is known. They should be easy to attach to
various components of system. They will all be within the 'enclosure' of
this device, at most 0.75 m or so from the controlling PIC. [Hey, is that
enough PIC related to let me change the topic of this message? :-)]

6: Good ideas for diffusers for the reservoir. The goal is to keep the water
stratified when in the drawdown state so that consistently cold water is
available for as long as possible.

7: Good ideas for bringing the cooling loop lines, and several termperature
sensor lines, out of the reservoir without compromising the pressure
integrity of the reservoir.

8: A simple way to sense when water is being drawn from the system.

n: Any general comments, including criticisms please (if couched politely).

===============

Addendum:

Expected user interface: one tricolor LED and one 'touch button'
(capacitively coupled input on sink deck). Touch button operates small
valves mounted directly below tap to select between output of cooler and
direct output of filter (no sense in filling the tea kettle with chilled
water). LED is green when valve has selected room temperature water, blue
for cold, red is reserved for potential future 'instant hot water' mode.
Unit reverts to cold water mode after a timeout. If unit is in recovery mode
the blue LED blinks, mostly on when nearly back to full capacity, lower duty
cycle when further to go.

Comments on this?

Thanks!!!

Bob Ammerman
RAm Systems

2006\03\19@214157 by blackcat

face picon face
A diagram would be nice.  How close is the cold reservoir (CR ) to  
the tap ?
If it is close why not have several TECs cool the water pipe feeding  
the tap ?
In addition to one cooling the main CR.
Have the TECs hot side connected to a small copper pipe ( SCP ) that  
runs from the
cooling loop.  Use a non-potable pump to move water slowly through  
pipe and
return it to the top of the cooling reservoir.  When the TECs are off  
they
can be retracted from contact with the SCP using a small motor and  
detecting
stall current.

Temp sensors
How about a MAX6575 or equivalent.   built in 8 device multi-drop  
capability.
3 connections ( Vdd [ 2.7 to 5.5 V ] , GND, Common I/O )
 $1.35 each    Is that too expensive ?

AGSC    ( ITPOP---ITIITBS )**
000000000000000000000000000000000000000000000000000000000000000000000000
00000

On 2006-Mar 18, at 11:50 AM, Robert Ammerman wrote:

Some of you may remember a thread that I started a month or two ago  
about
finding a potable water pump for a TEC based water cooler I wanted to  
build.
I  received many useful and interesting replies. Those, of course,  
are two
overlapping, distinct, subsets of all the replies :-)


Well, I have progressed in my thinking and want to expose my current
thoughts for comment. See the section after the line "******" for  
specific
areas where I am looking for ideas.

As currently designed, my system would consist of three primary  
components:

1: A cold water reservoir. This is fed by the output of the water  
filter, at
house mains water pressure, and the output is to the separate "good  
water"
tap at the sink.

2: A cooling loop. This consists of a water-to-water heat exchanger  
within
the cold water reservoir (just a coil of copper tubing), a small  
pump, and a
waterblock mounted to the TEC for extraction of heat from the system.

3: A heat sink. This would consist of a large container of water  
thermally
connected to the hot side of the TEC.

I expect to fabricate the cold water reservoir from a vertical  
section of
large diameter PVC pipe. This is both pressure-safe and safe for  
drinking
water. The reservoir will have two ports: (a) at the top, via a simple
diffuser that forces the water to spread out horizontally for the  
incoming
water, and (b) at the bottom for the cold water draw off to be sent  
to the
tap at the sink. I need to complicate things a little bit, though,  
because I
have to run a loop back from the tap which returns to the top port. This
allows me to keep the water in the loop at the cold reservoir  
temperature so
that it is immediately available at the tap. (Otherwise I'd have a  
problem
similar to waiting forever for the hot water when at a distance from the
heater and waste a lot of my cold water just filling the tubing)

The cooling loop is a separate closed loop for several reasons:
1: Its components do not have to be safe for drinking water.
2: It can operate at atmospheric instead of house mains pressure.
3: Its cooling liquid can contain additions to inhibit bacteria, mold  
and
corrosion as necessary.
4: Its cooling liquid can run below 0 C to provide more efficient heat
transfer to the reservoir

My heat sink will just be a large container of room temperature water  
(in
the basement in my case) thermally connected to the hot side of the  
TEC. I
can make a lot of cold water before the heat sink will get too hot,  
and if
it does the controller can just shut the system down, or refill the  
heatsink
with new tap water :-)

To maximize efficiency, the cooling loop (not including the pump  
motor of
course), the cold water reservoir, and the loop to the tap (about 2 m  
long)
would all be 'hyperinsulated'. Most of it would be inside several  
inches of
foil-faced polyisocyanurate foam (best R for given thickness, easy to  
work
with) sealed with foil tape. Both the up and down runs of tubing for the
loop to tap would be enclosed at the center of a single assembly of  
two or
three layers of standard foam pipe insulation wrapped with foil and  
sealed
with foil tape. With this construction, my computations show that I can
limit loses to 1 or 2 Watts or so, not counting whatever loss I get by
reverse conduction through the unpumped liquid in the loop from the heat
sink when the TEC is off.

Just a couple of numbers from my thinking:

Desired dispense temperature: 5 C
Recovery rate: 2L per hour assuming incoming feed at 20 C
Heat flow required for recovery above: 35 Watts
Reservoir capacity: 4L
Reservoir size: about 50 cm of  4" PVC pipe (sorry for the mixed  
units but I
really know nothing about metric pipe sizes).

********

So finally, questions/requests:

1: Any general comments, including criticisms please (if couched  
politely).

2: I need a way to get the water in the reservoir and the loop to the  
tap to
recirculate for two reasons: (a) to keep cold water at the top of the  
loop
near the tap, and (b) to mix the water in the reservoir so that it is  
all
cooled by the heat exchanger. I don't know if natural convection can  
do it
for me, but I don't think so without allowing for more heat loss to  
set up a
bigger temperature differential and I don't want that. Any good ideas  
here?
I don't want or need a real pump here, just something to keep the water
drifting along. Also this is something that I don't want to have in  
action
when I am in a drawdown state (i.e.: water has been used and I  
haven't yet
recovered from it), because I am hoping that the water will remain
stratified in the reservoir (warm on top where it comes in and cold  
on the
bottom where it is drawn). Note, by the way, that a checkvalve must be
included between the loop return and the top of the reservoir to prevent
the tap from trying to draw from the top instead of the bottom of the
reservoir. The recirculation could be driven in the tap loop, or in the
reservoir itself. Perhaps something magnetically coupled. Lack of wear
points would be great.

3: Any good insulation ideas. Especially those that would allow for easy
access for rework, repairs, etc.

4: Any good way to thermally isolate the heatsink / TEC from the cooling
loop when the TEC is not running to avoid thermal loss. (One of my prime
goals here is to make the 'idle efficiency' of this thing ridiculously
good - just for the challenge of it. The construction here is currently
planned as follows: (a) Large container with thermal 'slug'
bolted/soldered/epoxied/welded to it, (b) Slug/TEC/waterblock stack  
bolted
together, (c) waterblock plumbed into cooling loop. For details on the
waterblock I have see:
http://www.polarflo.com/index.asp?PageAction=VIEWPROD&ProdID=125&HS=1

5: I need cheap, simple temperature sensors to connect to PIC. Working
temperature range from 0 C to 30 C or so. Accuracy not as important as
precision, although it would be nice if they 'tracked' each other  
very well.
Response time doesn't have to be particularly fast. Linearity is not  
a big
deal if the correction function is known. They should be easy to  
attach to
various components of system. They will all be within the 'enclosure' of
this device, at most 0.75 m or so from the controlling PIC. [Hey, is  
that
enough PIC related to let me change the topic of this message? :-)]

6: Good ideas for diffusers for the reservoir. The goal is to keep  
the water
stratified when in the drawdown state so that consistently cold water is
available for as long as possible.

7: Good ideas for bringing the cooling loop lines, and several  
termperature
sensor lines, out of the reservoir without compromising the pressure
integrity of the reservoir.

8: A simple way to sense when water is being drawn from the system.

n: Any general comments, including criticisms please (if couched  
politely).

===============

Addendum:

Expected user interface: one tricolor LED and one 'touch button'
(capacitively coupled input on sink deck). Touch button operates small
valves mounted directly below tap to select between output of cooler and
direct output of filter (no sense in filling the tea kettle with chilled
water). LED is green when valve has selected room temperature water,  
blue
for cold, red is reserved for potential future 'instant hot water' mode.
Unit reverts to cold water mode after a timeout. If unit is in  
recovery mode
the blue LED blinks, mostly on when nearly back to full capacity,  
lower duty
cycle when further to go.

Comments on this?

Thanks!!!

Bob Ammerman
RAm Systems

2006\03\19@223722 by Robert Ammerman

picon face
>A diagram would be nice.  How close is the cold reservoir (CR ) to
> the tap ?

A diagram could be nice but here we go in << 1000 words:

Potable H20 flow: Leave bottom of reservoir, goes up about 2 m to tap.  At
top is T'off to tap and goes back down thru check valve, T's in with
incoming feed, and into top of reservoir.

Coolant loop flow: Leave coolant reservoir, go thru pump, peltier
waterblock, heat exchanger in potable water reservoir, back to pump.

Heat dump: Hot side of TEC directly connected to output of large water
container.

> If it is close why not have several TECs cool the water pipe feeding
> the tap ?
> In addition to one cooling the main CR.

I am assuming this is to avoid having to circulate the water to the tap.

{Quote hidden}

Seems like a lot of fuss to avoid the recirculation.

> Temp sensors
> How about a MAX6575 or equivalent.   built in 8 device multi-drop
> capability.
> 3 connections ( Vdd [ 2.7 to 5.5 V ] , GND, Common I/O )
>  $1.35 each    Is that too expensive ?

Not too bad. Surprisingly, even though I almost always put as much into SW
as I can to simplify the HW, for this (one-off) project I might prefer
something like the MAX6576 or MAX6577 instead, even at the cost of I/O pins
or (shudder) an external multiplexor.


Thanks for the input,

Bob Ammerman
RAm Systems


2006\03\19@232033 by blackcat

face picon face

On 2006-Mar 19, at 8:35 PM, Robert Ammerman wrote:

> A diagram would be nice.  How close is the cold reservoir (CR ) to
> the tap ?

A diagram could be nice but here we go in << 1000 words:

Potable H20 flow: Leave bottom of reservoir, goes up about 2 m to  
tap.  At
top is T'off to tap and goes back down thru check valve, T's in with
incoming feed, and into top of reservoir.

0000000  How about a pump that squeezes flexible tubing to slowly  
circulate potable
water.  Pump is located in return from tap path. It can be very small  
pump
and tubing.  Or something I saw years ago for about $10 each.  The URL
I provide is the closest I could come to finding the flow meter again.
Using this to move water would be pretty easy using magnetic coupling.
http://www.muiscontrols.com/sight_flow_indicators/plastic.html  00000000

Coolant loop flow: Leave coolant reservoir, go thru pump, peltier
waterblock, heat exchanger in potable water reservoir, back to pump.

Heat dump: Hot side of TEC directly connected to output of large water
container.

> If it is close why not have several TECs cool the water pipe feeding
> the tap ?
> In addition to one cooling the main CR.

I am assuming this is to avoid having to circulate the water to the tap.

{Quote hidden}

Seems like a lot of fuss to avoid the recirculation.

> Temp sensors
> How about a MAX6575 or equivalent.   built in 8 device multi-drop
> capability.
> 3 connections ( Vdd [ 2.7 to 5.5 V ] , GND, Common I/O )
>  $1.35 each    Is that too expensive ?

Not too bad. Surprisingly, even though I almost always put as much  
into SW
as I can to simplify the HW, for this (one-off) project I might prefer
something like the MAX6576 or MAX6577 instead, even at the cost of I/
O pins
or (shudder) an external multiplexor.


Thanks for the input,

Bob Ammerman
RAm Systems


2006\03\19@233035 by Robert Ammerman

picon face
> How about a pump that squeezes flexible tubing to slowly  
> circulate potable
> water.  Pump is located in return from tap path. It can be very small  
> pump
> and tubing.

This is called a 'peristaltic pump'. I like it for three reaons:

1: Simple
2: It eliminates the need for the check valve!
3: It might be something I could build myself

>  Or something I saw years ago for about $10 each.  The URL
> I provide is the closest I could come to finding the flow meter again.
> Using this to move water would be pretty easy using magnetic coupling.
> http://www.muiscontrols.com/sight_flow_indicators/plastic.html  

Maybe!

Bob


2006\03\20@085116 by Alan B. Pearce

face picon face
>3: Any good insulation ideas. Especially those that
>would allow for easy access for rework, repairs, etc.

Rather than the "foam in a can" stuff you suggested earlier, how about the
foam rolls you can buy for putting around pipes to keep hot water hot, and
keep cold pipes from freezing in a frost. Most DIY stores in the UK supply
this in yard lengths with a slit down the side for putting over existing
pipes.

>5: I need cheap, simple temperature sensors to connect
>to PIC. Working temperature range from 0 C to 30 C or
>so. Accuracy not as important as precision, although it
>would be nice if they 'tracked' each other very well.
>Response time doesn't have to be particularly fast.
>Linearity is not a big deal if the correction function
>is known. They should be easy to attach to various
>components of system.

To me the obvious item for this is some plastic cased transistors glued to
the pipe. Maxim (and probably others) make chips for PC processor
temperature management that handle these using SMBbus IIRC.

>6: Good ideas for diffusers for the reservoir. The goal
>is to keep the water stratified when in the drawdown
>state so that consistently cold water is available for
>as long as possible.

So what you are doing is a hot water cylinder in reverse. So you need a
small draw/return loop at the top of the reservoir instead of at the bottom
like a hot water cylinder has.

>8: A simple way to sense when water is being drawn
>from the system.

Why? It is not done with a hot water cylinder. By cooling the water at the
top as I suggest in 6:, the cool water will fall away to the bottom of the
reservoir where it can be drawn off.

>n: Any general comments, including criticisms please
>(if couched politely).

You mention refilling your water heatsink for the TEC from tap water. I
presume you would draw this from the filtered water, as I assume the reason
for filtering is to remove lime and similar natural "pollutants". If you do
not draw it from the filtered side, the heatsink will get limescale build up
much quicker.

2006\03\20@085645 by Alan B. Pearce

face picon face
>>  Or something I saw years ago for about $10 each.  The URL
>> I provide is the closest I could come to finding the flow meter again.
>> Using this to move water would be pretty easy using magnetic coupling.
>> http://www.muiscontrols.com/sight_flow_indicators/plastic.html
>
>Maybe!

Even the fan portion off a processor sized muffin fan (the little ones 486
processors used) mounted in a piece of perspex tube would do that. You could
even arrange an LED/photosensor to allow remote sensing of the flow rate.
Taken to the extreme it could probably be reasonably well calibrated.

2006\03\20@170002 by Robert Ammerman

picon face
> >3: Any good insulation ideas. Especially those that
>>would allow for easy access for rework, repairs, etc.
>
> Rather than the "foam in a can" stuff you suggested earlier, how about the
> foam rolls you can buy for putting around pipes to keep hot water hot, and
> keep cold pipes from freezing in a frost. Most DIY stores in the UK supply
> this in yard lengths with a slit down the side for putting over existing
> pipes.

Yes, this is what I intend to use on the doubled line running to the tap. I
am more concerned about what to do with miscellaneous gaps and spaces.

{Quote hidden}

Do you mean just using the natural TC of the transistor? Do you know any
part numbers for these parts?

>>6: Good ideas for diffusers for the reservoir. The goal
>>is to keep the water stratified when in the drawdown
>>state so that consistently cold water is available for
>>as long as possible.
>
> So what you are doing is a hot water cylinder in reverse. So you need a
> small draw/return loop at the top of the reservoir instead of at the
> bottom
> like a hot water cylinder has.

The hot water tanks I am familiar with have two ports on the top. The
incoming cold water is fed thru a 'dip' tube so that the port if effectively
near the bottom. This does not, of course, support a recirculating loop
directly. In my system I plan on haviing the recirculating loop draw cold
water from the bottom of the tank and return it to the top of the tank.

>>8: A simple way to sense when water is being drawn
>>from the system.
>
> Why? It is not done with a hot water cylinder. By cooling the water at the
> top as I suggest in 6:, the cool water will fall away to the bottom of the
> reservoir where it can be drawn off.
>

At this point, basically so that I know it is happining for logging, etc.
Also, I hope use that information to optimize recirculation flow to keep the
reservoir content laminar as much as possible during a 'not yet recovered'
draw down condition.

{Quote hidden}

Yes, although  I don't expect to have to refill the water heatsink very
often at all. Under nearly all circumstances normal dissapation to the
environment will allow it to stay cool enough.



Thanks,

Bob

2006\03\20@170507 by Robert Ammerman

picon face

> Even the fan portion off a processor sized muffin fan (the little ones 486
> processors used) mounted in a piece of perspex tube would do that. You
> could
> even arrange an LED/photosensor to allow remote sensing of the flow rate.
> Taken to the extreme it could probably be reasonably well calibrated.

Good, good, good. This could be a good way to get my flow sensor!

Bob

2006\03\21@043311 by Alan B. Pearce

face picon face
>> To me the obvious item for this is some plastic cased
>> transistors glued to the pipe. Maxim (and probably
>> others) make chips for PC processor temperature
>> management that handle these using SMBbus IIRC.
>
>Do you mean just using the natural TC of the transistor?

Yes.

>Do you know any part numbers for these parts?

Oh, (much digging through messy pile of product announcement sheets). Right,
found what I was looking for. Check out MAX6678, MAX6641/3 which use a
bipolar transistor which is embedded in the CPU die for processor
temperature control. There is also MAX6699 (which is definitely SMBbus) to
handle 4 external diode sensors, plus one on chip.

Also look at MAX7500/1/2 which are I2C devices described as "improved LM75".
Another possible might be Dallas DS600.

You would probably get enough of these through the sampling program for your
project, especially if you max out on each of similar devices such as the
MAX7500 family.

2006\03\21@072614 by John Snider

picon face
I was following this thread, and went to work yesterday (I service
MRI/CT scanners) to find the research people working with a watercooled
thermode. ( http://www.medoc-web.com/thermode.html ). The peltier device
heats up to cause pain, and the water cooling can rapidly change the
temperature on it. The cable to the thermode has power for the peltier,
a connection that looks like a thermocouple connector, and the
feed/return water lines. There is a small (1ft x1 ft x1ft) water chiller
that has the water at about 6 degs C. (An abnormal response to pain
stimulus is an indicator of neurological dysfunction - or something like
that)

2006\03\21@073255 by Luis.Moreira

picon face
Hi all,
I am in the process of upgrading one of our systems and the bit I am
looking at the moment has 24 IGBT H bridge modules. Each of these
modules as a driver board which I need to replace. This board will need
+ - 15V at steady current of around 300mA ( when switching IGBTs current
will be sourced from local storage caps).The IGBTs will be switched at
frequencies up to 350KHz. My biggest problem is how to supply power to
the boards as they need to be isolated from the rest of the system
(sitting at HV). The solutions I found are:

- Fit an of the shelf isolated switching power supply which seems good
but probably the price and possible problems with switching noise makes
this solution not a very good one.

-The other which was suggested by a friend is to supply the board with a
40KHz at around 20V peak sinusoidal generated by a resonant circuit.
this would reduce the size of the transformers on the boards. Voltage
would then be rectified and regulated.

Any ideas welcomed
Best regards
               Luis    


{Original Message removed}

2006\03\21@082055 by Russell McMahon

face
flavicon
face
> -The other which was suggested by a friend is to supply the board
> with a
> 40KHz at around 20V peak sinusoidal generated by a resonant circuit.
> this would reduce the size of the transformers on the boards.
> Voltage
> would then be rectified and regulated.

Essentially inductive power transfer.
If you don't mind 'some' inefficiency.

- Supply a pair of adjacent wires in eg flat mains power cable with
your sinusoidal power signal. Join the two wires at the far end to
make a long thin "loop" with the two wires around 5 or 10 mm apart.

- Resonate the loop (series or parallel) to maximise power transfer.

- Place open U cores across two wires. Wind a coil on U core. Resonate
coil. Rectify and use power.

UUUUU
U  X  U
U O  U

It works!
And well.

Isolation is whatever you want.
Ucores can added or removed where and as required.

I have had dozens of cores receiving power at once.

You can also signal at 100 kbps burst across this with a 100m loop -
but that's another story.

A more normal supply with simple isolating transformers or a SMPS at
each location is arguably easier.



       RM

2006\03\21@083721 by Alan B. Pearce

face picon face
>-The other which was suggested by a friend is to supply the board
>with a 40KHz at around 20V peak sinusoidal generated by a resonant
>circuit. this would reduce the size of the transformers on the boards.
> Voltage would then be rectified and regulated.

Umm, isn't this just the secondary side of a switchmode supply?

Just what sort of noise level do you need? we use switch mode supplies right
through satellite instruments without any problems with noise - provided
that care is taken. If a really low noise supply is needed, then a low drop
out regulator follows the switcher.

2006\03\21@142558 by Peter

picon face

On Sun, 19 Mar 2006, Robert Ammerman wrote:

>> How about a pump that squeezes flexible tubing to slowly circulate
>> potable water.  Pump is located in return from tap path. It can be
>> very small pump and tubing.
>
> This is called a 'peristaltic pump'. I like it for three reaons:
>
> 1: Simple
> 2: It eliminates the need for the check valve!

Just get the kind with three lobes. Two lobes needs the check valve.
Don't ask how I know this.

Peter

2006\03\21@154317 by M. Adam Davis

face picon face
Technically, two lobes will work as long as the tube spans over 180
degrees of the pump.

Or in other words, get a pump that always compresses the tubing with
at least one lobe/roller regardless of the position of the rollers.

-Adam

On 3/21/06, Peter <spam_OUTplpTakeThisOuTspamactcom.co.il> wrote:
{Quote hidden}

> -

2006\03\22@174504 by Peter

picon face


On Tue, 21 Mar 2006, M. Adam Davis wrote:

> Technically, two lobes will work as long as the tube spans over 180
> degrees of the pump.
>
> Or in other words, get a pump that always compresses the tubing with
> at least one lobe/roller regardless of the position of the rollers.

Yes, but the pumps I had to do with did not read the manual and leaked
very slowly so they got un-primed in a few hours. The three-lobed ones
do not leak apparently. This was with very little back pressure (say 1
meter H2O).

Peter

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