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'[EE] Best way to test an alternator'
2006\02\27@161135 by Padu

face picon face
Hi folks,

I visited the local junkyard this past weekend and I got a bosh N1 14V 34/90A alternator to play around (86-89 BMW 325).
As I have no experience with alternators, naively I hooked my oscope to the alternator and hand turned the polly but to my surprise no activity on the osc at all.

Googling for this part number, it seems like it generates 34A at 1800RPM and 90A at 6000RPM, and if I'm not mistaken starts operating at 1200RPM (so I understand that it would never work by hand turning the polly). But in addition to that, I read that it actually needs ti be plugged to a battery to work? Something called excitation (?!)

So my question is: how do I test it? It has 3 posts, a big one called D+, a smaller one called B+ and the third one is not labeled, but it is clearly connected to the alternator case, so I assume it is ground. I have a drill press that I could use to turn the polly I guess...


Cheers

Padu

2006\02\27@162428 by David VanHorn

picon face
The core should be magnetized a little, but you need to feed some current to
the field winding (the rotating part) before you'll get much out of the
output windings.

On a scope on the output terminal, you'll see DC voltage with significant
ripple, but since it's three-phase, the ripple won't go to zero.  If there
are missing pulses, then you have one or more open diodes in the output.

The rotor will be pretty hard to turn when the field is energized.

2006\02\27@164203 by Wouter van Ooijen

face picon face
> So my question is: how do I test it? It has 3 posts, a big
> one called D+, a smaller one called B+ and the third one is
> not labeled, but it is clearly connected to the alternator
> case, so I assume it is ground. I have a drill press that I
> could use to turn the polly I guess...

AFAIK an alternator needs an activation current for its magnet. So find
out how much and provide this (probably the smaller post), and maybe use
a motor to turn the shaft. IIRC you can do interesting things by varying
the activation current (I recall an article about using it to optimize a
widnmill).

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2006\02\27@165210 by Bob Blick

face picon face
All the auto part stores near me do free testing.

Cheers,

Bob



2006\02\27@165756 by Padu

face picon face
From: "David VanHorn" <spam_OUTdvanhornTakeThisOuTspammicrobrix.com>
> The core should be magnetized a little, but you need to feed some current
> to
> the field winding (the rotating part) before you'll get much out of the
> output windings.
>
> On a scope on the output terminal, you'll see DC voltage with significant
> ripple, but since it's three-phase, the ripple won't go to zero.  If there
> are missing pulses, then you have one or more open diodes in the output.
>
> The rotor will be pretty hard to turn when the field is energized.


One thing I'm still confused. The alternator is supposed to charge my
battery, and to energize the field I'm going to use the same battery... so
is it safe to assume that the + of the battery should be connected to both
D+ and B+ poles of my alternator?

Cheers

Padu

2006\02\27@170812 by Bob Blick

face picon face

> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same battery... so
> is it safe to assume that the + of the battery should be connected to both
> D+ and B+ poles of my alternator?

One typical connection uses the charge failure light in series with the
energizing terminal. But there are many variations.

Cheers,

Bob


2006\02\27@170831 by David VanHorn

picon face
>
>
> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same battery... so
> is it safe to assume that the + of the battery should be connected to both
> D+ and B+ poles of my alternator?


Yes.  The field will draw current, so it usually runs through the ignition
switch.  Then the output goes direct to the battery.

Most modern alternators have internal regulation, so you can think of it as
a mechanicaly driven current amplifier.  Put in 5A on the field, and get out
50A, assuming enough energy present on the shaft.

2006\02\27@171036 by David VanHorn

picon face
> AFAIK an alternator needs an activation current for its magnet.


It does, but the core has some residual magnetism.  If you have enough
battery to crank the starter, then you have enough field current to get
significant output, and from there on up, you're good.

2006\02\27@171354 by Robert Rolf

picon face


David VanHorn wrote:
> The core should be magnetized a little, but you need to feed some current to
> the field winding (the rotating part) before you'll get much out of the
> output windings.
>
> On a scope on the output terminal, you'll see DC voltage with significant
> ripple, but since it's three-phase, the ripple won't go to zero.  If there
> are missing pulses, then you have one or more open diodes in the output.
>
> The rotor will be pretty hard to turn when the field is energized.

No. It's only hard to turn if the output has a LOAD.
Otherwise no work is being done.

R

2006\02\27@171414 by Danny Sauer

flavicon
face
Padu wrote regarding 'Re: [EE] Best way to test an alternator' on Mon, Feb 27 at 16:01:
> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same battery... so
> is it safe to assume that the + of the battery should be connected to both
> D+ and B+ poles of my alternator?

Presuing this is similar to the alternators on my GM vehicles, the D+
lead (the one that's not a screw terminal, right?) is the "sense"
lead.  While it'll work aceptably if you just connect the two leads
direct to the battery, what you probably want to do is to get power
to D+ from an ignition-switched point in the fuse box.  That way, the
voltage regulator is referencing the voltage at the main power
distribution point and it magically compensates for the voltage drop
through the wiring harness (which can be as high as a couple of
volts).

--Danny

2006\02\27@171629 by Robert Rolf

picon face

Padu wrote:

> From: "David VanHorn" <.....dvanhornKILLspamspam@spam@microbrix.com>
>
>>The core should be magnetized a little, but you need to feed some current
>>to
>>the field winding (the rotating part) before you'll get much out of the
>>output windings.
>>
>>On a scope on the output terminal, you'll see DC voltage with significant
>>ripple, but since it's three-phase, the ripple won't go to zero.  If there
>>are missing pulses, then you have one or more open diodes in the output.
>>
>>The rotor will be pretty hard to turn when the field is energized.
>
>
>
> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same battery... so
> is it safe to assume that the + of the battery should be connected to both
> D+ and B+ poles of my alternator?

The B+ (heavy pole) is used to charge the battery.
The D+ (light pole) goes to the charging/voltage regulator which
varies the excitation of the field winding to control the alternator
output. Think of the excitation as the 'gain' control on the mechanical
motion of the core. No excitation, no output. Max excitation, max output (150 amps
on some big vehicles). Modern vehicles have a PWM chopper driving the
excitation. Ancient ones just had a relay whose coil was tied to the
battery voltage, and whose setpoint was adjusted with spring tension (sheese).


Robert


2006\02\27@172051 by Padu

face picon face
From: "Bob Blick"
> All the auto part stores near me do free testing.
>
> Cheers,
>
> Bob


Well, testing is the first step to get my hands dirt. I'll have to install
an alternator into an ATV to power electronics and servomotors in my next
mobile robot, so right now I'm only checking the feasibility of the thing...

Cheers

Padu

2006\02\27@173415 by olin piclist

face picon face
Padu wrote:
> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same
> battery...

Right.  But at engine idle speed or greater the alternator will produce more
power out than the field winding takes in.  There is a speed at which it
will break even, and below that it absorbes power.

Remeber that this alternator was not designed as a general purpose
generator, but as a generator in a specific environment.  The engine in that
car will either be off or running at a minimum speed.  Some older cars used
generators with permanent field magnets.  These don't have this issue, but
also produce less power for the same size and weight at normal operating
speed.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2006\02\27@173459 by David VanHorn

picon face
>
>
> No. It's only hard to turn if the output has a LOAD.
> Otherwise no work is being done.


It's quite noticable, even with no load.  The load makes it even harder.

2006\02\27@181355 by Robert Rolf

picon face
David VanHorn wrote:

>>No. It's only hard to turn if the output has a LOAD.
>>Otherwise no work is being done.
>
> It's quite noticable, even with no load.  The load makes it even harder.

Really? So where is the energy going if there is no load?
I suppose the DC field is providing huge Faraday drag on the core,
heating it?

Robert



2006\02\27@183119 by David VanHorn

picon face
>
>
> Really? So where is the energy going if there is no load?
> I suppose the DC field is providing huge Faraday drag on the core,
> heating it?


Well, I suggest that you grab one and try it.

Or, grab a stepper and notice the cogging that happens, even if the leads
are completely disconnected..  If the core weren't a permanent magnet, then
there wouldn't be any cogging.

2006\02\27@213654 by VULCAN20

picon face
First you need to know if it uses an internal or external regulator.  if
it has an internal regulator then that is all you need. I can send info
on hooking it up. if it has an external regulator you need to get a
regulator..  If you got to a auto parts store they can probably tell you
which it is.  The parts stores around here charge $5 USD to test them.

Most of the time the crankshaft drive pulley is about  twice as big as
the alternator pulley.  This means the alternator RPM  is about 1200 RPM
at engine idle(600 RPM).  The specs on this unit are that at engine idle
it will put out 34 amps  in the vicinity of 14 volts DC.  If you want to
load test it contact me off list and I can give you details on that.  I
used to work on do it your self wind generator using alternators

Bob

Padu wrote:

{Quote hidden}

2006\02\28@000403 by Denny Esterline

picon face
> Most modern alternators have internal regulation, so you can think of it
as
> a mechanicaly driven current amplifier.  Put in 5A on the field, and get
out
> 50A, assuming enough energy present on the shaft.

Not to be rude here, but this is WRONG, and potentially hazardous. I don't
know about the alternator in question, but certainly the ones on Daimler
Chrysler vehicles '97+ are regulated by the engine control module.
Connecting a full 12 volts to the field coils at high RPMs can produce high
voltage on the outputs (I've run 120 volt power tools this way in the field,
but don't call me if you manage to fry all the electronics in your car :-)

In another post the OP mentions he's using it for non-automotive purposes,
for that I'd suggest a mid-80's Chevy product. They DO have internal
regulation and I've retrofitted then into several non-traditional
applications with much success.

-Denny

2006\02\28@053324 by Michael Rigby-Jones

picon face


{Quote hidden}

Not be be rude but it is NOT wrong, just incomplete.  The voltage you get will be determined by the load, the RPM of the alternator and the field current.

Regards

Mike

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2006\02\28@064832 by Alan B. Pearce

face picon face
> Really? So where is the energy going if there is no load?
> I suppose the DC field is providing huge Faraday drag on the core,
> heating it?

Isn't it just the magnetic cogging of the poles? Rather like trying to turn
on unenergised stepper motor that has strong magnetic fields and close pole
faces.

2006\02\28@180259 by Peter

picon face


On Mon, 27 Feb 2006, Wouter van Ooijen wrote:

{Quote hidden}

To test the alternator as is just connect a 12V light bulb between B and
D and spin the alternator (NOT at motor rpm, a few tens or hundreds of
rpm max). The bulb will not light! If you want light connect another
bulb between D and ground.

Peter

2006\02\28@181810 by Peter

picon face


> One thing I'm still confused. The alternator is supposed to charge my
> battery, and to energize the field I'm going to use the same battery... so is
> it safe to assume that the + of the battery should be connected to both D+
> and B+ poles of my alternator?

Go find a voltage regulator before you blow up something. Here is a good
start:

http://www.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm

Peter

2006\02\28@182225 by Peter

picon face

For all the good start this pagre:

http://www.1stconnect.com/anozira/SiteTops/energy/Alternator/alternator.htm

should give, imho it is full of very dangerous circuits ...

Peter


'[EE] Best way to test an alternator'
2006\03\02@195826 by Padu
face picon face
From: "David VanHorn" <EraseMEdvanhornspam_OUTspamTakeThisOuTmicrobrix.com>
>>
>> No. It's only hard to turn if the output has a LOAD.
>> Otherwise no work is being done.
>
>
> It's quite noticable, even with no load.  The load makes it even harder.


Finally got some time to play with it a little more. I found the
alternator's PDF from bosch and it does have an internal regulator.
I connected the 12V battery to the smaller post and the pulley did become
harder to turn. In fact, before I was using my dremmel to turn the
alternator shaft. With the power on, the dremmel stalls and doesn't turn the
pulley. I had to use my power drill to turn it. I don't know if all
regulated alternators are like this, but I was monitoring the output (big
pole) on my oscope while hand turning the pulley. While the voltage level
went up or down depending on the speed that I was turning the pulley, the DC
output seems almost noiseless, which I found very nice.

One other side effect is that the pulley become a magnet. I wonder how big
is the magnetic field generated by the alternator when at full speed? This
is for my robot, and I will have magnetic sensitive components on the same
platform (devantech compass for example).


Cheers

Padu

2006\03\03@065907 by olin piclist

face picon face
Padu wrote:
> One other side effect is that the pulley become a magnet. I wonder how
> big is the magnetic field generated by the alternator when at full
> speed?

I don't think speed has much do to with it.  The magenetic field should be
proportional to field current.


******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

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