## How much power to field coils?

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charlesv842   10 mW

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### How much power to field coils?

I'm building a generator using a car alternator. I can't seem to find out how much power I need to supply to the field coils or any other details around that. The alternator has a four prong plug. Any help would be great!
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amberwolf   100 GW

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### Re: How much power to field coils?

Nevermind.

Unless it has it's own regulator built-in, then it depends on the load (current draw from the generator), and the voltage you're trying to output. If the load is not constant, you may have to design and build a regulator circuit to deal with the necessary changes.

This search
has a number of places that explain it in different ways (not eveyrhting is relevant though), but this one might be the easiest:
http://alumni.media.mit.edu/~nathan/nep ... nator.html

Some of the stuff in this google search on projects using alternators as generators may also help. (I have not viewed any of them so I don't know which would be most helpful.)

Last edited by amberwolf on Nov 18 2018 10:21pm, edited 4 times in total.

eee291   100 kW

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### Re: How much power to field coils?

I saw a Russian dude who did something similar.

He connected a 12V SLA to the field coils and ran the phases with a sensorless controller.

major   10 kW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 16 2018 11:44am
I'm building a generator using a car alternator. I can't seem to find out how much power I need to supply to the field coils or any other details around that. The alternator has a four prong plug. Any help would be great!
Hi,

You do realize that your typical car alternator has a single field coil on the rotor and the stator is the armature, don't you?

major

charlesv842   10 mW

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### Re: How much power to field coils?

I'm using a PCM controlled alternator. And it is internally reg/rec, so nothing to worry about there. It will be hooked up to an SLA an then an inverter.

I've seen some other people use AAs for the field coils. But which electrodes do I connect to? Can it be connected continuously? And if there's only one field coil, why so many electrodes?
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major   10 kW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 18 2018 10:09am
I'm using a PCM controlled alternator. And it is internally reg/rec, so nothing to worry about there. It will be hooked up to an SLA an then an inverter.

I've seen some other people use AAs for the field coils. But which electrodes do I connect to? Can it be connected continuously? And if there's only one field coil, why so many electrodes?
Typical passenger vehicle and light truck alternators use Lundell or 'claw-pole' field construction. This uses a shaped iron core on the rotor to produce a multi-pole field from a single coil winding.
From: https://en.m.wikipedia.org/wiki/Alternator_(automotive)

The two leads from the field coil connect to the slip rings.

major

charlesv842   10 mW

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### Re: How much power to field coils?

Still dont quite understand. I'm not really clear on alternators yet. As I understand it, the field coils are used in place of permanent magnets (wish they would have just said that in tech school). And the computer can vary the voltage to the coils to change the output current right? So about how much is that? Can it just be the full 12V from the battery? And which of the plug electrodes do I connect to? And why are there four?
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eee291   100 kW

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### Re: How much power to field coils?

You can't just run it as a motor from the plug.

You probably have to open the Alternator and remove the Diodes if you want to use it as one.
Then the wires will make more sense.

major   10 kW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 18 2018 4:54pm
Still dont quite understand. I'm not really clear on alternators yet. As I understand it, the field coils are used in place of permanent magnets (wish they would have just said that in tech school). And the computer can vary the voltage to the coils to change the output current right? So about how much is that? Can it just be the full 12V from the battery? And which of the plug electrodes do I connect to? And why are there four?
Did you read the wiki link article? Also do a Google. Type in "car alternator wiring schematic". Hit image search.

I don't know what model you have. Do some reading up on the subject.

charlesv842   10 mW

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### Re: How much power to field coils?

Yes, I read it. I've read other stuff on it too, including a textbook. Still none of it has answered this question.
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Hillhater   100 GW

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### Re: How much power to field coils?

eee291 wrote:
Nov 18 2018 5:10pm
You can't just run it as a motor from the plug.

You probably have to open the Alternator and remove the Diodes if you want to use it as one.
Then the wires will make more sense.
Did you read the OP ?
He doesnt want to use it as a motor, he is using it as a generator.
charlesv842 wrote:
Nov 16 2018 11:44am
I'm building a generator using a car alternator. I can't seem to find out how much power I need to supply to the field coils or any other details around that. The alternator has a four prong plug. Any help would be great!
This forum owes its existence to Justin of ebikes.ca

major   10 kW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 18 2018 9:30pm
Yes, I read it. I've read other stuff on it too, including a textbook. Still none of it has answered this question.
Why then do you use the plural field coils? How many field coils does your alternator have?

Over the 100+ years cars have used alternatives there have been hundreds of different alternator makes and models. And probably almost as many connector plugs. If you can't figure it out with existing literature and a multimeter, then get the service manual for the vehicle in which it was intended to be used. Or take it in to an automotive repair shop and ask for them to test it and look over their shoulder. Fat chance someone here can tell you about the pinouts with the information you post.

Good luck,

major

eee291   100 kW

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### Re: How much power to field coils?

Hillhater wrote:
Nov 18 2018 9:32pm

Did you read the OP ?
He doesnt want to use it as a motor, he is using it as a generator.
I've been replying to so many topics lately I'm starting to get confused

billvon   1 GW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 18 2018 10:09am
I'm using a PCM controlled alternator. And it is internally reg/rec, so nothing to worry about there. It will be hooked up to an SLA an then an inverter.

I've seen some other people use AAs for the field coils. But which electrodes do I connect to? Can it be connected continuously? And if there's only one field coil, why so many electrodes?
If it is internally regulated then there will only be one output - the positive.

If there's no internal regulator, then there will be field terminal(s.) Vary the current through them to regulate the voltage at the output.

If there are no internal diodes, then there will be 3-6 terminals for the stator windings. Connect them to bridge rectifiers.
--bill von

charlesv842   10 mW

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### Re: How much power to field coils?

OK, well, learning some new stuff here. Pinouts, thats the word I was looking for! Not sure what plural field coils are? Attached is a shot of the schematic, let me know if you need more.
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major   10 kW

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### Re: How much power to field coils?

charlesv842 wrote:
Nov 19 2018 9:12pm
... Not sure what plural field coils are? Attached is a shot of the schematic, let me know if you need more.
Plural means more than one. How many field coils does your alternator have?

I see no schematic.

major

mettleramiel   10 W

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### Re: How much power to field coils?

I don't know what you are going to use for power input, but let me tell you right off the bat that alternators are meant to run at very high rpm. Depending on what your power source is, it might be easier, smarter and more efficient to use a motor or dynamo.

Hillhater   100 GW

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### Re: How much power to field coils?

mettleramiel wrote:
Nov 20 2018 2:41am
I don't know what you are going to use for power input, but let me tell you right off the bat that alternators are meant to run at very high rpm. ...
?? High rpm ??.... Many alternators can produce max output below 2000 rpm .
This forum owes its existence to Justin of ebikes.ca

fechter   100 GW

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### Re: How much power to field coils?

The slip rings go to the field coil, so you can trace the wires going to them. Use an ohmmeter and measure the resistance of the field coil and you can calculate the current. Car alternators I've messed with before took around 2A at 12V for the field winding. They would normally run at less than this.
"One test is worth a thousand opinions"

major   10 kW

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### Re: How much power to field coils?

Hillhater wrote:
Nov 20 2018 7:54am
mettleramiel wrote:
Nov 20 2018 2:41am
I don't know what you are going to use for power input, but let me tell you right off the bat that alternators are meant to run at very high rpm. ...
?? High rpm ??.... Many alternators can produce max output below 2000 rpm .
Don't forget the small pulley. The alternator runs 2 to 3 times higher RPM than the engine. So at engine idle, the alternator may be at 2000 RPM, and it can output full voltage to keep the battery charged, but full rated output (watts) likely is available at 4 or 5000 RPM (alternator speed).

That's why you have regulator, slip rings and field coil instead of a PM field. Relatively easy (cheap) to vary an amp or two to maintain the proper output voltage needed to charge or float the battery.

major

charlesv842   10 mW

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### Re: How much power to field coils?

Awesome, more good info. Well I tried to post a photo. I think theres only one field coil. And I found the diagram, here, also attached.
For now, this is going to be a human powered bicycle generator and yeah, Im guessing it will be like 300W max.

Anyway, I found some more stuff on the diagram I didnt notice before. I see connections for the heavy posts to the battery. Then there's four more-S, FR, G, and L. Google says those are battery sense, field reg (yay), ground and indicator lamp. FR and G go to the PCM. I guess I have to find those. Do I need to worry about the others?

Also, what is full fielding? Max power to the field coil?
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major   10 kW

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### Re: How much power to field coils?

Also, what is full fielding? Max power to the field coil?
It is from a 12V system, right? So 12V or 12.8V would seem to be the upper limit for field excitation. That might be too much. It could be designed, for example, to regulate the field between 5 and 10V. You need the specifications for your particular alternator.

Or test it. Run a no-load voltage vs field current curve. Run the alternator at a constant RPM, let's say 3000. But doesn't matter, could be 3468RPM, as long as it stays constant for the test. Hook voltmeter to power output and ground (alternator case). Now vary the field current from zero up to that which it draws at 12V, in say quarter amp increments. Plot current on the x-axis and volts (on the power lead) on the y-axis..

Alternator curve
occ.png (5.56 KiB) Viewed 2775 times
From: https://engineering4uu.blogspot.com/201 ... rcuit.html

You should operate to the left of the knee. The knee represents saturation and is wasteful. If you have a battery on your system, you'll need to regulate the field to maintain proper charge.

Regards,

major

ACDC_comeback   10 µW

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### Re: How much power to field coils?

Well you can try Googling "flashing generator field", but word of warning first; you can burn out your generator's field coil by applying some of the direct battery to field coil fixes, so be careful and safe.

Hope this is even the problem, my only other thought would be the diodes because there is just not that much to these modern generators.

Good Luck.
Last edited by ACDC_comeback on Feb 28 2019 3:12am, edited 1 time in total.

amberwolf   100 GW

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### Re: How much power to field coils?

ACDC_comeback wrote:
Feb 28 2019 2:53am

You didn't say how and when this generator died? I
I don't know what thread you're reading, but this one doesn't have a dead generator in it.