Exciting the alternator?

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superstar
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Re: Exciting the alternator?

Post by superstar » Wed Apr 13, 2011 8:03 pm

Is it possible to make the VW alternater a one wire self exciting alternator like some GM alternators.

vwonnos
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Re: Exciting the alternator?

Post by vwonnos » Wed Apr 13, 2011 8:15 pm

My problem is, I can get it to charge but only without a light. Is it possible that others that have alternators that won't charge, would actually charge if they used more current to excite their alternator? I'm sure my wireing is correct because my old motor and alternator worked fine. What in the alternator has to be excited to start charging the battery?

When I put a direct 12 volts D+ it starts charging around 13.5 volts.

vwonnos
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Re: Exciting the alternator?

Post by vwonnos » Wed Apr 13, 2011 9:38 pm

Good info here.

Is it ok to use a hot 12v wire to excite the alternator and a diode to eliminate run on?
Whats the harm besides not haveing a warning light?

http://www.marinetteboat.com/forum/yaf_ ... Trick.aspx

http://www.ratwell.com/technical/ChargingSystem.html

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Re: Exciting the alternator?

Post by Dale M. » Wed Apr 13, 2011 11:28 pm

vwonnos wrote:Good info here.

Is it ok to use a hot 12v wire to excite the alternator and a diode to eliminate run on?
Whats the harm besides not haveing a warning light?

http://www.marinetteboat.com/forum/yaf_ ... Trick.aspx

http://www.ratwell.com/technical/ChargingSystem.html
With no warning light you don't know if its actually charging (got voltmeter?).

With out warning light you do not know when you have thrown alternator/fan belt and car over heats and cooks engine....

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Re: Exciting the alternator?

Post by Piledriver » Thu Apr 14, 2011 12:30 am

In a fit of rage I wired a T4 external alt on a new T1 internal reg alt that gave trouble... The T4 regs are available ~anywhere and seem pretty reliable.
(and are lifetime warranty at most places, as long as you don't mod the regulator, of course)

They pretty much wire up the same, idiot light works and all.
The alt WILL kick in without it with a blip of the throttle ~3K, the alt light isn't REQUIRED for it to work.


It's been many years since I did this, but it wasn't hard to figure out.
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superstar
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Re: Exciting the alternator?

Post by superstar » Thu Apr 14, 2011 6:15 am

If eliminating the idiot light and using a voltmeter, how should the alternater be wired to excite it.

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Re: Exciting the alternator?

Post by rostigbug » Thu Apr 14, 2011 7:47 am

That whiteish-yellowish thing on top is the brush carrier.
Take it off & see if the brushes are worn out.
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Re: Exciting the alternator?

Post by Dale M. » Thu Apr 14, 2011 9:33 am

superstar wrote:If eliminating the idiot light and using a voltmeter, how should the alternater be wired to excite it.
With isolation diode....

Image


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superstar
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Re: Exciting the alternator?

Post by superstar » Thu Apr 14, 2011 8:05 pm

Thanks Dale

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Re: Exciting the alternator?

Post by vwonnos » Mon Apr 18, 2011 12:28 am

I went ahead and purchased a chinese knock off and it works like it should. (For now.) LOL. :?

I will keep the motorola for a back up or try to get it fixed. But for the $94 and a few hours of my time, I won't have to worry about throwing a fan belt and cooking my motor because now my idiot light works like it should.

What a pain in the a$$ it was to change the alternator on a draw through turbo motor. I did it without removing the turbo or header. :wink: At least it was in a sandrail and I didn't have to pull the motor. :lol:

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Re: Exciting the alternator?

Post by tbirdusa » Fri Jan 20, 2017 2:01 am

I ended up locating my light bulb to excite the alternator in the engine bay and am pulling the + from the coil. Figured my ignition wire goes to the coil, I will just use the other tang for this. It works.

I get the why it works but don't understand this, my buddy says that once you blip the throttle over 2,000 rpm s, it will self excite. For that reason, no need to run the excite circuit. I get that having a light come on you if I throw a belt is a good idea but I have that covered with sensors and alarms with set points to let me know if a head or sump is too hot.

So, will it excite itself over 2,000 rpm s and he is right, therefor the circuit isn't necessary?

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Re: Exciting the alternator?

Post by Marc » Fri Jan 20, 2017 3:11 am

Unlike a generator, an alternator contains very little ferrous metal and retains residual magnetism poorly. A generator can sit idle for months and still work** but an alternator may not come to life without that external power provided to the field after it's been sitting for just a day or two. So, if the car is driven every day you'd probably get away without it...leave it parked for a week and all bets are off, though.


**generators which have sat idle long enough to lose all of their residual magnetism also need to be "polarized" (run briefly as a motor) before they'll work again - but that's another subject, polarization is never done to an alternator.

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Re: Exciting the alternator?

Post by tbirdusa » Sat Jan 21, 2017 2:49 am

That's the answer I was looking for. My car is a show and garage queen and doesn't get driven much. A year in between sometimes.....

Having the light bulb circuit in there grants me a pice of mind and two more wires in the way now. Thanks for explaining in simple terms of what's going on with the alt.

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Re: Exciting the alternator?

Post by JamesBrandenberger » Mon Feb 20, 2017 4:19 pm

vwonnos wrote:
Tue Apr 12, 2011 9:42 am
rostigbug wrote:IDK squat 'bout the newfangled internally regulated alts.
BUT I gotta ask...
do you have the big wire that connects the output of the alt to the battery hooked up?It should be a pretty fat one, mebbe' 10 gage?.
also where are you measuring the output??

Yes, the big wire is going to the back of the starter. I'm pretty sure the wireing is correct being that I just pulled an 1835 and the alternator would charge after I revved it to 2000 rpm. But this is an alternator that came on this motor and the guy said it worked for him. How else can I excite the alternator and still have a warning light?
First, it should be at least 6 AWG, most likely 4. And you said "the big wire is going to the back of the starter"??
The output of the alternator should connect directly to the positive battery terminal, not the starter...If that doesn't work than it's probably bad.

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Re: Exciting the alternator?

Post by Piledriver » Mon Feb 20, 2017 8:27 pm

VW ran the alt power wire direct to the starter, and it was ~8 gauge (metric equivalent, 4mm IIRC)
The rest of the trip to the battery is through much heavier battery cable.
This was literally the shortest path to the battery.

The stock alt put out 55A with a tailwind so 8 gauge was reasonable...
But 6 or 4 gauge would be better, ideally welding cable.
The ground side needs 00 at a minimum, also preferably swaged ends on welding cable, both for grounds and hot side.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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