I know this is a recurring topic but after following @Spoke 's excellent diagnostic procedures, it looks like I've lost a diode or two as it is only outputting about 11.2v. Bummer because I rebuilt the alternator myself before putting the car back together, I tested the diodes and they all tested good so didn't replace them and it cranked out ~13.5v for almost 6K miles before crapping out.

Anyway, I need to replace the alternator fairly quickly and wondering about best options, particularly if there are in plug and play high output units around these days. I came across this one on ebay that is re-manufactured to 75amp. Anyone know anything about them?

High output isn't critical as I've converted everything but the alternator light to LED, but do have a 100w stereo amp plus phone and tablet charging. So interested in best stock options out there since I don't have a local shop that can reman the one I have.

TIA

Hi Brent - last post said he had 4 kits remaining. Sounds like it may be perfect for ya?
http://www.914world.com/bbs2/index.php?sho...p;#entry3016080

@bbrock

Did you measure the voltages at D+, D-, DF on the VR connector as well as the battery? Does it seem like the voltage regulator is working?

That's a nice kit but a bit overkill for what I need I think.



@Spoke
You know what? I don't think it is! I bought a new solid state VR last week from O'Reilly and after swapping it in, the alternator light went out. But I just noticed that the light never comes on even with just the key on but car not started. With the old VR, the light is on when key is on, but stays on with car running.

Voltages from the VR plug on relay board to chassis with car running ~2000RPM are:

D+ - 11.7v
D- - 0v
DF - 9.4v

So D+ still seems low and DF is reading high. Also, shorting across D+ and DF and then starting the car shows 12.1v at the battery which is the same as with the car off.

Makes me think it is the alternator and maybe my original VR is working just fine?

When you shorted D+ to DF, did the GEN light come on before starting the car? If the alternator armature is ok, the GEN light should come on with key on/engine off.

Hmm, no it does not. I checked continuity between all three terminals between the VR and alternator plugs on the relay board. They are all good.

type 4 powered Westfalia type 2's had a 70 amp alternator vs the normal 55 amp. They had a fan mounted behind the pulley for extra cooling I think, and there is a different alternator wiring harness with heavier gauge wires.

@bbrock

The GEN light should light up with key on/engine off with D+ shorted to DF. DF goes to the armature which then connects to ground. Check the armature resistance by disconnecting the VR and everything off and check resistance DF to chassis. You should get a low resistance. I don't know what value resistance but should be less than 1000 ohms or so. Probably less than 100 ohms.

Sorry to ask so many measurements but with a system like this and the pain of changing the alternator I would want to be damn sure the alternator was bad before replacing it. Besides these measurements are quite easy to make.

@Spoke
DF to chassis at the VR receptacle with everything off is reading open circuit. Don't know if this is relevant, but D+ to chassis reads 0 ohms.

I'm very grateful for all the measurements and guidance. I am NOT looking forward to replacing the alternator, so very much appreciate your willingness to walk me through turning every stone to make sure it is necessary. I'm thinking if I do, I'll go ahead and install the crank position sensor for a megasquirt conversion I'm planning this winter while the engine is out.

You do know that you can replace the alternator without removing the engine, yes? The left-front piece of engine tin comes off just for that reason.

--DD

@bbrock

This is not good. The circuit you tested is a wire to the alternator, then the brushes on the armature, then the armature to ground. So one of those items is bad. The alternator likely needs to be rebuilt or replaced.

Make sure your measurement is correct. Don't want to replace the alternator based on a measurement with an issue.

If it's the brushes, you might get some reading if the alternator is turned a bit. Maybe nudge the car in gear to slightly turn the engine/alternator. I've seen brushes give different resistance readings as the armature turns slowly. If high resistance more than 100 ohms the brushes need attention.



This is looking back into the GEN light and to the power rail the GEN light is on. This is good to know the GEN light is ok. With the open circuit of DF and knowing the GEN light is good, the alternator is likely in need of repair/replacement.

This would also mean your VR's are all likely good.

It has been a long time and I might not be remembering correctly, but it seems like it was still a bit PITA when I did it before. I'll give it a go though.



Alright, I'll pull the alternator and have a look. I replaced the bearings, brushes, and slip rings when I rebuild this alternator when assembling the car, in addition to going through the testing procedure for components outlined in the FM. Probably did something stupid there. Part of the rebuilt is documented here. Most likely I'll order a new alternator but it will be good to know what is screwed up.

Thanks for your help!

@Dave_Darling
I pulled the alternator tonight without dropping the engine. Not fun, but less work than dropping the whole motor.

@Spoke
Mystery solved and you were right. Armature is bad. I found a cooked wire connecting the armature windings to the lower slip ring. Completely melted the wire and the solder on the slip ring. I could replace the wire but doubt it would fix the underlying cause. Too hard of a part to replace to gamble.

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I went ahead and ordered the 75amp reman from ebay. Found some threads here and elsewhere about using Vanagon or transporter alts. Vanagon alts are something like 96 amps and use a completely different housing so won't work without mods. The late transporter will work with some minor mods. However, I couldn't find any for sale. All searches devolved to the 55 amp alternators.

Diagnosed, solved, and to be resolved. I love happy endings. Zoom zoom!

buy a bosch al75x

@Spoke
One last gnawing question is why is the solid state VR not lighting up the GEN light on the dash? I like the idea of switching to the solid state unit but would like to know the GEN light will still light if there is an open circuit on the armature or other malfunction.

@bbrock

The GEN light electrical path goes through the VR relay then to the brushes/armature to ground. If the brushes are not connected like yours then the GEN light will have no path to ground. The VR controls the amount of energy delivered to the armature to keep the battery voltage in a specific range. Actually the VR keeps D+, not the battery voltage in check. If all the diodes are ok, the battery voltage should follow D+ so in a sense, the battery voltage is regulated.

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Thought I'd close this out with an update. A little over a week ago I installed the 75amp reman alternator offered on ebay: https://www.ebay.com/itm/352740748134?fits=...O4AAOSwxOJetblj

It arrived quickly, was plug-n-play (no long stud to short on the cover), and works like a champ. With the solid state VR from O'Reilly installed, I'm reading 14.4v with car running at the battery and ~13.8v on the stock voltmeter with the 100 amp stereo running at a decent volume. Happy with the purchase so far.

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Hello, I purchased the same Alternator, installing it today, did you add the capacitor ( noise cancelling) form your old alternator to this new one? should I do that , is it needed? also I have read about adding a fan pulley, my original 55 amp did not have a fan, but wonder is the 75 amp would be better with one? any thoughts. thanks

I got a High output Ebay alternator in the past..Had it tested Alternator shop and put out a full field output of 55 amp....not even close to the advertise 70 amp. ;-(
Still running good though....

If you can locate a local starter/generator/alternator rebuilder you might be miles ahead. I never had luck with the reman items on eBay.

70 amp 1979 VW Vanagon alternator Remy #14062 Rock Auto was around 125 shipped without core. Currently out of stock. Plug and play, removed fan and installed a Vanagon rubber cooling elbow. Put your email in at Rock Auto to be notified when they are available.

@jwsnlutz Sorry this reply probably comes too late, but I did transfer the capacitor over from my old alternator.

Bummer to hear these haven't tested with the advertised capacity. Mine is working well even though I can't verify amperage output. I completed a 1,200 mile round trip to Canada last week and the car performed flawlessly. Alternator holds a consistent 13.8 at the factory voltmeter regardless of what equipment is running.