What can fry an alternator?

Jacob Wisdom

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The alternator on one of our class 12's keeps blowing. We DNF'd after burning through 3 of them at the Baja 500, so had the car completely rewired in preparation for the 400. The car was just taken out testing with the new wire job and once again the alternator fried (this time a 90 amp).

What can be going on here? The batteries are new. We've tested the electrical system separately and are well below rated output of the alternator. We can test the system sitting in the driveway for hours and there is no issue, but as soon as we're out in the desert bouncing around we lose the alternator.
 

green787

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Your electrical system is just pulling too much current.... Try to find a 120amp Alternator or have one built..... Check for something shorted to ground.... install a shunt & meter, so you can actually know how much current you are drawing....



With everything shut off, see how big of a spark jumps in the dark when you hook up the last battery terminal.... pos or neg, there should be no spark at all.... if something is shorted to ground or something is pulling current, like the memory in your tape deck/stereo for instance, there will be a small spark.... but that's no bueno for keeping the battery charged when not in use..... If something is shorted there will be a large spark..... this is not a good thing.... if the spark is so large it makes you say Jeeeezzzus..... then you have a serious problem with your electrical.... and the alternator just can't keep up.....

In rare cases you could have a shorted battery, and that would take out your alternator as well.... But it probably wouldn't start the car either, it would just go dead immediately or start smoking.... I have called the fire department because of this in the past, so i know it can happen especially when the battery is bouncing up and down like in off road....
 
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swiftracing5

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Lithium batteries? Are all the alternators from the same place and which place?
 

Bricoop

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The alternator on one of our class 12's keeps blowing. We DNF'd after burning through 3 of them at the Baja 500, so had the car completely rewired in preparation for the 400. The car was just taken out testing with the new wire job and once again the alternator fried (this time a 90 amp).

What can be going on here? The batteries are new. We've tested the electrical system separately and are well below rated output of the alternator. We can test the system sitting in the driveway for hours and there is no issue, but as soon as we're out in the desert bouncing around we lose the alternator.
What voltage is the alternator producing? We've killed an alternator with metal dust, causing an overcharge which then killed the battery. We've also killed an alternator due to vibrations and a poor install (don't overtighten single wire.).
 

dzrt performance

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more than likely, as already pointed out....you have too much load on it. however, there are other things to look for too.

alternator speed.......some people change pulley sizes to try and speed up the cooling fan or get more out of the alternator. there is a mechanical speed limit the alternator bearings will will die at if exceeded.

heat.......VW's are notorious for getting very dirty and this degrades the cooling of the alternator.

wire size.......some try and run a small 8 gauge wire off the alternator.........for 100 amps you need to be at least 2x that size

poor grounding........jest because the alternator is sitting in a cradle that is connected to the block, make sure to have a good ground strap on it.
 

J BomBer

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How much stuff are you running? Try putting a 55 amp one on, we stopped using hi amp long ago due to constant failures.
 

Bricoop

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The alternator on one of our class 12's keeps blowing. We DNF'd after burning through 3 of them at the Baja 500, so had the car completely rewired in preparation for the 400. The car was just taken out testing with the new wire job and once again the alternator fried (this time a 90 amp).

What can be going on here? The batteries are new. We've tested the electrical system separately and are well below rated output of the alternator. We can test the system sitting in the driveway for hours and there is no issue, but as soon as we're out in the desert bouncing around we lose the alternator.
When you say "one of" do you mean you have others with similar setups that haven't experienced this issue? Have you opened any of the broken ones to see obvious damage?
 

Jacob Wisdom

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Your electrical system is just pulling too much current.... Try to find a 120amp Alternator or have one built..... Check for something shorted to ground.... install a shunt & meter, so you can actually know how much current you are drawing....



With everything shut off, see how big of a spark jumps in the dark when you hook up the last battery terminal.... pos or neg, there should be no spark at all.... if something is shorted to ground or something is pulling current, like the memory in your tape deck/stereo for instance, there will be a small spark.... but that's no bueno for keeping the battery charged when not in use..... If something is shorted there will be a large spark..... this is not a good thing.... if the spark is so large it makes you say Jeeeezzzus..... then you have a serious problem with your electrical.... and the alternator just can't keep up.....

In rare cases you could have a shorted battery, and that would take out your alternator as well.... But it probably wouldn't start the car either, it would just go dead immediately or start smoking.... I have called the fire department because of this in the past, so i know it can happen especially when the battery is bouncing up and down like in off road....
Could be, we've done multiple tests, including by using a current meter to confirm we aren't over-stressing the alternator. Based on everything that we've seen so far, we are far under-utilizing the rated current of the alternator. The only thing we don't know is whether we are finding an arc somewhere when going through rough. We were hoping the rewire would control for that possibility
Lithium batteries? Are all the alternators from the same place and which place?
No they're not lithium. We've purchased different alternators from different sources and of varying amperage. It doesn't seem to be the issue at play
What voltage is the alternator producing? We've killed an alternator with metal dust, causing an overcharge which then killed the battery. We've also killed an alternator due to vibrations and a poor install (don't overtighten single wire.).
Don't recall exactly but the voltage was always in normal specs relative to what we're used to
I'm wondering if you're charging the field with full voltage instead of using a resistor?
This I do not know, but our wiring was never a problem previously. We won the SF250 then when we came back for the B500 the issues began.
is it a one wire?,
IIRC yes, it's on my uncle's car so I'm less familiar with it than he is.
more than likely, as already pointed out....you have too much load on it. however, there are other things to look for too.

alternator speed.......some people change pulley sizes to try and speed up the cooling fan or get more out of the alternator. there is a mechanical speed limit the alternator bearings will will die at if exceeded.

heat.......VW's are notorious for getting very dirty and this degrades the cooling of the alternator.

wire size.......some try and run a small 8 gauge wire off the alternator.........for 100 amps you need to be at least 2x that size

poor grounding........jest because the alternator is sitting in a cradle that is connected to the block, make sure to have a good ground strap on it.
We have matched our pulley size to what our engine builder (Wiks) recommends, so I'm confident that isn't the issue. I'm less inclined to believe it's heat, because nothing has changed that would affect it (as far as we know). Wire size is an interesting thought. We did go up in size of the alternator but did not increase the gauge of the cable. Grounding is a possibility but again, I'd be confused why the issue would spontaneously occur.
How much stuff are you running? Try putting a 55 amp one on, we stopped using hi amp long ago due to constant failures.
We would be pushing a 55 amp to the limits but I somewhat agree with your assessment, the aftermarket alternators seem to be an issue
Where are you getting your alternators from?

Also, what's your fan look like? Balanced recently?
We've purchased them from a number of different places including our engine builder (Wiks). We always buy what is recommended by our builder.

As far as I know the fan is in good shape but I have not personally looked at it. The engine is off a fresh rebuild from Adam...not sure if balancing the fan is part of that.
When you say "one of" do you mean you have others with similar setups that haven't experienced this issue? Have you opened any of the broken ones to see obvious damage?
We have another class 12 that runs a similar setup (similar in the sense that it's another VW powered desert buggy). We have had many Type 1/Type 4 powered race buggies through the years from class 11 to class 12, this is the first time we have experienced this particular issue.

We opened them up but none of us know enough about alternators to ascertain where the failure is. Looking inside of them, there are clear indications that they got hot. We're trying to get one to a shop that can tell us specifically what went wrong
 
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partybarge_pilot

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Try taking a couple dead ones to Richer auto electric in Oceanside for a teardown and evaluation. They have built a lot of racing alternators with excellent results. Just because they were new doesn't mean they were right.
 

BCarr

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Coming from someone who had to change a 90A out the night before a B500...

Thinking you had this problem on the same car with both the 55A and now 90A alternators.

It was mentioned that you service bay tested the alt with the engine running...were some or all loads (pumper, lighting, etc) on during this charging system performance test?

Some example measurements to ponder...what were the voltage measurements at idle rpm? >3k rpm? Such as:
a) measure Vbatt across the +/- battery terminals, engine off, run switch on
b) measure Vbatt across the +/- battery terminals, engine running at idle
c) measure D+ to ground, engine running at idle
d) measure Vbatt across the +/- battery terminals, engine running >3k, loads on
e) measure D+ to ground, engine running > 3k, all loads on

I'd prefer electrical current measurements, but those are a lil tougher to measure unless inductive probe is available, so in interest of keeping it simple, just consider voltage measurements (every one of us has a DVOM, right?

From another perspective, if your setup is a one-wire 90A alternator...for those, regulator excitation is now inside the alt and is done off alternator rpm (and sometimes with no external connection for regulator excitation or alt warning lamp). If this is your rig's component setup, then something likely happened to the field circuit (internal). Maybe not big enough internal components ;)

For the 90A, make sure the alt to batt wire is at least #6 gage (if system current draw when loaded is greater than say 70A, then move to #4). And make sure there is no cable voltage drop on a) engine to frame ground and b) battery neg terminal to frame ground.

Feel your pain cause we were there once. Really tough to do keyboard diagnosis, but hopefully with all these responses the folks here gave, you have some checks to make (no celebration until problem is solved). And you hinted that there are other VW rigs at your disposal, so if their alternator setups are the same maybe then you can compare measurements from :).

Anyways, diagnosis of electrical issues is about getting measurements when the system is being used in actual/normal use cases. And lots of "don't give up" candy.

BTW, I don't post much, but because of prior experience on the 90A I felt compelled. And pretty sure we did an electrical conservation assessment on the car and thus bounced the one-wire 90A back on the 1600 rig...
 

brad inch

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sometimes things get painted and put back together.and the grounds dont work right.take the motor and trans out and grind all the paint off. all to mounts.also any place a ground would mount.had a customer come in and said the only way his car would start was to push the clutch in. so i watched and the clutch cable turn red and smoked.added a ground from the motor to the frame and fixed it. did you change to battery as they have plates that come loose.
good luck brad
 

Jacob Wisdom

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Thanks to everyone that has offered their insights. My uncle, his navigator and an electrical expert worked their ass off over the weekend and seem to have resolved the issue. They're headed down to the 400 today so we'll find out this week. It appears to have been related to voltage drop in the alternator's excitement feed.

If anyone sees 1221 on the side of the course, please throw us your spare alternator 🤪
 
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