Author Topic: alternator brush failures, what's the cause?  (Read 633 times)

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dnix71

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alternator brush failures, what's the cause?
« on: October 19, 2017, 08:47:28 PM »
My daily ride is a 1995 Toyota Corolla, 1.8L DX sedan. I bought the Toyota after my Ford van timing chain jumped at 180K miles. I miss having a big vehicle, but I do so much driving that I need the small car.

I transferred the inverter setup from the van to the Corolla. 1k true sine inverter, plus fuses, disconnects and a 12v ultra-capacitor module to help start big loads.

The inverter ran a window a/c in the van and I tested the transferred hardware and it would still do it in the Corolla. But the Corolla only had a 70 amp stock alternator, so I bought a direct bolt-on replacement rated at 130 amps. I don't run the window a/c, I just wanted to know if it was possible. I do run a leaf blower and some small appliances occasionally from the inverter.

Everything went fine for about 6 months and then one day on the way home the battery idiot light came on as I was pulling out of the parking lot at work. I have a plugin digital volt meter on the vehicle cigarette lighter port, so I glanced down and the reading was less than 12v. I turned off the a/c and radio and wondered if I would make it home. As I approached the first traffic light I revved the engine in neutral and the voltage suddenly came back up to normal. It stayed normal for the rest of the ride home (16+ miles in city traffic).

I ran a few errands that evening with no trouble, but the following morning when I started the car the battery light wouldn't go out. I had just done the front brakes the night before and had a c-clamp on the front seat next to me. Out of frustration with this flaky alternator, I opened the hood and whacked the alternator with the c-clamp. The engine rpm dropped immediately and the battery light went out. For a while that was my fix. Open the hood and give the alt a whack.

I had heard an unusual clicking sound on the radio before the failure, and then before each subsequent failure so I was pretty sure it was the brushes. I resisted changing the alt because it isn't nearly as easy to do as some cars. But after a lot of raising the hood in the morning to give the alt a whack, I took the alternator off and took apart the brush section.

The brushes looked fine. There was no dirt present, but one slip ring was smeared with carbon and the other was bright and clean copper/brass. I used a foam-backed fingernail file to clean up the brushes, canned electrical cleaner to blow out the slip ring area and resoldered the pigtails to the brushes. That fix lasted for a couple of months and then I was back to having to whack the alternator (sometimes more than once a day) to keep it running.

Having practice removing the alt, I figured out a way to remove the brushes with the alt still on the vehicle and clean it up like before.

So here I am again, wondering how long before it goes weird on me. The local auto parts store no longer sell replacement brushes by themselves, and the brushes are not chipped, worn or burned, but the same slip ring issue exists. One is smeared with carbon and one stays clean.

Any thoughts on what is going on here?


joestue

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Re: alternator brush failures, what's the cause?
« Reply #1 on: October 19, 2017, 09:42:48 PM »
wrong type of brush for the job, or the wrong spring tension. there are dozens of different types of brushes. carbon, graphite, metal impregnated, different hardness's, etc.

its only one brush because the polarity matters. i forget which polarity get eaten up first.


you can buy cheap brushes from ebay and try one and see if it works, or you could also pull the brush out of a vacuum cleaner, kitchen appliance, etc, and file it down to the right size.

dnix71

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Re: alternator brush failures, what's the cause?
« Reply #2 on: October 19, 2017, 10:34:17 PM »
I noticed that there is very little tension on these brushes, but I was reluctant to increase it. I did have a Black and Decker drill many years ago that had brush springs that would soften from the heat and the drill would stop working. Adding a tougher spring fixed the drill. The brushes are not very long, maybe 1/2 inch sticks out, so if I did add a tougher spring, it would probably be a good idea to replace the brushes. They seem to be soft carbon. That is probably a good idea for extending the life of the copper slip rings.

Matching materials isn't easy. I had a VW Rabbit many years ago. I loved the tin can on wheels, but there were metallic, non-metallic and semi-metallic brake shoes and if the rotors didn't match, the car would stop just fine but the brakes would start making horrible squealing noises after driving for 1/10 of a mile.

joestue

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Re: alternator brush failures, what's the cause?
« Reply #3 on: October 20, 2017, 09:43:49 AM »
I noticed that there is very little tension on these brushes, but I was reluctant to increase it.

should be at least 2, not more than 4 psi.

dnix71

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Re: alternator brush failures, what's the cause?
« Reply #4 on: October 21, 2017, 04:45:52 PM »
I seem to have it fixed for now. Lately I could only go a couple a miles before having to get out and bang the alternator. I drove home and got out my upright air compressor and a blow gun with a rubber tip and blew out all the loose dust under the hood, then with the engine running repeateded the process. I also blew air into all the openings of the alternator, including the backside where the brushes are.

I suspect the alternator design is poor. The original is sealed, the replacement is open frame. It is also mounted with the back (brush side) facing the exhaust manifold and mere inches away. There is a heat shield on the manifold, but the alternator gets stupidly hot anyway.

The small size of the car has caused me other heat problems. I had a brake leak on the passenger side rear because someone replaced the muffler with a slightly longer one. That placed part of the muffler about 2 inches from a wheel cylinder. I had the rear brakes done completely and within a year the back was leaking. I never saw or smelled the fluid because of it's location, but when I looked under the car in the back I began cursing the idiot that replaced the muffler. They knew it was too close. I fixed that by adding a sheet metal shield to the wheel well that was cut to fit between the muffler and the wheel cylinder.

I may need to add a sheet metal shield to the exhaust manifold to protect the alternator.