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Brat issues....electrical


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7 replies to this topic

#1 Numbchux

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Posted 10 December 2011 - 09:47 PM

So, I had the failure of that wire from the battery terminal to the fuse box. took it off, cleaned it up, soldered it, etc. And those symptoms were fixed, (like....stuff works again).


Put it in the rally trailer, and hauled it up to the offroad park just north of here for the day today.....had a couple problems.


Battery was dead, ok, no surprise, the thing's been sitting for awhile. Jumped it, and headed out. Over the course of the few hours that we were out on the trails, I discovered that the volt gauge fluctuates quite a bit with the engine speed. In fact, it would peg all the way to 18v if I didn't have any accessories on (headlights and heat on kept it below 14v the whole time).

So, the alternator is charging...

But the battery wasn't being charged. Thought it might have been the battery, so we swapped batteries with one in a buddy's Jeep. It charged just fine in his rig....

The volt gauge is reading the voltage coming off the alternator. And it responds when jumper cables are hooked up directly to the battery terminals. Sooooo.....theoretically they are connected.


Any ideas?

Edited by Numbchux, 10 December 2011 - 09:54 PM.


#2 grossgary

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Posted 10 December 2011 - 11:54 PM

you're a hundred times better at elecrical than me chux but i'll mentally vomit and maybe it'll help. :clap:

18Volts is not right so are you suspicious of the alt or the gauge itself (you seem to suggest you believe the 18V to be accurate)?

would engine off voltage at battery terminals compared to engine on voltage at battery terminals tell anything?

if voltage is the same then maybe there's resistance in one of those lines?

#3 Crazyeights

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Posted 11 December 2011 - 12:06 AM

Try some voltage drop tests across positive and negative sides of the circuits to verify it's not an in circuit resistance problem.

With the engine running, connect the positive volt meter lead to the alternator output lead (the large one) and the negative lead on the volt meter to the POSITIVE terminal on the battery. If the circuit is good and there is no resistance, the voltage reading should be less than .1 volts. Anything more and there is a bad connection.

Next connect the positive lead of the volt meter to the case of the alternator and the negative lead to the negative post on the battery. Same rules apply. If the grounds are good the voltage should be less than .1 volts.

If all of these tests pass and the IGN wire to the alt is good, the alternator may be faulty (IE bad diodes or...).

Good Luck - hope this helps someone.

#4 edrach

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Posted 11 December 2011 - 01:12 AM

18 Volts at the battery terminals with the engine running indicates a bad voltage regulator in the alternator (most of the brat alternators have internal regulators). Cheapest fix is to find a used alternator at the wrecking yard and replace the bad one.

Secondly, it sounds like you have a defective battery that's not taking a charge. Sounds to me like an open cell. Any autoparts store will gladly check your battery and hope to sell you a new one. Also, they would check your alternator too. An open cell in the battery could also result in no load on the alternator which could account for the 18V reading at higher rpm.

In any event, have both battery and alternator checked.

Which year Brat? I'm not sure when Subaru went to the internally regulated alternators. Early models (like the gen1 version) might have had external voltage regulators.

Edited by edrach, 11 December 2011 - 01:18 AM.


#5 okie bill

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Posted 11 December 2011 - 09:21 AM

This would be really really strange. Should show up when measuring neg. side voltage drop. http://ultimatesubar...ad.php?t=128521

Bill

#6 Numbchux

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Posted 11 December 2011 - 12:42 PM

I'm sorry, I had thought about adding this to my previous post about my electrical issues with this rig (turned out to be the wire at the fusible link box). But decided the symptoms were different enough that I would start a new post.....so I forgot some of that crucial background information. Like, it's an '84 brat, stock EA81. AFAIK the entire electrical system is almost completely stock. If you've seen pics of my brat, don't be fooled, only the decals say turbo, it never was.


Another piece of information from the other thread that I should have re-iterated. My brat is not stored at my home. It's at a friend's shop, about 25 miles from my house, and not in a direction that is on the way to anywhere....so diagnosing problems are a bit difficult. Closest auto parts store to the shop is about 18 miles one way.


Also, as soon as I finish building the 5-speed, it's getting an EJ. So bandaid fixes are preferred for now.



Alright, all that said. Let me simplify the symptoms a bit:

All of the symptoms all day match up with a failed battery. Frozen, or just plain dead. Not accepting a charge. Basically, I'm running off the alternator.

BUT, early in the day, I swapped batteries with a buddy's jeep. His battery had a great charge, which allowed my rig to restart when necessary. After about 4 hours in his Jeep, my old battery had been charged very well. It started the jeep again when we got back to the trailers, and when we swapped it back in the brat, it easily restarted. So, it's not the battery.

Also, with the good battery in the brat, the volt gauge still jumped all over the place.



In my experience, a car with a good alternator/regulator, but with a completely failed battery, will show some pretty crazy voltage variation related to the engine speed.

With the engine running, it's the same symptoms that I noticed when that terminal at the fusible links corroded. Except, when that happened, and the engine was turned off, jumper cables to the battery terminals didn't help.

It's like there's a diode in the system, allowing the battery to discharge, but not charge.



Here's the only pic of the brat from the day...checking the connections while I wait for a jeep to turn around and come give me a jump start to get another run at that hill:
Posted Image

#7 superjetflyer

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Posted 11 December 2011 - 12:45 PM

I don't want to sound dumb but..... How do i start a new topic?

#8 edrach

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Posted 11 December 2011 - 03:08 PM

I don't want to sound dumb but..... How do i start a new topic?

Pick the appropriate forum (old gen, new gen, or others) and click on New Thread in upper left of screen.




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