Alternator bad? Voltage regulator maybe?

[Dave (archive)]

AS wrote:

Yeah, I figured that after thinking about it. The current would go out from the "+" battery post so the red probe on the DVM on there would've been backwards to the electron flow.

The only device that I know of that would've been on was the clock in the radio. No lights, including dome lights, were on. The key was not in the ignition switch so it wasn't even partially turned to enable some of those circuits.

I figured if a diode in the rectifier were shorted then that might be the cause of the drain through it. I found a basic schematic at:

http://www.alternatorparts.com/understanding_alternators.htm

If a diode were shorted, wouldn't that mean that there would be current flowing through it (back to ground)? I always thought a diode would blow open due to the heat of the leakage current but then these are high-current diodes and the leakage current is only half an ampere.

The reason the amp draw may be a little high is because of the keep alive memory in the radio and computer. Here's how to get around that. Hook up your amp probe as before between the +post and +cable. Now take a jumper wire and place it between the +post and +cable. Leave it there for at least 15 seconds (some take up to a minute). At this point your amp probe will read zero. Once you remove the jumper wire the probe should read much lower than in your initial test.

All that is moot though as I agree with JohninKY's original post, you have a bad diode since it's only charging 12.5 volts. BTW... that shop that says they can't jump the car, then test the alt is suspect. It sounds like they have an idiot proof tester of some sort and only have idiots to test with.
;-)

NAPA sells a very good reman alt with a lifetime warranty. Be sure to ask for their premium line as they also have a cheaper line with a 3 year warranty. They also sell a new one for many applications for not too much more.

 

[Dave (archive)]

The reason the amp draw may be a little high is because of the keep alive memory in the radio and computer. Here's how to get around that. Hook up your amp probe as before between the +post and +cable. Now take a jumper wire and place it between the +post and +cable. Leave it there for at least 15 seconds (some take up to a minute). At this point your amp probe will read zero. Once you remove the jumper wire the probe should read much lower than in your initial test.

All that is moot though as I agree with JohninKY's original post, you have a bad diode since it's only charging 12.5 volts. BTW... that shop that says they can't jump the car, then test the alt is suspect. It sounds like they have an idiot proof tester of some sort and only have idiots to test with. ;-)

NAPA sells a very good reman alt with a lifetime warranty. Be sure to ask for their premium line as they also have a cheaper line with a 3 year warranty. They also sell a new one for many applications for not too much more.

PS I just reread your first post. That $118 alt from Pep boys is a great price for a lifetime warranty! I once bought a $22 alt for a Chevy from AutoZone. I asked if they had anything of better quality. He said it had a Lifetime Warranty so I bought it. Darn thing lasted 8 years!

 

[VanguardLH]

PS I just reread your first post. That $118 alt from Pep boys is a great price for a lifetime warranty! I once bought a $22 alt for a Chevy from AutoZone. I asked if they had anything of better quality. He said it had a Lifetime Warranty so I bought it. Darn thing lasted 8 years!

Each of the stores that I went to (after checking the warranty and price) is selling a rebuilt for $118 to $129 and each has a lifetime warranty (the $129 unit include roadside assistance to get a jump if the battery is bad or, in this last case, the alternator won't charge the battery so the battery is dead and I need a jump to start the car; didn't get any details on how long that plan lasts). As I recall, Napa's rebuilt ran around $179 for standard quality, $224 for premium, and $290 new. This is for an old 92 Subie Legacy that gets maybe 7K miles on it per year.

I figure if it has a lifetime warranty (for the original car in which it gets installed) then I can pop in another if it fails. PepBoys has been around long enough that they'll probably still be around for years from now. O'Reilly has been around for maybe a couple decades (but when through name changes). There are some things I won't buy from either, like brake calipers or wheel bearing, but a lifetime alternator is okay. Replacing the alternator is not much more difficult than taking out the battery. Making sure I don't overtighten the belt is the only hazard.

 

[VanguardLH]

The reason the amp draw may be a little high is because of the keep alive memory in the radio and computer. Here's how to get around that. Hook up your amp probe as before between the +post and +cable. Now take a jumper wire and place it between the +post and +cable. Leave it there for at least 15 seconds (some take up to a minute). At this point your amp probe will read zero. Once you remove the jumper wire the probe should read much lower than in your initial test.

Presumably the half ampere was flowing through the DVM (to measure it at that rate) was for the clock/radio but I don't know if I left it connected long enough to setup the clock/radio. I do know what you're talking about because I had to replace the clock/radio (twice because the salvaged unit failed but I removed its face to put on another salvaged unit whose display was faded and had an iffy press button). I can try what you suggest to see if the current draw drops after, say, a minute of shorting the battery "+" to cable.

All that is moot though as I agree with JohninKY's original post, you have a bad diode since it's only charging 12.5 volts. BTW... that shop that says they can't jump the car, then test the alt is suspect. It sounds like they have an idiot proof tester of some sort and only have idiots to test with.

The idea is to also measure the surge current while or after starting. Although the battery itself passed their automatic tester (first a handheld one and then in a load tester), they said one of the tests is during startup. So, yeah, it might be an idiot tester but it's free at the stores. A more complicated tester involving human cognition would cost money. The one store said that the alternator can be tested in the car. The others want me to yank it out so it can be mounted on their tester (so its belt runs the alternator). While the alternator isn't that tough to remove (and put back in), I'd rather not do it if not necessary, plus an in-car test might find a different problem, like a short in the harness, a short in a dash guage, or whatever.

I'm sure that whatever tester is used at whichever car part store would all qualify as an idiot tester: follow hookup procedure, press a button, and wait for a good/bad status. An idiot tester that tests with the alternator in the car just makes it simpler for me to do the test.

 

[Dave (archive)]

While the alternator isn't
that tough to remove (and put back in), I'd rather not do it if not necessary, plus an in-car test might find a different problem, like a short in the harness, a short in a dash guage, or whatever.

You're making this more complicated than it is. Shorts cause fuses and fusable links to burn out, not drag the voltage output down. You've already determined the alt can't put out more than 12.5 volts even though your battery voltage was well below that. It should have been putting out 13.8v, if not more on a dead battery.

If you had a problem with your harness or dash gauge not energizing the alt, or the alt voltage not getting to the battery, the battery voltage would have read well below 12 volts, not 12.5v. 12.5v is sort of a magic number. It shows the alt is trying but one of the diodes is burned out.

Testing it for amperage output like the shops want to do, whether on car or on the bench tester, or testing for starter draw while cranking, isn't going to show a different result. You really need another alt.

 

[Dave (archive)]

Shorts cause fuses and fusable links to burn out, not drag the voltage output down.

Let me rephrase that: Shorts cause fuses and fusable links to burn out, not drag the voltage output down - for more than a few seconds anyway.

 

[Dave (archive)]

You're making this more complicated than it is. Shorts cause fuses and fusable links to burn out, not drag the voltage output down. You've already determined the alt can't put out more than 12.5 volts even though your battery voltage was well below that. It should have been putting out
13.8v, if not more on a dead battery.

If you had a problem with your harness or dash gauge not energizing the alt, or the alt voltage not getting to the battery, the battery voltage would have read well below 12 volts, not 12.5v. 12.5v is sort of a magic number. It shows the alt is trying but one of the diodes is burned out.

Testing it for amperage output like the shops want to do, whether on car or on the bench tester, or testing for starter draw while cranking, isn't going to show a different result. You really need another alt.

Dontcha hate it when they never come back to tell you you were right, and thanks for the help. I know I do. </talking to myself>

 

[NewsGroupie]

Dontcha hate it when they never come back to tell you you were right, and thanks for the help. I know I do. </talking to myself>

just wantja to know..I feel your pain.

 

[VanguardLH]

Dontcha hate it when they never come back to tell you you were right, and thanks for the help. I know I do. </talking to myself>

I haven't had the time to take in the car. As I said, it usually just sits in the carport. Since last November, I've probably put around a hundred miles on it. Also, I was going to have my buddy come along in case there was a problem with the car on the way to or back from the car shop but he didn't call last weekend, I couldn't reach him, and he called on Thursday to say he'd stop by to drop off his trailer (for yard waste removal) but had to leave to prepare for his son's cub scout trip that he was leaving on. A family member kept disappearing when they said that they would help. I'd be pissed with both people if it weren't that this is still a low priority repair. I really only have the weekends to get at this problem but have gotten disappointed the last 2 weekends with promises of help but didn't get any.

I put the DVM from the "+" battery post to the cable and saw no amperes this time. Was a bit surprised that there was no current flow but then found out the 2A slowblow fuse had blown. So I'll disconnect and recharge the battery and just remove the alternator to get a new one. Everything points at the alternator so I'll just yank it out and get another one (with a lifetime warranty this time).

 

[VanguardLH]

All that is moot though as I agree with JohninKY's original post, you have a bad diode since it's only charging 12.5 volts. BTW... that shop that says they can't jump the car, then test the alt is suspect. It sounds like they have an idiot proof tester of some sort and only have idiots to test with.

Got a new alternator. Didn't bother driving in the car or removing the old one to have it tested. Nothing else looked like the culprit than the alternator. Used my newer car to pickup the alternator (from PepBoys, $118 rebuilt, lifetime warranty), put it into my old 92 Subie, and tested the voltage. The battery had already been fully charged. Voltage was 13.93V so it was definitely above the 12.5V before. It wasn't the 14.4V that I thought it was supposed to get to but the battery was charged and I didn't have another person available to rev the engine while it monitored the voltage to see if it went up.

So it looks okay for the alternator. I drove the old car back to the car store for the core refund. Smelled something. Nope, not the alternator (I've smelled a burnt alternator whose bearings went before and it wasn't that varnish smell from the bearings getting super hot and heating up the windings). It came from one side. Good grief, now the front right brake is dragging. I put my hand on each wheel (well, on the wheel cover) and the front right was significantly hotter. Could be some rust on the slider pins is the problem since the car has been sitting idle in the car port for 8 months and maybe just driving it some will get rid of the problem. But just in case, I'm hunting around for a brake inspection, preferrably free. I'll take it back to where I had the brake pads replaced last summer. They worked on the calibers instead of replacing them and one had a rust ring on one of the slider pins that they had to burnish off. Might be the same problem again.