Alternator, and drain

[NickR]

Some strange symptoms, which I would like a second opinion on, please.

92 Tercel, mtx, 295,000kms (Daughter's car).

Daughter reported a burning smell, and the CD player (aftermarket install, several years ago) doing strange things. Subsequently parked the car, and later found it wouldn't start (would not crank/turn over). An hour or two later, I went to have a look at the car. I could find no wiring problems, on a brief visual inspection. I tried it, and it started (though the battery sounded a bit flat, because it cranked slowly). I drove it home, and it went normally, except the "no charge" warning light would come on at idle (about 900rpm).

I checked it with my multimeter, and it registered about 12 volts at idle across the battery terminals, and about 13 volts at higher rpm. I disconnected one battery terminal, and found a significant drain (over 250 mA, which is the maximum reading on my cheap little multimeter). I suspected the alternator of causing the drain, and so disconnected the alternator, but the drain continued. I then did the old trick of pulling out the fuses, one by one, and when I pulled the dome fuse out the drain dropped to about 0.5mA. The CD player is wired up via the dome fuse (the CD player won't work when the dome fuse is pulled, and nor, of course, will the interior lights). All doors were closed, by the way, and the dome light was switched off.

With the dome fuse removed, I re-tested the voltage at the battery terminals with the engine idleing. Still only 12 volts (with the "no-charge" warning light coming on).

I put the battery charger on the battery, and the current was initially high, suggesting the battery was indeed flat. Aftyer a couple of hours charging, the current slowly dropped.

My diagnosis is that there are two problems: First, the alternator (the original) is very weak, and needs to be replaced; second, there is some sort of short, causing a drain, and it is most likely due to the CD player, or the wiring for the CD player.

One possible further clue: my daughter leaves her car in an absolute mess. Half empty pop cans everywhere. I found one Coke can on the floor, and all the Coke had drained out, leaving a sticky mess. It is possible that spilled liquids messed up the wiring somewhere.

Does my diagnosis sound plausible? Does anyone know if there is anything else on the dome fuse circuit, other than the interior lights and CD player? Any other ideas? Thanks.

(It was a PITA removing the alternator, by the way, the main bolt having rusted in.)

[mike_nj]

hi first have your battery tested a bad battery wont accept a charge.you can start the car and diconnect neg terinal and see if car still runs if it does alt putting out.Also on the radio you need to know where they hooked up the memory wire shouid have 2 power wire

[StealthSeo]

you have a alternator ghost and he is haunting you b/c your alternator is dying and is stuck between this life and the next. put it to rest by replacing it and then check the wiring of the stereo, something doesnt seem right there.

[NickR]

Thanks for the replies.

It gets curiouser. I took the alternator to the parts store, planning to buy a new one, but thought I might as well ask them to test the old one first. It tested fine! I re-installed it, and it was ineed now charging properly, with a good 13-14 amps (depending on rpm), and well able to handle extra load, like headlamps and rear defrost.

Three possibilities: 1. There is an intermittent fault in the alternator, sometimes it works and sometimes it doesn't; 2. I had the battery charger on the battery for a few hours while I was removing the alternator. Maybe the alternator only works with a fully charged battery (sounds strange)?; 3. I cleaned up the connections on the alternator (both the main wire and the little plug) and the battery ground terminal, before re-installing it.

I also think my diagnosis about the CD player may be wrong. When you disconnect the power, and reconnect it, you can hear a strange whirring sound (it's resetting itself?) that lasts for about 10 seconds. Whenever I tested for a drain, by connecting my multimeter across the battery post and terminal I effectively completed the circuit, restoring power to the CD player, so there was a temporary drain while it re-set itself, but the drain then stopped after 10 seconds.

So, what was the original problem? A bad battery, or a bad connection? Would a bad battery work fine (and allow the alternator to work fine) when it is re-charged?

[Donald]

Were the terminals on the alternator tight? If not that might have been your problem along with corrosion or dirt build-up. When you cleaned and reinstalled the wiring that might have been all it needed.

[NickR]

The main terminal on the alternator (the one with the thicker wire that is bolted on) looked good, though I cleaned it up anyway. The other connections however (the 2 smaller wires that just plug into the alternator, and are probably something to do with voltage regulation?) were a bit dirty and corroded. I cleaned them up with sandpaper and electrical contact cleaner. Maybe they were the problem.

[NickR]

Oh dear! The problem is back. Low voltage when the engine is running. The voltage increases slightly when you raise the rpm, but it's still too low. Replaced the battery with a known good one, but it made no difference.

Are alternators known to have intermittent faults? If so, maybe it was OK when tested, and worked OK for a bit afterwards, but then failed again. I removed the alternator, checked the brushes (they looked OK), reinstalled it, but still low voltage. There is a slight whine coming from the alternator.

Or maybe there's a short somewhere, which only drains voltage when the engine is running?

I am at a loss, and don't know what to try next. Any ideas would be gratefully received.

[Tercel GTS]

The rectifier is most likely bad on yours. That's the part the battery stud is made to. I can send you one if you need.

To test it remove the rectifier from the alternator. Use an ohm meter to test first from battery stud to stator terminals. Reverse the leads on the ohm meter, you should get a reading in one direction but not in other. Then test from one of the stud mounting holes to the stator terminals. Again you should get a reading in one direction but not in other.
Also while the rectifier is out check the stator to housing for a short. Do a good physical inspection of the stator to the best of your ability looking for melted insulation between the wires and the metal. Let us know what you find.

[4speedsleeper]

an easy way to solve thise problem is to replace the battery and altenater ayt the same time.

[NickR]

4speedsleeper: it's tempting to replace both battery and alternator, but expensive. And I'm not 100% sure that the problem doesn't lie somewhere else, like in the wiring harness somewhere. (Though I'm fairly sure it's not the battery, since I got the same symptoms when I replaced it with a known good battery.

TercelGTS: I think you may be getting me close to diagnosing the problem. Here's what I have found:

1. When I remove the rectifier from the alternator, everything checks out fine: testing the resistance between the stud (B+ terminal) and the other 3 terminals, I get 2.5 ohms (approx) in one direction; and infinite ohms in the other direction.

2. But, when the rectifier is attached to the alternator, I get a strange result: 2.5 ohms in one direction, but 100 ohms (approx) in the other direction. I get the same results if I test the resistance between the stud (the B+ terminal) to the alternator housing. Doesn't this mean there's a drain at the alternator? 100 ohms would allow 0.12 amps (=12volts/100ohms) to flow, which is more than should be flowing with the engine off.

3. Investigating further, I find that if I remove the voltage regulator from the alternator, I get the same readings from the rectifier as I do when I remove the rectifier (2.5 ohms in one direction, and infinite ohms in the other).

4. Testing the voltage regulator, there are 3 terminals, so 6 different ways to measure ohms (3 pairs of terminals, each one can be tested in 2 directions). The 6 readings I get are: 100, 100, 100, 11, 3, 3, ohms.

I am not quite sure what to make of this. But my feeling is that the voltage regulator is bad. Some of those readings ought to be infinite ohms, surely, not 100 ohms?

By the way, what do you mean by "stator" terminals? Are those the 4 little terminals on the rectifier, which attach to the wiring looms on the alternator casing? (Which do not rotate, hence "stator"?)

Can regulators be purchased separately? At auto parts stores?
Thanks again for your help.

[Tercel GTS]

Not at autoparts stores however a rebuilder in your area would most likely sell you one. When attached the rectifier will give inaccurate readings. I'm thinking you didn't understand where to test though.go from the B+ post to the places those 4 terminals should attach. Then go from one of the 3 ground spots back to the same 4 places. The 4 terminals produce a/c power then it goes through the diodes to seperate the - pulses to the top smaller plate and the + pulses to the larger lower plate with the stud. And yes, those 4 terminals are part of the stator.

[NickR]

Thanks again, GTS. Turns out the problem was not the rectifier, but some weird intermittent short, so that the resistance between the B+ terminal and the alternator case was about 6 ohms. What had me puzzled, and why it tested out OK in the shop, was that the problem was intermittent. The resistance varied, depending on how I held the alternator, or if I banged it with my hand. So that short would explain not only the low voltage (intermittent) but also the burning smell, and why it seemed to have drained the battery at one point.

I found this very useful sight on how to test a Toyota alternator: http://www.autoshop101.com/forms/h8.pdf

Replaced the alternator, and all working fine now.