Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
I'm hoping someone can shed some light on my recent alternator failures. I've had three alternators fail this year. The first, was the original, so I assumed it was worn out and I replaced it with one from AutoZone, which was close to the track. Two races later that one failed. I took it back and they gladly replaced it. I then took the new alt. to my local alt. shop and had them completely go through it. They replaced the bearings but said everything else looked good. This past weekend at the end of the day, the car barely started as I went to load it. What happens is, I'll start the car, and it idles fine with 14+ volts to the battery, then the idle shifts/changes and then the voltage changes to 12. I've checked all the connections, grounds etc. I did a search, but didn't really see anyone with the same symptoms. Any help would be greatly appreciated. Thanks, Eric
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: NWR, OR
Car #: 30
Year : 1992 Posts: 8523
Status: Offline
posted
You could also have a bad battery. Batteries are really six separate cells in series, rather than a single unit. Often a single cell fails -- your change of 2 volts could be the clue.
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
Jim, each time the alterntor failed, I had it bench tested and it was bad. After I replaced the alternator each time, the battery recharged and the car ran fine. Could a bad cell in the battery somehow have some effect on the alternator???
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: NWR, OR
Car #: 30
Year : 1992 Posts: 8523
Status: Offline
posted
You wouldn't think so.
I know I fought this battle with two bad batteries, and finally had to buy a brand-new one to fix it. It would work fine one session, and then not start for the next -- or the reverse. I never did look at the alternator, though.
Three bad alternators in succession seems like enough to make you think about what's common -- which is obviously not the alternator.
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
I just swapped batteries from my '97. The car starts, 14 volts to the battery and at the alternator. I let it idle for about 5 minutes, then it changes to 12 volts at the battery and alternator. Does switching the kill switch effect the alternator? I don't use it. The last time I switched it was during the last alternator failure. Everything appears to be in order.
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
Bypassed the kill switch, same thing, 12 volts. If the alternator is not charging, no sense in trouble-shooting. The problem is, I replace the alternator each time and the issue goes away. I can't get it to drop to 12 volts with a new alternator. I guess I'll go eat a big plate of turkey and think about it.
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
quote:Originally posted by Eric Richter: Antonio, voltage stays at 12
That ain't right. I think you're blowing voltage regulators because of an intermittent open circuit somewhere (even if the intermittent open circuit is the battery itself or kill switch).
1. Test that battery ... hook up a light to it and shake it a little.
2. Run a dedicated ground strap to the alternator body.
3. Jumper around the big terminals of the kill switch with some fat battery cable.
Depending on your kill switch wiring, #2 may effectively accomplish #3.
Alternators don't like to see open circuits. In a perfect world we would all be running 3-circuit kill switches that dissipate the alternator output through a resistor to ground when we "kill".
'99+ car, by any chance?
-------------------- Visit the Midland City Arts Festival!
Region: NW/OR
Car #: 04
Year : 90 Posts: 1765
Status: Offline
posted
Sounds like you are blowing diodes, probably from and intermittent open circuit in your kill switch wiring.
I always preach to replace these switches regularly (2-3 years) since they do not last forever and can be a major PITA.
So today I go out into the trailer to see how cold the car is and if I should think about putting in anti-freeze. The dash on my car won't light up, the whole car is dead. I wiggle the kill switch, and magically it all works if I hold it just right. Time to put in the new switch I bought last Winter....
I'd bet your switch is bad and its killing your alternators.
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
The manual says that you should not have more than 20ma of current with everything shut off. I tested this and have 3.5ma. Doesn't seem like I have any shorts, at least with things off. I'll pull the alternator, have it rebuilt, replace my kill switch and hope for the best.
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: NWR, OR
Car #: 30
Year : 1992 Posts: 8523
Status: Offline
posted
If the problem is inside the alternator at all, I'd go with Greg's idea about the diodes. High RPM with no battery connected puts too high a reverse voltage on them. It doesn't sound like your installation should be doing that, but after all, by definition you've rewired the car. Check your work again, as if somebody else did it.
BTW, one open cell in the battery is all it takes.
Short circuits are *probably* not your problem, open circuits or too much resistance in the paths to/through the battery *probably* are. A short in the charging circuit tends to be apparent in the form of the car falling on its face as the ECU starves for +12, lights dimming, melted insulation, bad smells, hissing batteries, smoke, etc.
I still think you should run a dedicated ground to the alternator ... takes less time and effort than hoping for the best and being wrong.
The only failed kill switch I saw taken apart, the issue was dirty contacts. Switches need to wipe their own contacts clean. When the car is off and the alternator is at no risk, cycle the kill switch several times so it can wipe itself clean. This could be your high resistance /intermittent open circuit right there.
P.S. JB, would you agree the diodes can break down in the forward direction too? ... spikes of 100V?/200V?/More? when the battery load isn't there (whether by design of the kill switch install or an unintended high resistance/open).
Region: NWR, OR
Car #: 30
Year : 1992 Posts: 8523
Status: Offline
posted
Mr. Jumper, once you get voltage in the forward direction, you get current flow, and the diode clamps to a more-or-less fixed voltage across it. If too much current flows, the diode can overheat and fail, but the failure mode is different from reverse voltage.
In short (pardon the pun), if the output is shorted the forward diodes are at risk; if the output is open, the reverse diodes are at risk.
Region: Houston
Car #: 91
Year : 1991 Posts: 2171
Status: Offline
posted
quote:Originally posted by Jonathan Christiinan: i suggest ordering an alternator from Mazda, i have tried the auto zone and pep boys alternators, all of which give problems.
Same with starters, they are cheap chinese rebuilds.
-------------------- Do I turn my 99 Hard S into a killerfast SM or seek a donor?
quote:Originally posted by Jim Boemler: Mr. Jumper, once you get voltage in the forward direction, you get current flow, and the diode clamps to a more-or-less fixed voltage across it. If too much current flows, the diode can overheat and fail, but the failure mode is different from reverse voltage.
In short (pardon the pun), if the output is shorted the forward diodes are at risk; if the output is open, the reverse diodes are at risk.
jim
10-4, I get that part ... the forward diodes are at risk under short due to over-current... but the diodes have a voltage limit in the forward direction too ... and when the alternator is spinning and we instantly take the battery load away, there is a voltage spike through the diodes in the forward direction, is there not? (Unless they have some other over-voltage protection built in ahead of that?).
In any case, I think we agreed years ago that having the alternator loaded by the battery at all times was the way to go.
-------------------- Visit the Midland City Arts Festival!
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
Should I leave the dedicated ground permentely? Should I run it back to the battery or on the frame somewhere? The kill switch I have I ordered from Advanced Autosports and is wired per their instructions. See Antonio's post from 4-27-07. The problem I still have is, once I put the new alternaor in, everything is fine untill it stops charging the battery, voltage drops below 12 and the ECU shuts the car off. I'm getting a different alternator,new kill switch and runing a seperate ground and I just put in a new battery.
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: NW/OR
Car #: 04
Year : 90 Posts: 1765
Status: Offline
posted
If you put in all that new stuff, your at 99% on fixing it for sure.
To be a little more thorough, check all the connections in the switch install and factory ground straps for tightness. There is a ground at the battery (depending on switch install), the rear of the PPF, and on the driver's side of the head.
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
Kent, that I can't be too sure of, not having a voltage guage, which I'm also putting in. If I'm driving the car, It depends on how much I'm using the brakes, wipers etc. I've never tested it while idleing.
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: So Cal
Car #: #29
Year : 1993 Posts: 232
Status: Offline
posted
Greg, I would much rather find the reason or the problem that is causing the failures, than just replacing everything but, I can't seem to on this one. I did put the old battery in my '97, so if the alternator goes out in that car I'll know it was the battery. Eric
-------------------- 2009 SoCal SCCA SM Champion "Only boring people get bored"
Region: Lone Star
Year : 1990 Posts: 4253
Status: Offline
posted
Eric, do you have a voltmeter?
I would try to figure out the problem before putting in another alternator.
Check resistance from the alternator ground (my shop manual shows two ground connections, one for the regulator, one for the field) to the car's body. It should be very low.
Regarding a kill switch, some don't wipe, so they are throwaways. I had a plastic key switch that lasted one year. Don't use that kind.
Mark, as far as diode ratings, in forward mode, they are rated for current, not voltage, but I think JB and I are just being picky...too much voltage = too much current.
-------------------- "Your victory is tainted! Asterisk! Asterisk!!!"--Lisa Simpson
Region: Lone Star
Year : 1990 Posts: 4253
Status: Offline
posted
Measure it and post what it says, we're looking for something obvious. The manual doesn't show a resistance spec for the ground, I would expect to see less than 1 ohm. Jiggle the harness/wires while you do this (battery disconnected).
-------------------- "Your victory is tainted! Asterisk! Asterisk!!!"--Lisa Simpson
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I did put the old battery in my '97, so if the alternator goes out in that car I'll know it was the battery. Eric
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