Voltage regulator

Reversed polarity on the alternator circuit will damage it for definite.
An alternator without good grounding or connection to the battery will blow it's internal regulator, an external regulator and or diodes in very short order.
Hence all the warnings about never ever disconnecting the battery and or ground with the engine running.
You may have to get your newly rebuilt one checked again.
Sorry to be the bearer of bad news
Malc
 
Oh, no, I have replaced all this stuff after the polarity was reversed. So this is all new hardware that hasn't seen a reversed polarity.
 
It sounds like you need someone who has first hand electrical problem solving skills. I would offer to help in person except that I am 475 miles away. PM me and lets see if we can solve this problem.
 
Thanks for the kind words and offers, Malc, TILLA, and Tom.

At this point, I'm almost ready to hit up sparkfun and build a 90A regulator myself.
 
Similar thing happened to me. My CS wasnt holding a charge (when i'd go to start the car, it wouldnt turn over unless i boosted it). so i measured the voltage at the battery with the car running and it went from 16-19V depending on engine speed. even though i knew this was incorrect i decided to go for a spin to see if the battery would charge. when i was about to park, i heard BANG! the battery exploded - it overheated and blew the pressure caps off. so i doused the car with 16 litres of water to get the battery acid off it.

i figure my VR is at least dead and maybe the alternator. it appears to be the original part.

should i replace it with the original alt and VR or do a 90A upgrade? i havent seen any clear concise instructions on how to do that anywhere. i just want to get the car running at this point.

how do i test the alternator and VR to determine which is not working?

thanks
brett
 
Similar thing happened to me. My CS wasnt holding a charge (when i'd go to start the car, it wouldnt turn over unless i boosted it). so i measured the voltage at the battery with the car running and it went from 16-19V depending on engine speed. even though i knew this was incorrect i decided to go for a spin to see if the battery would charge. when i was about to park, i heard BANG! the battery exploded - it overheated and blew the pressure caps off. so i doused the car with 16 litres of water to get the battery acid off it.

i figure my VR is at least dead and maybe the alternator. it appears to be the original part.

should i replace it with the original alt and VR or do a 90A upgrade? i havent seen any clear concise instructions on how to do that anywhere. i just want to get the car running at this point.

how do i test the alternator and VR to determine which is not working?

thanks
brett
Click to expand...

To get more ampergae, the alt itself must be upgraded. The most common bump is to use a 65A alt from an E12, since that bolts into the stock alternator bracket used on the E9. Later alts require later brackets, which are a huge pain to install with the engine in the car.

To test to see if the VR is dead (a virtual certainty if your voltage got to nearly 20) you unplug it and jump the 2 bottom pins on the connector. If the charge light goes off on the dash, the regulator is dead. If it is still lit, the alt is toast.

The connector looks like this:

. _| - |_
. | - . - |

The two lower pins are what you want to jump.
 
thanks for this! question: the test you suggest would mean that no matter what either the VR or ALT would be dead - the light can only be either on or off. so what state would the light need to be if both the VR and ALT were ok?

thanks
brett
 
Once again, my car is eating batteries. It is infuriatingly erratic. I've got a voltmeter reading the voltage as I'm driving. It will usually hover around 13.5V, but it will vary wildly, going down to 11.2 and up to 15. The idiot light remains on. I'm fresh out of ideas, sicne this is the 4th voltage regulator and the 4th battery. Rebuilt alt, too. Alt. belt is tight.

Help would be much appreciated.
 
This problem sounds suspiciously like diodes. If you have a shorted diode the voltage can appear to be normal or slightly high or low because the meter averages. However, this condition will quickly eat batteries. It's been years since I done this but I would use a scope (ac mode, 0.5 volt scale, auto sync) and simply look at the voltage on the main power lug of the alternator. You should see little arcs / scallops of about 0.25 volts peak to peak under normal conditions. If there is a bad diode you will see major spikes every 6th scallop.

If you don't have an oscilloscope (for me this is hard to imagine) you should be able to find a older shop with one. You can also check around with any EE friends you might have. Alternately you can take apart the alternator, locate the diodes, and measure each diode with a meter they should all have about the same forward and reverse resistance; however forward resistance should be low and reverse very, very high.
 
Wouldn't the diodes have been replaced when they rebuilt the alternator? I know the diodes (and the brushes) got fried on the last one due to my error.

I still have the 65A alt from an early E24, which is internally regulated, I haven't tried that one in a while.
 
Diodes should be at least checked with an alternator rebuild. However, in my day I've installed more than one set of bad replacement diodes. The final test after a rebuild should find a bad diode; however if the test only looks for approximate voltage and positive current flow a diode could be missed (there are usually 6). The rebuilded would either need to stress the alternator to capacity (and find it weak) or put a scope on it an see the failure. I suppose that the test quality would be determined by the rebuilder.

When you say your battery is dying what happens? Is it simply not taking or holding a charge? Is it boiling off water? A bad diode will not only cause a battery to undercharge the continuous voltage spikes from the diode can often boil the battery water away (all cells). Additionally, a bad diode will generally create a nasty engine speed tied whine in your radio.

In the end there is little to go wrong with an alternator. You active "alt" light also make be think diode but the widely varying voltage makes me think you could have a ground problem. Are you sure that the alternator is grounded well to the engine, and that the engine is grounded well to the body, and that the battery is grounded well to the body? If the starter works well then the Alternator / engine ground could be the culprit. If you are inspired you can make up a ground strap to connect the alternator chassis directly to the battery (this would need to be pretty heavy cable (<#6 if possible).
 
It seems like it isn't getting a charge. It sees a higher voltage (I measured it with a Fluke when the car was running) but after I turned the car off, the battery's total charge is reduced.

While I was driving, the volts would be pretty steady at 13.5 or so for about 10 min. Then, it would decrease, over the course of about a min, to 11.8, then drop over a couple more min to 11.2, at which point I was really freaking out. Then the voltage kicked back on, up to 15V, and held there. Then the car started acting very strangely, and my radio cut out, just like it did when I ran a different battery down, even though the voltage was well above acceptable levels.

So, it looks like it isn't getting a return current, but a return voltage, which to me makes no sense. Hence I'm about ready to take the whole car apart again and swap in another complete wiring harness I've got. This electrical stuff is killing me.

Alternatively, I could try my original alternator. Anybody know a place that will rebuild the alt and send the same one back?
 
Where are you measuring voltage? At the battery? The erratic voltages could be due to grounding / path resistance. You should be seeing between 13.4 and 14.4 volts when charging.

Will the battery take a charge with an external charger? If not the alternator won't charge it either.

Is the battery a wet cell type? Can and have you checked the fluid level? (Top with distilled water if needed / possible) Bad diodes tend to boil away the battery fluid over time.

How are you starting the car since the battery won't do it? These older designs really don't like being jumped. If you are jumping from a running car you can actually damage the alternator / diodes and voltage regulator. I always recommend jumping from a second battery if possible and then with a non-running car if not. If the second car must be running to get enough oomph you would be better off to re-position the jumper cables a bit to get a better connection first.

You say you're on your 4th battery, how long has it been installed? Does the car get driven for long drives (>15 minutes) regularly? How quickly has your car eaten it forth battery? It seems like there could be a correlation between

A wet cell battery's nominal open circuit voltage should be about 12.6 volts if it is charged. Any lower open circuit voltage would indicate a problem with the battery..

If the battery is not taking a charge there are 5 probable reasons:
1. The battery is bad. This can be low water, dead (shorted) cell(s), or general sulfated / stratified. This is caused by age, defects, and under driving / charging.
2. If you only drive a little bit the battery may not be getting a complete charge (this also leads to sulfation/stratification)
3. Your charging circuit could be faulty (regulator, alternator, diodes, wiring)
4. Your main wiring is resistive (if the starter works then the battery to starter path is OK but it does not mean the alternator to battery is OK). Generally the alternator will be grounded to the engine so ground is unlikely. However, the positive terminal connection to the battery has four failure mode: 1) connection at alternator, 2) cable break, 3, connection to battery connector (probably), and 4) battery terminal post (unlikely if starter works with charged battery).
5. The battery can have internal connection problems (open / weak circuit) usually due to bonding or corrosion.

It is actually possible to improve a sulfated (stratified) battery a bit by charging at a higher voltage (perhaps 15.5-16 volts) for an hour or two.

If your battery is totally shot (no fluid or internal open circuit) your symptoms are not unlikely. The question is, did the battery cause the symptoms or is there something else wrong that causes the symptoms (and kills your battery). Jumping?

I think the two tests I start with are:
1. Inspect the battery if possible
2. Disconnect the battery and try to charge it. Measure the voltage after charging - look for 12.5-6 volts.

REMEMBER - IF YOUR BATTERY IS SULFATED AND YOU CHARGE IT THE RESULT CAN BE EXPLOSIVE HYDROGEN GAS DISCHARGE! BE CAREFUL WHEN JUMPING BECAUSE THERE ARE ALWAY SPARKS!!
 
Wow, that's a good bit of info to digest. Let me see f I can break down the answers...

The battery(ies) used were all Optima Red Tops, so they are dry gel cells. No gassing issues. They are also all less than 4 months old. I think we can pretty conclusively rule out the battery being the problem, since my issue has happened over three different batteries. The last two have accepted external chargers with no issues. (got the charger after my second battery went legs up) The latest problem (not charging) showed up during my last drive, but it must have been going on for a while, since the car was on a less than 30 mile round trip. (perhaps an hour of total run time, mostly at low speed)

The car will start just fine if the battery has sufficient charge. It idles fine too, until the battery is discharged too much.

After checking the Blue Books, it would seem that, like you said, I have a Diode problem. To remedy this, I will take the 65A internally-regulated alt I have laying around, ground it, and jump the external regulator connection. That should work, unless it is a wiring issue, something I am very much dreading.
 
Dry cells... hmmm - I think I may have read somewhere that you used them in a prior thread. I do not know how dry cells will react to diode issues. However, a bad diode will usually make your radio sound like a buzz-saw (unless it is more modern with great filtering. It will usually cause your alternator light to come on, and it will greatly limit your ability to charge your battery. Additionally, it could possibly serve as a sort of rev limiter by starving the coil for power as well as messing with the fuel injection system!

Since you seem to have a fluke meter - try measuring the AC voltage across the battery terminals. Depending on the meter design, you should not see more than 2-3 volts of AC. A good article on the subject:

http://findarticles.com/p/articles/mi_qa3828/is_200508/ai_n14900160
 
To be honest, I haven't taken the car above 3k in a very long time, since the driveability has been suspect at best. It does have a fresh coil, though, as the old coil was way out of spec. Changing the coil after my little negative misadventure helped the driveability greatly. So, the coil should still be good. Hopefully. I've only noticed driveability issues when the battery goes low.

As for the radio, given the electrical natuire of my issue, I removed the fuses that link the external amplifier to the head unit to reduce power costs. The head itself is the suprisingly good Pioneer Avic Z1. (went for a juxtaposition with my coupe: ultra modern right next to very retro) So, in terms of internal filtering, I would say it has a large amount of it. When I did put the amp fuse back in, I heard no power feedback.

Thanks for the help so far. I'll report back when I put the other amp in.
 
Ok, I installed a refurbished 65A alternator with internal regulation, grounded it to the chassis with 10g wire, and bypassed the regulator.

The idiot light is off, the voltage is very constant at 13.16V at idle, and the Fluke registered next to no AC voltage. I think it works, although the voltage is pretty low. It dips slightly (.2V) when the lights are on, but that's about it.
 
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