Opel GT Forum banner

1 - 13 of 13 Posts

·
Resident Whippersnapper
Joined
·
1,218 Posts
Discussion Starter #1
Hi folks. I've been working on the Opel again, putting all the lights back in in preparation for getting it back on the road. I recently had a problem with the alternator, basically there was a short when I flipped the headlights (not in headlight wiring, in passenger running light circuit) and the 30A alternator B+ fuse popped. Ever since then, when I fire up the car, and the alternator starts charging, the warning light stays lit, while the ammeter shows charge. Voltage at idle is 14.6 volts. Alternator is a Delco Remy 634 5 11 1 70A LT.

Please help!
 

·
Registered
Joined
·
18 Posts
I had a similar problem with a tractor. One of the diodes in the bridge rectifier had failed. Checking with a Digital Multimeter still showed the peak voltage In spec, but the RMS voltage was slightly lower. since the three phase waveform was missing one phase and the warning light would pulse.
It’s possible that the short caused one or more diode failures. Of course, tractor and Opel wiring for the charging circuit may be different.
It could also just be the voltage regulator.
Hope this helps.
 

·
Opel Rallier since 1977
Joined
·
1,712 Posts
I had a similar problem with a tractor. One of the diodes in the bridge rectifier had failed. Checking with a Digital Multimeter still showed the peak voltage In spec, but the RMS voltage was slightly lower. since the three phase waveform was missing one phase and the warning light would pulse.
Yes this is the common problem that shows the light still lit, and that I have seen multiple times with the GM alternators: 1 or more diodes in the rectifier circuits blowing out. The short may have taken out 1 or 2 diodes before the B+ fuse blew.

You can test this by gradually increasing the load on the alternator and monitoring the voltage at the battery terminals. With more loading, the output voltage will drop more than normal if some diodes are blown out, and the lmap will glow brighter. You can use the heater fan at varying speeds to put more load on the alternator, and then the headlights to put an even higher load on the alternator. The fact that the ammeter shows charging is saying that the battery is taking a charge so that is another load on the alternator.

OP, where are you measuring the voltage, and is this the alternator type with the connector with 2 terminals on the side?
 

·
Resident Whippersnapper
Joined
·
1,218 Posts
Discussion Starter #4
I'm measuring the voltage at the B+ output on the back of the alternator, and my alternator does not have the terminals on the side, it does have the B+ and D+ terminals on the back of the case.
 

·
Opel Rallier since 1977
Joined
·
1,712 Posts
Measure the voltages at both of the B+ and D+ terminal while running and let us know. That will be an added indication of the issue.
 

·
Resident Whippersnapper
Joined
·
1,218 Posts
Discussion Starter #7
I pulled the alternator a while back, and didn't feel like reinstalling it to test voltages. So I took the alt. to an electrical rebuild shop. Gil suggested that the internal voltage regulator is toast but the rest of the alt. is fine, probably. I will let you guys know what the shop says.
 

·
Resident Whippersnapper
Joined
·
1,218 Posts
Discussion Starter #8
Both you guys were correct, I got the alt. back today and the shop said that one of the diode trios (three diodes in one part) were bad. They also replaced the front bearing and did some other minor stuff. I reinstalled it, the alternator works, but now I have a different problem: when the car is running, the ammeter gauge stays at about 12 or so amps. There is no indicated discharge on the gauge with the ignition off, or ignition on, engine off.
 

·
Opel Rallier since 1977
Joined
·
1,712 Posts
Good deal! How long have you run the car with this charge indication? With the full diode bridge installed, the output and overall system voltage will be higher, and that will cause the battery to charge for quite a while as it absorbs a higher level of charge at the higher voltage. I would expect you to have to drive 20-30 minutes before the charge rate wil taper off. That would be normal.

You want to check the voltage across the battery terminals at a fast idle (1500 RPM or so, and it ought to be in the range of 13.6 to 14.6 volts. (That voltage will tend to drop lower when things get hot; that is normal.) If that is good, then do some static battery checks to see if the battery is taking and holding a full charge. After you drive it for a while to properly charge the battery, then stop and wait 30 minutes to let it 'rest' (technically, it dissipates the 'surface charge' inside) and then measure the voltage on the battery. It ought to be 12.6 ot 12.7 volts for a fully charged, and good battery. That battery voltage should not drop hardly at all after a day of rest if the batteyr is in good shape.

BTW, on your ammeter, if you turn the key to RUN but don't start the engine, does the ammeter deflect a tiny bit towards discharge when you turn the key? And does it indicate a noticeable discharge if you have the key in RUN, the engine not started and the heater blower motor on, or if you push the brake pedal and the brake lights come on? These are just checks of the ammeter itself.
 

·
Resident Whippersnapper
Joined
·
1,218 Posts
Discussion Starter #10
BTW, on your ammeter, if you turn the key to RUN but don't start the engine, does the ammeter deflect a tiny bit towards discharge when you turn the key? And does it indicate a noticeable discharge if you have the key in RUN, the engine not started and the heater blower motor on, or if you push the brake pedal and the brake lights come on? These are just checks of the ammeter itself.
Yes, when the key is turned on the gauge does deflect slightly, moreso when accessories are turned on without the engine running.
 

·
Opel Rallier since 1977
Joined
·
1,712 Posts
OK, good, so the ammeter appears to be working. Just to be clear on one matter: When everything is off, is the ammeter at 0A (in the middle) or is it at 12A?
 

·
Opel Rallier since 1977
Joined
·
1,712 Posts
OK good.. so the gauge is good. Drive the car for 20-30 minutes and see if the charge rate settles back towards 0. I've ben through this after repairing an old genenrator, and it just took some time to get the battery 'topped up' with charge. Let us know what you find.
 
1 - 13 of 13 Posts
Top