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Charging circuit question

Jill_ski

Jill_ski

Member
Joined
Oct 12, 2021
I know this has been done before but I haven’t found any threads with my symptoms. I was hoping you guys could help me out.

I bought my ‘79 244 knowing it had a bad alternator. I finally found one that would be compatible with an internal regulator. I got it all hooked up and had advanced auto charge my battery. Today I wanted to test my charging circuit to ensure it wasn’t just the alternator that was bad. I did a loaded test on my car. Turned it on and turned on a heavy load of headlights turn signals and hazards. I read 12.1 volts on the battery terminals and 12.1 volts on the alternator. (Measured positive to case). I have inspected my excitor circuit and my lamp illuminates. What could be keeping me from getting the 13.5-14v after the car is turned on?
 
When you connected the alternator. Did you connect and verify the case ground wire was in good condition? You can get a good enough ground to light the lamp but it won't charge with a bad case ground.
 
dl242gt said:
When you connected the alternator. Did you connect and verify the case ground wire was in good condition? You can get a good enough ground to light the lamp but it won't charge with a bad case ground.
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I did verify it was good. But I didn’t chase it down. I can run continuity from the battery negative to that terminal to check? Or is there a better way?
 
Jill_ski said:
I did verify it was good. But I didn’t chase it down. I can run continuity from the battery negative to that terminal to check? Or is there a better way?
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The metal case of the alternator has a connection for the ground wire I am referring to. If you suspect that ground wire is bad. You can use the negative side of a jumper cable from the case of the alternator to a good place on the engine block for testing. If you still don't get any charging. Then I'd say the alternator has a bad regulator or some bad diodes.
 
oldschoolvolvo said:
Here is some good reading material:

Dave's Volvo Page - Volvo Adjustable Voltage Regulators

Dave's Volvo page. Adjustable Voltage Regulators.
www.prancingmoose.com
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So I’ve stepped thought the charging portion of this document. It says at the bottom of that section that it could be “somewhere more obscure”. All of the tests in that section are considered passing. But I’m still only at 12.6v. Any ideas on the more obscure places to check?
 
dl242gt said:
The metal case of the alternator has a connection for the ground wire I am referring to. If you suspect that ground wire is bad. You can use the negative side of a jumper cable from the case of the alternator to a good place on the engine block for testing. If you still don't get any charging. Then I'd say the alternator has a bad regulator or some bad diodes.
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Great idea! I’ll give that a try tomorrow. Thank you.
 
What changed between the original 12.1v reading and the latest 12.6v reading? If you rev up the engine with minimal load (no lights, no fan, etc.), what's the voltage reading? What alternator did you install - original bosch/volvo from a later model year, or something else?
 
bobxyz said:
What changed between the original 12.1v reading and the latest 12.6v reading? If you rev up the engine with minimal load (no lights, no fan, etc.), what's the voltage reading? What alternator did you install - original bosch/volvo from a later model year, or something else?
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The change is that I charged the battery. It’s been in now a couple days and I’m getting 12.1v while it’s on. I installed a duralast 13023. I have currently tested the diodes, which test good. I have cleaned all of my grounds and re-attached them, I have driven it to try and “self-excite” the alternator. No dice. I have no battery lamp on the dash (which to my understanding means that my charging circuit is working). I have ran every test in the Hanes manual. All are testing good. I just don’t have any charge. Really stumped. I appreciate your help.
 
With key on engine off, what cluster warning lights light up? I don't have '79 wiring diagrams, but the '80 diagrams show the alternator, parking brake, brake failure, bulb failure, and lambda-sond warning lights all tied into the alternator wire. If you unplug the small wire going into the alternator, do the dashboard lights go out?
 
bobxyz said:
With key on engine off, what cluster warning lights light up? I don't have '79 wiring diagrams, but the '80 diagrams show the alternator, parking brake, brake failure, bulb failure, and lambda-sond warning lights all tied into the alternator wire. If you unplug the small wire going into the alternator, do the dashboard lights go out?
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Let me try
 
bobxyz said:
With key on engine off, what cluster warning lights light up? I don't have '79 wiring diagrams, but the '80 diagrams show the alternator, parking brake, brake failure, bulb failure, and lambda-sond warning lights all tied into the alternator wire. If you unplug the small wire going into the alternator, do the dashboard lights go out?
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Yes they all go out
 
OK, exciter circuit seems to be working fine, and the lights going out after starting mean that the alternator is producing some voltage, just not the 13+volts you'd like to see on a cold engine.

Was the replacement alternator new, or used? Either way, was it tested at a parts shop?
 
It was remaned. I currently just pulled it to take it for a bench test at the parts store.
 
You can try running 12v to the D+ small red wire. Make sure you use a fuse wire. If that doesn't make it charge then it's a bad regulator on there. Don't see how it tested good at the store if you can get it to work in the car.
I have had weird problems like this with the box store alternators. One I had from Autozone was shorted from the B+ wire to the D+. So it read the same voltage on either terminal and no charge light on. lol It had very low resistance between the two terminals off the car.
 
Well autozone and advanced auto both had a hard time testing my alternator. So I retuned it. Anyone had any luck with the alternators from IPD?
 
Jill_ski said:
Well autozone and advanced auto both had a hard time testing my alternator. So I retuned it. Anyone had any luck with the alternators from IPD?
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If I was buying on line I would consider the FCP Euro option as they have the best warranty. While you don't get a great warranty Rock Auto and Parts Geek have good prices as well.
 
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