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Battery/generator issues - Testing generator

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BrandonBJ8

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I keep having to jump my car to start it so there must be an issue with the battery or generator. The battery was reading around 12v with the car off. After I got the car running, the battery read up to about 12.8v with the RPMs in the 2000-2500 range. The indicator lamp first didn't go off until about 2500rpms, but after revving it up there a few times it stayed off at around 1000 RPMs. I checked the brushes and they appeared to have some spring in them left.

I also hooked up a voltemeter to the D+ on the generator (and ground the DF). The generator itself never generated more than about 3.75v.

Any ideas? Thanks!
 
Watch this video by John Twist. The video explains how to polarize the generator and a very quick and easy way to test the charging system by removing one of the battery leads while the car is running above 2000 rpm. DO NOT USE THIS TEST IF YOU ARE RUNNING AN ALTERNATOR!!!

https://www.youtube.com/watch?v=wH_yIeKsBSM
 
Here's a manual that you might find helpful.
https://docs.google.com/file/d/0B2H...NDNmLWI0YTYtNjY5ZjQxZTA2NGFm/edit?usp=sharing

With only 3.75 volts on D, the warning light should never have gone out. I'm guessing you may have multiple problems.
Generally, a voltage in that range would indicate that the voltage from D is not making it's way back to the field windings inside the generator. Check the voltage on the F terminal. If it is lower than D, the problem is inside the control box (probably dirty contacts). If it is the same as D, then look for a problem with the wiring to the field coils, or an open coil, etc.
 
So my F voltage is in the 0.5 range. Looks like I may have a control box issue. Silly question...how do you remove the cover? There are 2 black "rivets" on the cover but you can't actually remove those. Then I have 3 screws (2 left side, 1 right) holding the entire unit in place (which are rusted so I might have to drill into them). I want to make sure there isn't an easy way (snap-off) to remove before I start drilling.

Thanks!
 
I went ahead and removed the stripped screws and removed the voltage regulator. Here's a few pictures of it with the cover off. I've since cleaned the contacts with some sand paper but that's about it. How does this look? Anything I can test now that I have it off?
photo 1.jpg
photo 2.jpg
photo 3.jpg
photo 4.jpg
photo 5.jpg
 
I expected it to look much dirtier on the inside. I may try it again after cleaning the contacts and wires before buying a new one.
 
Looks OK, although I'm curious about the discoloration around the battery terminals.

Main thing to look for with it off the car is nearly zero ohms between the F and D terminals. If you find a relatively high resistance (like 50 ohms or more) then most likely either the voltage regulator or current regulator contacts are not conducting. There is a circuit diagram for it in the manual I linked to above, page 21. Terminal D is at the bottom, the line to terminal F runs around the right hand side. On top is the "field resistor", just below that is where the two sets of contacts should be shorting out the field resistor. Use your ohmmeter to find out where the circuit through the contacts isn't being completed.
 
5 ohms is still too much; it should be down below 1 ohm. Basically a direct short, but many digital meters won't read zero even with the leads shorted together. 5 ohms may still be contacts, but it could also be a bad connection somewhere, like maybe between the terminals and the rivets that connect to them.

One other bench test is to manually open the regulator contacts and check that the resistance between F and D goes to roughly 60 ohms then drops immediately when you let the contacts close again. (Correct value should be in your service manual.)

There are other tests you could do, but they are more of a hassle (equipment and setup required) off the car, IMO. At least on a TR3, my preference would be to do the other tests on the car.
 
I am having similar issues with the charging circuit in my BJ8: battery being drained, ignition light on when engine is running below 2500 rpm. I measured voltage between terminal D and ground at idle: 0.5v

I then ran the engine up to 3000 rpm and voltage increased linearly to 2.5v

Resistance between D - F is 11.2 ohms.

The Lucas generator test document (referred-to earlier in this thread) suggests that this is an issue with the field coils ...? Has anyone else seen similar results? If possible, can someone with a known healthy charging system measure the resistance across D-F with the lead son D&F removed?

thanks,
steve
 
SteveHall64Healey said:
Resistance between D - F is 11.2 ohms.

The Lucas generator test document (referred-to earlier in this thread) suggests that this is an issue with the field coils ...? Has anyone else seen similar results? If possible, can someone with a known healthy charging system measure the resistance across D-F with the lead son D&F removed?
Click to expand...
Just to be clear, are you measuring across the D and F terminals on the control box, or generator? 11.2 ohms is way high either way; the generator should be around 6 ohms, while the control box should present very close to 0 ohms with the wires disconnected.
 
Yes - resistance across D-F of 11.2 ohms is the generator with the leads removed.

Resistance across D-F at the control box is 67 ohms- type is RB340 and range is 55-65 ohms - a bit high but not way out...

thanks
steve
 
SteveHall64Healey said:
Yes - resistance across D-F of 11.2 ohms is the generator with the leads removed.
Click to expand...
Normally, the generator field resistance is measured from F to ground. You're checking the field and armature in series. 11 ohms is still high, but could be just a dirty brush or commutator; so I'd try measuring them separately.
Resistance across D-F at the control box is 67 ohms- type is RB340 and range is 55-65 ohms - a bit high but not way out...
Click to expand...
That is correct only with the regulator contacts blocked open (or enough voltage on the D terminal to hold them open). With no voltage applied, the regulator contacts (both sets on a RB340) should be closed, shorting D to F.
 
Problem solved (I think). I went back to some earlier advice in this post re dirty contacts in the voltage regulator. I removed the voltage regulator and under a strong worklight noted a significant build-up of material between 2 of the 3 sets of contacts within the unit. After carefully removing the material, I noted that the resistance of D-F at the control box dropped to near zero (from 67 ohms). After re-installing the unit, the ignition light no longer indicates a fault. After a few drives, I will see if the battery is depleted at all.
 
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