Help? Gas station Shop installed New Alternator.
Drains battery overnight. Worked OK before New Alternator replacement.
It draws 3amp between B+ and heavy brown wire, key out.
1985 XJ6.

The 3 Amp Drain is through the alternator itself.
Since the test was from the battery terminal direct to the B+ on the alternator and the case, I dont think there is another drain like a light etc.
We already did the check by removing all the fuses. No change there.

Gas station Shop says it is due to weak battery.
Test battery:
Took battery cable off for two nights, starts right up.

Test Alternator Drain:
As I understand it, the B+ post is always on,
even when you turn off the key.

I measured the battery post to battery cable and it shows 2.8 amp drain.
I measured directly from battery post to alternater post using 10 amp setting and meter test probes from battery+ to alternator b+ post.
Alternater test shows 3amp drain measured directly without any of the brown alternator wires connected.
This means a continuous drain of 3amp hour after hour.

Does draining that many amps appear correct to you?
Or is there a problem with the alternator?
I read some where passive drain s/b 20ma to 50 ma range.

Alternator has two heavy posts; right post is 300ohm to case ground.
left post is 800ohm to case ground.
Other push on connector to dash warning light is 80ohm(recheck)? Brown and black wire.

Hoping someone can help out.
Gas station shop giving me the runaround.
Need more info to troubleshoot it.

Where can I get specs/test procedures for Lucas A133 Alternator?
What should I do next? Gas station Shop does not know what the problem is, and does not know how to test it.

Thank You,
Brighton Ray

 

Yes, 20-50ma is about where you wanna be....closer to 20ma on a car of this vintgae, I'd say.

I'd start pulling fuses until the draw goes away and then narrow it down from there.

Cheers
DD

 

The 3 Amp Drain is through the alternator itself.

Since the test was from the battery terminal direct to the B+ on the alternator and the case, I dont think there is another drain like a light etc.

We already did the check by removing all the fuses.

 

Did you try a different alternator? Most alternators today are rebuilt, and, because of that, are not failsafe. Try it and see what happens.

Also, check your ground wire to make sure it's not shorting out on anything (dumb, I know, but you'd be surprised).

 

I took the Jag to my regular repair people and they checked it at the battery post. Yes, test light indicates you have a drain. Then they pulled the brown wires off the alternator and the drain stopped.

I had the mechanic call over to the Gas Station Shop and expain that when he pulled the brown wires off the alternator, the drain stopped.
Now for a second time, The Gas Station shop has replaced the New Alternator.

Then later we did some amp measurements and discovered the
3amp drain right at the alternator itself. Key out. That is not within normal range.

Question:
Does anyone know the specs for ohms and amps at the alternator posts?
We are trying to find out if that amount of drain
indicates another faulty alternator, maybe bad diodes.

 

You need someone more knowledgeable than me for this one. But I did spot this info in an XJS Faq (for the full article go to the XJS forum, follow FAQ, then XJS book, page 190 or thereabouts).

XJ6, XJS, and XJ12 do have some common roots.

ALTERNATOR EXCITATION: The field on the XJ‑S alternator is excited through the warning light, so if this light is burnt out or disconnected charging may be intermittent. According to Randy Wilson, “A common enough design. Lots of alternators will respond like this... some would never charge. Here’s what happens: the alternator needs a signal to indicate the key is on, and a power source to boost itself into a charging condition... bootstrapping, if you will. This power requirement is low enough that a lot of alternators use the power flow through the charge light for this purpose. This is called the exciter. And, in reality, key on is not really an important condition to the alternator. You just don’t want to be driving the exciter full time, lest your battery will go flat overnight. Once the alternator is charging, it becomes self-exciting, and no longer needs or uses this external power source (oversimplification). Thus the light goes out.
“The exciter is used to induce enough of an electromagnetic field to start the current generation. However, there is always some residual magnetism floating around in a used alternator. With this residual, the alternator can generate a little bit of current, if you spin them fast enough. In the case of Lucas (and others) the current needed to self-excite is fairly low -- low enough that the current from the residual magnetism can meet the demand. This usually happens at 2500-3000 engine rpm. And as soon as the alternator is up and charging, operation is as normal. You don’t have an outside exciter source, but you don’t need it any more.
“The moral of all this is that silly charge system idiot light is a double-sided test. Everyone knows it is bad when the light is on with the engine running. Few people know that it is equally bad if the light stays off with the engine not running, but the key is on.”

So you might want to check the charging light behaviour and the connection to the alternator.