Real Time help: new alternator voltage fluctuates with revs.

[hotgemini]

Need ideas, just installed a new alternator. Charge light stays on permanently.

Voltage increases proportionally with revs, 12v at idle increases to 18v by 1600rpm. Increases quite linearly.

Thoughts, ideas on what to check?

 

[OGBeno]

Voltage regulator?

 

[hotgemini]

BJ74 W/ External regulator, regulator is unchanged, simply undid the three pin plug on the old alternator, plugged in the new one.

It does seem like the field windings are getting a constant 12v, vis a vis the output voltage increases with RPM.

How do I probe the wires to the three pin plug to determine if something is awry there? the colour code is correct but obviously that only tells you so much.

 

[jblueridge]

Old alternator was retired or died a violent death?
I had an MGB alternator that blew a winding and in turn somehow fried the old-school external regulator.

 

[hotgemini]

Old alternator was retired, new alternator was meant to be a bolt-in 110 amp upgrade. It nearly did bolt in, except for having the wrong pulley and the wrong clocking of the upper mounts. Swapping pulleys fixed the former and have ordered a 15mm longer belt which should fix the latter issue.

Vendor has recommended triple checking the wiring-to and earth-of the regulator, will do that this afternoon and cross my fingers. Heading away for a long weekend trip in 52 hours time....

 

[hotgemini]

Have triple checked wiriring, pulled the brush holder apart on the new alternator to confirm no internal shorts or funny business, appears to all be in order. Pulled the external regulator apart to make sure it didn't have a stuck contact or any funny business.

Tried swapping brush holder assemblies between alternators, no change.

Tried adding a seperate earth to the earth stud on the starter (there isn't one stock), also no change.

I'm getting stumped and I can hear the whooshing sound of my upcoming long weekend away.

Thoughts? Suggestions? How does one probe the external regulator to confirm correct operation?

Is there any possible issue with the regulator designed for a 55a alternator now being fed from a 110a alternator? All my reading says no, but thought I'd ask the brains trust.

In short, HELP!!

-Adam.

 

[hotgemini]

Just swapped in the voltage regulator from my other BJ74 which is working fine.

No change in the behavior, charge light still on solid, voltage increases proportionally with RPM.

Ideas?

 

[hotgemini]

Have probed the 6 pin plug at the regulator and all appears to be in order. Only thing that I'm not sure of is the IG voltage is about 0.7 to 1 volts below the Batt+ voltage. Not sure if that is significant

 

[jblueridge]

Sorry, but you seem to be the best expert.
It seems to me you have tested everything.
Did you post in the Diesel & 24Volt Forum?

 

[hotgemini]

Nah, haven't posted in the 24v forum. Dropped it off at the auto-sparky in the morning, should know something in the next 3 hours.

 

[jblueridge]

No auto-electric guy in our town anymore. Huge loss.

 

[AndrewHadji]

this ever get resolved? Would be good knowledge to have :-D

 

[hotgemini]

So both of my custom-built 110a alternators had been made without connecting one wire internally, which triggers one of the two coils in the toyota reg (different setup to most comparable regs from other manufacturers). With that fixed they worked, but the voltmeter in the dash still varied a bit. Have since fitted a plug-in upgrade to a solid-state regulator which has fixed that, although at idle the new alternator doesn't quite put out enough to extinguish the charge light, so it juuuust glows. I might try to find a smaller pulley.