Reducing charge with rpm?

G

Gus

Member
Righto, before I chase this electrical problem, I thought I would ask for advice.

Has anyone seen an ammeter charge decrease as engine rpm increases? It runs fine, ammeter responds to lights and horn correctly, 8 amps at fast idle. When I get up to cruising speed I noticed the ammeter dropped to a slight discharge. No lights on etc.

I swapped the original cutout for a diode and the problem is still there. I suspect a faulty ammeter.

Any ideas?

Gus
 
Gus said:
Righto, before I chase this electrical problem, I thought I would ask for advice.

Has anyone seen an ammeter charge decrease as engine rpm increases? It runs fine, ammeter responds to lights and horn correctly, 8 amps at fast idle. When I get up to cruising speed I noticed the ammeter dropped to a slight discharge. No lights on etc.

I swapped the original cutout for a diode and the problem is still there. I suspect a faulty ammeter.

Any ideas?

Gus
Click to expand...
Are you sure the belt is not slipping at the higher RPM? Good Luck:)
 
Doesn't sound like an ammeter failure. When an ammeter fails, it just quits.

I suppose a shorted generator winding could cause this. After running at high RPMs for a while, does the generator feel hot?
 
The generator charge rate will fall off very slightly after it goes past it's peak efficiency speed, but not as much as you indicate. There is something wrong inside the generator. You can remove the band and make sure all the brushes have good tension against the commutator. Also see that the commutator doesn't look burned, or running out of true as it's spinning. You could have a poor connection at the solder joint between the field coils, loose connections to brushes, worn brushes, bad ground at mounting bolt, etc. The other day I took apart a generator that had a very stiff wire from the output post to the brush. That will either add to the brush tension or more likely take away some tension.

Your armature could have loose windings that move at higher RPM and short out.
 
Thanks guys, very helpful. I'll start with the gen and go from there. I'll let you know what weird and wonderful things I find.

Gus
 
I took the gen (powerhouse) out yesterday and you were quite right, the commutator was slightly out of true. Not much but enough for me to see when I spun it by hand. It didn't measure out of round either so I suspect the shaft is the culprit, I lapped the conical mounting surfaces but that didn't change anything.

I used a fine file and spun it to file the high spot down a little but that was pretty ineffective.

Any tips on how to check whether it is a shaft or commutator as the culprit?
Gus
 
Stick it in a set of V-blocks or a lathe and you'll see where the problem is.

Many commutators wear eccentric which the lathe will show and a quick cut will straighten them up. Then a mica cutter [ or a hack saw blade] can be used to undercut the commutator sections.
I then usually wrap the commutator with fine sand paper and 'seat' the brushes before reinstalling the generator.
 
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Just curious; why would you have to "turn down" a commutator at all ? That is to say, wouldn't the shaft be true when made and stay that way ?

Marc
 
I doubt the shaft is bad. How much did the brushes move in and out as you turned the armature? A few thousandths should still work OK, but much more and you would need to do some carefull turning of the commutator. I made a special shaft so I can chuck the armatures in my lathe. It takes a very sharp cutting bit to trim the soft copper, or you can easily ruin it.

Do the brushes slide easily in the holders, and do each of the springs have good tension on the brush? I've seen a few powerhouse brushes stick in the holders.

I've quit restoring generators, at least for a while, until I can get caught up on my own needed work. If you want me to turn and test the armature, I can do that for no charge, except the postage both ways.
 
I had the same problem with my last AA; The third brush seems to have a shunting affect at higher rpms. I just kept fussing with the adjustment till I got an acceptable charge rate at road speeds.
 
3rd brush generators are/were designed to charge less at high speed ..teens and twenties cars did not want to over charge battery at highway speed as on a prolonged trip. they reach there peak at faily low speed and drop off as speed increases.
 
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