Generator voltage

C

cfordman

Member
with the engine running what is the voltage output of the generator? with a fully charged battery at 6.44 volts on the battery side of the cutout (diode) im reading upwards of 12 volts on the gen side. I thought it would be lower.
 
Fordman, are you REALLY sure your diode is correct polarity? If SO, with the fan belt off, the generator will "motor" all by itself & run the battery down. Bill W.
 
You should only see about 7/10 volt drop across the diode. If you have 12 volts on the input terminal and battery voltage 6.44 on the output terminal, then it sounds like you have an open diode or poor connection.
 
Voltage varies with the third brush position, load and RPM. I'm not sure how you are measuring the voltage and what you are using. The voltage difference you are reading between the generator and the battery side of the cutout seems too high; a 5 1/2 volt drop would be seen as heat in the diode. Can you test the diode to see if it good?

Pete
 
I'm with Tom, seems like an open diode too. With the engine running jump around the cutout and see what happens..i.e do what the reverse current relay is suppose to do. Do not leave it on, just for testing.
 
Is it a cutout or a regulator?

Perhaps it is a "fun projects" voltage regulator that looks like a cutout

Ever since they first came out I have wondered how it works, when they first came out i asked if it worked by dumping to ground and was told it didn't ---so if it doesn't dump to ground all it can do is limit the batt side voltage ---if this is how it works then the generator voltage would higher, perhaps much higher
 
The Model A generator is capable up to like 34 volts depending on how well the field is excited. So the 12V you're seeing is well within the realm of possibility.

More than likely an open circuit somewhere between armature and battery. I would expect to see something like 8 volts or so while the battery is charging.

Joe K
 
thanks to all who weighed in. I had posted earlier I thought I might have reversed connections when charging the battery and blown the cutout diode as generator quit soon afterwards. this wasn't the case but all of you who said blown diode were on top of the problem. COLD SOLDER joint causing an open. the generator is now turning out 7.5 volts at idle and the battery thru the diode is getting 6.5v. the ammeter is charging again. ole murphys law: just as I started the A and got out to look at the volt meter she died. wouldn't start, heard the electric pump spinning up, yup, outta gas. this is a great forum!!!!!
 
Because cfordman has closure, I'm gonna shameless hijack this thread 'cause you guys seem to know what you're talking about with these new fangled diodes. I had just put on one of those Fun Projects regulators. Was carefull to set up the third brush exactly as in the instructions. Went on a tour this weekend. 50+ miles, no problems. Then if started momentarily loosing power, kind of like when a condensor starts to go. I slapped on a new condensor, no change, and the loss of power became a dead out stall. Checked the voltage at the points, terminal block, coil. A fraction of a volt at all those spots. Checked the battery, and it had 6+ volts. Fuse was good 6V on both sides of the fuse block. While we were on that side of the engine, just for giggles I rapped on the voltage regular, and then I got normal 6+ volt readings at all those test spots. Slapped on the old diode cutout that I had, reset the 3rd brush for 6 amp charge, and took off for home.

Was cruising along nicely for about 20 miles, when it just stalled. Checked fuse, and it had blown. Popped in a new fuse, and smelled smoke. It was coming from the horn. Disconnected the horn leads, taped them off, and set off for home. But now the ammeter will not go above 0 amps regardless of the 3rd brush position. Wiggles below 0 at idle, but at anything above idle, just 0.

I don't know if the short in the horn was just coincidence or somehow related to the regulator going south. The genny was charging 6 amps before the horn short, now nothing. Could the short have fried the diode cutout? Or is my genny toast?
 
With regard to the fun products voltage regulator....

I have not seen a circuit description from the company that makes the product, but my understanding is that it's a "shunt" type of regulator. What this means is that the circuit will short the output to ground at a variable time to keep the average voltage constant. Thus, if the load is low, the output will be shorted to ground maybe 50 % of the time. If the load is high, then the output may not be shorted at all. Another why of saying this is that the "duty cycle" varies depending on the load.

Anyone have any other info ?

Marc
 
Well, I just answered my own question. Replaced diode cutout with an original cutout. Started engine, zero volts at the generator post, 6+ at the battery side. The generator is kaput.
 
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