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Had my 1940 110 rewired by an electrical shop. Everything fine for a 30 days then the amp. nailed positive and the distributor rotor had such a high voltage it melted the plastic in the cap.

Today replaced the cap and the voltage regulator and yes polarised it.

Same thing happened this afternoon.
Suggestions where to start looking please.
The shop is over an hour away so rather solve in my garage.

thank you
John Miller

There is PDF manual in the archives of this site called AutoliteGenerators which I found most interesting in describing the operation of the generator and regulator.

I am an Electronics Engineer and thought I knew everything to know about this subject and started messing with the voltage regulator in the old 50 Chevy in 1959.

Soooooo if the Ammeter pegs you are in danger of destroying the Ammeter not to mention the potential for a wiring fire.

If it pegs to the full charge side this tells me that the generator is putting out too much power.

I use the term power (Watts, Volts times Amps=Watts).

The voltage regulator when operating properly regulates the voltage from the generator when the engine is running to about 7.5 Volts for a 6 volt car. It limits the current as well and I would guess about 50 Amps. 50 Amps X 6 Volts = 300 Watts.

The limiting factor is the amount of heat the winding on the armature of the generator can take as the armature is the source of output from the generator.

The wiring of the car is another limiting factor and the main power to the ignition switch is quite heavy and can get real hot should a short occur.

Jim

Might also be good to rule out any chance the field wire is shorting somehow. Bent terminal, chafing, too long of screw, something shorting out the field resistors under the regulator etc.

I'm having a problem trying to connect what's happening on the primary side to what could happen on the secondary side to melt a rotor. Sure, the generator field could be grounded and max out the generator output and if left unresolved will certainly destory the generator, regulator, battery, perhaps the ammeter and likely some of the primary wiring, not to mention the fire hazard. But how do you translate that to something on the secondary voltage side that can produce those kind of temperatures. Really strange - melting a cap/rotor? - unheard of in my 50 years of old car experiences.

What's the diagnosis from the electrical shop that performed the work? What voltage do you see at the battery while the ammeter is pegged?

Hi John:

Okay, let's get down to some garage mechanics to sort out your problem.

The only way for the ammeter to peg positive is if either the generator is full fielding, or the gauge is hooked up backwards and you have a short circuit.

I will rule out the later because you said the thing was fine and the went haywire.

So go to your generator and you should have three wires:

a) a large red one on the heavy post - armature
b) a small tan one on the small post - field
c) a small black wire screwed to the generator - ground

Disconnect the tan wire. If the problem goes away you have a short circuit between the generator and the regulator in the tan wire.

If the problem persists then you probably have a shorted field winding in the generator and the unit will need to be repaired.

I wont concern myself with the other phenomenon because it is too wierd. I assume you are using a 6-volt battery.

Quote:
"distributor rotor had such a high voltage it melted the plastic in the cap."

I'd sure like to see a pic of the melted area of the cap. It's not clear to me what makes u think the rotor got so hot to melt the cap. Does that mean the cap is melted IN THE TOP CENTRE of the cap????? Quite frankly it is nearly impossible for the rotor to do that.


POssible causes of distributor HOUSING to get so hot it melts something (but not the way described above):

Wire INSIDE of distributor that connects to points is frayed insulation and touching metal of dist housing. BUT pegging the ammeter implies the COIL is shorted AND a bad distributor wire. Otherwise a good coil only draws about 3 amps. 3 amps not enuf to melt as described. ***** Maybe it's a 6volt coil on a 12v conversion?????? ****

Wait a minute. I'm not familiar enuf with this particular model but is the ignition circuit independent of the ammeter circuit????

You want to know the generator is properly wired to the regulator and the rest of the car. Keep in mind the power supplied from the generator comes from the armature.

They say do not connect radio noise suppression capacitors to any terminals on the regulator or the field connection of the generator.

The regulator regulates voltage output first as long as the current is in the proper range.

The regulator pulses the field winding by rapidly opening and closing the contacts on the voltage relay in the regulator.

If you have a voltmeter you would expect the voltage to be close to the 7.5 on the armature connection but the field will vary depending on the load and it will be a pulse waveform and be difficult to read with a digital type meter.

You would want to be ready to measure the voltage coming from the Armature terminal of the generator when the problem occurs.

Jim

Turned out to be the generator.
In for a rebuild this week.
Thanks to everyone saving this file for the future.
John Miller

ok. Great. Glad u found a solution. But it is still not clear to me how a bad GENERATOR caused a distributor CAP to "melt".