Mysteries of starter and generator circuits

[DonaldSmith]

My starter would crank well for a bit, but not long enough to start the engine. I would push the button again, but harder, and maybe get a brief "unk". The battery was charged and the connections were tight. I had opened and cleaned the starter switch,and it checks out fine.

It seems the hotter the engine got, the worse the problem got. But today, with the engine cool, I couldn't get enough cranking to start it. I will need a good cranking to check the compression. So I re-studied the starter solenoid circuit.

Chrysler had a brilliant idea. Instead of directly grounding the solenoid relay circuit (power comes from the starter button), they grounded the circuit thorough the generator armature windings. With the engine not running, this would be a good ground, but as the generator commenced running, the generated current would cancel out the grounding current. Thus, the starter could not be cranked while the engine was running.

As a fix, I disconnected the solenoid wire at the A post of the generator, and directly grounded the wire. Now I can crank till the battery runs down. A jumper wire to the solenoid will allow me to crank at the engine compartment when I check the compression.

But I wonder if this problem is an indicator of a fault in the generator. We shall see. in the meantime any information on the generator theories and practice of would be helpful.

[Don Coatney]

Can you post a schematic to better explain what you are saying?

[DonaldSmith]

I'll try. if this works, there may be no end to the stuff I attach.

[Kevinb71]

Based on that schematic, a condition where the solenoid won't pull in but will pull in when you ground the A wire, would definetly indicate a problem in the generator. Could just be bad brush's or maybe more serious in an armature problem. That is a very interesting circuit as you said as it would prevent accidental (or intentional) running of the starter when the car is running. Check your generator brush's!

[DonaldSmith]

Hmm...

At the 2003 National DeSoto Club convention, after my dome lights ran the battery down, someone gave me a jump with a 12 volt power pack. Then my generator stopped working. I had it rebuilt, but maybe the brushes have worn down in the meantime.

Over teh next years, I have had intermittent but persistent failures to crank; after an initial burst, the starter circuit would be dead, more frequently after the engine and generator have heated up.

At the Fourth of July parade this year, the temp gauge pegged, the car stalled, and the starter was non-resonsive. Someone got a jumper pack and by then the car started right up. Maybe it took time for things to cool down, or maybe the 12 volts jumped the generator brushes and completed the relay circuit.

Our 6-volt starters may be bullet-proof, but maybe the 12-volt jumpers damage the generator (and maybe even the regulator, which is conected to the same "A" post as the ground line from the starter solenoid).

Hmm... i think I'll leave the wire grounded directly, instead of grounding it through the generator armature circuit.

[Andydodge]

This is why I run 12 volts..........lol.........it works......lol.......hang on....just getting into my flameproof suit......right, got it on, zipped up........right, go your hardest!!....lol.......andyd

[Jim Saraceno]

Here are some links to electrical system and starter system diagnosis and repair. Hope it helps.

http://www.imperialclub.com/Repair/Lit/Master/014/cover.htm

http://www.imperialclub.com/Repair/Lit/Master/168/Cover.htm

http://www.imperialclub.com/Repair/Lit/Master/118/page01.htm

[Plymouthy Adams]

most staters with integral solenoids have the starter solenoid going to ground through the starter brushes..thus if open in he brushes, the starter is in-op..a worn brush can be just enough reistance to prevent picking up the solenoid, thus a light tap on the start will seat the brush and oft time allow the starter to engage..fail to see the tie in to the generator...

[greg g]

What is the source of that schematic??? It does't look like the one in my shop maual.

Which I have synopsized below. Some schematics refer to the solenoid as the relay and visa versa, some assemblies have a seperate relay which pulls in the bendix after and that connects the starter to the main power.

As far as I know all wires to and from the generator go through the VR. The Bat connection feeds the ign switch and other circuits through the Amp gauge. I think the diagram you posted is generic, not MOPAR

[DonaldSmith]

The schematic is for my DeSoto, and comes from the DeSoto Shop Manual. Yes, the solenoid or relay is (was) grounded through the generator armature.

So maybe I should kick the generator when the car won't crank. Or keep the temporary fix - leave the wire directly grounded.