JD B gen charging

Dick Boudrie

New User
I have a 1946 JB B where the generator is not charging the battery. The system is negative ground. I have carefully tried to follow John T's troubleshooting guide. This guide convinces me the generator is OK and it is possibly the cut-off relay. I replaced the relay with a new one, but still not working. The gen was polarized before I added the new relay so I shouldn't have damaged the relay upon install. I have carefully traced the wiring, convinced myself there are no open wires and grounds are good (used jumper wires to ensure.) The part of the guide that points to a bad relay is where I ground the F-term and jumper between the GEN/A term and the BAT term of the relay. The ammeter show charging.

When I turn on the lights the ammeter shows proper discharge current. I question the proper function of the light switch which is in the circuit from the F-term. How do I know in the proper setup that the light switch circuitry is properly handling the wire from the F-term?
 
Dick,
Thanks for asking such a clear question. Electrical issues are my weakest suit and I'm looking forward to all the good advice that will follow. I wish I was better at diagnosing problems, should have listened better when I was growing up... not that I'm grown up now. :)

Bob
 
Dick, does it start to charge

After you ground out the Gennys FLD post

ORRRRRRRRRR

NOT until after you ALSO jump BAT to GEN/ARM on
the cutout relay??????????? IE does it take BOTH

If it charges as soon as FLD grounded, but NOT otherwise, the wires open from FLD up to light switch orrrrrrrrrrrrr light switch isn't well grounded (Common problem) orrrrrrrrrr if it charges on HIGH but NOT on Low, the switches field resistor is bad/open.

Remember the Cutout Relay and the light switch and the genny, of course, all need a good frame ground.

If it only charges after BAT is jumped to GEN/ARM on the cutout relay, that tells me the relay isn't closing so it may not be well grounded, or is bad. Its supposed to close once the gennys voltage reaches a pre set voltage higher then normal battery charging BUT IT NEEDS A GOOD GROUND TO WORK.

If the light switch is good and well grounded a meter on its terminal that wires down to FLD on the Genny should read near zero ohms on high charge but a few ohms on low charge WITH RESPECT TO FRAME GROUND.

John T
 
In the process of exercising the light switch I realize some positive results. My previous post concluded whether there was charging based on ammeter readings. A voltmeter does show expected increases in voltage.

With the switch in the high charge position and fast idle I see about 5A and 7.2V at the BAT term of relay. With the switch in the low charge position I don't see much of a reading on the ammeter and 6.8V on the BAT term. With the engine off I have about 6.4V of battery voltage.

Also how much of a voltage drop should I see on the wires between the ammeter and the BAT term of the relay? With 7.2V on BAT of relay I see about 6.8V at the battery term.

In the low charge position of the light switch is it typical that there is little or no ammeter reading?

I believe I need to get a new light switch. While doing these tests and going for the different positions I can see erratic performance.
 
With the switch in the high charge position and fast idle I see about 5A and 7.2V at the BAT term of relay.

SOUNDS GOOD ENOUGH

With the switch in the low charge position I don't see much of a reading on the ammeter and 6.8V on the BAT term.

STILL SOUNDS GOOD ENOUGH

With the engine off I have about 6.4V of battery voltage.

Also how much of a voltage drop should I see on the wires between the ammeter and the BAT term of the relay?

THERE SHOULD BE VERY LITTLE VOLTAGE DROP ACROSS A GOOD WIRE AND GOOD CONNECTIONS

With 7.2V on BAT of relay I see about 6.8V at the battery term.

THOSE SHOULD BE NEAR THE SAME unless theres a bad or loose or rusted connection

In the low charge position of the light switch is it typical that there is little or no ammeter reading?

Not that surprising, Id expect maybe an amp up to 3 (subject to light switch condition and its resistor and its ground quality) but those ammeters aren't all that accurate

I believe I need to get a new light switch. While doing these tests and going for the different positions I can see erratic performance.

I AGREE

John T
 
Get the connections cleaned up so the 7.2 & 6.8 are close to the same and you will see a better charge on the low setting. Do this before replacing the light switch as it may cure the problem. Right John?????
 
RIGHT, there has to be a resistive connection somewhere for such a relatively drastic voltage drop in the circuit from genny to light switch to relay............

John T
 

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