1941 B will not hold charge, PLEASE HELP...

[Tim Shanks]

I have a tractor trek for Ag Awareness in 2 weeks and I'm having a little problem. I put in a brand new walmart 12V battery. I reran all my wires for the battery terminals to the starter and to the Alternator. I followed the wiring diagram at the link below. Except, I do NOT have a Ignition Coil or Distributor, or even a warning light, even though I would like to put one in. Instead of a Ignition Switch, I have a simple ON/OFF Toggle Switch to excite the alternator to start charging. I have traced all wires with an OHM meter and checked for resistance on them all. Found no resistance on the wires. When the Alternator excites, it pumps out 13 to 14 volts. But, if I leave the tractor sit for even a couple of days or even a day, the battery be dead again. Any suggestions to check?

Also, on the AMPERES meter, if the needle goes to the right (+) side, is that charging or discharging. I could never get those damn things right.

Thanks for the help.

T. Shanks
12V Alternator Schematic

 

[TxAllisMan]

Take a test light and go from chassis ground to positive battery post and start unplugging wires.

Sounds like a voltage regulator is staying excited.

 

[TxAllisMan]

Ment to say when you find your voltage draw while unplugging wires the light will go out.

 

[Tim Shanks]

Actually, unless the Alternator has a regulator in it, there is none.

 

[Tim Shanks]

Sorry folks, I pointed you all to the wrong page for the wire diagram... Please see the correct link below.
Alternator Schematic

 

[Bob M]

Tim - Last thing first:

The ammeter should swing to the right (+) when the battery is being charged. Just remember "+" is good; "-" is not so good!

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Presuming your B wired up correctly, your new Walmart battery is healthy and there's not some other external electrical load that's left on (not likely on a "B"...), the battery running down is from a low current draw thru the alternator when shut down.

To verify take a VOM or digital multimeter and set it to the DC milliamp range. Disconnect all the wiring at the alternator (the cable to the BAT terminal and the aux plug). Now with the battery connected and your toggle alternator control switch "off", use the meter to measure current beween each alternator terminal and it's mating wiring harness terminal. Look for the following:

The #1 aux terminal should show no current whatsoever. (Any current flowing here says the external wiring is wrong.)

The #2 terminal should show a vanishingly small current flow (typically a few MICROamps). A flow measured in MILLIamps says the internal regulator is "leaky" and needs replacement. You can either replace the regulator yourself ($12 or so) or swap in a fresh alternator.

Finally current flowing at the BAT terminal should be on the order of a few milliamps. Anything greater than 10 - 15 milliamps means there's a problem with the alternator's internal rectifier bridge. Cheapest fix is probably replace the alternator with a fresh rebuilt unit.

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Hope this helps...

 

[Anonymous-0]

It needs a diode in line to keep the alt. from drawing from the battery when not in use, or unhook the battery cable when not in use.

 

[Jon Hurley]

I just put a disconnect on the positive cable of my "51 A. works great now.

 

[Tim Shanks]

I was reading yesterday and someone said he fixed his issue of a dead battery by putting a disconnect switch in on the positive terminal. The picture attached is how I wired it. But the funny thing is, before I turn the switch on with the tractor running, I get 11.8 or 12volts on the battery itself, and nothing coming from the alternator. Then when I flip the toggle switch on, I get 13-14 volts from the alternator at both the alternator and at the battery. But when I when I turn off the switch I still get 13 volts at the battery, BUT at the alternator I now get 16 volts...

Anyhow, if I leave things hooked up the way they are now, will I end up screwing myself or will it work?

Thanks

Tim Shanks

My Alternator wiring now