12 volt conversion, voltage drain issues

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PCnerd73

New member
We have a 1949 Farmall C with a belly mower, got it used last year. 12 volt conversion was already done. Last year, it seemed to have a weak battery. This year I've put on new LED lights (grounded directly to the battery) new alternator, new battery, new voltage restrictor, new kill switch and a new headlight switch. Replaced all wiring, including the battery leads. All connections have been cleaned and greased.
Pretty sure I blew out the alternator diodes when I arced the battery on the body, so replaced it. New kill switch at the same time, since the old one didn't work. Still had draw after that, so got new light switch and voltage restrictor. Re-wired the remaining lines when putting those in, so everything is new. Plugs and wires were done last fall.
Everything appears to be wired correctly, and functions just great when the battery is charged. It used to discharge in a few hours, tested it last night (just got the new light switch in yesterday) and it seemed fine. Won't start this morning, and battery is at 1.9 volts. I'm just not sure what else to look at... Hoping someone here has some ideas to throw my way.
It's completely possible I have something wired incorrectly, just removed one wire at a time and put it back how it was previously. Of course I have no idea if it was right before, and it's hard to find diagrams.
 
To find the battery drain. Disconnect one battery cable and fully charge up the battery.

Multi-meter, DC amps selected. Connect one multi-meter lead to the empty battery terminal and the other lead to the disconnected battery cable.

Disconnect one appliance (light, alternator, switch, etc.) at a time. When the multimeter shows no amperage draw, that is the appliance or circuit causing the battery drain.
 
ajhbike":2cazlwer said:
Eugene...just curious but is it better to disconnect and test the ground?
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The initial problem is a significant voltage drain, sapping the battery over night. You could use continuity instead of voltage to help locate the problem area(s).

I find it easier to use battery voltage. Also, using battery voltage you can look for voltage drops in the circuit or appliance during the tests.

Edit. Start with the alternator. My guess is that you have a 3 wire alternator and it's still excited when you shut off the tractor.
 
Sorry, wasn't clear...you said to disconnect the battery cable....which cable...the positive or the ground. Your system made sense and is simple...I just wanted to know which battery cable to disconnect to test. John
 
ajhbike":3qi20eep said:
Sorry, wasn't clear...you said to disconnect the battery cable....which cable...the positive or the ground. Your system made sense and is simple...I just wanted to know which battery cable to disconnect to test.
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Doesn't make any difference.

I should have said amps in my previous post instead of volts. Most, even the inexpensive multimeters, will handle 10 amps.
 
I will add that it doesn't matter which battery lead is used for testing current draw, as it should be the same amount in either. For safety, the cable connected to the frame should always be disconnected first, and; therefore, is best for this test. The reason to disconnect the one connected to the frame first is, if the wrench slips or hits the metal of the tractor it will not arc, since this terminal is already connected to the frame. If you disconnect the ungrounded terminal first, a slip could connect the positive directly to the negative through the wrench you are holding resulting in a possible burn, or if you are really unlucky a battery explosion. Lead-acid automotive batteries vent small amounts of hydrogen and can explode if an arc ignites it. Originally these tractors were positive ground, but modern systems and conversions are usually negative ground, so either could be the best one to unhook first. Installation is the reverse of removal, ungrounded first, grounded last.
 
I installed a blocking diode on the back of my 3-wire alternator as part of my conversion. Current only goes one-way. Without it, the tractor can keep running at there will be enough voltage to keep powering the coil and also be a source of battery drain.
 
If you have a Delco alternator, trace the small wire that is nearest the big hot-all-the-time post back to where it is connected to your ignition circuit. Wire in a simple push button switch. When you start the tractor, push the button to excite the alternator. When you shut it off that circuit will then be open and unable to drain your battery. An alternative is to wire a diode into that circuit. Button is cheap and foolproof.
 
Gary Dotson":2ckhhi94 said:
The diode is cheaper easier and even more foolproof.
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I sometimes forget that my standards are not quite on par with those expressed here. There is practical and there is excellence.
 
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