Parasitic load on battery

[joshuabardwell]

A few days ago, I went to use my tractor and the battery was dead. Like, won't even light up the dash dead. It had been a few weeks since I had last used it, but it was still pretty unexpected. The key wasn't in it, so it's not like I left the lights on or anything. So I put a charger on it and walked away. The next day, the charger still doesn't show that the battery is topped up, which was a little surprising. I decided to test for parasitic load. I disconnected the negative lead from the battery post and put my multimeter in-line. It showed 0.12 amps.

That doesn't seem like much, but maybe over time it adds up. It's 2.88 amp-hours per day. That's just over 20 amp-hours per week. Unfortunately, I can't for the life of me find the amp-hour rating of my tractor's battery, since nobody seems to care about car batteries' amp-hours, only their cranking amps, but the Internet seems to say that a small car battery might have as little as 40 amp-hours. I know deep-cycle marines get up around 100 amp-hours. And of course a standard car battery is depleted at around 50% charge, so it seems plausible that a .12 amp parasitic load could run my battery down in about 2 weeks.

The next thing I did was to reconnect the negative lead and go to the fuse box and check for parasitic load on each of the circuits. I pulled each fuse out and put the leads of the multimeter across the terminals. Each circuit registered zero. I don't know what to make of that.

The next thing I did was disconnect the negative lead again and put the charger back on the battery. At least that will allow it to get up to full charge in a normal amount of time.

Any further suggestions are welcome...

[cyrush]

Your loss may be through the alternator regulator which of course is not fused!!

Set up multimeter as before on battery leads then disconnect the alternator and see what happens ??

[k0ua]

That kind of a parasitic load is easily enough to kill the battery in 2 weeks just like you said. The other thing is that once a starting battery goes flat dead, you have done a lot of harm to that battery. They are not made to run flat, like a trolling motor battery is. It may charge up and work again, but it will never be the same. The regulator or leaky diode in the alternator (hum.. didn't you have a leaky diode in a welder? ) Anyway good luck in finding the problem.

James K0UA

[MBTRAC]

For equipment that's not used regularly I'd suggest fitting a battery isolator, it's a simple & easy solution to any parasitic load

[RickB]

That draw is about 6 times the level that gets my attention. 20 milliamps is about all you want from radio memories, ECU's . etc.

[joshuabardwell]

Your loss may be through the alternator regulator which of course is not fused!!
Set up multimeter as before on battery leads then disconnect the alternator and see what happens ??

Will do. Should the alternator normally have current flow with the ignition off?

[k0ua]

Will do. Should the alternator normally have current flow with the ignition off?

No, I don't think so. or maybe microamps.

James K0UA

[joshuabardwell]

I disconnected the leads from the alternator. I think I got all of them: there was one big one bolted on (probably the main DC output from the rectifier?) and one small plastic connector with two wires coming out of it (possibly an alternate AC output?). Anyway, the parasitic load was still there.

I'm really at a loss. Are there any other unfused loads? If not, then does that mean the issue must be in the alternator's circuit?

I'm starting to think I should just install a battery isolator and be done with, but I do hate the idea of my tractor not being shipshape.

[joshuabardwell]

I just had one more thought that I'll share. The whole testing the fuse box thing... as I think about it, if the issue is a wire that is shorting to ground, and if the short is between the positive battery post and the fuse box, then I don't believe I will measure any current at the fuse box, will I? So I think the problem could still be really anywhere between the battery and the fuse box. Maybe the answer is to trace backwards from the negative post of the battery.

[k0ua]

On my tractor the molex connector is the regulator connection. and the ring terminal goes to the 60 amp slo blow fuse and then to the battery. The Diode trio (one for each phase of the 3phase alternator) are inside the alternator and so is the regulator.. The regulator circuit works thru the key though. and is not powered unless the key is on. But if you had a leaky diode in the diode trio it would allow current to flow possibly. Pull the 60 amp fuse and see if the leakage current goes away. And pull the ring terminal to see if it is in the alternator. In fact I would do that first.

James K0UA