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Phantom or ghost drain on battery

1776 Views 9 Replies 4 Participants Last post by  Dick in Texas
I have a 2007 NH TC-30. It has been a great machine but has developed a very trying issue! When shut off, the battery slowly drains until, after anything longer than 3 days, it does not have enough juice to crank. It is easy to jump and runs fine then. And if it has run long enough to recharge the battery, I can shut it off and let it sit for 3 days BUT no longer! The 15 amp fuse, when pulled, stops it. But I don't know how to trouble shoot to figure out what is in that circuit that is causing the phantom drain. Any ideas?
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Vehicles, including tractors, with computers put a constant drain on the battery. With a new battery, my '89 truck could sit for about a month and still start. If the battery was old and weak, a few days between runs would result in no start.

By contrast, cars from the '60s had no computers and could sit for 6 months or longer with a 3 year old battery and still start without a boost.
Thanks for the input. The battery is an 04/20 and very strong when charged. This is a new thing. Battery held up for days and days until this started. And pulling the 15 amp fuse stops it (which might be the case in your scenario as well, I realize).
Vehicles, including tractors, with computers put a constant drain on the battery. With a new battery, my '89 truck could sit for about a month and still start. If the battery was old and weak, a few days between runs would result in no start.

By contrast, cars from the '60s had no computers and could sit for 6 months or longer with a 3 year old battery and still start without a boost.
You're on the right track by pulling that 15 amp fuse. You may already know this, but your problem is often called "parasitic draw" or "parasitic drain." If you want to search around more for pointers on your problem, using those terms will probably help.

The normal procedure for figuring out what is causing the draw is to make sure any electrical accessories (headlights, etc.) are turned off, unhook the negative battery cable and place an ammeter in series from the negative cable to the negative terminal of the battery. The reading you get will show how many amps you are drawing. "Normal" values here, assuming there is something on your tractor that would always draw some current with the key off (a computer, as Tudor suggested), will be on the order of a few milliamps. Anything beyond that is a source of concern. In your case, I would expect you to see a few tenths of an amp draw.

From there, one would remove a fuse and check if the ammeter reading drops. If not, replace the fuse and remove another one. In your case, it seems you have it pinpointed to the 15 amp fuse. Doing this test with your 15 amp fuse installed, then removed (and observing the resultant amp drop), would confirm the culprit is in that circuit.

After that, it's a matter of determining what is on that 15 amp circuit (an owners manual should give some insight), and then systematically unhooking the various components on that circuit to pinpoint the actual culprit.

It may seem cumbersome, but when you get in the decision tree mindset by narrowing down fuses then components, it isn't so bad.
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One possibility is you have a bad diode in the charging system that it is draining back through. Some systems do not cut the power to the alternator circuit when the key is turned off and it can bleed or leak past a diode in the regulator/rectifier of the alternator/charging system with the key in the 'Off' position.
All very good stuff! I had used a circuit continuity light in line with the negative lead to the battery (so I could tell if I got a change without going and looking at a meter). The light is on with the key off, until I pull the 15 amp fuse. So I am pretty sure the problem is in that circuit. Unfortunately, I am not adept enough to narrow it down further (I have a degree i physics - we know why things work, but not how!). The leaky diode in the regulator/rectifier sounds right. I will get someone who is a little handier than I to help me check that out. THANKS!
So, guys, I definitely have A/C across the battery terminals with the engine running. I understand that is a sure sign of a bad diode in the regulator/rectifier/alternator unit. I ordered a new alternator - due Friday. I'll get it on and see if things are better. If not, it goes back and we try the next steps! THANKS!
That sounds like you made the right decision to replace your alternator.
A.C. current will make your lights work if they are incandescent, but your battery will not accept A.C. current as a 'Charge' current, and that will leave you with a dead battery.
By finding the 'A.C.' current with your voltmeter across the battery terminals, you found the source of it, the Alternator.
Your Alternator usually has built-in diodes and a voltage regulator on that engine, so it is either a 'Replacement' unit or having it 'Rebuilt'.
Most cases you just replace it with a new or 'Re-manufactured' unit, and that should take care of the problem for you.
A.C. current would make 'LCD' lights either 'Flicker' or not work at all.
Good luck with it and let us know if that took care of the problem.
Not necessarily. There are technical reasons for this (some beyond my understanding), but a non-zero AC reading at the battery terminals when the engine is running is not a sure sign that you have a bad diode. Go ahead and measure AC voltage on one of your other vehicles without a parasitic drain (car, etc.). I bet you get a nonzero reading with your meter.

With that being said, is the AC voltage test the only thing you did to identify the alternator as a culprit? Did you repeat your test light procedure after reinserting the 15 amp fuse, and disconnecting the alternator output wire? If the alternator is your problem, the test light will go off if this is a bad diode causing your drain. If the light stays on with the alternator disconnected, it is not your issue. Go ahead and do this if you haven't; save yourself some time and effort this Friday.

Do you have access to an owner's manual? That will tell you what is on that 15 amp circuit. I doubt the alternator interfaces with this fuse at all, but I don't know your machine, so can't say for sure.
So, guys, I definitely have A/C across the battery terminals with the engine running. I understand that is a sure sign of a bad diode in the regulator/rectifier/alternator unit.
Guys, I found the circuit! It turns out that everything runs just fine with the 15 amp fuse pulled. It controls hazard lights and turn signals, not used much on a farm, but I had tampered with one side to connect a sprayer to the light switch for a convenient on/off when driving and spraying. So I am up and running - at least until I discover something else that is on that circuit that is more vital. I will take it up to the local O'Reilly's so they can test the alternator while running, just to avoid any future surprises.
Thanks again for the help!
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