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JohnZion 11-03-2013 12:33 AM

Huge Voltage Drain Problem - Ideas?
Today I noticed (according to the Xantrex battery monitor) that the batteries were being drained at a rate of -40A. The Xantrex also said the batteries were at 37% of charge, and at -275Ah (for 4 Trojan T125s). Normal high draw rate is -10 to -15A.

These are new batteries, installed 2 weeks ago. They were charged to 75% yesterday. I shut off ALL power (refrigeration, bilge fuse, main breaker, battery switch) and still the drain was -40 A. I started the engine, which normally shows that +40 A is going into the batteries. Xantrex showed -8A, and battery percentage and Ah still dropping. That then changed to -40A with engine still running.

I turned off the engine, and the voltage was 13.0, the voltage draw was -74A!!!! And battery at 17% charge. And this is with everything turned off.

The battery ground to engine looks fine. The bilge pump fuse was pulled. Refrigeration turned off. Still -40A to -74A drain. :eek:

Any ideas of what to check next? Maybe the Xantrex is wrong? It has been flashing "Charge Battery Full" all of the time, full or not, since batteries were replaced.

Meantime I have disconnected the batteries to keep them from draining. But this is not ideal, as I am a live aboard.


Gladrags1 11-03-2013 07:28 AM

Re: Huge Voltage Drain Problem - Ideas?
4 Attachment(s)
Can you test the voltage of the batteries with a tester when the Xantrex tells you they are at 17%? The voltage would be expected to be very low if that is the case. I suspect you are going to find that the batteries are fine and there is a problem with the Xantrex. Check documentation for Xantrex to see if there are any error codes. Maybe reset it and see if that corrects it?


JohnZion 11-03-2013 07:47 AM

Re: Huge Voltage Drain Problem - Ideas?
Thanks Tod, that's a good idea and I will try it this morning.

Ajax_MD 11-03-2013 08:56 AM

You definitely need to check this with an independent meter.

JohnZion 11-03-2013 09:31 AM

Re: Huge Voltage Drain Problem - Ideas?
I put a meter to the batteries and they read .10 amps lower than the Xantrex reads. I disconnected the batteries overnight, reconnected them this morning, and the unusually large voltage draw is gone. I have yet to reconnect the starting battery. There had been water in the bilge, but that is now dry. Could a small gauge bilge pump wire short have drawn -40 amps? Did resetting the Xantrex solve the problem, or is there something else?

TQA 11-03-2013 10:22 AM

Re: Huge Voltage Drain Problem - Ideas?
Just because the batteries are new does not mean you can not have one with a failed cell. I would check them individually.

The symptoms you give fit that scenario.

desert rat 11-03-2013 10:39 AM

Re: Huge Voltage Drain Problem - Ideas?
Chedk the bateries one at a time with a meter. If they are not dead your monitor is lying to you. If they are dead look for a fried wire. 40A melts insulation.

JohnZion 11-03-2013 12:32 PM

Re: Huge Voltage Drain Problem - Ideas?
I did check the batteries individually, they each read 6.22, they are 6 volt batteries. They are hooked together in a series. Would I check the individual cells with a hydrometer?

erps 11-03-2013 12:53 PM

Re: Huge Voltage Drain Problem - Ideas?
Is your house bank combined with your starting battery? If the voltage in your new house bank is higher than an old starting battery, the juice is going to run downhill into your starting battery and show a decrease in your housebank amp hr. reading.

fryewe 11-03-2013 01:12 PM

Re: Huge Voltage Drain Problem - Ideas?
You can check the specific gravity of each cell if you have a hydrometer small enough to use the limited electrolyte volume of your Trojan batteries. The sp. gr. of each cell should be within about 5 points of the average (.05).

Wire gauge as small as 16 can carry 40A without damage. Wire insulation damage may not be evident.

You should be looking for a place that a very low resistance to ground has developed…40A at 12V is 0.375 ohms equivalent resistance. You isolated loads and still had the current flowing and that indicates a near-short circuit to ground somewhere.

The best way to isolate something of this nature is to split your distribution system with switches or breakers or fuses while monitoring your instruments until the condition clears…then split the offending half again…and again…until you find the culprit. Near the end you may have to lift leads to isolate the fault.

Good luck.

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