Battery showing charging when no charge applied

[labatt]

We're having a strange issue... and I thought all of our battery issues were gone when we replaced them in Ft. Lauderdale. We currently have 4 slimline AGM batteries, total 800AH. There's a Xantrex 1000 hooked up to them to monitor, and I've verified the accuracy of its reading. Today, we used all of about 250AH of capacity, and a few hours ago everything was reading correctly. I was just glancing at the Xantrex a few minutes ago, and it showed us at 98AH used (I know it's an estimate based on discharge and charge, but the point is that it thinks there has been a substantial charge to the batteries) and the battery voltage at 12.35v. It also showed that the batteries are receiving a charge - at times it's reading it as over 500AH of charge, and then it goes back to the proper discharge of -3.9, and then back up to a positive charge, etc. - but the generator, engine, etc. are not running. Obviously, a 500AH charge is never going to happen anyway, so it's a false reading of some sort. First off, I don't understand how the bank is at 12.35v. It should be closer to 12.5v-12.6v with the discharge state it was in a few hours ago. Second, where should I start looking for the reason why I'm showing a positive charge to the batteries when there shouldn't be one? All of the cables are new, terminals are new, and everything has been properly sized. The charger is new too, but the charger should be irrelevant since it's not even on. Any thoughts? Chris

[artbyjody]

Double check the grounding on the AC charger side and the DC side...

Weird it would be demonstrating two conflicting issues and a ground would be would be were I would trace...

[scottyt]

i would do a double check on the shunt, the resistor thing that the link hooks too. if the connections get loose it might show some funny things. even better would be to test the lines with an ohm meter, to see if the wire might have failed. i mean the little wire that goes to the link

[scottyt]

from xantex trouble shooting page

Troubleshooting Incorrect Readings

Incorrect Voltage Reading

1. Measure the voltage between the blue wire and the black wire on the terminal strip at the back of Link 1000. If the voltage at the back of Link 1000 and the voltage displayed differ by more than 0.05 volts, contact Xantrex Customer Service for further assistance.

Incorrect Amperage Reading

Incorrect Amperage Reading Link 1000 measures current by measuring a tiny voltage drop across the shunt. The shunt can be identified by its construction. It's made of two brass blocks connected by several copper strips and is mounted on a phenolic base. It is connected to the battery negative cable and to the system ground.

Amps Reads +/- 509 AMPS or "OL"

2. An open circuit or bad connection in one or both of the shunts for the associated battery, will cause Link 1000 to read its highest or lowest possible value for that battery, usually +/- 509 amps or "OL." To determine if the problem is with Link 1000 or in the system wiring, remove the shunt sense wires for the affected battery bank from the terminals on the back of Link 1000. Connect Link's terminals to each other and to the black wire terminal.

it sounds like the shunt wiring like i thought. i would check it like it says above and go from there

[labatt]

Just a followup... the discrepancy between battery voltage and the number of amp hours reported used is probably due to the fact that this problem may have been going on for a day or two. I usually run the generator until the Xantrex amp hours used reports close to 0. If there has been "false charge", the amp hours used has been wrong and I may not have been fully charging the batteries. Let's write it off to that. I hooked up my voltmeter to the batteries to watch what happens when the Xantrex reports a positive charge. The volts stay constant at 12.36v the whole time. My multimeter maxes out at 10A, so, not knowing exactly how it works, I'm hesitant to measure amperage on the batteries for fear of blowing a fuse. If I have most everything turned off, does the multimeter report the DRAW across the batteries? Or will it report something else in "Amp" mode? Anyway, just thought i'd add this info. Chris

[labatt]

I'll check the shunt wiring in the morning... I'd be "happy" if it was just the Xantrex...

[scottyt]

i think you are on the right track on the charging issue. esp if you shut it down when it says "0". if the amp limit on the meter says ten you should be able to put it in line up to ten amps. i would shut everything off except the link, and a few lights and check it.

i would still bet the shunt wires or something else related caused you to under charge, like you think. unless you have been cooking the batteries by over charging, i seriously doubt it is a battery issue. you might want to check your solar controller when the sun come up just to make sure its not over charging