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Old 13-02-2011, 11:54   #1
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Smoking Hot Ground Wire

We have been having some battery issues for about a week. The house bank didn't seem to be holding a charge well and could only run the Lectra San (which draws about 30 amps for a couple minutes) when fully charged.

This morning we started charging using an Iota 75 amp charger and within minutes smelled an acrid smell and saw a small amount of smoke coming from the main house bank ground wire which had become hot enough to melt the rubber/plastic coating. The charger was putting out about 65 amps at the time.

The ground wire is about three feet long and runs form the battery negative post to a shunt for the battery monitor. This piece of wire was a 6 gauge wire at least 20 years old. The ground wire from the other side of the shunt to the engine block is a 1/0 gauge wire.

I replaced the hot 3 foot piece of 6 guage ground wire with a similar length 1/0 gauge ground wire and we started charging again, this time using the engine alternator which only puts out about 35 amps. Quite frankly, I was a bit spooked by the hot wire and concerned the the Iota was putting out too much amps for this set of batteries.

We have been charging now for about 3 hours starting at 35 amps decreasing slowly to 13 amps with no problem. No hot ground wire. No acrid battery smell. Batteries are warm, but not hot. They are in the engine compartment so some warmth is normal. Batteries were filled with water a week ago. None of the cells were unusually low.

The battery bank is a 440 hour bank made up of 4 Trojan T-105 6 volt golf cart batteries wired in series/parallell to make up a 12 volt bank. Two of them are about 4 years old and the other two are about 2 years old. One set of two have cases that bulge somewhat. We have been using this arrangement for two years and living aboard for the past 6 months, mostly on the hook. We've been charging the battery bank about twice a week with the Iota charger running off either a Honka 2kw generator or on shore power. Added the Lectra San about 4 months ago and it was working fine until a few days ago.

Sorry for the long post, but my concern is that even though the problem seems to be fixed, maybe there is some other issue besides the too small ground wire.

Is it possible that the ground wire has been undersized for the last couple years and did what it could for as long as it could, then finally just gave up?

Or was the hot ground wire just a symptom and I should be looking for something else that caused the problem?

All thoughts are welcome.
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Old 13-02-2011, 12:25   #2
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The #6 wire was not too small for that current. It must have been a bad connection at one of the ends. Replacing the wire repaired the connection. #1/0 is a better choice.
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Old 13-02-2011, 12:29   #3
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Hi,
have you checked the replaced old wire for corrosion internally? If not I would start there.
Second check each battery independently - mixing old and new batteries in one bank is not recommended.

good luck! Marco
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Old 13-02-2011, 12:48   #4
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Using a good multi meter do a voltage drop test on the connections to isolate the area of high resistance.
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Old 13-02-2011, 13:29   #5
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sounds like your old ground wire was corroded to fu$k,and acting like a resistor,hence heating up,replacing it and cleaning contacts was the correct thing to do.
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Old 13-02-2011, 14:01   #6
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I would check the batteries witht the bulging cases, this is not normal, I would bet those batteries are defective/bad.
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Old 13-02-2011, 14:13   #7
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Quote:
Originally Posted by daddle View Post
The #6 wire was not too small for that current. It must have been a bad connection at one of the ends. Replacing the wire repaired the connection. #1/0 is a better choice.
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Originally Posted by atoll View Post
sounds like your old ground wire was corroded to fu$k,and acting like a resistor,hence heating up,replacing it and cleaning contacts was the correct thing to do.
Well, the #6 wire had a layer of corrosion on each terminal end and when I pried it apart, the area where it melted had some greenish corrosion on the wires. Maybe the wire was the problem?

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I would check the batteries witht the bulging cases, this is not normal, I would bet those batteries are defective/bad.
It doesn't seem normal to me either.

Quote:
Second check each battery independently - mixing old and new batteries in one bank is not recommended.

good luck! Marco
Yu're right, but I was just too cheap to buy 4 new batteries when the two old ones were "just" two years old. I should have done it when we were in the states. I can hardly wait to find out what they are going to set me back in Marsh Harbour.
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Old 14-02-2011, 22:29   #8
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They'll cost you a few drinks, for sure :-)

I think you probably had at least two things going on:

(1) the AWG6 wire was old, corroded, and likely had very high resistance at the terminal ends; and

(2) the bulging batteries may have internal damage to the plates and should be replaced.

Actually, ALL the batteries should be replaced with new ones. It's costly, alright, but at least you'll know what you've got and you can take care of them. I'd also add HydroCaps or WaterMiser caps to reduce the loss of water.

By the way, four T-105's in series/parallel gives you 450AH at the 20-hour rate. These batteries can easily take 90A in the bulk & acceptance charging stages; your Iota is not too big.

I don't agree that the AWG6 wire was large enough, even had it been new. For a sustained 75A charge -- which the Iota can put out -- 1/0 is a much better choice. It offers much lower resistance and this is very desirable when dealing with battery charging.

Check ALL your battery connections. The series/parallel jumper cables should be clean and tight. Ideally, they should also be 1/0 or larger. The wise thing to do would probably be to replace all the cables with new ones which have been properly terminated.

Bill
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Old 15-02-2011, 00:02   #9
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Your #6 wire would be peachykeen at 65 amps if you were running AC or high voltage DC electricity, but you are running neither. So even without the corroded terminations, the heat buildup of 65amp, 12 voltsdc through a #6 wire is BAD for fire suppression. Kicking up the wire gauge was a very astute plan. As for warped battery cases, very few times is this a good sign, sorry. You could waste money getting them load tested or drain the kitty on new ones and have peace of mind. Would I replce all 4, depends if I had the money or could put the old ones on one bank and new ones on the other. Good Luck
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Old 15-02-2011, 05:52   #10
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Update

Thanks all for the wise counsel. I feel better now.

We were able to find 4 new 6 volt golf cart batteries in Marsh Harbour. Only cost about twice the US price. These are generics that the battery guy said were made by Trojan. Who knows, but they seem to be working well. Put them in yesterday and charged with the Iota with no problems.

The hydrocaps sound like a good idea. I'll look into those when we get back to the US.
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