Boiling Batteries

[Stu Jackson]

DH, ITWMB, here's what I'd do.

Disconnect all the house bank batteries. Reconnect one pair (2 - 12s to make 24V) and reconnect them to the charger. Do one pari at a time and see what happens.

Also, don't forget the connections behind each switch and all of the grounds.

[DeepFrz]

You say they are hot. What is hot? Is your charger temperature compensated?

[Dockhead]

Originally Posted by Stu Jackson

Agreed, but the comment was about a poor connection. Have you checked them all? Just trying to help from 10,000 miles away.

Believe me, I'm grateful for the attempt

I will check all the connections, but still don't see how that could cause all the batteries to be overheated equally, when the voltage is correct everywhere. It seems simply impossible unless there's a bad cell in all four pairs of batteries simultaneously. I'm missing something, I'm sure

[Dockhead]

Is anyone familiar with the Victron temperature sensors?

I found this:



which is marked "KL10" and "8-25 [little square mark which might or might not be a degree mark]"

I didn't think this belongs to the Multiplus charger/inverter because it is marked to 25 degrees, which is obviously not enough, and because it seems to go with Victron battery monitors.

But my Victron battery monitors were BMW-600's, which don't have temperature sensors, so maybe this is the correct sensor.

Anyone have a clue?

[Dockhead]

Originally Posted by Stu Jackson

DH, ITWMB, here's what I'd do.

Disconnect all the house bank batteries. Reconnect one pair (2 - 12s to make 24V) and reconnect them to the charger. Do one pari at a time and see what happens.

Also, don't forget the connections behind each switch and all of the grounds.

Excellent idea. I'll do just that.

[DeepFrz]

Does your temp. sensor look something like this? Check the one for your charger.
Temperature sensor for BMV-702 - Victron Energy

Oops, sorry, that is for the monitor not the charger.

[Dockhead]

Originally Posted by DeepFrz

Does your temp. sensor look something like this? Check the one for your charger.
Temperature sensor for BMV-702 - Victron Energy

Oops, sorry, that is for the monitor not the charger.

That's exactly it. But I have never had a 702 monitor. So it seems that this must be the right one. In any case, I'm trying to install it.

[woodenboats]

The marking on the cable lug containing the temp sensor means that it's made for a 8mm bolt and a 25 square mm cable. European stuff ...

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[witzgall]

Victron also makes a nice 24 v batter balancer, designed to keep 12v batteries that are in series in balance.

It has to be the connections, cables, charger or the batts themselves. Isolate and test.

Do you have the separate voltage sense wires run?


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[Jim Cate]

DH, I'm left needing more data:

How hot are the batteries actually getting? A good place to use your IR thermometer.

How much current is actually flowing during the "boiling" that you are observing?

Are you getting rapid electrolyte loss?

These bits of info will help isolate your problem.

Finally, I can't understand how folks think a high resistance connection somewhere in the circuit can cause excessive current to flow. someone please explaing that idea to me.

Jim

PS I too think you are possibly seeing 'gassing" rather than boiling...

[CarlF]

Before trying other things, check the most likely problem of a shorted cell. It doesn't do any good to measure a battery's voltage while it's connected to other batteries in the bank.

First. Stop charging. If it continues you could even have a "thermal runaway". If I understand your setup, the easiest thing to do is to one-by-one remove the jumper between the two 12v batteries in a battery pair. This will remove both of those batteries from the bank. Then briefly turn on the charger. When you have taken the bad pair out, the charging amperage for the rest should be very low (don't worry about the voltage - it's the amperage that is the problem right now). You can then put a voltmeter on each of the disconnected batteries. One will show a voltage around 10v or less.

Unfortunately, the boiling may have damaged the whole bank.

Here's a good explanation:

Thermal runaway in batteries - how to spot and prevent heat damage to your batteries

If all the batteries are good, then you can turn back to the charger. I believe the Victron temp sensor is standard for all their products. The picture looks like it. But this won't help if you have a shorted cell.

[zboss]

Have you confirmed the temperature sensor is not bad?

[chris95040]

Originally Posted by S/V Illusion

The most likely cause is a high resistance connection somewhere in the charging system.

Nah, really dont see this as a possibility.

v = i * r

For a given voltage (v) (which, critically, dockhead has measured at a sane float level) an increase in resistance (r) will -decrease- current (i). If some active gizmo was reacting to that resistance by increasing voltage, then maybe something weird could happen, but dockhead has ruled this out by measuring the voltage at the battery while the problem was occurring.

The only sensible option i've heard is the shorted cell. With a shorted cell, all of the voltage of that series loop is being applied to the remaining cells in that circuit. (again v=ir can convince you of this, r=0 for a short, so v=0 across that short. Your measured voltage is therefore divided amongst the remaining good cells.)

The shorted cell will therefore impact all batteries **in series** with that cell.

If you've got banks in parallel that are also getting hot, then i'm perplexed.

i guess its possible this is just too high a float voltage for these batteries. I mean, it is, right?

[Dockhead]

Originally Posted by zboss

Have you confirmed the temperature sensor is not bad?

Temperature sensor is not connected.

[Dockhead]

So here's the upshot:

Stu Jackson's method was the right approach. Should have thought of it myself.

The mystery is solved -- shorted cells in TWO pairs simultaneously, heating up the whole bank.

Although I manually switched the Victron to float mode, this did nothing but limit the voltage -- it was pumping its full output (I measured it with a clamp meter) into the bad batteries.

Once the bad batteries were isolated, everything returned to normal.

It is a grievous design fault of the Victron, in my opinion, that you can't have any AC power at all on board without the battery charger working, and you can't regulate the output. It complicated my work yesterday trying to fix it, not to mention life on board.

This also seems to be the cause of my fried alternator -- the demand for full power when the batts went bad finished it off.

So I guess a whole set of new batts is in my future on top of the alternator rebuild