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**Dockhead** · 22-08-2015, 06:18

My batteries are boiling again

I have been switching my Victron charger/inverter to float manually, but they are boiling again.

The voltage -- just measured at the batts -- is correct -- 27.6 volts (equivalent to 13.8v). Yet the charger is pushing a lot of current through them, and they are boiling

I don't understand this -- I thought that this happened as a result of voltage too high??

I have a temperature sensor which I never connected because the the charge current was never high enough to cause high temperatures -- 70 amps through 420 amp/hours of batteries. Obviously this will be a band-aid at least so I'm trying to find it so I can hook it up.

But meanwhile -- why is this happening?

S/V Illusion · 22-08-2015, 06:26

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

transmitterdan · 22-08-2015, 06:29

Dockhead,

That's a lot of current. It doesn't seem possible for 27.6V to push that much current through a fully charged battery. So either the batteries are not charged (check SG to be sure) or the voltage is not what you think it is. There aren't too many other possibilities.

Can you turn down the float voltage to 27V for a test?

**Dockhead** · 22-08-2015, 06:56

Quote:

Originally Posted by transmitterdan

Dockhead,

That's a lot of current. It doesn't seem possible for 27.6V to push that much current through a fully charged battery. So either the batteries are not charged (check SG to be sure) or the voltage is not what you think it is. There aren't too many other possibilities.

Can you turn down the float voltage to 27V for a test?

That's not what current is going through -- that's the maximum current the charger can produce. I just meant that the charger is not oversized and therefore I never had temperature problems before.

The voltage has been checked a few different ways -- it's exactly the correct set float voltage per the Victron specs. It's higher than what Trojan specify -- 26.4. But that's what Victron call "storage voltage" and after 24 hours (I think) the voltage goes down to this. There is no way that I know of to reduce the voltage manually. I've never had problems before and I would not think that 27.6v could possibly boil the batteries.

I have also checked the voltage in individual batteries. It varies a little (my bank is made up of four pairs of 12v batts. Each pair is wired in series to produce 24v. But the variation doesn't seem nearly enough to boil the batts, and besides that, they are all approximately the same temperature.

The electrolyte is not low, either -- all cells well filled this time (I caught it in time maybe).

One thing which is different from my normal usage of these batteries is that I have spent the whole summer in marinas and ports with very little anchoring. So the batts have been getting discharged rather little; mostly only for long sails. And every night they get put back on the charger. I know they were getting overcharged with excessive absorption cycles resulting from this, and after I realized that, I started putting the charger manually on float as soon as the bulk phase was over. I am surprised that they continue to get hot.

jstevens · 22-08-2015, 07:01

Since you haven't hooked up the temp sensor, does your Victron have a manual setting for batt temp? I also haven't hooked up the temp sensor on my Xantrex charger. It has a manual control which I normally set to Hot for dockside charging.
While crossing to Portugal I was using my generator to charge the batts through the Xantrex and it took a lot of gen time to get the batts to even 80% charged. So I moved the manual setting to Cold and the Xantrex put out a lot more current at around 14.7v. That worked well for the crossing, with only a few hours of charging each day, but then I took a berth in Cascais, plugged into shore power, and caught a flight back to the states for the next month - forgetting to move the switch back to Hot.
Shortly after I returned to Portugal I discovered the batteries were nearly dry because of overcharging. They were brand new Rolls, installed just before I left Florida, and they were toast.
It does sound like you have a different problem, just the same symptoms, but hooking up the sensor (or checking the manual setting) sounds like a good idea.

John

DeepFrz · 22-08-2015, 07:28

Shorted cell or battery in the mix?

CarlF · 22-08-2015, 07:43

I'd also rule out an internally shorted battery - it happens.

Disconnect each battery pair in turn and see if the charging amps drop.

Tayana42 · 22-08-2015, 07:48

Dockhead, mine was a different charger boiling my batteries but the charger developed a short that kept it at bulk mode never dropping to float levels. Check the charger at each of the stages.

S/V B'Shert

**Dockhead** · 22-08-2015, 07:59

Quote:

Originally Posted by DeepFrz

Shorted cell or battery in the mix?

Yes, but wouldn't that mean that just one battery heats up?

All of mine seem to be about the same.

Maybe I don't understand the principle.

P.S. I have an Argus battery tester which can detect shorted cells and which analyzes the general condition. I tested all the batts a couple of weeks ago and all of them were ok -- in fact surprisingly good. I will test them again this evening after they cool off.

exMaggieDrum · 22-08-2015, 08:43

Bubbling does not mean "boiling" necessarily. A wet cell being heavily charged can produce hydrogen gas and still only be warm to the touch. Have you measured the temp of the batts? I doubt they are at a temp to boil the electrolyte. But since they are bubbling so aggressively they are probably pretty warm just from the shear amount of current going in.

I would suspect a bad cell or multiple bad cells.

But the charger could be bad too. But from info given I would suspect the batts first.

transmitterdan · 22-08-2015, 09:03

Quote:

Originally Posted by Dockhead

Yes, but wouldn't that mean that just one battery heats up?

A shorted cell puts higher voltage on the remaining cells. The overall voltage may be 27.6V but that assumes 12 cells. If one cell is shorted then that puts 27.6 volts on 11 cells which is too much for float.

Check the specific gravity of all cells. A shorted cell will stick out like a sore thumb.

Stu Jackson · 22-08-2015, 09:11

Quote:

Originally Posted by S/V Illusion

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

Most likely the case.

Unless your charger, alternator or solar/wind system is pumping out an incorrect voltage for your bank you will not over charge.

Chargers produce the voltage, they know nothing about current except for the maximum amperage they are rated to produce. Batteries limit the current based on battery acceptance.

**Dockhead** · 22-08-2015, 09:37

Quote:

Originally Posted by transmitterdan

A shorted cell puts higher voltage on the remaining cells. The overall voltage may be 27.6V but that assumes 12 cells. If one cell is shorted then that puts 27.6 volts on 11 cells which is too much for float.

Check the specific gravity of all cells. A shorted cell will stick out like a sore thumb.

OK, I'm going to check them all.

But -- wouldn't a shorted cell affect just that battery? The per cell voltage would be ok in the other batteries, right?

In my case pair of batteries since I'm 24v.

But all the batts are equally hot, not just one pair. It doesn't make any sense to me.

**Dockhead** · 22-08-2015, 09:42

Quote:

Originally Posted by Stu Jackson

Most likely the case.

Unless your charger, alternator or solar/wind system is pumping out an incorrect voltage for your bank you will not over charge.

Chargers produce the voltage, they know nothing about current except for the maximum amperage they are rated to produce. Batteries limit the current based on battery acceptance.

That corresponds to what I think I know about it, and means I am stumped --

I have measured voltage at all the batteries (8 of them) and it's correct everywhere -- 27.6 volts, right on spec.

How can too much current be going through the batts if the voltage is correct?

Only by a shorted cell it seems to me. But I can't have a shorted cell in all of them simultaneously.