Half bank boiling.

[buck_canuck]

Hello fellow DIYers. Just joined the forum so yes, I have a problem. I did a search first but didn't find what I'm looking for. My problem? I have a 24v system and off grid for 15+ years. I'm using (8@6v) L16 US batteries for the first time. They are in series and then paralleled for the 24v. 1/2 the system is boiling. The other half is not. The batteries are 5-7 yrs old. With a battery hydrometer the cells in the boiling batteries are reading from high fair to good. The other bank is reading good on all cells. What am I missing? I have never run into this problem before. We are only able to make it thru 1 night of power and hope that the sun is shining the next day to keep us going before firing up the generator. We have 1440 watts of solar which used to keep us going. Now it's a struggle. Any help would be appreciated.

 

[Hedges]

Entire string boiling? Or only some cells, because others in series are low?
Note the SG of each cell and the voltage across each.

Alternatively, one string is open circuit (or dried up? but you said SG good) and you are over-charging the boiling one?

 

[CoolWill]

You are using them for the first time, but they are 5-7 years old? So you got them used? Sounds like you are missing an opportunity to get some new batteries!?

Seriously though, have you measured the current going into each string while they're charging?

 

[yodamota]

being those are L16s, 1440 watts is not enough to charge those batteries on the best of days.

have you cleaned all the connections on the batteries?

 

[HRTKD]

have you cleaned all the connections on the batteries?

^ This!

@buck_canuck, when charging (or discharging) check the amps going to each battery bank. If you see a large disparity, then you know there is a problem. Either the battery or batteries in the other bank have high resistance (I think I have that right) or you have some poor connections. Check the temperature of each cable and connection. Anything hotter than the rest is a red flag.

 

[buck_canuck]

Thanks for all of the replies folks. To clarify a few things, Hedges: 1 whole string is boiling. Coolwill: I have been using these batteries for 4 years actually. 1st time using L16s. I used golf cart batteries previously. yodamata: I'm not sure where you live but 1440 watts does indeed fully charge L16s here. HRTDK: All connections are good. All of the cables on the boiling string get hot. I will check amps. Thank you

 

[littleharbor2]

I'm not sure where you live but 1440 watts does indeed fully charge L16s here.

You'd be doing good to get 40 amps charging out of that array. 8 L-16's would want about 80 amps minimum to PROPERLY charge. This may very well be why you are having problems. When do you equalize your batteries?

 

[400bird]

I have been using these batteries for 4 years actually.

1st time using L16s. I used golf cart batteries previously.

This confuses me, how are the L16s 4 years in use and 1st time?

Also, there is a minimum recommend charge current for lead acid batteries. It's not just about what you need to recover the energy you used.

 

[OzSolar]

I'm using (8@6v) L16 US batteries for the first time. They are in series and then paralleled for the 24v. 1/2 the system is boiling. The other half is not. The batteries are 5-7 yrs old. With a battery hydrometer the cells in the boiling batteries are reading from high fair to good. The other bank is reading good on all cells. What am I missing?

All of the cables on the boiling string get hot. I will check amps.

Is this when you're charging with the solar or the generator?
What size are your battery cables?

1440 watts/~24v = ~60 amps. ~30 amps/string should have a hard time heating up the battery cables is what I'm getting at.
And that's only when everything's is perfect which is not that often. You could be chronically undercharging your batteries (sound familiar?) and probably have been for quite some time.

Based on what you've described the string that is boiling is getting the bulk of the charging current from the solar. (as has already been mentioned)

I would note:
-voltage of each battery
-voltage of each string
-voltage drop between each string of batteries back and the charging sources in the power center
-total amps charging
-amps going into each string

IMHO, this isn't the sort of job for a hydrometer that reads from low to high. If it doesn't read the actual specific gravity I would upgrade to one that did. This is my favorite hydrometer. It was on sale for $32 last time I looked.

 

[littleharbor2]

1200 watts (maybe), divided by 28 volts charge voltage = 42.86 amps, best case scenario. 8 L-16's @ 24 volts have 780 to 890 amp hours. Not a good current to Amp hour ratio.

 

[Hedges]

Disconnecting one string to charge the other, 0.1C, would be closer.
I suggest disconnecting both strings, let settle 12 to 24 hours, check voltage of each battery (each cell if possible.)
Charge each string separately, disconnect and let settle. If some batteries lower than others, charge those individually (6V or 12V charger? Maybe power charger off inverter while using other battery string and PV?)

Boiling all 12 cells in series does not make sense unless charging voltage is too high.
Boiling 12s while not boiling the other 12s seems odd too, unless one bank taking more current than the other, SoC or something like that.

Is it some cells of each battery boiling? or all cells of all batteries in one string.

 

[glandpuck]

As a manager of a Trojan FLA bank, I advise this: Use your tools to manually stir up the electrolyte (assumes levels are to spec) in each cell, like an in and out series with a turkey baster. Make certain charging current is properly flowing into the strings (no corrosion or loose bolts). Make certain that your absorb voltages and absorb time are properly set. Depending on the battery, this may be 1-3 hours. After confirming that make certain that your charging amperage is adequate for the strings. After you have reached a 100 percent charge state as measured by SG and cell voltage, I would equalize the batteries following manufacturer's instructions. This will surly boil them all. If you cannot successfully do this, then there is a problem somewhere such as breaker, fuse, connection, charger etc.

 

[yodamota]

this is a good read for most FLA. at least this is what I base my maintenance/float/absorb/charger specs on

https://rollsbattery.com/wp-content/uploads/2019/11/Rolls-Battery-User-Manual.pdf

 

[buck_canuck]

Thank you everyone for the responses. Going to have a company come in and check things.