Battery cells are not settling

morpho

Ok, I tried to not come back and ask another dumb question. But I can't get this new bank to settle into a groove.
I launched it in Jan and the sg readings are all over the place. In a single battery they can range from 1285 on the high side and 1260 on the low side. I ran a couple of EQ's on it but it made no difference at all.

Thanks.

Raj174

Hi morpho,
From your signature, it looks like you are over paneled. The battery banks max charge current is about 30 amps and you might manage that with 1800 to 2000 watts of PV depending on system loses. Try limiting the charge controller amps to 30 and see if that helps. 

morpho

Hi Raj,
I have it set at 25 amps currently so I don't think this is the issue.
Absorb is at 58.8 volts
Float at 56 volts
I don't know!? Its not burning through distilled water, no radical shifts in anything. The cells are consistently out of sync with each other. I know before I take any readings which ones will be "off"

Strange...to me anyway.

Vic

Hi morpho,

It will take some time,  and some cycles to 80% SOC or a bit lower for the battery to settle in.

Am not sure where the charge parameters came from,  but Floating at 56 V,  seems quite high,  to me.

What is the target SG that you are looking for?

FWIW,   Vic

morpho

Hi Vic,
the charge parameters came from the deka specs for the battery. Albeit the high end of the spec...so there is that. But they really don't spend all that long in float. Well, thats not totally true now as spring is here and we are getting float for 3 hours a day now. But up until recently we would hit float just in time for the sun to vanish over the horizon. 

Deka is saying Absorb 2.4 -2.45 v per cell, Float 2.3 - 2.35 v per cell
I set the current limit to 25 Amps as recommended by a bunch of people here, but in just looking up the spec sheet again, it says 30% of 20hr rate. (230)

What would my ideal sg be...? The spec sheet says 1.265 So that sounds good to me, but if things have been getting too much you would think the lowest end of the spectrum would at least hit the 1.265 while the others shoot way past it.

morpho

I knew I had asked the 30% of the 20/h rate question before. I just went back in old posts and it was determined I would only want to hit that 30% in the dead of winter to try and get the system charged with limited daylight hours etc. Not a problem here for the most part. I just turn on the gen anytime I think it won't make it on its own.

Could it be the batteries never get down to 80% SOC? We hit 85% SOC as sort of the bottom. Maybe it has seen 80% a couple of times at the most since it was launched.

The fact that I am seeing SG readings in the 1.285 range...should this concern me? That seems pretty high, to me anyway.
The previous bank (same batteries) were always, always - no matter what I did - 1.260 across the board. Just under what the spec sheet said was 100%

Vic

Hi morpho,

Thanks for the data  -- Personally,  I would try to cycle the batteries below 80% SOC,  perhaps to about 65 - 70 % SOC,  a few times,  and see if the SGs settle in better.   Some batteries require more cycles than others.

56 volts does seem high,  but Deka knows their batteries ...  perhaps they are Lead - Calcium batteries,  which appear to like --3mV per cell,  per degree C Temperature Compensation ...  my guess.

You could try cycling the batteries to about 65 - 70% SOC,  but they would need to be charged to at least 85 - 90% SOC soon,  thereafter,  to be safe.   Also,  using SG measurements for the SOC values would better than other estimation methods for these SOC values.

This battery bank is young.  It is good that you are paying attention to them.

Forget where you are located,  but,  it is always a good idea to use a Remote Temperature Sensor (RTS),  on all charge sources.

The range of SGs does  not seem too excessive,  but cycling Deep Cycle batteries is good for them.  And with my batteries,  deeper cycling (but not below 50% SOC)  seems to help reduce the SG of cells which have high readings.

YMMV,   please let us know how you are doing.   Thanks,   Vic

morpho

Thanks Vic.
Cool...nobody yelled: "RUN FOR YOUR LIFE!" or even worse..."you need a new bank" so that makes me happy.

They are like weird little critters living in a box in the utility room. Living, breathing, ....demanding, little acid spitting demons! but I love them all.

Ok, I will try and let em get a few drops into the sub 70% range and see what happens.

You said taking sg readings is more effective a way to get the SOC, but if they are all over the place...what can be gleaned from those readings?

I have 2 RTS on the bank and the temps are well within the happy range; though I have been thinking of getting a glass thermometer and taking readings in the cells to confirm things are what they say they are.

WaterWheel

morpho, like you I'm also a bit over paneled for my battery bank size although not as much as you.        I've found that the 1st battery in the series has a higher SC than the others in the group after a good charge for several hours after the sun goes down and they are resting.     If that is the case for your bank the float charge at 56v may be aggravating things,   56v sounds more like an absorb voltage;  float usually is between 52v and 53v.

Try checking SG after a full charge or equalization and allowing the batteries rest with no load before checking SG.

morpho

Thanks Foolami, I will have a look at that.

Vic,
I thought it would be super easy to get the batteries to a lower SOC, but they just keep charging back up again!  I turned on everything in the house, every light, fan, opened the fridge and freezer once in a while to get them to kick on, turned on the tv, dvd, all the computers, turned the monitors up to full brightness, plugged in anything and everything that could be charged etc etc. Probably for a good 7 hours before I went to bed...Didn't even come close to getting down below 78% SOC.  Darn you PV and your "free power" falling from the sky and all things efficient in this house!

I am probably going to have to shut off the array to actually get down to a 65% soc. Too funny