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Author Topic: Battery Bank temperature questions  (Read 699 times)
heatherhopper
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« on: July 11, 2017, 02:14:57 PM »

Anyone else with a battery bank noticed a step change in operating temperatures this year?
What temperature compensation adjustments do others make for summer operation?
My bank is six years old and lives in a relatively uncontrolled environment so the annual temperature profile is quite broad but comfortable. For the first time this spring/summer, though, I have needed to concern myself with high temperatures.
Easily rectified with an old PC cooling fan as a temporary measure but I'm wondering if this is just a localised temperature blip or something a bit more permanent and widespread.
The high thermal mass of the bank provides a very slow but quite telling environmental monitor. Although there are some external factors specific to my installation to consider, and I'm still working through these, all the evidence seems to point to higher and less variable ambient temperatures. Weather station data sets will need quite some manipulation although at first glance cooling degree days are up some 100% this May/June.
I should add that battery status is fine and and I have not changed the charging regime although this is also subject to some changed weather patterns.
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Off grid 6kW Proven 2.8kW PV, SMA SI/SB/WB Inverters, 4x576ah Rolls batteries @ 24v, 25kW Biomass Boiler, Wood Stoves, Spring/Well water. Sorry planet - I did try.
bautsche
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« Reply #1 on: July 11, 2017, 02:35:22 PM »

Hi heatherhopper.

The only time I ever had an issue with temperature of my battery bank was when my bank was on the way out - fast.
It would overheat during a charging cycle (obviously).

My bank now sits in a shipping container, not air conditioned.

I'll try and post (separately, as it just ate my entire post trying attaching it here) a graph of the temp between 1. Mar. and 7. Jun. this year. If you want data from particular months, let me know.

HTH somewhat.
Eric
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bautsche
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« Reply #2 on: July 11, 2017, 02:35:55 PM »



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eabadger
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« Reply #3 on: July 11, 2017, 03:45:17 PM »

one of mine got hot on one terminal, eq charge seems to have fixed it, my bank 1000a fla about 6 years old.

steve
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1600w PV main array at 24v, excide 2v 1000a forklift cells now x 2, 320w PV secondary array at 12v. Enfield 1944 ex RAF 5.6kw diesel genset (now in pieces, big ends gone), Petter AC1 28v diesel charging set at 2.8kw.
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heatherhopper
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« Reply #4 on: July 13, 2017, 11:37:59 AM »

Thanks for that info Eric. My bank temperature shows a similar profile with slightly lower and higher extremes. The bank is housed in an insulated box with vents in a building subject to significant seasonal swings. I have been seeing peaks around the 35c mark this year (which triggers the SI high temp warning) but more interestingly to me has been the higher sustained minimum in the mid-20's. Previous summers it would peak well before 35c and regularly drop back to low 20's.
I have made some changes which will influence the temperature profile but these were all over 18 months ago. Most obvious was partially (and very crudely) insulated the building. This has had minimal effect on the mid-winter temperatures, which was not what I was hoping for, but will certainly have affected cooling air flow in the summer when there is high solar gain. The forum mantra regarding insualtion does not apply to all circumstances!
My tentative conclusion is that the weather is the main culprit. Sustained (rather than peaking) higher temperatures this year than the previous four. Simple mean temperature differences do not really give a clear picture but cooling degree days using integration do. The bank temperatures seem to rise incrementally with these sustained ambient temperatures without the usual cool down periods during float. In addition we have had higher wind generation overall this summer - not higher winds necessarily  but more sustained meaning that inverter, diversion and bank activity has been more constant.
Still interested in whether anyone adjusts their compensation settings seasonally and also where they position their sensors. I have not previously had cause to consider changing from the SI default 4 mV or sensor position in the middle of the bank. Note I have swapped out the temp sensor for a spare just to be sure.
Steve - I am fairly confident that the battery status is ok - SG checks (such use as they are for a working bank) are fine, charge/discharge cycle times and profiles are unchanged, charge and discharge capacity is unchanged and there is no significant variation in either cabling or casing temperatures as checked with a trusty old Raytek scanner. Water use is maybe a little higher but not excessively so, given the increased bank activity. Which brings me back to the compensation settings although the only way to really get this right (in my opinion) is the laborious task of matching float setting to cell status and this a laborious task even without higher fluctuating temperatures and I have no desire to go through that again for what might simply be a single summer's anomaly.
Problem, if it is indeed one, will probably go away in a month or so anyway. Maybe I'll just wire up the PC fan for automatic operation. 
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Off grid 6kW Proven 2.8kW PV, SMA SI/SB/WB Inverters, 4x576ah Rolls batteries @ 24v, 25kW Biomass Boiler, Wood Stoves, Spring/Well water. Sorry planet - I did try.
heatherhopper
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« Reply #5 on: Today at 03:00:39 PM »

Eventually managed this issue by reverting to a set of "summer" charge parameters. Over a couple of weeks the bank temperatures returned to what I consider normal. Shorter days now and back to the charge settings that have been in use all year round for the last few years.

For now I'm inclined to believe the issue resulted from a combination of higher ambient temperatures and some not-very-well -thought-through insulation improvements. Think I will reverse some of the latter before next spring as the winter benefit was probably negligible.

The fan ventilation proved to be a poor idea as this simply masked the true bank temperature.

Given Eric's gloomy experience though I'll still be keeping a close eye on these batteries - they have had a very busy life these last seven years and are not well-matched to the size the system has become.

Bit surprised no battery experts could give some insights into sensor positioning and temperature compensation etc - I can't be the only one whose batteries live in a seasonally sensitive environment. Of course these are just FLA batteries so obviously a bit passť in these exciting times and maybe the real world experts have relocated to other, more rustic and less dynamic, places.  whistlie

While pondering the battery thing I got to look at the "system" data from some different perspectives. Although the Sunny Island suggests lifetime DC round trip efficiency at a suspiciously good 94% I have been recently recording short term data showing it at 88% (which is more in line with numbers declared by Nowty for his SI some time ago). Interestingly external monitoring data for the complete "standalone grid system" efficiency also show a change  - see this year to date summary below. I'll be interested to see how the next five months pan out as I don't have complete data for previous years. Perhaps something permanently changed regards the battery status Feb/Mar. Perhaps (I hope) there is always a step change in battery losses with seasonal change (theory suggests there should be unless the environment is very strictly controlled). There is a lot going on in the system and some issues with the data accuracy (and my own faculties) so perhaps I'm talking nonsense! Plenty of numbers to amuse myself with this winter though.

I also collected a gallery of pretty pictures of the batteries for future reference. First two are before parameter changes and second two a few weeks after. All taken at the end of the SI Boost (Bulk/Absorption) cycle. Hot spot temps not excessive but there is few degrees creep in the hours after the batteries settle down so 35c+ was becoming uncomfortably regular and these are external not internal temperatures.












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Off grid 6kW Proven 2.8kW PV, SMA SI/SB/WB Inverters, 4x576ah Rolls batteries @ 24v, 25kW Biomass Boiler, Wood Stoves, Spring/Well water. Sorry planet - I did try.
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