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Author Topic: Battery Bank temperature questions  (Read 1278 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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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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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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heatherhopper
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« Reply #5 on: September 21, 2017, 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.

Edit note - unreadable pic replaced by .pdf attachment









* System summary.pdf (62.41 KB - downloaded 11 times.)
« Last Edit: September 22, 2017, 12:46:21 PM by heatherhopper » Logged

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offthegridandy
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« Reply #6 on: September 22, 2017, 09:03:32 PM »

Hi Heather late to pick up on this as I've been absent.

Are your cells in an insulated box or in an insulated (somewhat building?

My kit including the FLa cells are in a small uninsulated timber frame shed with a tin roof facing south; about 300Mtr above sea level in Mid Wales. The cells are inside the building in a box with about 50mm of insulation to 4 sides and base. Lid is not insulated.  Box is vented to out side via ducted vents to out side.  Although the shed can get hot on a sunny day I've never noted any radical over temp issues with the battery.  I guess the insulated box keeps the outer hot air away from the cells maintaining a steadier temp inside the box.

Obviously mid winter and maybe below freezing, the battery temp stays above outside air due to heat generated in operation.

I think maybe as you say you need to start be removing the insulation and maybe improve ventilation.

Cheers
Andy
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heatherhopper
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« Reply #7 on: September 23, 2017, 06:51:22 PM »

Thanks for those comments Andy.
Batteries are in a similarly configured box to your own. The building walls are mixture of different blocks and a variety of insulation - and still evolving. The roof was simple clear corrugated plastic with plenty of ventilation but this was prone to condensation so I added a layer of spare bubblewrap underneath which cleared up the condensation problem. Getting too enthusiastic I then added a layer of multiwall poly ( salvaged from a worthless "conservatory") under that 18 months ago and plugged up much of the ventilation. Solar gain is now quite significant so all this is probably the main culprit as you say.
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« Reply #8 on: September 23, 2017, 08:37:43 PM »

Hi Chaps,

I think I've just been lucky insomuch as I never managed to get around to insulating mine. I always meant to but then after a couple of winters here I never bothered as the temperature in the battery/inverter/generator shed rarely gets below 5 degrees due to all the inverters, controllers and insulation. In the summer I just leave the door open as it faces north and is protected by a steep bank from any weather that does come that way.

I've a couple of large fans that come on when the generator is running if the door is closed.





I got a little carried away with the insulation when I was building it.



Loads of Rockwool and Kingspan



I check mine regularly with both an IR thermometer and a couple of times a year with the camera from work.



I think I've just been lucky.  

Paul

PS, those forklifts in the corner are just for starting the generator  Grin
« Last Edit: September 23, 2017, 08:40:50 PM by camillitech » Logged

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eabadger
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« Reply #9 on: September 24, 2017, 01:55:32 PM »

also well worth checking your leads carefully see my post where they were failing and resulting heat, heated the terminals!
am going for solid connectors when the copper bar arrives.

steve
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« Reply #10 on: September 24, 2017, 02:25:38 PM »

also well worth checking your leads carefully see my post where they were failing and resulting heat, heated the terminals!
am going for solid connectors when the copper bar arrives.

steve

Aye Steve, but if you had run an IR thermometer over your leads under load every week you would have found the issue straight away and saved some grief.



Here's an iffy one like yours detected before any apparent fault developed. I've found many like this just using a cheap IR thermometer and not the camera. Charge controller connections, fuses and inverter connections all get a monthly 'once over'. An IR thermometer is second only to a good hydrometer in battery maintainance in my book.

Cheers, Paul
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'Off grid' since 1985,  Proven 2.5kW, SI6.OH, WB1200, SB3800,SB2500,WB6000, 800ah Rolls, 4.75kW PV ,4xTS45, Lister HR2 12kW, , Powerspout pelton, Stream Engine turgo, 60 x Navitron toobs and a 1500lt store. Outback VFX3048 and 950ah forklifts for backup
eabadger
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« Reply #11 on: September 24, 2017, 04:07:33 PM »

yep got one, now!
but if op has not, maybe a thought?
i just saw temps going up on controllers and when on eq by hand.

steve
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heatherhopper
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« Reply #12 on: September 24, 2017, 11:53:09 PM »

Steve - like Paul, I have regularly checked the whole system with an old, but reliable, Raytek IR thermometer and occasionally with a thermal imager (see pics in earlier post), the latter more recently diverted from it's normal duty of watching my heating dissipating into the atmosphere. With the batteries in an insulated box I admit that this has been mostly limited to the tops but I have made the front panel removable since this became an interest. Casing profiles are always fairly even and the leads and terminals have always been significantly cooler although I did check them physically after seeing your post on the subject.

Clearly I'm becoming a bit obsessed by this temperature subject but it is not well covered wherever you research FLA (or indeed other types) operation - be it Batt Uni or just experienced anecdotes on here. Seems to me it is quite a crucial subject not just as a failure mode but for the overall performance of the bank. I guess there is such a variety of off-grid systems in operation in the real world that there is no easily defined set of rules. I had always been aware of the massive difference lower temps make (hence the insulation efforts) but rarely bothered about the impact of higher temp ranges until I started to look at the data I now have available. I know what temperature range I would like to operate in - question is how to achieve it.

Still interested to know where people position their temp sensors and why and what charger compensation parameters are in use. Again there will obviously be no common golden rule but any different experiences would be helpful.
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eabadger
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« Reply #13 on: September 25, 2017, 08:29:54 AM »

the lead was cool or at least the ir said it was, one terminal was hot when high load or charge, i removed cleaned checked resistance and all seemed ok, but lead sounded odd, but no visible problems until i cut insulation.
now why one terminal was 20* hotter than the other i dont know, but now all checked for the noise and now fine.
but look at colour of the copper and you can see it has got hot over time.

steve


* batt con.JPG (563.88 KB, 1632x1224 - viewed 86 times.)
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Westie
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« Reply #14 on: September 25, 2017, 11:24:46 AM »

the lead was cool or at least the ir said it was, one terminal was hot when high load or charge, i removed cleaned checked resistance and all seemed ok, but lead sounded odd, but no visible problems until i cut insulation.
now why one terminal was 20* hotter than the other i dont know, but now all checked for the noise and now fine.
but look at colour of the copper and you can see it has got hot over time.

steve

The hot spot looks nearer the LH end in the pic, the battery terminal acted as a heatsink so all the heat got shunted to that i guess.  If that had been on a long run of cable I would have melted and gone up in smoke by now. Looking at the way that has failed  I'd be checking all the straps on the pack,  could be down to poor quality copper.
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