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Author Topic: Funny Goings On in the Old Tin Battery Shed ...  (Read 9909 times)
Eleanor
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« on: October 21, 2009, 12:23:07 AM »

Hopefully, I’ll be able to explain this and it doesn’t seem like a load of gobbledegook  flyingpig

We have a battery bank comprising eight 110 Ah 12V leisure batteries which are arranged as four pairs to create a 440 Ah bank @ 24V. The batteries are numbered from 1-8 from left to right and the odd numbered batteries are connected to the negative bus bar and the even ones to the positive one. We’ve been running this configuration for a few months with a mix of solar, wind and generator power with no particular problems. We generally try not to discharge the batteries very deeply, more than 20% is rare and often not as much as this.

However, on Friday night I had done my usual few hours of PC and reading light and decided to check on the battery bank. It was at 25V which was fine so I carried on for another hour. On checking again it was 24.5V! I decided to go and switch everything off and by the time I got back to the tin shed it was heading for 24V! It actually got as low as 22.5V and this was in a very short time. At this point I switched off the inverter and decided that I must be more disciplined with battery charging in the future.  Having said this I know there is no way that I had used enough to completely flatten the battery, the battery monitor reckoned about 25 Ah which agrees with my rough estimate.

The next day it was sunny and as I hadn’t disconnected the PV I let it charge and all seemed normal. Battery voltage rose nicely as expected and the battery monitor SOC reached 100%. It was as if nothing had happened. The following day was not quite as sunny but there was still some charging. Did the usual evening PC etc and went out to the tin shed late at night to find battery at 22.5V again.

Switched off inverter and this time had the gumption to disconnect the PV. Left it alone for 12hrs after which the battery voltages were the interesting thing I thought! (Table 1). Half of them look flat (~11.5V) and the rest look OK (~12.5V)! Battery monitor says 23.93V. At first it looked as if all the batteries attached to the positive bus bar had a low voltage but the trend is reversed for 7 & 8. Did SG measurements on all the cells expecting to find disastrous results (Table 1)  stir

Decided to give the batteries a bit of a charge to see what would happen. On charging the voltage went straight to 28.2V and all batteries showed 14.1V. After 45 mins they were at 30V and stayed there for 90 mins. Everything switched off after that.

The next morning the battery monitor showed 25.58V and the individual batteries showed around 12.8V. These values were stable for several hours. No comedy low values! Measured SG again and the new values are shown in Table 2.

Hopefully someone will have seen this before and be able to explain it or maybe suggest more tests. I know it’s a leisure bank with limited life expectancy and at some point we’ll upgrade. I feel there’s still a lot to learn yet about batteries ..  garden

Table 1                  
                     

Batt No                     
1   1260   1265   1270   1265   1240   1235   12.56V
2   1245   1235   1270   1270   1270   1260   11.40V
3   1245   1255   1230   1255   1230   1235   12.50V
4   1220   1215   1255   1255   1230   1235   11.46V
5   1235   1235   1245   1250   1225   1205   12.44V
6   1205   1200   1245   1240   1245   1235   11.52V
7   1240   1275   1280   1270   1245   1250   11.38V
8   1255   1265   1275   1245   1235   1270   12.58V
                     
   Date:   19/10/2009      Time :   14.30      
   Temp:   8.5 C               
   BMV :   23.93V               
                     
Table 2                     
      
Batt No                     
1   1270   1270   1275   1265   1240   1240   
2   1260   1245   1280   1275   1275   1270   
3   1260   1260   1265   1265   1235   1235   
4   1240   1230   1255   1275   1250   1240   
5   1250   1255   1260   1260   1240   1225   
6   1230   1225   1260   1260   1260   1250   
7   1275   1285   1285   1285   1245   1255   
8   1255   1275   1280   1245   1245   1270   
                     
   Date :   20/10/2009      Time :   13.30      
   Temp :   10 C               
   BMV :   25.58V               


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KenB
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« Reply #1 on: October 21, 2009, 07:59:21 AM »

Eleanor,

It is quite normal for batteries connected in parallel strings to go out of balance like this. 

(A better configuration would have been 96V 110Ah - but as most small wind and solar inverter systems are intended for low voltage operation - this was not a route available to you).

The charging current will always follow the route of least resistance, giving one string an advantage over the others.

I would recommend that you give the batteries an individual equalisation charge.   Take 2 of them out of the bank and charge them individually with a 12V charger, until their cell specific gravities are returned to normal.  Repeat this with the other 6.

Batteries do need a lot of attention, especially when connected together in banks.   We are all too familiar with car batteries that seem to last for years with no attention - not so with wind and pV systems.


Ken
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Justme
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« Reply #2 on: October 21, 2009, 10:22:51 AM »

Where on the bus bar do the chargers, solar & inverters connect?
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billi
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« Reply #3 on: October 21, 2009, 11:29:56 PM »


Quote
Decided to give the batteries a bit of a charge to see what would happen. On charging the voltage went straight to 28.2V and all batteries showed 14.1V. After 45 mins they were at 30V and stayed there for 90 mins. Everything switched off after that.

does that mean they discharge fast and charge fast  Undecided  ?

Eleanor  in my case it was the battery , but that is a while ago and still mystery to me , you have wet cells , i had gel cels , so there is  a hope to  get it sorted ...

I might be wrong

But perhaps your windturbine  and your PV  kept up the Batteryvoltage to your pleasure , without noticing any defect , now the turbine is gone you cycle them deeper and find out they are unbalanced ....

Perhaps even when the windturbine was working , you never charged them fully ( just a guess)
 
I am not able to help a lot here , but in my old bank there where two batteries not as they should be and decreased the performance of the other two (= the whole bank)  and that  seemed  to cause fast charge and fast discharge

Billi
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Justme
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« Reply #4 on: October 21, 2009, 11:50:12 PM »

Bats
2
4
6 & 7 look shot to me.

Can you wire up the good 4 bats to 24v & then test just using the good ones.

You could also wire up the 4 bad one & try to charge them & see how you get on.

What SOC meter are you using?

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billi
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« Reply #5 on: October 21, 2009, 11:53:53 PM »

Quote
What SOC meter are you using?

  Justme , it will not be the one you prefer  Grin   (not funny and no time for jokes)
Billi


* tn_more system pics 088.JPG (86.15 KB, 671x503 - viewed 852 times.)
« Last Edit: October 21, 2009, 11:55:45 PM by billi » Logged

1.6 kw and 2.4 kw   PV array  , Outback MX 60 and FM80 charge controller  ,24 volt 1600 AH Battery ,6 Kw Victron inverter charger, 1.1 kw high head hydro turbine as a back up generator , 5 kw woodburner, 36 solar tubes with 360 l water tank, 1.6 kw  windturbine
Stuart
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« Reply #6 on: October 21, 2009, 11:55:04 PM »

Eleanor, Measure the cell voltages when the bank is under load this will show up the weak cells straight away.
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Justme
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« Reply #7 on: October 22, 2009, 09:59:55 AM »

Billi, I dint think it would be.

However some just measure V & then quote SOC. This does show that ah counters might not be as good as people think. They do need resetting after a good FULL FULL charge.

Just going on an ah counter you end up under charging the bank so it sulphates so then you under charge it some more.

I think the wiring might also be an issue if you look at the bats that are failing all apart from one is on the same side.

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« Reply #8 on: October 22, 2009, 10:08:03 AM »

Justme

It looks like a Victron one Eleanor is using and they reset automatically , but i agree one cannot rely on them 100 % ( or even they fool you)

I got over 200 AH more  into my battery  2 weeks ago after the monitor reset himself to 100 %

Billi
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« Reply #9 on: October 22, 2009, 03:04:40 PM »

Justme

It looks like a Victron one Eleanor is using and they reset automatically , but i agree one cannot rely on them 100 % ( or even they fool you)

I got over 200 AH more  into my battery  2 weeks ago after the monitor reset himself to 100 %

Billi

Thats a hell of a lot.

Dint see in the specs when I was sourcing my set up any that said they did auto resets. Mind some of the details available for some products is well misleading at best & down right lies at worst.
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Navitron solar thermal system
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« Reply #10 on: October 22, 2009, 10:15:13 PM »

well to be honest we have been away so no draw (only fridge-freezer) , but my bet is that the PV pumped  the battery with full blast and then normally the Battery´monitor resets himself far too early to 100% 

Normally  the monitor is wrong by 60-80 AH  , but do i know if my charge controllers are right ?  facepalm

Eleanor hope you are well

Billi
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Eleanor
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« Reply #11 on: October 24, 2009, 12:18:14 AM »

Billi, yes thanks, fine. I haven't managed to electrocute myself or dissolve in sulphuric acid yet ..  stir I've been reading the comments (thanks to everyone) and having a think  Huh

Clearly there is something amiss and I've decided to take action to find what it is. I think that the battery monitor Vs Smart Gauge discussion is probably a bit of a red herring here. Yes, we do have a Victron battery monitor but it's really just used as an expensive volt meter and the fact that it shows nett current is useful for seeing what's going in and out of the battery bank. I sometimes look at Ah used but more as a cross check to confirm my own mental calculations than to determine battery capacity (no idea what it is now). I expect we'll have to buy a Smart Gauge to satisfy our curiosity but I can't imagine ever shaking off the addiction to volts, amps and SG.

Stuart, I measured voltage under load as you suggested. I'm not sure what you consider to be a load but I connected a 500W panel heater for 5 mins which I thought would be a reasonable test.

V Before      After 5 min

1    12.93      12.51
2    12.98      11.53
3    13.01      12.10
4    12.95      11.97
5    12.98      12.55
6    12.98      12.02
7    13.02      11.52
8    12.95      12.55

I suppose that points the finger at No 2 and No 7? Funny, I always suspected No 6!  fight

It seems to me that batteries are a bit like children - perfectly well behaved individually but get a few of them together and who knows what they might get up to  facepalm

I've taken out No 1 and No 2 and singled them out for special attention as suggested by Ken. We have a 12V charger which can be set to 15A so I've had a go at charging them individually. I think they were pretty well charged as I couldn't get the SGs to increase very much over a three hour period despite the batteries bubbling nicely. The charger output had dropped to around 2A quite quickly so I'm thinking that the batteries were having an equalisation charge for most of the charging time  Huh

The results are below :



Battery No 1

Cell                  1           2          3           4            5              6

Time (min)

0                    1260     1265      1275     1265       1245       1240
30                  1260     1265      1275     1265       1245       1240
60                  1260     1265      1275     1265       1245       1240
90                  1260     1265      1275     1265       1245       1240
120                1260     1260      1270     1260       1245       1240
150                1260     1265      1270     1260       1245       1240
210                1260     1265      1270     1265       1245       1240


Battery No 2

Cell                   1           2          3           4            5              6

Time (min)

0                    1255     1235      1275     1280       1275       1265
30                  1255     1240      1280     1280       1275       1270
60                  1255     1240      1280     1280       1280       1270
90                  1255     1240      1280     1280       1275       1270
120                1260     1240      1280     1280       1280       1270
150                1260     1240      1280     1280       1280       1270
180                1260     1240      1280     1280       1280       1270


After a couple of hours some of the SGs started to go down instead of up! I think that's probably because we don't have a temperature compensated hydrometer (yet!). I'm wondering if it would be worth trying to charge the batteries over a longer period with the smaller 3A charger? It does seem that there may be some sulphation present in some of the cells.

Anyway, the task for tomorrow is to do a capacity test on both batteries to see what they do. Hopefully Martin isn't reading as he'll find out that we haven't got just one 12V MSW inverter  faint lurking in the thin shed, there are two!  horror I can see a light bulb opportunity here  Roll Eyes Possibly not the 100W variety, an inspection of the light bulb vault seems necessary to determine the appropriate wattage for this particular test  whistlie

So, if all goes well tomorrow it will be the Light Bulb Race. Who will win, are we betting on Battery No 1 or Battery No 2?  tumble
« Last Edit: October 24, 2009, 12:31:36 AM by Eleanor » Logged

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merkland
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« Reply #12 on: October 24, 2009, 10:26:31 AM »

Looking at Eleanor's various results it looks as if it is the cells nearest the point where two batteries are connected + to -  are the ones in poorest shape. I wonder if there would be any benefit in swapping the batteries over so that they are connected by their opposite poles i.e. if battery 1 is on the left and battery 2 on the right, move 1 to the right position and 2 to the left.
Any one else have thoughts on this and is it something which should be done on a regular basis?

merkland.
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« Reply #13 on: October 24, 2009, 10:47:24 AM »

Personally, I'd go for "give 'em a good bubble" as whole banks a go - charge them right up, and leave them fizzing for a couple of hours, it isn't called an equalisation charge for nothing..... then I'd implement the wiring regime as suggested on the Smart Guage site - it may look messy, but the maths makes a lot of sense.........
« Last Edit: October 24, 2009, 10:50:57 AM by martin » Logged

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Justme
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« Reply #14 on: October 24, 2009, 11:17:14 AM »

Can you post a pic / drawing of how the bats are wired.

It does seem that bats 2 4 6 & 7 are duff.

Make 2 small 4 bat bank using bats 1 3 5 & 8 in one & 2 4 6 & 7 in the other.

Use bank 1 & fully charge then test. Then fully charge bank 2.
You could even split it down to 4 banks of 2 bats. If you do that I would put the bats that are the closest (voltage wise) together.
1 & 3
2 & 7
4 & 6
5 & 8

They all need a long charge (like 10 hours followed by an EQ charge)

Then leave for 10 - 12 hours with no load & test ANY under 12.6 (or better yet 12.Cool with no load are shot.

Choose the best 2 4 or 6 bats to make a new bank. (I would guess you only have 4 that are good enough)
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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