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Batteries, Balancing etc.


andrew9484
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Hi All,

I recently completed my install consisting of:

Axpert 5kVA
16 x 12V 100 AH batteries in 4 strings
8 x 320W Panels
BMV 702
No balancers

Firstly i am fully aware that my battery arrangement is by no means ideal. It was result of gradual upgrades. I would have done differently if i had known my needs from start.

The batteries are between 1 and 2 months old. My Midpoint has been ranging between 0.2% and 2%. It deteriorates towards 2% as the SOC decreases. I have checked the battery voltages at 70% SOC while they are discharging; and again at 75% while charging. The midpoints were disconnected to measure voltages. See file attached.

On discharge the 2nd battery in string 3 seemed very low; and i imagine this is outside of what could be safe?

1. What deviation is reasonable / safe?
2. Would battery balancers resolve this issue?
3. If the battery is assumed to be faulty or at minimum inconsistent with rest; i don't think there would be easy way to prove this to the supplier? Especially since it seems to improve on charging.
4. I really would not like to have to replace batteries already due to the expense. If i replaced one then there is risk of issues with others in near future as well i guess. If i had to take the decision to replace all batteries; what would the best option be considering i would like 400 to 500 AH @ 48V? and what is it likely to cost? and are there recommendation for good quality at reasonable price?

Any other comments or suggestions welcome.

Thanks

Andrew

 

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I would definately think theres a problem with battery 1 on string 2 and battery 2 on string 3. At that volts their basically dead and the others have to compensate for the lost energy.

Sent from my S60 using Tapatalk

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I concur.

To confirm without any doubt. Charge bank to 100%, then run all the batts through a load tester, one by one, if you cannot measure each cells gravity.

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I would stretch my neck to say replace the 2 faulty batteries but get HA-02 battery balancers from ChrisR to keep them happy. I've got a mixed bank at this stage, new batteries, old batteries, all 105ah though but after i've installed the balancers my batteries are looking better than ever. Thing is to eliminate the bad cells ASAP.
You can check which cells are the troublemakers with either a hydrometer or even a digital multimeter (voltmeter) put the prongs into the electolyte to get the cell's voltage. Outside one's tested with one prong on the battery terminal of course and the adding the result to get the 6th cell voltage. Anything below 2.1v (on a charged battery) is suspect but after a load charge you'll immediately point out the culprit

Sent from my S60 using Tapatalk

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Dont start over yet!

Chuck out S2B1 and S3B2 (can you not get warranty replacement?) and drop down to 3 strings, monitor these batteries for a few days to see if they are performing as expected. If performing ok then get 2 more of the same to build up the 4th string again.

Get a battery balancer for each string which is not very expensive compared to replacing 16 batteries.

What batteries are you using currently?

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4 hours ago, pilotfish said:

Dont start over yet!

Chuck out S2B1 and S3B2 (can you not get warranty replacement?) and drop down to 3 strings, monitor these batteries for a few days to see if they are performing as expected. If performing ok then get 2 more of the same to build up the 4th string again.

Get a battery balancer for each string which is not very expensive compared to replacing 16 batteries.

What batteries are you using currently?

I did as per your suggestion. Midpoint now mostly between 0.2 and 0.5% but i have not tested at significant discharge yet. I have vision 6FM100-X batteries

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9 minutes ago, andrew9484 said:

I have vision 6FM100-X batteries

I have a 4 battery string of the same batteries in a very simple inverter backup role (so no cycling) - 1 of the batteries failed after 4 months. So added to your 2 that makes 3 failures out of 20 batteries that I know of, not a very good record as far as I am concerned.

They are however a reasonable choice according to their data sheet and should give you around 1300cycles at 30% DOD, so lets hope that we have both rooted out the bad apples and are left with serviceable equipment - I hope it works out well for you.

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10 hours ago, Czauto said:

You can check which cells are the troublemakers with either a hydrometer or even a digital multimeter (voltmeter) put the prongs into the electolyte to get the cell's voltage. Outside one's tested with one prong on the battery terminal of course and the adding the result to get the 6th cell voltage. Anything below 2.1v (on a charged battery) is suspect but after a load charge you'll immediately point out the culprit

The Vision 6FM100P-X is an maintenance free AGM so no hydrometer or access to electrolyte unfortunately - but the method used to produce the original spreadsheet will reveal a bad battery.

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6 minutes ago, pilotfish said:

I have a 4 battery string of the same batteries in a very simple inverter backup role (so no cycling) - 1 of the batteries failed after 4 months. So added to your 2 that makes 3 failures out of 20 batteries that I know of, not a very good record as far as I am concerned.

They are however a reasonable choice according to their data sheet and should give you around 1300cycles at 30% DOD, so lets hope that we have both rooted out the bad apples and are left with serviceable equipment - I hope it works out well for you.

Ok. that is not a good sign! I informed the supplier and they say I can take them back and they will test. So hopefully they will replace them (although it may seem they are fine when tested separately. I will be away few a few weeks but will take them in once i am back and send you an update.

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