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BATTERY BACKUP TIMES


Dries le Grange
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Good day

Assistance with the following will be appreciated very much.  As a pensioner I rely on this system to benefit me for many reasons.  Installation done a few months ago.

Equipment installed

1 X 5kW Axpert King Inverter

12 X 315W Canadian Solar KuPower CS3K panels (3 X 4).

4 X 12V X 200Ah GoldShine Gell Batteries 

Settings mostly default.  Batteries however set in 05 as USE and 27/28/29 at default for the 5kW unit.

In January the vendor disconnected and tested the batteries with a proper tester (not multi meter).  All 4 passed in green as good.

My problem:  The manual indicates a battery backup life of 20 hrs with a load of 500VA, 8.9 hrs at 1000 VA and 3.7 hrs at 2000 VA. However, I only get 2 hrs 50 min backup time at an average 325 VA load (peak load was 505 VA).  This whilst the solar panels provided a little input of around 100W (late afternoon and rainy).

Low battery alarm sounded at 45.7 V (3hrs 50 min).  Switched of the little loads there were.  System eventually switched off.

What surprised me way more than the above:  When Eskom power was restored approximately 2 hours later, the unit came on line and indicated a battery level of 53.2 V, 90% battery capacity charging at 5A.  Impossible for the solar panels to achieve this obviously.

Please tell me what is going on here.

Thanking you in advance.

Dries

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Hi I have a similar system with half your battery capacity, it seems these systems with SLA batteries are best for short duration load shedding 2hours or so. About a month ago our local power station went up in flames which has resulted in 12-24 hour outages with some areas lasting days. This has reduced the capacity I'm  able get out of my batteries. Last night I was only able to get 2,8kwh when I previously I got 3,5kwh from the same battery last month.

This is the fault of the technology and why lithium ion phosphate batteries have become more popular.

[quote=]Lead–acid batteries lose the ability to accept a charge when discharged for too long due to sulfation,the crystallization of lead sulfate.They generate electricity through a double sulfate chemical reaction. Lead and lead dioxide, the active materials on the battery's plates, react with sulfuric acid in the electrolyte to form lead sulfate. The lead sulfate first forms in a finely divided, amorphous state, and easily reverts to lead, lead dioxide and sulfuric acid when the battery recharges. As batteries cycle through numerous discharges and charges, some lead sulfate is not recombined into electrolyte and slowly converts to a stable crystalline form that no longer dissolves on recharging. Thus, not all the lead is returned to the battery plates, and the amount of usable active material necessary for electricity generation declines over time.[/quote]

 

 

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I think the problem is a little bit more complicated, the lead acid batteries should ideally only be used at C/10, thus for the 4 12V 200Ah batteries, presumably in series for 48V and at C/10 max, at 20A, thus providing for 960W more or less of power, then also should probably not be cycled lower than 20% of capacity used with 80% capacity remaining in the battery, unless you are happy to have a short-ish lifespan. Sulfation is a problem, but also a problem is that lead acid cells don't really like deep discharging (and deep does even remotely mean down to 0%).

A friend/acquaintance designed a little desulfation circuit to rejuvenate all the various batteries (golf cart batteries etc.) that got donated to him due to them being non-functional. Anyway, I found the article which disappeared after Al's website seemed to have disappeared,  here  for anyone that needs to and wants to investigate this.

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3 hours ago, Kalahari Meerkat said:

I think the problem is a little bit more complicated, the lead acid batteries should ideally only be used at C/10, thus for the 4 12V 200Ah batteries, presumably in series for 48V and at C/10 max, at 20A, thus providing for 960W more or less of power, then also should probably not be cycled lower than 20% of capacity used with 80% capacity remaining in the battery, unless you are happy to have a short-ish lifespan. Sulfation is a problem, but also a problem is that lead acid cells don't really like deep discharging (and deep does even remotely mean down to 0%).

A friend/acquaintance designed a little desulfation circuit to rejuvenate all the various batteries (golf cart batteries etc.) that got donated to him due to them being non-functional. Anyway, I found the article which disappeared after Al's website seemed to have disappeared,  here  for anyone that needs to and wants to investigate this.

Hi we are not discharging the batteries that deep by choice. The poor state of utility grid means that we are experiencing what true offgrid looks like. The inverter switches off due to low voltage the previous night and switches on in the morning when the sun comes up, stays on during the day and eventually switches off due to low voltage again the next night without the grid coming back some days.

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37 minutes ago, Buyeye said:

Hi we are not discharging the batteries that deep by choice.

I'm fairly certain that it is not by choice, but the point is that if you regularly go down to 50% or less SOC, then things will start going wrong and desulfation should get the batteries back to a much better state where it will keep things going for longer than now. But also note that the current capabilities of these batteries are also usually not what everyone expects, based on the "200Ah" or whatever spec, that's 200Ah usually cumulative if drawn over 10 or more hours.

Either way you both may be able to rejuvenate your batteries for use for a few more years longer, but you will have to do something about it and also you will have to ensure that the renewable input side can charge the battery fully when the grid disappears like a fart in the wind 🙂 presumably the solar side can produce enough energy to actually fully charge the battery during a decent day of sunshine and generate some more power to boot...

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Thanking you all for the feedback.

These GEL deep cycle batteries of mine being about 7 months old and protected by the inverter not to drain below the preset value, might have discharged to that level maybe 12 times.  Only used as backup after hours for electronic equipment (350W).

Would not have expected it to be "useless" so soon.  At a cost of R4000 ea I would have expected a few years of good life.

The max charge current is set at 60A total of which 30A max is supplied by Eskom where the 12 pannels could not deliver what is required.

Could you perhaps suggest Lithium Ion batteries best suited for my system?

 

Kind regards

Dries

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@Dries le Grange, if you are only ocasionally using the batteries and are running mostly off commercial power with solar mix, then the lead acid batteries are probably the betterer option 🙂 only thing is, once the batteries are charged, then a float of probably just below 13.8V/battery should not be exceeded, I'd think, thus for the 4 batteries in series, let's call it 13.7V each, thus 54.8V float or even 54V even should be ok. (I am assuming its a 48V with the batteries in series...)

Lithium (LiFePO4) batteries aren't really suited for ocassional use, since they self discharge and even if only used once a week and recharged would not be ideal, these should be cycled daily, not deep cycled, but say down to 50% and charged back up to 80% and they should give a long life.

For your Gel Cells, I'd say if you are handy with electronics, make up 4 desulfators and connect one each to each of your batteries, also add a toroid to the negative and positive lead going to the inverter, that should stop the high frequency pulses from getting to the inverter and possibly confusing it, after a week or two, you batteries should be in a much better condition and if I were you, I would leave the desulfators connected, if the batteries are fine, they won't do anything, except draw a minor amount of power, if the batteries are getting worse, the unit would prevent it from getting very far.

 

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Thanks for your valuable inputs Meerkat.  Float is set at 54V on the inverter for the 4 batteries in series.  I have no knowledge of desulfators but will get someone local to assist.  Much appreciated.

Was not aware of the cycled discharge requirement for Lithium batteries.  Good to know.

Regards

 

Dries

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20 hours ago, Kalahari Meerkat said:

For your Gel Cells, I'd say if you are handy with electronics, make up 4 desulfators and connect one each to each of your batteries, also add a toroid to the negative and positive lead going to the inverter, that should stop the high frequency pulses from getting to the inverter and possibly confusing it, after a week or two, you batteries should be in a much better condition and if I were you, I would leave the desulfators connected, if the batteries are fine, they won't do anything, except draw a minor amount of power, if the batteries are getting worse, the unit would prevent it from getting very far.

 

Please provide info on these desulfators.

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