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How long should my batteries last?


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Posted (edited)

Hi Guys,

I have a feeling that this questions has been asked, but was unable to find anything using the search function, so please accept my apologies if it has been asked before.

Installed a system purely to combat the load shedding, with the view to install panels at a later stage. So it is a 5kva Hybrid system, currently connected to 4 200mah Gel batteries. The system is just under a year old. (Bought two additional batteries 6months ago - total of 4)

Currently we drawing around 450w (4-5amp) during load shedding.  Based on that, how long should the the batteries last?

I just went to https://www.digikey.co.za/en/resources/conversion-calculators/conversion-calculator-battery-life

According to this calculation on 800 ah (I assume this is correct with 4x 200ah batteries) consuming 12A, should have 66hrs of usage... but there is no way I getting anywhere close to that amount... So wondering what I am doing wrong?

Edited by nelian
Incorrect spelling
Posted
6 minutes ago, nelian said:

Hi Guys,

I have a feeling that this questions has been asked, but was unable to find anything using the search function, so please accept my apologies if it has been asked before.

Installed a system purely to combat the load shedding, with the view to install panels at a later stage. So it is a 5kva Hybrid system, currently connected to 4 200mah Gel batteries. The system is just under a year old. (Bought two additional batteries 6months ago - total of 4)

Currently we drawing around 450w (4-5amp) during load shedding.  Based on that, how long should the the batteries last?

450W on the AC (230v) side? That's not 4-5 amps, more like 1.8-2 amps.

Posted
3 minutes ago, YellowTapemeasure said:

450W on the AC (230v) side? That's not 4-5 amps, more like 1.8-2 amps.

I just relaying what is on the inverter panel.  Currently 119w pulling 3A... or am I just looking at this wrong?

Posted
2 minutes ago, nelian said:

I just relaying what is on the inverter panel.  Currently 119w pulling 3A... or am I just looking at this wrong?

Hi. 
 

The inverter info is probably displaying 119w load with 3A (battery current) which is at 48v give or take the losses. 
 

Theoretically if you have 4 x 200AH 12V batteries, you cycle them down to 50% depth of discharge. That equates to 4800wh or 4.8kwh. A constant 600w (12A x 48V) load would then last 8 hours. Definitely not 66 hours. 
 

Hope that makes sense. 

  • nelian changed the title to How long should my batteries last?
Posted

Please confirm, you say a 5Kva system, is that a 24V system? That would be quite unusual... Just reading into saying you have 4 batteries in total and 2 were purchased bout 6 months ago.

I have a similar system but on a 3kva, 24V inverter with 4 x 205ah batteries. That gives me a bank of 410ah. I also draw about the same watts as you at night and my setup will give me 12 hours at that sort of draw to a 50% SOC. I did this last night for the first time due to an unexpected fault.

Normally I tend to draw about 30% out of my batteries on a daily basis just to get round poor incoming voltage from Zesa in the early evening.

As you will see elsewhere in this forum, you can kill lead acids very quickly by drawing them down too deeply(like I did last night).

Posted
11 minutes ago, Achmat said:

What is the voltage of the batteries. You would also not mix older batteries with new batteries. 

All 4 are the same make. Gold shine 12v200ah

Posted
Just now, nelian said:

All 4 are the same make. Gold shine 12v200ah

If you were running 2 batteries before then I assume its a 24v setup. 

Adding another 2 would make it 4 x 200ah at 12v with 2 in parallel and 2 in series giving you 400Ah at 24v. You should also never run them down to less than 50%.

Posted
29 minutes ago, nelian said:

calculation on 800 ah

You won't have 800ah, in series add voltage ie 12v x 4 = 48v (if your inverter is a 48v model), then ah stays the same at 200ah.

 

Posted
1 minute ago, Dougiedanger said:

You won't have 800ah, in series add voltage ie 12v x 4 = 48v (if your inverter is a 48v model), then ah stays the same at 200ah.

 

He was running with only two batteries before so it's safe to assume its a 24v system. 

Posted

@Achmatand myself commenting at the same time, basically your inverter size will tell us how your batteries are setup, either 24v or 48v. That will give you the size of the battery bank, which is basically the same in watts, either 24v x 400ah bank or 48V x 200ah, ie 9600w.

As stated never take the batteries below 50% SOC so useable capacity is 4800w, or 10.5 hours at a 450w draw. However note that the lifespan of these batteries will be severely compromised by drawing to this level regularly.

Also the inverter will not be able to determine SOC accurately and so it is highly recommended to have  BMV to do this and to be honest a battery balancer. The inverter may well run these batteries to a lower SOC than 50% which will cause more or less permanent damage if done several times.

Posted

OK, thank you everyone. OK, I can safely say that I have a 5kv hybrid 24v system, currently running 4x200ah batteries, giving me a total of 400ah.

So, as I mentioned, it was mainly to combat the load shedding, and in all honesty, we haven't had that many occasions, however, the original 2xbatteries weren't lasting 4hrs (Unless I switched off all the lights) so added the two additional batteries, which worked fine for a couple of rounds.  But of late, it doesn't seem to be lasting more than 2hrs. So they have been running completely flat.

Had the installer come out, and he tested the batteries, and said they were fine...

So based on all the feedback, it seems these batteries are toast... because we ran them below the 50% SOC...

ok... load shedding starts tonight, let see how they run...

Posted

Sorry @nelian, I unfortunately learnt the expensive way that lead acids are not properly protected by the average inverter which uses battery voltage to guess at the SOC which is never accurate.

Due to also purchasing a 24V inverter (killed my first set of lead acids inside a year, due to similar reasons) and finding that 24V lithium batteries were not readily available to replace them with, I had to stay on the lead acid path so opted for Trojans that have a good track record on handling some abuse and coupled that with a battery balancer and bmv to protect them. So far happy with my decision but had I been on this forum longer when I made the call, I may have thought more about dumping the 24V inverter and upgrading to a 48v one so I can could then explore getting a lithium battery instead of staying with the lead acids which need more attention.

 

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