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Advice Needed - Axpert 5Kva Voltage Drop

Devon D

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I'm hoping someone has had a similar experience and can point me to the problem. During load shedding this weekend, the backup system only lasted about 1.5 hours each time we were shed. Today I did a simulation. Switched the mains off. Batteries at full charge. Load was at 10% - 12%. Within 1 hour, the battery capacity had dropped to 80%. Then it dropped from 80% to cut-out in 15 minutes. Battery cut-out is set to 42V. Checked battery voltage after cut-out and they were all between 12.9V and 13.1V


  • 1 x Axpert 5Kva Inverter
  • 4 x 200AH Gel Batteries
  • No Solar
  • Installed December 2018

This set-up used to give me around 10 to 12 hours at +-10% load, and would easily last the 4.5 hours of load shedding.

Is the problem with my batteries or inverter?


Thanks in advance.

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  • 1 month later...

Greetings everyone.

I am having the same issue as Devon. My setup is a few months old (everything was brand new). In todays load shedding, my King inverters shutdown in 2 hours. I have a record of the wattage use during load shedding (08H00 to 10H30), and the wattage remains below 1000w. so for two hours I used 2kW. I check the batteries and they were around 49V when everything shut down. 

What could be the issue?

Firmware is: 71.93



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I'll take this one I guess. The voltage bounce is explained here: "The cell voltage will rise somewhat every time the discharge is stopped. This is due to the diffusion of the acid from the main body of electrolyte into the plates, resulting in an increased concentration in the plates. If the discharge has been continuous, especially if at a high rate, this rise in voltage will bring the cell up to its normal voltage very quickly on account of the more rapid diffusion of acid which will then take place."https://www.powerstream.com/1922/battery_1922_WITTE/battery_WITTE.htm#toc


Unfortunately we are not properly trained on sealed lead acid batteries when we get them installed. You need a good size battery to use SLA batteries which makes them worse since that means you could probably afford lithium batteries for the same price. For example lets say you have a 5kw inverter which requires a 200amphour battery so you would then need to buy eight  12volt 200amphour batteries and set low voltage cut off at 49,2 volts which is around 50%. that would give you 4,8 kwh divided by 1000watts gives you 4,8 hours. so 4 batteries gives you 2,4 hours. Obviously if you have 100amphour batteries much less.

If you run them past that then you start to lose capacity like both of you did. at the price of eight 200amphour gel/sla batteries you can get about two  3,5kwh pylontechs or similar which gives about 6kwh usable and a battery management system(bms) to protect your investment.

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Thanks for the helpful advice. I considered that. I do have 8X200AH gel batteries ( should have said that, sorry). I think I must test voltage while load shedding to see if the Inverter is giving the correct voltage. I have a feeling the Inverter is being way too conservative. I was hoping someone can suggest settings that will stop the inverter from shutting down the moment the voltage drops below the threshold. where it should stay on for a bit before shutting off.

Lipo prices have changed this year compared to what was around last year. It is something to consider now. I still put it out there, can anyone advise if there is something else  with the king inverter to get 50% out of the batteries?





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