Hi!

Is it possible to connect Kepworth 12v 100ah lifepo4 lithium batteries and correctly configure the Axpert vm iv 3.6K -24v inverter to work with them? The battery does not have any interfaces to communicate with the inverter. I tried to put in program 5 (battery type) Other manufacturers - the inverter reports that the battery type is incorrect (warning 62). If I select User-Defined in program 5 (I set parameters in programs 25, 26, 29), then the inverter does not see the battery at all - there is nothing on the display where information about the battery is displayed. The only inverter began to work with the battery, if I specify the type of battery AGM in program 5. but in this case, I can't set the minimum value for the voltage of a discharged battery and the maximum value for the voltage of a fully charged battery. Advise please what I should to do.

Thank You.

Leonid.

Edited January 23, 20233 yr by Leonid49

On 2023/01/24 at 12:50 AM, Leonid49 said:

If I select User-Defined in program 5 (I set parameters in programs 25, 26, 29), then the inverter does not see the battery at all - there is nothing on the display where information about the battery is displayed.

That's the setting you need, unless you find that your Kepworth have a BMS with comms. This would be unusual with a 12 V module, I would think.

You should check that your modules are allowed to be connected in series. 24 V is pretty low (almost any MOSFET is rated to at least 60 V), so it should be OK, but if the manufacturer forbids it, you may lose your warranty.

What version of display (U2) firmware are you running? Unfortunately, there is no VM IV firmware publicly available that I know of, but if it has a low minor firmware version number, that might indicate that the firmware is immature.

It might be that the inverter is working just fine with the USE battery type, just that the display is missing that data. If you use monitoring software, that might not be a huge concern.

To inverter is connected two batteries in series. The manufacturer of these batteries allows to connect up to 4 batteries in serial. Each battery haves oun built-in BMS.

Hi @Leonid49, you will need a balancer to keep the two batteries SOC's in sync to get the maximum out of the batteries.

Otherwise, one of them will charge slightly faster than the other one due to internal resistance differences etc. 

This will result in the BMS of the higher charged one stopping the bank charging before the lower charged one is fully charged. 

On the discharge cycle, the lower charged one's BMS will disconnect before the capacity of the higher charged battery is fully used.

The cycle is repeated and the gap between the SOC's on each of the batteries gets bigger and bigger so your effective capacity will get smaller and smaller. 

A battery balancer will keep the SOC's of the batteries in sync ensuring that you get maximum capacity from the two batteries in series. 

https://www.geewiz.co.za/hubble-battery-balancer/185924-lithium-24v-battery-balancer-equaliser-suitable-for-all-battery-types-24v.html 

 

 

Check what the recommended voltages & amperages are for your batteries

Should looks something like this:

Voltages on the inverter should be set for these voltages x 2 as you have 2 in series.

Amperage will stay the same i.e. in this case 11A 

15 minutes ago, Sc00bs said:

Hi @Leonid49, you will need a balancer to keep the two batteries SOC's in sync to get the maximum out of the batteries.

Otherwise, one of them will charge slightly faster than the other one due to internal resistance differences etc. 

This will result in the BMS of the higher charged one stopping the bank charging before the lower charged one is fully charged. 

On the discharge cycle, the lower charged one's BMS will disconnect before the capacity of the higher charged battery is fully used.

The cycle is repeated and the gap between the SOC's on each of the batteries gets bigger and bigger so your effective capacity will get smaller and smaller. 

A battery balancer will keep the SOC's of the batteries in sync ensuring that you get maximum capacity from the two batteries in series. 

https://www.geewiz.co.za/hubble-battery-balancer/185924-lithium-24v-battery-balancer-equaliser-suitable-for-all-battery-types-24v.html 

 

 

You shouldn't need a battery balancer. The trick is to properly balance the two 12V batteries before you put them in series. If done correctly you shouldn't have any problems after that. Worse case you might need to rebalance the two batteries once a year. Before connecting the batteries in series connect both in parallel then charge them for 12 hours. I use 12v lifep04 drop in for 24v ups systems all the time no issues so far.

Thank You.

50 minutes ago, TaliaB said:

You shouldn't need a battery balancer. The trick is to properly balance the two 12V batteries before you put them in series. If done correctly you shouldn't have any problems after that. Worse case you might need to rebalance the two batteries once a year. Before connecting the batteries in series connect both in parallel then charge them for 12 hours. I use 12v lifep04 drop in for 24v ups systems all the time no issues so far.

I agree with @TaliaB to some extent

Will it work without a balancer - Yes

Will the batteries stay at the same SOC's by themselves while charging in series over time, probably not. I think that the question that no one can really answer is how quickly they will get out of sync as this really depends on how evenly matched the batteries are. 

Starting with equal SOC's will definitely help. Top balancing them will help to get them at the same voltage. If you want you could bottom balance them as well by discharging them in parallel fully and then recharge. 

With lithium battery chemistry the big voltage changes only happen at the bottom and top ranges SOC, so that is the best place to get the batteries balanced to make sure they are at the same SOC's. 

To keep them 100% balanced, the best way is to just get a battery balancer.

 

Be careful with workload. Brand shop on Aliexpress only declared charging current as 0.5C. Discharging current not declared so it could be same (50A). In that case you will not be able to get workload over about 1200W.

Also item description on this seems official store says nothing about sequential connection batteries.