Charge / discharge rating for multiple 48V server rack batteries

[fredrikfriis]

I currently have two vestwoods VE48100E 5,12kwh batteries connected to a Deye 12k hybrid inverter with RS485. Each battery current is max 100A. The two batteries are monted in an enclosure with a 125A fuse. The inverter is set to charge/discharge at max 100A, but it is capable of max 240A.

I'm thinking of increasing storage to 20kwh with two more batteries. With four batteries capable of 100A each, 240 amps should not be an issue. (Assuming properly sized cables)
*But*

[1]
My batteries have a push connector, not thread/nut, so i have to use the included cables. I can't find if the "passthrough" current is higher than 100 amps. Will ask Vestwoods. Any thoughts?
Alternatively I can run a new set of 70mm² wires from the inverter to a busbar in the enclosure, and use the included 25mm² wires from there to the batteries.

[2]
Is the battery-inverter communication clever enough to split the requested current evenly between the batteries, when the total requested current is above the max of each of the batteries?

[3]
If a battery were to unexpectedly trip out, will the remaining batteries pick up the load and carry on with an error message, or will the whole system trip offline immediately?

 

[TM48]

As it's configured now you are passing up to 200 amps though the inverter cables. You don't show the inverter but if it only has a single set to battery terminals you may need to use buss bars between the two sets of batteries and upgrade the cables between the inverter and bus bars. Those cable connectors look to be the same as I use. You should be able to source them however I would check the maximum rating on the ones you have. If your inverter has two sets of bat connectors you could just duplicate what you have now. I would not daisy chain the new batteries on the existing ones.

 

[Tsolar]

You could double your main battery cables to the inverter, assuming you are able to land them in the inverter. Also, you should move either the positive or negative cable to the other battery, connecting the main cables to "opposite" corners of the battery bank, this causes the current to flow much more equally from each battery to the inverter, with the main inverter cables both hooked to 1 battery, and then jumpers to the second, the battery with both main cables hooked up will see more charge and discharge use, with the 2nd battery just tagging along for the ride.

From a quick googling of those batteries, it looks like there are two different versions, a P1 and P2, the P1 appears to be a 15cell battery, and the P2 appears to be a 16cell battery. You must be absolutely sure that if you get more batteries in the future, that they match what you currently have. If you do currently have the 15cell version, and you are wanting to continue upgrading your battery storage in the future, I would think about ditching the 15cell version and going with 16cell versions from here forward. The 16cell is way more common across all different manufactures. Technically they are both "48v" batteries, but the 16 cell will have roughly 3.2v higher pack voltage than the 15cell. This also means the 15cell is only 4800wh and the 16cell is truly 5120wh of storage. I really have that manufactures have "cheaped out" and made 15cell 48v batteries, it just makes a mess of things, and makes them much less universal, and something customers have to watch out for.

The BMS doesnt really control how many amps each battery in a bank will charge and discharge, other than just completely shutting off charge or discharge if the BMS sees an issue, at that point the other battery will makeup for whatever is lost from the faulted one. Weather or not that BMS fault triggers the other battery or inverter to shut down also, who knows. The current flow from each battery is a function of voltage, the battery is the voltage source, the inverter is the consumer, so the current flow depends on the strength of the battery, to maintain its voltage, and also any resistance in the path between the battery and inverter. That is why you want to move a cable, so one cable from the inverter is connected to each battery, equaling the cables and connections from each battery to the inverter, causing a more equal flow of current from each battery to the inverter.