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Paralleled Seplos Battery Bank asymmetric current.

TheTallOne

New Member
Joined
Mar 10, 2023
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2
Location
Broadstairs, Kent, UK
Newbie here, please be gentle.

TLDR: My paralleled DIY battery banks are discharging and charging at different rates. The master pack at 100A, the slave at about 60A. This ratio seems to be consistent, I do not know the cause.

I have a pair of DIY 48v/16s/320aH battery banks, both run by Seplos 200A BMS 10e (one has bluetooth, the other doesnt, other than that they're identical). I have set identical settings for both BMS and then paralelled them with DIP switch settings according to the manual. However, when discharging (and I assume charging, though I haven't checked), one pack takes more load than the other, at a ratio of 100/60. This is a problem because a)I don't want to wear one pack more than the other and b) my DC fuses are 125A, which means my inverters (rated to 115A) can't export at max capacity without blowing the fuse on the master pack.

The inverters are a pair of Sunsynk ECCO 5.5kw, in parallel and as far as I can tell, working fine.

DC cables are the same lengths (to within a couple of cm) on both packs, connections all seem to be good. I feel like I'm missing something obvious here but I cannot think of it. HELP!

My only thought is that I wonder if my DIP switch settings are correct. My reason for wondering is that when I paralleled my inverters, the slave inverter just inherited all the settings from the master. When I paralleled my BMSes, it didn't, I had to connect to the slave manually and set everything, then set the switches for paralleling. But there's two possible settings, CAN and RS485. I'm using the CAN settings, is this where I've gone wrong?

Many thanks in advance!
Jon
 

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Swap your inverters on the outside ends of the bus bar, and the batteries in the middle, also make sure lugs touch the bus bar all the same.
I had in the past put a washer by mistake under the lug, and that battery was lagging 5A on a 40A total load of two batteries. Be meticulous and eliminate any imbalance in the battery feeds, check the crimps even if they appear solid. A resistance meter can pick up a bad crimp.
Also swap the fuses around to eliminate that as well.
 
which firmware are you using and are all packs at the same firmware? If you use CAN Settings are you using the correct protocoll in the BMS and the inverter? Are the cable pins as needed by the inverter and the BMS?
 
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