Modbus BMS

[jwrgorman]

Just a question about checking state of charge from BMSes - any recommendations for a BMS that can expose state of charge (in % or Ah or Wh) of a 24VDC, 100Ah battery for example over a modbus register? Thanks!

[SunEagle]

If you are referring to an FLA type battery then there really isn't any measurement except the acid level that tells you what the SOC is.

If you are talking about a Lithium chemistry battery then a BMS might be able to provide accurate SOC data. As to how that is shown, I think it is up to the owner but for me I would like to see the value in a %.

[jwrgorman]

Yes a 24V LiFePO4 battery is what I'm thinking - clearly you can measure voltage but that is not really a measure of SoC - and yes ideally a percentage would be great. I think there are devices like this one: http://www.cruzpro.com/vah110.html that use Peukert's Law to determine a percentage of capacity available, but agree it's not a simple linear relationship to time or current flow.

[Ampster]

Yes a 24V LiFePO4 battery is what I'm thinking - clearly you can measure voltage but that is not really a measure of SoC - and yes ideally a percentage would be great. .....

There are a lot of $100-200 BMSs that calculate SOC from Amps in and out. Daly, Chargery and a few others. Will Prowse has done a few reviews. You can find his videos on Youtube. I have an Orion Jr BMS that does that but it costs $600.

[jwrgorman]

Thanks Ampster that Orion gear looks awesome, will read up on those.

[tom rickard]

I use the Batrium BMS, and the REC BMS. Both of these report SOC as a % over CAN bus and can communicate with many inverters including Victron and SMA.