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BMS sizing and CAN bus Multiplus II

Lasertrapper

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Jan 20, 2022
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Thanks so much in advance for input! Newbie. I have the MULTIPLUS-II 12/3000/120-50 2X120V inverter, Cerbo GX and GX touch 50, and am planning qty4- 4S 300Ah prismatic packs in parallel, hoping to be able to run my 120v roof air (Dometic Penguin II w/ soft start) for at least a few hours. It would be nice to connect the BMS's to the Cerbo which apparently uses CAN bus so am looking for appropriate size BMS with this communication feature. I've looked at Seplos, but doesn't look like they have 12v version. Daly lists a few, looking for feedback & suggestions for other BMS?
 
(4S * 3.2V * 300Ah) * 4 = 15,360Wh

Typical draw of RV rooftop A/C is about 1500W, so you should be good for "at least a few hours."

Very few options natively support CAN communication, and none are cheap. REC and Batrium come to mind for 4S.

I'm in the process of deploying a Batrium for a 14S Lithium NMC battery within a Victron ecosystem. It's been a real learning process.
 
Thanks for the info!

Any experience with Daly? Is that an unreliable option?

Also, as far as sizing, is it best practice to size all 4 BMS a bit more than the max output of the inverter? Do I use the 2400 watt number for my 12/3000 Multiplus II?
 
Daly is commonly used by folks on this site. I don't know if it has any CAN communication ability.

IIRC, the MP can do 3000W for about 30 minutes in an overload situation. You definitely want to plan for that.

3000W/12V/.85 = 294A (.85 is efficiency factor)

You can "split" that among batteries and divide by 4 as long as you keep in mind that your batteries won't be perfectly balanced. If each battery has a 100A BMS, then that should be more than enough to handle the current.

Overkillsolar sells a 120A BMS for 4S. They're pretty popular. I used one for a 24V battery I built.
 
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