Dialing in my setup - 280 lifepo4 24v bank, 48v 800w panels - need BMS advice

[CamaroMan]

Hi all -

so received my victron 100/30 controller and waiting for quotes on batteries (will be going with lifepo4 cells 280ah or 320 ah) -

Inverter will be around 5k to 8k maybe 10k..

What size BMS do i need? Can i not just buy the largest one? Why match? Can get a 500a unit that I believe I can set the output to via app...

 

[John Frum]

Is this a stationary or mobile setup?
How many pv panels and what are the pv panel specs?
What system voltage?
320 amp hour cells don't really exist, I suspect you are shopping aliX or similar.

 

[timselectric]

If you need 500a worth of output, you're going to need more battery. After a lot of research, I chose the 200a JK BMS for each of my 280ah batteries.

 

[CamaroMan]

Is this a stationary or mobile setup?
How many pv panels and what are the pv panel specs?
What system voltage?
320 amp hour cells don't really exist, I suspect you are shopping aliX or similar.

stationery with no hookups-

Have been reading about setting the BMS up as a charge only setup and not load -

BMS wired for charging only - Endless Sphere

 

[John Frum]

I don't recommend going bareback on the discharge path.

 

[timselectric]

Ditto

 

[Rocketman]

A 5k inverter is doable at 24v (but just barely), if going above that go to 48v. You will be happier in the long run.

Also by going to a higher battery voltage your amps for the inverter drop in half. (And cables drop in size too).

I used an Overkill BMS (JDB) and it has worked well, JK’s also seem to get high marks too.

 

[CamaroMan]

Thanks- im looking at 10000w to run shop compressor with a soft start.. currently budgeted for 24v battery bank - 48v is gonna kill the no n existent funds right now -

 

[Rocketman]

Well then you have a math problem…

10,0000w /24v = 416amps (that is 4/0 wire)

There are several issues. First, (assuming 8 cells of 300-ish amp hours). That is over a 1C discharge rate - most cells have a 1C limit. Also you have to have bus bars that can handle that rate (most can’t).

Second is the BMS, there are two types of bms - contactor and FET based. Most FET based (JDB, overkill, JK, etc) are limited to 100 to (maybe) 200 amps of power.
If you go with the contactor based BMS - these are expensive- Batrium, Rec-BMS and Orion are the ones I know. (I used a Batrium in my MotorHome). The BMS is much more expensive, plus you need a lot more additional stuff around it. I went with Batrium so I could use the house battery to boost the starting battery to help start the big diesel engine (12v 544ah battery)

Even then, the Multiplus 12/3000 inverter is not happy when running the air conditioner. Too much ripple (which means my 4/0 wires, fuses, shunts, bus bars, etc. are providing too much resistance).

Looking at this math, you will need at least two 24v batteries to run a load that large (probably three Or four). At 48v the math becomes easier, but you will still need probably two 48v batteries in parallel to comfortably run a 10,000 w load.

Is your load really 10,000w? That 83 amps @ 120v. Inverter math gets easier using the correct starting values.

 

[CamaroMan]

apologies - its a split phase so 5000w for 110v and 5000 for 220v (received it this week), running amps of compressor motor is 24 @ 220 which = around 3200 watts running with an 80% efficiency on the inverter, everything else is lower, bench grinder and charging power tools and some shop LED lights all at 110v.

I did buy a microstart ASY-368-X72-BLUE soft start module too for the initial pull, rated 10 amps higher than needed - hopefully the system will do ok for my needs -

What type and size bms do you recommend, and is it worth using the BMS on the load side or can i run a monitor for over charging or something?

 

[CamaroMan]

just ordered a Daly 250a 8s 24v BMS for 166 on amazon - 5000 at 220 = 208 amps, so 250 gives me good head room i think-