Is lifepo4 battery maximum discharge a battery or bms limitation?

[guyroch]

Hi everyone,

I have four SOK 200ah batteries that I'd like to install in a motorhome. The motorhome is already set up for solar, but it has lead acid batteries, and since I already own the 4 SOK batteries that is what I'd like to use. The already-wired inverter (2000w @ 12v) and solar charge controller already support lithium batteries, I would just need to change a few settings.

The thing is don't have the space to drop in the 4 SOK batteries with their black box, but I can fit the 16 cells in 2 rows of 8 cells, so I'm thinking of doing that.

I guess I could use the existing 4 BMS in a true 4S4P layout, but I'm thinking of going with a single BMS in a 4P4S setup with this BMS, rated for 260 amps.

In a 4P4S configuration with a 2000w inverter, I need 2000 / 12 = 166 amps. So, it's going to be a walk in the park for the BMS, I would think.

Where I'm not clear is the discharge rate of the original SOK batteries, with its original max discharge rate of 130 amps (source). Is that maximum discharge rate a battery (or cells) limitation, or the original SOK BMS itself?

If it's the cells, a 4P4S configuration is probably a non-starter since 130 amps * 12v is barely 1500 watts (the inverter is 2000w).

Thanks

 

[HighTechLab]

It's a BMS limit. The cells can do 206A continuously but the BMS isn't designed to. In any case you have plenty of capacity for the 2000w inverter with 4 batteries...even 2 SOK batteries would be enough for the 2000w inverter.

 

[guyroch]

It's a BMS limit. The cells can do 206A continuously but the BMS isn't designed to. In any case you have plenty of capacity for the 2000w inverter with 4 batteries...even 2 SOK batteries would be enough for the 2000w inverter.

Thanks for the fast reply, really appreciated

 

[mikefitz]

You need nearer 200 amps for a 2000 watt inverter at full power in a 12v system.
4P4S is problematic.
800 Ah seems a lot for a small RV.
Wouldn't two SOC be enough in parallel and save taking well constructed batteries apart?

 

[guyroch]

You need nearer 200 amps for a 2000 watt inverter at full power in a 12v system.
4P4S is problematic.
800 Ah seems a lot for a small RV.
Wouldn't two SOC be enough in parallel and save taking well constructed batteries apart?

Thanks, and I agree that 2 SOK could be (barely) enough... there is certainly a fair amount of truth in the SOK batteries being well constructed. The RV is actually a class A motorhome, and we do go off gird for several days in between locations while on the road, and 5kw puts me in a very uncomfortable limit. I do have an onboard generator that I can use occasionally, and I'm very mindful of my surrounding and I dislike having to start the generator due to noise and fumes for those that are also camping nearby.

Why is 4P4S problematic with a 2000w inverter and 260 amp BMS? I'm planning to use either 2/0 or a pair of 2 AWG cables between the battery bank and the inverter, max of 3-4 feet.

 

[TomC4306]

Thanks, and I agree that 2 SOK could be (barely) enough... there is certainly a fair amount of truth in the SOK batteries being well constructed. The RV is actually a class A motorhome, and we do go off gird for several days in between locations while on the road, and 5kw puts me in a very uncomfortable limit. I do have an onboard generator that I can use occasionally, and I'm very mindful of my surrounding and I dislike having to start the generator due to noise and fumes for those that are also camping nearby.

Why is 4P4S problematic with a 2000w inverter and 260 amp BMS? I'm planning to use either 2/0 or a pair of 2 AWG cables between the battery bank and the inverter, max of 3-4 feet.

Because you lose visibility into the individual cells at 4p. Those four cells will be reported as one.

 

[John Frum]

According to the authoritative source all 3 versions of the sok 206ah battery have a "Maximum Continuous Discharge Current 100 A".

SOK 12V 206Ah LiFePO4 Battery Bluetooth&Built-in heater | SOK Battery

Restock on 10th April. Latest V8 version Bluetooth BMS, top battery cells balance function.Bluetooth&Built-in Heater Function SK12V206H designed for cold weather using! Can safely charge at temperatures down to -20°C (-4°F) by a standard charger or solar charger. The heater pads which draws...

www.us.sokbattery.com

Marine Grade 12V 206Ah LiFePO4 Battery,Sealed Plastic Box | SOK Battery

Latest V8 version BMS.

www.us.sokbattery.com

12V 206Ah LiFePO4 Lithium Iron Phosphate Battery Pack | SOK Battery

Restock on 15Th April.

www.us.sokbattery.com

 

[guyroch]

Because you lose visibility into the individual cells at 4p. Those four cells will be reported as one.

Fair enough, but visibility into the individual cells is not something I really care that much about personally.

 

[guyroch]

According to the authoritative source all 3 versions of the sok 206ah battery have a "Maximum Continuous Discharge Current 100 A".

SOK 12V 206Ah LiFePO4 Battery Bluetooth&Built-in heater | SOK Battery

Restock on 10th April. Latest V8 version Bluetooth BMS, top battery cells balance function.Bluetooth&Built-in Heater Function SK12V206H designed for cold weather using! Can safely charge at temperatures down to -20°C (-4°F) by a standard charger or solar charger. The heater pads which draws...

www.us.sokbattery.com

Marine Grade 12V 206Ah LiFePO4 Battery,Sealed Plastic Box | SOK Battery

Latest V8 version BMS.

www.us.sokbattery.com

12V 206Ah LiFePO4 Lithium Iron Phosphate Battery Pack | SOK Battery

Restock on 15Th April.

www.us.sokbattery.com

Thanks. I guess this is a moot point if the actual discharge rate is a BMS limitation, since I would be using a 260amp BMS in the 4P4S configuration.

 

[Oldwave]

If you want the best continuous output a Victron battery with an external bms will be expensive but the most compact.