Calculating amps?

[Alderon57]

Hi, all.
My system is going to consist of an 8S x 280ah battery (7.1kwh), a GroWatt All-in-One with the 3000W inverter, and somewhere around 2000W of solar panels with AC backup.
Two questions on calculating amps:
- Should the 24V BMS be rated below, the same as, or higher than the inverter?
- What size fuse / breaker should be immediately off the positive lead of the battery?

I have ideas based on things I have seen, but how do you actually calculate the real values?
Thanks for any and all instruction!
Ron

 

[sunshine_eggo]

Hi, all.
My system is going to consist of an 8S x 280ah battery (7.1kwh), a GroWatt All-in-One with the 3000W inverter, and somewhere around 2000W of solar panels with AC backup.
Two questions on calculating amps:
- Should the 24V BMS be rated below, the same as, or higher than the inverter?

Depends. Do you want to use the full 300W of the inverter? If so, you must allow 3000W/24V/.85 (inefficiency factor) = 147A from the battery.

- What size fuse / breaker should be immediately off the positive lead of the battery?

147A * 1.25 = 184A, round up to 200A

 

[740GLE]

Pushing a BMS to the nameplate is also sketchy, I’d source a 200a BMS, which maybe challenging.

Or it’s a good excuse to snag another 8 cells and have parallel 280ah batteries each with 100a BMS. 560ah at 24v sounds mighty nice.

 

[sunshine_eggo]

Pushing a BMS to the nameplate is also sketchy, I’d source a 200a BMS, which maybe challenging.

The one exception I would make is for the Overkill. Steve tested them at > rated current extensively, and they hold up. Many folks using them run them to the max.

If one truly intended to run at max current for 24/7/365, yeah, I'd change my tune and likely look at lowering the load to 50% of rated, but with the typical use profile that runs at a much lower average load, I wouldn't hesitate to design for 100% for Overkill.

Or it’s a good excuse to snag another 8 cells and have parallel 280ah batteries each with 100a BMS. 560ah at 24v sounds mighty nice.

+1

 

[Alderon57]

Thanks for the fast replies! I was thinking of doing another parallel battery in the future, so maybe a 200A isn't crazy. Andy has a link to one in one of his videos.

 

[740GLE]

Sounds like we all agree more battery capacity is always the solution. ?

 

[Ironman]

Or...you can have your BMS run a solid state relay like Chargery does to switch the DC load. That way the BMS does not handle high amp loads on a printed circuit board.

 

[Alderon57]

Or...you can have your BMS run a solid state relay like Chargery does to switch the DC load. That way the BMS does not handle high amp loads on a printed circuit board.

I'm not familiar with this. Can you give more details?

 

[sunshine_eggo]

I'm not familiar with this. Can you give more details?

charger model power, specially design the equalizer, smart balancer and lipo balancer for R/C model

The 300A and 600A DCC are basically custom relays that work with the Chargery.

They have an additional feature that when they're in the OFF position, they are still connected to the battery through a resistor - pre-charges the capacitors.

 

[Alderon57]

charger model power, specially design the equalizer, smart balancer and lipo balancer for R/C model

The 300A and 600A DCC are basically custom relays that work with the Chargery.

They have an additional feature that when they're in the OFF position, they are still connected to the battery through a resistor - pre-charges the capacitors.

Cool. Thanks! Appreciate the link.