Dual overkill BMS for 2000watt inverter.

looking to purchase 8-270 ah lipo to power my Magnum 2000watt inverter.
Going to split to 4 cells and 120amp Overkill bms.
My calculations say the 2000 watt inverter will consume 166 amps.
So two Bms will be required. Thoughts?
12 volt system.

I plan on doing the same after reading about the success of it in another thread.

Just here to share my experience with the same BMS. How long do you expect to run 166 amps?

I have the Overkill 8S on my 72ah batteries and I was able to burst 176A ~4500w for my dryer. It quickly settled to 350w for the remainder of the dryer cycle.

I just ran a quick stress test of ~3000w at 117A to heat a liter of water from a kettle while simultaneously brewing coffee (1500w each appliance.) I wouldn’t recommend even that
long term and I did notice the heat gradually climbing.

Also, by default the BMS protection is set to 110A maximum but I changed it to 120A max for this test. Bottom line - it got the job done for my morning tea and coffee. ?

rv camper, wifes hair drier draws 1500 watts.
120 amp Bms only gives me 1400.
staying on the safe side for about $140

Tdevery said:

looking to purchase 8-270 ah lipo to power my Magnum 2000watt inverter.
Going to split to 4 cells and 120amp Overkill bms.
My calculations say the 2000 watt inverter will consume 166 amps.
So two Bms will be required. Thoughts?
12 volt system.

Click to expand...

If you get 2000W of power on the AC output side of the inverter, due to conversion loss, the DC input current will be about 195A based on about 15% conversion loss.

Tell DW to use medium heat. Better for the hair, better for the electric system.
Otherwise yes a 2000w inverter can easily go 166 amps continuous and even a bit higher.

Oh I missed the

Tdevery said:

rv camper, wifes hair drier draws 1500 watts.
120 amp Bms only gives me 1400.
staying on the safe side for about $140

Click to expand...

oh I misunderstood you were building a 12V system. Is there any chance that you’d rethink a 24V system? You’ll definitely run 1400-2000w continuous no problem. For my capacity test I’ve run 1500w continuously for all 68ah using my 3000w growatt inverter.

Tdevery said:

looking to purchase 8-270 ah lipo to power my Magnum 2000watt inverter.
Going to split to 4 cells and 120amp Overkill bms.
My calculations say the 2000 watt inverter will consume 166 amps.
So two Bms will be required. Thoughts?
12 volt system.

Click to expand...

2000 ac watts * 1.5 low frequency inverter fudge factor / 12 volts low cutoff = 250 dc amps
250 dc amps / .8 de-rate factor = 312.5 bms amps

When I run my factory ac in my fifth wheel through my Multiplus, my 712 shows around 95-105 amp draw after settling past the startup surge.

my inverter is only 12 volt input

I have also run my AC with an easy start, for about 20 minutes on my 4-6volt agm batteries.
batteries are about 6 years old and need to be replaced

If you have 8 cells why aren't you creating two batteries, each with its own BMS? That would give you 240 amps and some redundancy, just in case.

The 4s2p setup is what I'm using and it works great.

HRTKD,
The head of this thread is

"Dual overkill BMS for 2000watt inverter"​

So I am going to use 2 overkill Bms for each 4 cell of batteries.

Yup good idea. Will did have a video using 2 BMS in parallel with one set of batteries. Basically the same thing pairing 1 BMS per 4 cells. At least you can separate each group and use them independently. ??

Tdevery said:

HRTKD,
The head of this thread is

"Dual overkill BMS for 2000watt inverter"​

So I am going to use 2 overkill Bms for each 4 cell of batteries.

Click to expand...

So four total BMS?

No, i will have 4 batteries per BMS
Total of 8 batteries and 2 Bms.
These going into my 2000watt charger/inverter. hardwired into the RV.
The Magnum will switch over to shore or generator (Honda 3000watt inverter) when power is detected.
also have 600 watt solar.

Tdevery said:

No, i will have 4 batteries per BMS
Total of 8 batteries and 2 Bms.
These going into my 2000watt charger/inverter. hardwired into the RV.
The Magnum will switch over to shore or generator (Honda 3000watt inverter) when power is detected.
also have 600 watt solar.

Click to expand...

I think we have a failure to communicate. Do you mean cells or batteries? 4s means four cells making up a single 12v battery.

4s, i might have caused confusion, new at this.

Tdevery said:

4s, i might have caused confusion, new at this.

Click to expand...

No problem. The shorthand naming convention we use takes a bit to get used to.

Using two of the Overkill Solar 4s BMS you have a rated capacity of 240 amps. The numbers that smoothJoey came up with in post #8 are worst case, but useful. Using his first number of 250 amps, it's only 10 amps over what the two combined BMS are rated for. The Overkill Solar BMS has been tested to operate at that rating continuously, which is good. Even better is if you're unlikely to every really run the inverter continuously at that rate. His second number is based on the idea that a lot of these BMS devices are crap and that the folks selling them are pulling ratings out of their butt. Hence, the ratings are overstated. However, the Overkill Solar BMS has a very good reputation and the ratings do seem to hold up under testing.

As long as you aren't abusing the inverter, your plan is OK. The 600 watts of solar will help mitigate the draw on the battery. So if you're pulling large numbers of amps when the PV is producing lots of watts, the BMS will be even less stressed. If you really wanted to hedge your bet, another four cells and another BMS would spread the load, reducing the stress.

Your system isn't that different from mine. 4s2p using Overkill Solar BMS, 640 watts of PV on the roof. Where we differ is that I also have 640 watts of PV on the ground and only a 1,000 watt inverter. I'm planning to upgrade to a larger inverter, probably 2k or 3k watts, eventually.

HRTKD said:

His second number is based on the idea that a lot of these BMS devices are crap and that the folks selling them are pulling ratings out of their butt.

Click to expand...

Not really.
I de-rate quality hardware by .8 and mystery meat by .66 to .5.
If it was a Daly I would de-rate by .66.
Very few things I would push to 100%.