BMS 120Amp to Inverter question

[V84x4]

New to DIY so thanks in advance

Building a Self-sustaining system for my computer room

3 x 235w 7.8amp 32V Trina Solar panels
Victron 150/85 Controller
4 EVE 280Ah 3.2V cells (in series 280Ah 12V)
Victron 500A shunt
JBD 120A BMS

I understand that a 120amp overkill BMS will only support up to 1536 watts

My question is Can I buy a 2500 or 3000W inverter for future-proofing (More Batteries)
And just be careful about the amount of amp draw (Not over 1500 watts) for now
until I build my next Battery bank?

Or....... can I buy another piece of equipment to monitor and make sure I DO NOT draw too many amps
until I can afford to build another 12V 280Ah battery bank?

I want to be safe

best regards, Rick

 

[John Frum]

Those 280ah cells should not be discharged at a continuous rate of >.5c(140 amps) as they get hotter inside.
So the bms is only really a small bottleneck at 120 amps.

 

[V84x4]

Those 280ah cells should not be discharged at a continuous rate of >.5c(140 amps) as they get hotter inside.
So the bms is only really a small bottleneck at 120 amps.

Can you elaborate, please ( are you saying my batteries are the bottleneck? )

how many batteries will I need be to be able to run a 2500 or 3000 Inverter, please

Kindest regards, Rick

 

[John Frum]

Can you elaborate, please ( are you saying my batteries are the bottleneck? )

how many batteries will I need be to be able to run a 2500 or 3000 Inverter, please

Kindest regards, Rick

Assuming a 12 volt system.
3000 ac watts / .85 converison factor / 12 volts low cutoff = 294.12 service amps
294.12 service amps / .8 fuse headroom = 367.65 fault amps.
You need batteries amd BMSs to handle 300 amps.
One 4s 280AH 12.8 volt battery can deliver 140 amps continous without too much stress.
The BMS can deliver 120 amps continuous without too much stress.

By the math above you would need 3 batteries each with 120 amp bms in parralel to handle the max load of the inverter.

 

[V84x4]

Assuming a 12 volt system.
3000 ac watts / .85 converison factor / 12 volts low cutoff = 294.12 service amps
294.12 service amps / .8 fuse headroom = 367.65 fault amps.
You need batteries amd BMSs to handle 300 amps.
One 4s 280AH 12.8 volt battery can deliver 140 amps continous without too much stress.
The BMS can deliver 120 amps continuous without too much stress.

By the math above you would need 3 batteries each with 120 amp bms in parralel to handle the max load of the inverter.

For MAX load.....Now I see what you are saying.....Thank you

but let me be a bit more specific.....
If I purchase a 3000W inverter now but only run approx 800w load (Till I get more batteries)
Is that OK to run on my 12V 280ah ( a few hours a day ) ??

Thanks again for your help
Regards, Rick

 

[John Frum]

For MAX load.....Now I see what you are saying.....Thank you

but let me be a bit more specific.....
If I purchase a 3000W inverter now but only run approx 800w load (Till I get more batteries)

How will you enforce this policy?

Is that OK to run on my 12V 280ah ( a few hours a day ) ??

Its not the time its the current.

 

[V84x4]

How will you enforce this policy?

Its not the time its the current.

By only hooking up no more than 800 watts worth of equipment at a time
Example:
A computer that draws 400W and a monitor that draws 150W

regards, rick

 

[BigGun]

Put a 150 amp fuse inline -- anything more than that the BMS should shut down

 

[RCinFLA]

You really need to understand the difficulty of running a 3kW inverter from 12v batteries.

300 amps and 12v supply means every little bit of voltage drop really hurts. The more voltage drop from batteries to inverter means more battery current is needed to supply same output power, which creates more voltage drop. It is vicious circle that is a downward spiral.

 

[V84x4]

You really need to understand the difficulty of running a 3kW inverter from 12v batteries.

300 amps and 12v supply means every little bit of voltage drop really hurts. The more voltage drop from batteries to inverter means more battery current is needed to supply same output power, which creates more voltage drop. It is vicious circle that is a downward spiral.

So in reality I should really be running 24V batteries and then just buy a 24V inverter
So 8 x EVE 280ah batteries in series and then a 24V 3000W inverter like the AIMS 24V 3000W inverter ???

Regards, Rick

 

[HRTKD]

@V84x4 , I'm doing what you're looking into. I run dual 280 Ah 12v batteries, each with a 120 amp Overkill Solar BMS. I have a Victron Multiplus 12/3000 inverter that I'm bringing online. The tricky part to the Victron model name is that the "3000" is volt amps. The actual output is limited to 2400 watts. For my system this is fine. I need enough to run a microwave, coffee pot, laptop, battery charger and maybe the air conditioner in my RV, but not all at the same time.

I have been running on a 1000 watt modified sine wave inverter for the past couple of years. That worked great to run everything but the microwave and certainly not the air conditioner.

 

[HRTKD]

So in reality I should really be running 24V batteries and then just buy a 24V inverter
So 8 x EVE 280ah batteries in series and then a 24V 3000W inverter like the AIMS 24V 3000W inverter ???

Regards, Rick

Since you're starting from scratch, that's what I recommend. You have no 12 volt loads, so you might as well go 24 volt.

Yes, to an 8s battery. Good to see you thinking that way already and not going down the path of two 12 volt batteries in series.

 

[V84x4]

Since you're starting from scratch, that's what I recommend. You have no 12 volt loads, so you might as well go 24 volt.

Yes, to an 8s battery. Good to see you thinking that way already and not going down the path of two 12 volt batteries in series.

So should I return my 12V BMS to get a 24V BMS
Or can I just order another 12V BMS and run the second battery pack in series?

regards, Rick

 

[HRTKD]

So should I return my 12V BMS to get a 24V BMS
Or can I just order another 12V BMS and run the second battery pack in series?

regards, Rick

I would not run two 12 volt LiFePO4 batteries in series. You can, but the 24 volt battery is a simpler setup.

Running batteries in series is old school lead acid thinking. With a BMS on the LiFePO4 batteries, there are charging issues that can come up when they're put in series.

 

[BigGun]

Do you already have 4 Eve cells -- If so --getting 4 more cells to match up might be a problem --hopefully they stay in balance

 

[V84x4]

Assuming a 12 volt system.
3000 ac watts / .85 converison factor / 12 volts low cutoff = 294.12 service amps
294.12 service amps / .8 fuse headroom = 367.65 fault amps.
You need batteries amd BMSs to handle 300 amps.
One 4s 280AH 12.8 volt battery can deliver 140 amps continous without too much stress.
The BMS can deliver 120 amps continuous without too much stress.

By the math above you would need 3 batteries each with 120 amp bms in parralel to handle the max load of the inverter.

Just ordered 4 more 280ah 3.2v matching cells to make a 24V battery and an 8S BMS 100amp
But I still don't know how to calculate what size inverter I can run on 8s 24V 280ah battery and be safe
So how do I know what the continuous amp rating is of this 8s 24V 280ah I am about to build?

Regards, Rick

 

[John Frum]

Just ordered 4 more 280ah 3.2v matching cells to make a 24V battery and an 8S BMS 100amp
But I still don't know how to calculate what size inverter I can run on 8s 24V 280ah battery and be safe

Regards, Rick

100 amps * 24 volts low cutoff * .85 conversion factor = 2,040.00 ac watts.
A 2000 watt inverter is a perfect fit for your bms.

 

[V84x4]

100 amps * 24 volts low cutoff * .85 conversion factor = 2,040.00 ac watts.
A 2000 watt inverter is a perfect fit for your bms.

If I get a 200 amp BMS does that mean I can get a 4000-watt inverter?
Sorry to be so dumb........But
I still do not see where you are getting the 100 amp continuous for your math........ Is it the BMS amp rating?

Sorry to keep bugging you
But this is the last piece of the puzzle
Regards, rick

 

[John Frum]

If I get a 200 amp BMS does that mean I can get a 4000-watt inverter?

Yes

I still do not see where you are getting the 100 amp continuous for your math........ Is it the BMS amp rating?

Yes

 

[John Frum]

If I get a 200 amp BMS does that mean I can get a 4000-watt inverter?

Sorry, spoke to quickly.
The next bottleneck will be the cells themselves.
The limit will be ~140 amps(.5c).
140 amps * 24 volts low cutoff * .85 conversion factor = 2,856.00 ac watts.

This would allow a 3000 watt inverter.