Questions

[Pneuma]

Hello ya'll I am trying to put together a solar system 8s 24v 100ah battery bank 3kw inverter
So Im wondering what size BMS I need? my guess is something like 150Ah? (3000/24=125) I dont know if the math is correct or not

Also I am trying to work with MPPT and I saw that Will said to use BMS for the loads and not for charging and I was wondering if Anyone would be able to simply elaborate on that . WHere would the BMS need to be installed?


Thank you all!

 

[John Frum]

Assuming its a cheap high frequency inverter...
Also assuming no dc loads
3000 ac watts / .85 conversion factor / 24 volts low cutoff = ~147 dc amps
147 dc * 1.25 fuse headroom = ~183 fuse amps
If you buy a commodity grade bms you should either buy one rated for minimum 300 amps or use a smaller bms to remote control your inverter.

 

[John Frum]

BTW 147 amps is going to be a fairly brutal assault on those batteries.

 

[Pneuma]

BTW 147 amps is going to be a fairly brutal assault on those batteries.

I am planning on buying another 8 down the road and upgrade. I do not believe I am going to pull 3000w so Im just choosing a larger ineverter for later upgrades. Please let me know what you think. should i do this or just go with a smaller inverter alltogehter also the inverter is inside the all in one Growwatt 24v with a 2kw Mppt charge controller.

 

[Pneuma]

Assuming its a cheap high frequency inverter...
Also assuming no dc loads
3000 ac watts / .85 conversion factor / 24 volts low cutoff = ~147 dc amps
147 dc * 1.25 fuse headroom = ~183 fuse amps
If you buy a commodity grade bms you should either buy one rated for minimum 300 amps or use a smaller bms to remote control your inverter.

Thank you!

 

[John Frum]

I do not believe I am going to pull 3000w so Im just choosing a larger ineverter for later upgrades.

I hope you meant bms.
A bigger inverter would just make things more out of proportion.
How much do you expect to pull and how are you calculating?

 

[Pneuma]

I hope you meant bms.
A bigger inverter would just make things more out of proportion.
How much do you expect to pull and how are you calculating?

I am planing on running a desktop a laptop maybe a LED tv a fridge and a water heater and in warmer mounts AC because I'll be moving to texas

I want to be be able to run the computers and the tv couple hours a day the fridge would have to be 24/7 and the water heater for washing dishes and shower.

This is the system that I have mentally drawn
I also would love to incorprate being able to use 12V at one point.

The 3.2 fortune raw cells at 100Ah with 2C 8s 24v
Daly BMS. I was going with 150Ah but now atleast 300Ah
A 300Ah Fuse at the positive of the battery
Growatt 24V SPF 3000TL LVM – 3kW 120Vac Stackable Inverter 2kW MPPT Charge Controller Split Phase 120V240V capable with two or more units
And have not decited on the panels yet.

 

[John Frum]

water heater sounds like a big load
Air conditioning is also very big
How will how cook?
How will you boil water/make coffee?
Look at my signature about how to do the math.
That is the very first thing to do before you buy anything.

 

[Pneuma]

water heater sounds like a big load
Air conditioning is also very big
How will how cook?
How will you boil water/make coffee?
Look at my signature about how to do the math.
That is the very first thing to do before you buy anything.

Thank you so much for that!

I'll be cooking and heating up water for coffee/tea with propaine

I might not be able to run a water heater unless fully charged and nothing else is working correct?
Also In the worksheet it has the fridge, tv, furnace fan, lights and microwave running at the same time but in reality I wont be. like I will be running the microwave maybe for 5 minutes and in that 5 minutes, would I be able to shut other stuff off to compensate?

 

[John Frum]

Thank you so much for that!

I'll be cooking and heating up water for coffee/tea with propaine

I might not be able to run a water heater unless fully charged and nothing else is working correct?
Also In the worksheet it has the fridge, tv, furnace fan, lights and microwave running at the same time but in reality I wont be. like I will be running the microwave maybe for 5 minutes and in that 5 minutes, would I be able to shut other stuff off to compensate?

Yes you can juggle loads.

 

[Hedges]

in warmer mounts AC because I'll be moving to texas

AC will draw a surge current, probably 5x whatever nameplate rating is, perhaps for a couple 10ths of a second.
It the inverter can't deliver, it won't start. Capacitors and/or BMS & battery has to supply the power.

You can probably run a small window air conditioner with the 3kW inverter. Bigger, and heavy, low frequency, expensive inverters (backed by suitable battery) will do more.
An inverter drive split unit is probably much easier starting so you could have a bigger one for a given inverter.