so many gadgets - but also so many brain cells

[moonlitsouls]

ok so ive watched like 73 videos on DIY builds for the Lithium battery

I bought 4x 3.2 280ah batteries and plan to connect them in series to create a massive 12v battery to run my truck camper with integrated solar system

i am going to purchase an overkill solar BMS rated at

(4s120aBMS+Bluetooth)​

so heres my question , for a 400 watt solar system and a 2000w inverter , is this the correct BMS?

furthermore, i see this BMS has low temp cutoff and a mobile app

I see a lot of people adding victron shunts and victron battery sense to their battery box

do i actually need that? or does this BMS already do all of that? I do plan on using a Victron MPPT controller and a their battery monitor , so since im already going to be using their bluetooth features i feel like the shunt and the smart sense could be fun little gadgets but im not sure what to do about that

thanks!

 

[MisterSandals]

120aBMS

2000w inverter

2000w / 12.8v = 156 amps

The 120a BMS will not handle the full power that your inverter is capable of drawing.

12.8v x 120a = 1536w

 

[Hedges]

120A x 12V = 1440W, which is less than 2000W.
You might do better with 8x cells and a 24V inverter.

Then again, it might deliver the 0.15 second starting surge needed for a 450W A/C as well as the continuous operating current.

 

[moonlitsouls]

2000w / 12.8v = 156 amps

The 120a BMS will not handle the full power that your inverter is capable of drawing.

12.8v x 120a = 1536w

120A x 12V = 1440W, which is less than 2000W.
You might do better with 8x cells and a 24V inverter.

Then again, it might deliver the 0.15 second starting surge needed for a 450W A/C as well as the continuous operating current.

this just got a lot more complicated , and i was just starting to understand the 12v, my RV is all 12v , so how do i convert the 3.2 x 280ah cells to 24v ? i think it will be easy to switch the inverter to 24v , i see that everywhere

 

[moonlitsouls]

i think im about to give up and get a pro to figure all this out. i am out of my league. anyone know a guy in NYC area lol??

 

[Hedges]

"Pro" means he gets paid money to do this. Doesn't necessarily convey competence.

You would need 8 cells X 3.2V/cell to get 24V.
Yes, plenty of 24V inverters.
For additional cost you can get 24V to 12V DC/DC converter. Loads would be limited to the peak it can handle.

But like I said, if your continuous load is well under the 1400 to 1500W we computed, might be fine with the 12V 2000W inverter.
Depends on peak surge current and how fast BMS disconnects.

Discussion here about "Discharge Overcurrent Delay"

https://www.reddit.com/r/OverkillSolarBMS/comments/fue716

 

[moonlitsouls]

"Pro" means he gets paid money to do this. Doesn't necessarily convey competence.

You would need 8 cells X 3.2V/cell to get 24V.
Yes, plenty of 24V inverters.
For additional cost you can get 24V to 12V DC/DC converter. Loads would be limited to the peak it can handle.

But like I said, if your continuous load is well under the 1400 to 1500W we computed, might be fine with the 12V 2000W inverter.
Depends on peak surge current and how fast BMS disconnects.

Discussion here about "Discharge Overcurrent Delay"

https://www.reddit.com/r/OverkillSolarBMS/comments/fue716

ok so thats not too bad to understand , i could potentially buy 4 more cells , run a 24v system at 560ah correct? then buy a 24v inverter @2000w and then a 24 to 12v stepdown

maybe this will also allow me growth within the system to purchase even more solar panels?

thanks for your time and help


to clarify , im not sure yet about the watt usage of the AC that the truck camper comes with but i think its 9000 btu's if that helps. probably at least 1500 watts

I also have an onan LP generator so if i need to run that to use the ac, i can

as far as continuous loads, nothing crazy , ill be using the tv the propane furnace , a couple chargers and thats it , all on 12v . as far as appliances , maybe one at a time , a toasted here and there , maybe a blender but no microwave

but it would be nice to run the a/c on 70 degrees through the inverter without needing to run a generator , but its winter here and thats not really a priority for me right now.

i would guestimate my actual wattage use at any given time to be well under 500w

i am confused though, i see a lot of people with 2000w-3000w inverters running battle born batteries, i wonder how many amps that BMS is rated for ?

 

[MisterSandals]

then buy a 24v inverter @2000w and then a 24 to 12v stepdown

I have not seen any mention of what your power needs actually are. OP, why do you think you NEED a 2000 or even a 3000w inverter? What are your AC (household current) power needs? Appliances?

 

[moonlitsouls]

I have not seen any mention of what your power needs actually are. OP, why do you think you NEED a 2000 or even a 3000w inverter? What are your AC (household current) power needs? Appliances?

ok i have a better idea , im going to wait until i take delivery of my rv , build out my 280ah lithium battery , swap that in , and use the current setup in the RV the way it is right now until i do my own energy audit and see how things perform with whats already inside , be back in 30 days

 

[Hedges]

to clarify , im not sure yet about the watt usage of the AC that the truck camper comes with but i think its 9000 btu's if that helps. probably at least 1500 watts

If A/C has label rating of 1500W, then you're going to need 7500W surge to start it.
My 48V 6000W Sunny Island would do that but not any 2000W inverter.
There are several quality brands configured for use with shore power and generators, for mobile applications like RV or boat.
These take care of bonding/isolating neutral/ground depending on whether shore power is connected.

When you mentioned "camper" I thought a cabover with small A/C.

If you have an Onan generator, best setup will be an inverter/charger capable of starting the load, PV panels sufficient to keep it running with plenty of sunlight, auto-start of generator when batteries get low. Preferable not to have to run the generator continuously when A/C cycles on and off, should just kick in occasionally when more Wh are needed.

Once you tabulate all your loads, how many you plan to run at once, what locations/season you plan to visit, you can design a good system. Having the generator lets you keep battery and PV smaller than otherwise needed.

 

[HRTKD]

Just because you have a 2000 watt inverter doesn't mean you need to pull a full 2000 watts. In most trailers, the only things that would pull a bunch of watts would be the microwave and the air conditioner. The microwave might be doable, but you need to verify that your microwave will pull fewer amps than the BMS can handle.

Many of us compromise and use a battery system just like yours for everything in the trailer except the microwave and air conditioner.

I have eight 280Ah cells. I created two batteries, each with its own 120 amp BMS. As long as both batteries are online, I can pull 240 amps. I could run the microwave off this, but my inverter isn't big enough (only 1000 watts) to do that. Eventually, I'll upgrade the inverter.

 

[moonlitsouls]

If A/C has label rating of 1500W, then you're going to need 7500W surge to start it.
My 48V 6000W Sunny Island would do that but not any 2000W inverter.
There are several quality brands configured for use with shore power and generators, for mobile applications like RV or boat.
These take care of bonding/isolating neutral/ground depending on whether shore power is connected.

When you mentioned "camper" I thought a cabover with small A/C.

If you have an Onan generator, best setup will be an inverter/charger capable of starting the load, PV panels sufficient to keep it running with plenty of sunlight, auto-start of generator when batteries get low. Preferable not to have to run the generator continuously when A/C cycles on and off, should just kick in occasionally when more Wh are needed.

Once you tabulate all your loads, how many you plan to run at once, what locations/season you plan to visit, you can design a good system. Having the generator lets you keep battery and PV smaller than otherwise needed.

Just because you have a 2000 watt inverter doesn't mean you need to pull a full 2000 watts. In most trailers, the only things that would pull a bunch of watts would be the microwave and the air conditioner. The microwave might be doable, but you need to verify that your microwave will pull fewer amps than the BMS can handle.

Many of us compromise and use a battery system just like yours for everything in the trailer except the microwave and air conditioner.

I have eight 280Ah cells. I created two batteries, each with its own 120 amp BMS. As long as both batteries are online, I can pull 240 amps. I could run the microwave off this, but my inverter isn't big enough (only 1000 watts) to do that. Eventually, I'll upgrade the inverter.

ok guys thanks a lot , i feel much better about this now. Im going to take a step back , evaluate and then attack it from a more educated and informed position.

 

[Just John]

ok so thats not too bad to understand , i could potentially buy 4 more cells , run a 24v system at 560ah correct? then buy a 24v inverter @2000w and then a 24 to 12v stepdown

24 volt system is good in a lot of ways. The extra voltage means half the amps, and wire size and wire costs, fuses, relays or whatever you need are easier. A 12 volt system on the other hand is already working. A 24v to 12v converter is reasonable and reliable if needed.

to clarify , im not sure yet about the watt usage of the AC that the truck camper comes with but i think its 9000 btu's if that helps. probably at least 1500 watts

Look into adding a "soft start" kit. It's cheap and helps reduce the startup current of the unit, thus peak amps. Very commonly used to help generators for RVs.

I also have an onan LP generator so if i need to run that to use the ac, i can

What is the wattage of the generator? Does it allow you to pretty much run everything simultaneously? Might give a hint to inverter sizing.

but it would be nice to run the a/c on 70 degrees through the inverter without needing to run a generator , but its winter here and thats not really a priority for me right now.

That is the most serious power surge there. In the RV world, a 2000 watt inverter generator will usually work with a hard start capacitor, a 3000 watt always will. Generators have better surge capacity, unless you buy a more expensive inverter.

i am confused though, i see a lot of people with 2000w-3000w inverters running battle born batteries, i wonder how many amps that BMS is rated for ?

I'm pretty sure 100 amp, could be 120 amp BMS. Notice a lot of those use multiple Battleborns, you can parallel connect them (thus 200+ amps)

 

[moonlitsouls]

24 volt system is good in a lot of ways. The extra voltage means half the amps, and wire size and wire costs, fuses, relays or whatever you need are easier. A 12 volt system on the other hand is already working. A 24v to 12v converter is reasonable and reliable if needed.

Look into adding a "soft start" kit. It's cheap and helps reduce the startup current of the unit, thus peak amps. Very commonly used to help generators for RVs.

What is the wattage of the generator? Does it allow you to pretty much run everything simultaneously? Might give a hint to inverter sizing.

That is the most serious power surge there. In the RV world, a 2000 watt inverter generator will usually work with a hard start capacitor, a 3000 watt always will. Generators have better surge capacity, unless you buy a more expensive inverter.

I'm pretty sure 100 amp, could be 120 amp BMS. Notice a lot of those use multiple Battleborns, you can parallel connect them (thus 200+ amps)

appreciate this info

its an onan lp 2500 w generator

the ac is a coleman mach 8 13,500 BTU , part # 47203B876

i reached out to coleman to see how many watts the surge is for startup

im not sure about my daily power needs but i want room to grow and i want the appropriate sized inverter to sustain at least 600w solar and 2x 280ah DIY batteries

Im going to do the overkill solar 120a bms in each , if i run a 2000w inverter with a 4000w surge i should be good with that bms , even if i run the ac at 1500 w , the BMS 12v x 120amp can cover that no? i dont plan on exceeding 1500w unless i add the second battery

you bring up a good point about the battle born which helped me to understand this all a bit better , i run the cells within the battery in series to increase the voltage giving me 12.8v @280ah , but if i run two of those batteries in parallel , im still at 12.8 volts but now 560ah , BUT now i have 240amp capability between 2 BMS ? am i getting that right? thanks

 

[HRTKD]

you bring up a good point about the battle born which helped me to understand this all a bit better , i run the cells within the battery in series to increase the voltage giving me 12.8v @280ah , but if i run two of those batteries in parallel , im still at 12.8 volts but now 560ah , BUT now i have 240amp capability between 2 BMS ? am i getting that right? thanks

That is correct.

 

[Sojourner1]

If you haven't seen this video it might help with understanding some of the system.

 

[MisterSandals]

i run the cells within the battery in series to increase the voltage giving me 12.8v @280ah

Putting the batteries in series will give you 12.8v x 2 = 25.6v @ 280ah (guessing just a typo)