12V 280ah or 12V 560 with heavy loads and choosing the BMS

[Off Gridin' It]

I am about to begin a battery build. I have eight 280ah Lishen EVE Cells on the way.
I am trying to decide if I should build two 280ah 12v battery packs or one 560 12v battery pack.
The reason i am conflicted is the loads i am putting on this in regards to choosing the BMS.

I have a completely off grid 21.5 ft camper with a 1200 watt array going to a 100 Amp Renogy Charge Controller and also a 500 watt ground deploy array going to a 50 amp Victron charge controller For a total of 1700 watts.
Currently i have 800 ah (400 usable) of Deep Cycle Hybrid Gel batteries installed and this new pack will replace the GELS.
I run the entire camper off this system including the 13,500 BTU air conditioner.
I have a 4000 Watt AIMS inverter charger with a 12000 watt surge.

So i need your thoughts on this. With a 4000 watt inverter and taking into account the efficiency loss of the inverter I need a pretty large BMS.
4000 watts ÷ 12 volts = 333.33 amps
333.33 amps x 1.20 (efficiency loss) = 399.99 (Round to 400 amps).

So would it be best to run a 12 volts 560ah battery with a 500 amp Daly BMS or should i go with two 280 ah batteries each with there own 250amp BMS?

It has to be 12 volts. I am not switching out components to change over to 24 volts so please don’t suggest going 24 volts.


that do you all think?

 

[SolarRat]

It has to be 12 volts. I am not switching out components to change over to 24 volts so please don’t suggest going 24 volts.

4000 watts on 12v?

I just bought a very cheap brand new old stock 3000w pure sine wave inverter...12v... off craigslist. So cheap i had to buy it..., but was it? The amperage at those watts is ridiculously stupid. Fire hazard. You need a cable the size of my arm to power that. Do I sell it and buy something more reasonable? That would be smart.

333 amps? 400 amps? If that Aims inverter is the only thing keeping you at 12v, sell it. You said not to tell you to go to 24v. If you want 4000w of safe, reliable power go with 48v. It would be much cheaper than 12v in the long run. And it will last longer, run cooler etc. But with your 8 cells....

"So would it be best to run a 12 volts 560ah battery with a 500 amp Daly BMS or should i go with two 280 ah batteries each with there own 250amp BMS?"

To answer your question, if you insist on this setup, I'd do just one pack but get a much lower (cheaper) amperage BMS that can use an external relay to turn on/off the high amperage feed.

 

[Off Gridin' It]

My battery interconnects and wires to the inverter are 4/0 so I’m not worried. Plus it would be more involved then just switching the inverter to go 24 volts. I don’t want to have to run external relays because that would complicate things and make expansion more difficult later.
I prefer things to be simple. The less you convolute a system the more efficient and simpler to expand and repair if necessary.

why wouldn’t you suggest the 500amp if going 560ah?

Just a side note. I do plan on eventually switching over to a 24 volt system. Just not now because i have to many other irons in the fire. I plan on possibly going to a 6000 watt 24 volt inverter. I love seeing how far i can push solar

 

[SolarRat]

that would complicate things and make expansion more difficult later.

There is no "expanding" a 12v 4000w system. You are maxed...

I know where you are coming from. My "cheap" shed system is 12v. I made it 12v so it would be simple to modify or adapt in an extended power outage (I'm in hurricane country). But I have trouble just feeding 750w of PV to it with just one controller. I need huge cables, and the high amps makes the charge controller run hot.

If my batteries could be made into 24 or 48v I'd do it in a heartbeat. I'd sell my inverter and buy a new one of the correct voltage, and then get a simple 48 to 13.8 converter to run my 12v loads.

why wouldn’t you suggest the 500amp if going 560ah?

That would be fine if the price is what you want. I've been away from the solar thing for a couple years but 500 amp BMS's used to cost a fortune. If they came down in price, go for it. If not, I'd just go with a smaller and cheaper bms that can handle your charging amps and use the output to trigger a large relay for your loads. I wouldn't really want 500 amps going through a BMS unless is was top quality. My thinking may be outdated?

Heat is the enemy of all electronics. Amps create the heat. 400 amps at 12v is "only" 100 amps at 48v. Take the life expectancy of your chargers/inverters into account when pricing a system...the less amps means less stress and less heat.

My entire house is fed by a 100 amp breaker. Just sayin.

I'm in the market for 4/0 cable for my 3000/6000 inverter. No way in hell I'm paying today's prices...

 

[Off Gridin' It]

There is no "expanding" a 12v 4000w system. You are maxed...

I know where you are coming from. My "cheap" shed system is 12v. I made it 12v so it would be simple to modify or adapt in an extended power outage (I'm in hurricane country). But I have trouble just feeding 750w of PV to it with just one controller. I need huge cables, and the high amps makes the charge controller run hot.

If my batteries could be made into 24 or 48v I'd do it in a heartbeat. I'd sell my inverter and buy a new one of the correct voltage, and then get a simple 48 to 13.8 converter to run my 12v loads.


That would be fine if the price is what you want. I've been away from the solar thing for a couple years but 500 amp BMS's used to cost a fortune. If they came down in price, go for it. If not, I'd just go with a smaller and cheaper bms that can handle your charging amps and use the output to trigger a large relay for your loads. I wouldn't really want 500 amps going through a BMS unless is was top quality. My thinking may be outdated?

Heat is the enemy of all electronics. Amps create the heat. 400 amps at 12v is "only" 100 amps at 48v. Take the life expectancy of your chargers/inverters into account when pricing a system...the less amps means less stress and less heat.

My entire house is fed by a 100 amp breaker. Just sayin.

I'm in the market for 4/0 cable for my 3000/6000 inverter. No way in hell I'm paying today's prices...

In regards to maxing out the system.

You can expand a 12 volt system with no problem. Many believe you have to have 24 volts or higher to have a large system but that isn't true especially if you've planned for that future expansion. My system started out at with an 800 watt array but now I have 1700 watts. I have massive 4/0 cabling for battery interconnects and connection to the inverter so it can handle anything I might through at it. Plus the system is localized to one compartment which means not needing needing to spend a lot on wire because they aren't very long. I also have two charge controllers for that size array and can go up to 2200 watts with the current setup. The only factor keeping me from expanding at this point is actual physical space.
However, had I known I would have ended up going this big I would have started with 24 volt.

In regards to the BMS, Daly has a 500amp and it is less then $200.00 if I order from Alibaba.

 

[sprint2freedom]

It has to be 12 volts. I am not switching out components to change over to 24 volts so please don’t suggest going 24 volts.

P = I ^2 * R

Getting the same power at 12 volts vs 48 volts involves 4 times the amperage, and power lost to resistance heating is a factor of 16 times higher.

Everything is going to run much hotter, cables yes but especially terminals.
It's difficult to properly implement protection with such high currents. Appropriate high quality breakers and fuses in that range are expensive, if you can find them.

As for continued expansion at 12V (to 400 amps and beyond).. at some point you'll need to double or triple up on those 4/0 conductors, or move to heavy copper bus bars for the entire circuit.

Staying at 12V is simply insisting on using the wrong tool for the job.

 

[Off Gridin' It]

P = I ^2 * R

Getting the same power at 12 volts vs 48 volts involves 4 times the amperage, and power lost to resistance heating is a factor of 16 times higher.

Everything is going to run much hotter, cables yes but especially terminals.
It's difficult to properly implement protection with such high currents. Appropriate high quality breakers and fuses in that range are expensive, if you can find them.

As for continued expansion at 12V (to 400 amps and beyond).. at some point you'll need to double or triple up on those 4/0 conductors, or move to heavy copper bus bars for the entire circuit.

Staying at 12V is simply insisting on using the wrong tool for the job.

Can we stick to answering the question I asked in the original post? My system runs phenomenally and with no heat. I know this because besides the actual act of feeling it with my own hands I also used a infrared thermometer and it runs cool.

So, that being said lets not focus on 12 volt vs 24 volt. I'm not changing something thats not broken.

The question at hand that I asked is...

Would it be best to run a 12 volts 560ah battery with a 500 amp Daly BMS or should i go with two 280 ah batteries each with there own 250amp BMS?

 

[HRTKD]

Would it be best to run a 12 volts 560ah battery with a 500 amp Daly BMS or should i go with two 280 ah batteries each with there own 250amp BMS?

I chose to go with two 280 Ah 4s batteries. It works well for me. I'm not pulling a lot of amps yet since my inverter is only 1000 watts. A future 2000 or 3000 watt inverter will work OK in my system. The cable distances are less than 2' between the components.

I used the 120 amp Overkill Solar BMS. I don't see my system ever using the full 240 amps that I can pull out of the two batteries.

 

[slick99]

From what I know, if you have 2x120A BMS, your max discharge rate is 75% from 240A. So only 180A.

later edit: it was about lithium batteries, parallel connections provide 75% of power output

 

[HRTKD]

From what I know, if you have 2x120A BMS, your max discharge rate is 75% from 240A. So only 180A.

Do you have a technical reference for that?

 

[slick99]

sorry, it was about lithium batteries, parallel connections provide 75% of power output

 

[HRTKD]

sorry, it was about lithium batteries, parallel connections provide 75% of power output

I would still like to see a technical reference for that. I haven't seen the 75% derate before.

 

[slick99]

i've read it here

i have also spoke with a JBD reseller, asking if I can use 2x 200A BMS for 2x200AH batteries, and they said that current after paralel connection can't exceed 200A.

 

[HRTKD]

i've read it here

i have also spoke with a JBD reseller, asking if I can use 2x 200A BMS for 2x200AH batteries, and they said that current after paralel connection can't exceed 200A.

I'm skeptical. While my load expectations are well under the 240 amp combined rating, I think my system could handle that.

 

[noenegdod]

I am about to begin a battery build. I have eight 280ah Lishen EVE Cells on the way.
I am trying to decide if I should build two 280ah 12v battery packs or one 560 12v battery pack.
The reason i am conflicted is the loads i am putting on this in regards to choosing the BMS.

I have a completely off grid 21.5 ft camper with a 1200 watt array going to a 100 Amp Renogy Charge Controller and also a 500 watt ground deploy array going to a 50 amp Victron charge controller For a total of 1700 watts.
Currently i have 800 ah (400 usable) of Deep Cycle Hybrid Gel batteries installed and this new pack will replace the GELS.
I run the entire camper off this system including the 13,500 BTU air conditioner.
I have a 4000 Watt AIMS inverter charger with a 12000 watt surge.

So i need your thoughts on this. With a 4000 watt inverter and taking into account the efficiency loss of the inverter I need a pretty large BMS.
4000 watts ÷ 12 volts = 333.33 amps
333.33 amps x 1.20 (efficiency loss) = 399.99 (Round to 400 amps).

So would it be best to run a 12 volts 560ah battery with a 500 amp Daly BMS or should i go with two 280 ah batteries each with there own 250amp BMS?

It has to be 12 volts. I am not switching out components to change over to 24 volts so please don’t suggest going 24 volts.


that do you all think?

Basically do it either way, there really isnt any difference.

The way did it was 1 large bank (16 280ah cells at 12V) with an electrodacus that turns components on and off instead of having to isolate the battery with a switch of some kind. I just like that better than having a bms disconnect the battery.

I don’t want to have to run external relays because that would complicate things and make expansion more difficult later.
I prefer things to be simple. The less you convolute a system the more efficient and simpler to expand and repair if necessary.

Im not going to argue with you on this because it is all personal preference, but I am going to disagree with this statement.

Adding an external relay is simple for anyone who has/is doing what you have done. Granted, if your mindset is fewer individual components make repairing simpler then you are correct, but remember all the parts are still present, they are just in fewer "boxes" so it looks less "convoluted", but the complexity just has a nice cover over all the convolutedness. If a bms fails, it could be simply because the "switch" failed. If it is an external switching device of some kind, you replace that and you are on your way. If it is contained within the BMS "box" then the whole BMS is changed out because 1 component failed.

 

[noenegdod]

i've read it here

i have also spoke with a JBD reseller, asking if I can use 2x 200A BMS for 2x200AH batteries, and they said that current after paralel connection can't exceed 200A.

That should be 300amps, No?

 

[Just John]

From what I know, if you have 2x120A BMS, your max discharge rate is 75% from 240A. So only 180A.

later edit: it was about lithium batteries, parallel connections provide 75% of power output

What are you talking about?

 

[Just John]

i've read it here

i have also spoke with a JBD reseller, asking if I can use 2x 200A BMS for 2x200AH batteries, and they said that current after paralel connection can't exceed 200A.

That is so not true.

 

[slick99]

This is what they told me

 

[frthompson]

The seller's response in the previous post does not make sense to me. However I have often heard the 75% recommendation repeated, and assumed its just a cautionary guideline in case the load is not being shared equally among the batteries and their bms's. But many people parallel batteries for increased AH and amps.