BMS sizing Questions

[BeerBrewer]

I'm planning upon adding solar power to my Travel Trailer in the next year of so and I'd like do it in stages. The plan right now includes at least 200 ah battery of power (at 12V), four 100-150 Watt solar panels, a new converter for lithium cells, MPPT solar controller and a 2000 watt pure sign wave inverter. My first step is to replace the lead acid battery with a DIY 12v or 24v Lithium LiFePo4 battery. I've seen several sellers on Alibaba/Aliexpress selling brand new 3.2v 100ah LiFePo4 cells for around $75-$80, making a DIY battery A LOT cheaper than a Battle Born or Lion 12V battery. I know that I'd need to add a BMS, but I not certain which to choose.

I've read that I need to size the BMS for the maximum discharge rate on the batteries, even if it its for a very short time. So I'm thinking that the max draw will be when my wife uses the hair dryer for 5 minutes or whenever the 2000 inverter is maxed out. I've looked at specs for some 2000 watt PS Inverters and they all claim the max DC power draw is around 198 amps at 12v and 99 amps if I use a 24V volt inverter. So does this mean that if I build two 100ah 12V lithium Batteries in parallel that each battery will need it's own 100 amp BMS or should I build one 200ah battery (using all 8 cells) using one 200 amp BMS?

What about if I convert the travel trailer over to a 24 volt battery system? Should I build two 12v batteries connected in series with each battery having its own 50 amp BMS or is it better to build a single 24V battery using all 8 100ah cells using a single 100 amp BMS?

I'm also having issues finding a BMS with a low temp shot-off. If you folks have a favorite BMS I'd love to hear it.

Thanks

 

[Bob B]

@OverkillSolar is selling a 120A BMS with Bluetooth. If you put 2 of them in parallel, you would double the capacity. I don't know the continuous current rating of this BMS, but maybe he will check in and get you the specs .... or you could search for his posts.

The other option is to use a Chargery BMS. The only limitation of current draw with the Chargery is the shunt you choose and the relays ... and where you place the relays. I am using this BMS and trying to control the inverter power switch instead of having the full current go thru the relay. A similar strategy can be done with the SCC and AC charger.

There are extensive threads on both of these BMS if you search ... and there is an extensive thread on choosing relays for the Chargery.

HERE IS one of the threads when you have time .... near they end is a discussion about current draw.

HERE IS one of the Chargery BMS threads. The search tool is your friend

 

[BeerBrewer]

Do I have the sizing correct? Meaning the BMS needs to be able to handle the max DC amperage drain at any given point?

 

[JoeHam]

Yes on the BMS and note that many of the Chinese versions should be derated by up to 50%.

And I would recommend you look at fewer 300 or 400 watt panels if shading is not an issue.

 

[BeerBrewer]

I agree on- solar panels, I only meant that I'm planning on installing at least a total of 400 -500 watts worth of panels. I have not picked out the panels just yet. I'm starting with the battery and I'm having enough trouble deciding between a 12v or 24v system. Once i decide that ill tackle the BMS.

Can you suggest a non-Chinese BMS?

 

[Craig]

I agree on- solar panels, I only meant that I'm planning on installing at least a total of 400 -500 watts worth of panels. I have not picked out the panels just yet. I'm starting with the battery and I'm having enough trouble deciding between a 12v or 24v system. Once i decide that ill tackle the BMS.

Can you suggest a non-Chinese BMS?

non Chinese BMS would be electrodacus , Batrium, or Tiny BMS probably still made in china but designed elsewhere.

I would go 24V system it saves tons of hassles and allows more power for less wiring and money. you can easily make a 100Ah 24v battery with 8 cells and 1 BMS for around half of what a Battleborn would cost.

 

[JoeHam]

non Chinese BMS would be electrodacus , Batrium, or Tiny BMS probably still made in china but designed elsewhere.

I would go 24V system it saves tons of hassles and allows more power for less wiring and money. you can easily make a 100Ah 24v battery with 8 cells and 1 BMS for around half of what a Battleborn would cost.

And you could get a single 400w panel.

 

[BeerBrewer]

non Chinese BMS would be electrodacus , Batrium, or Tiny BMS probably still made in china but designed elsewhere.

I would go 24V system it saves tons of hassles and allows more power for less wiring and money. you can easily make a 100Ah 24v battery with 8 cells and 1 BMS for around half of what a Battleborn would cost.

I looked at the ElectroDacus , Batrium, or Tiny BMS web sites and was impressed. The ElectroDacus SBMS0 and DSSR20 modules might be exactly what I'm looking for! ...thanks!!