Will this Work? 12V 380Ah LiFePo with 200A BMS

smaroukis

Staying Positive (Sequence)
Joined
Jun 5, 2020
Messages
10
Hello looking for some help before I order some parts.

Main question -- is it ok to use a 200A BMS on a 380Ah battery bank (1C) if we fuse it on the (+) side at 200A?

I'm looking to do a DIY build for a Van/RV with ~ 600W of solar. I'm running an induction cooktop and a desktop/monitor so I wanted a large battery bank.
I'm looking to stay with 12V because it's more standard for cargo van upfits, and I don't want to have to go through all of the 12V appliances and check if they can work at 24V.

I also want to charge from the alternator so I'm looking at the Renogy B2B & MPPT 50A charger, a 2000W inverter, these 190Ah LiFePo batteries, and this 200A BMS. My schematic is below. I also read that we don't need to connect the MPPT charger to the BMS, although I have not verified the overvoltage settings on the Renogy one.

My main question is can I damage the 200A BMS if I happen to draw more current? I've provided the 200A fuse on the main (+) going from the batteries to the loads. The inverter is 2000W and I'm expecting around 30A of 12Vdc loads, putting my total load around 240A peak (including inverer efficiency at 85%).


image.jpg
 

zorlig

Solar Enthusiast
Joined
Mar 12, 2020
Messages
180
The 200a BMS means that it will cut power itself if you go over that, so you don't need a duplicate fuse.

You should derate it though.
 

smaroukis

Staying Positive (Sequence)
Joined
Jun 5, 2020
Messages
10
Thanks. Due to the de-rating I am going to go with 2 x 4S 12V 120A BMS in parallel since I'm not comfortable running the 200A BMS up to the limit at max inverter output. I'll buy two shunt monitors to makes sure the discharge / charge amps on both paralleled battery banks are similar.
 

rboothe

New Member
Joined
Nov 10, 2020
Messages
33
Thanks. Due to the de-rating I am going to go with 2 x 4S 12V 120A BMS in parallel since I'm not comfortable running the 200A BMS up to the limit at max inverter output. I'll buy two shunt monitors to makes sure the discharge / charge amps on both paralleled battery banks are similar.
I'm working out the same model. Can you please tell me how exactly you connected them in parallel? Did you stack the pos and neg lugs on top of each other, connect them with bus bars or wire, or some other way? For some reason, this has me tripped up...
 

smaroukis

Staying Positive (Sequence)
Joined
Jun 5, 2020
Messages
10
I'm working out the same model. Can you please tell me how exactly you connected them in parallel? Did you stack the pos and neg lugs on top of each other, connect them with bus bars or wire, or some other way? For some reason, this has me tripped up...
I connected two cables from a positive bus bar to the batteries (one for each) - make sure this is of the same length as to match resistances (when charging each BMS should read the same current, half of the total, if not your impedances are off either due to the wire impedance or the battery internal impedance due to different states of charge). You shoulnd'tconnect the two batteries with a bus bar straight to the (+) of each because you need to fuse each battery individually.

The (2) x 120A BMS's I used has blue cables (B-, connected the battery negative) and black cables (C-, connected to the "system" side, going to either a shunt or your main negative terminal). For the parallel BMS I connected all 6 of these cables (3 on each BMS) to a 6 screw/ 2 stud Blue Sea systems 2128 bus bar, which worked perfectly. Then off the 5/16" stud I connected the shunt inline to the main negative system terminal.

A drawing is attached. The main thing to note is that there there is nothing really keeping the B1 and B2 at the same charge level, which is why it is important to 1) match the lengths of wire going to and coming from each (positive and negative) and 2) make sure they are the same SOC when you connect them in parallel. Although if one battery is charging faster than another, it will end up discharging into the other battery when the charger is removed, but you shouldn't rely on this to keep them in sync.

The main thing I noticed with this BMS is that the SoC algorithm is determined by voltage, which is not good for LiFePo batteries. The shunt needs to be calibrated for your true 100% SoC, which you get to by charging each cell up to 3.65V (see top balancing elsewhere) before reconfiguring as the battery banks shown. The voltage of the LiFePo battery banks varies greatly depending on loading/charging and how long they have been sitting disconnected. For example, I set my solar charger to 14.4V for a few days, then I would leave the batteries disconnected for a for days and they would come down to 13.5V -- then the BMS thinks they have lost 75% of their capacity!
 

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rboothe

New Member
Joined
Nov 10, 2020
Messages
33
I connected two cables from a positive bus bar to the batteries (one for each) - make sure this is of the same length as to match resistances (when charging each BMS should read the same current, half of the total, if not your impedances are off either due to the wire impedance or the battery internal impedance due to different states of charge). You shoulnd'tconnect the two batteries with a bus bar straight to the (+) of each because you need to fuse each battery individually.

The (2) x 120A BMS's I used has blue cables (B-, connected the battery negative) and black cables (C-, connected to the "system" side, going to either a shunt or your main negative terminal). For the parallel BMS I connected all 6 of these cables (3 on each BMS) to a 6 screw/ 2 stud Blue Sea systems 2128 bus bar, which worked perfectly. Then off the 5/16" stud I connected the shunt inline to the main negative system terminal.

A drawing is attached. The main thing to note is that there there is nothing really keeping the B1 and B2 at the same charge level, which is why it is important to 1) match the lengths of wire going to and coming from each (positive and negative) and 2) make sure they are the same SOC when you connect them in parallel. Although if one battery is charging faster than another, it will end up discharging into the other battery when the charger is removed, but you shouldn't rely on this to keep them in sync.

The main thing I noticed with this BMS is that the SoC algorithm is determined by voltage, which is not good for LiFePo batteries. The shunt needs to be calibrated for your true 100% SoC, which you get to by charging each cell up to 3.65V (see top balancing elsewhere) before reconfiguring as the battery banks shown. The voltage of the LiFePo battery banks varies greatly depending on loading/charging and how long they have been sitting disconnected. For example, I set my solar charger to 14.4V for a few days, then I would leave the batteries disconnected for a for days and they would come down to 13.5V -- then the BMS thinks they have lost 75% of their capacity!
Amazing. Unbelievable helpful. Thank you!
 
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