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4s3p 12v LiFePO4 500A BMS Help Needed

Installer here. In a situation like this, we use a 3p 4s configuration with a single BMS. No need for parallelling BMS units and in fact you'll face more issues with your batteries in the long run. Orion has a great paper on this (link below). Here is what a similar configuration would look like:

Orion BMS - Strings, Parallel Cells, and Parallel Strings (PDF)

View attachment 32823

Quote from the document:

"In the above configuration, the amp hour capacity is increased without increasing the pack voltage.
Even though 8 cells are used, because each cell is paralleled with one other cell, the BMS can treat
each pair of cells as a single cell. This allows the designer to use a smaller BMS. The above
configuration is a “4S2P” configuration. The “2P” indicates that there are 2 cells paralleled together,
where-as the “4S” indicates that there are 4 of these pairs in series. If each cell is 10 amp hours and
3.3v, the battery pack above would be 20 amp hours (10 amp hours x 2 cells) and 13.2 volts (3.3 volts x
4 pairs).

Even though there are twice the number of cells in this configuration, for this setup, a BMS capable of
monitoring only 4 cells is necessary. In the case of cells which are parallel together and then assembled
into a single string, as shown above, the BMS will “see” the two paralleled cells as a sing cell with twice
the capacity and half the internal resistance of a single cell. Since there is a busbar between the two
positive and two negative terminals of the batteries, the voltage of both cells is forced to be equal. "


So you would simply be using 3 cells in parallel instead of the 2 cells in parallel as shown above and you'll use a single BMS.

Generally the recommended BMS for this configuration (recommended by Victron) is REC BMS. There are others that would work also (Batrium, Orion Jr) but REC is the standard IMHO.

With REC (and the others), the BMS "talks" to the Victron system (inverters, charge controllers) and tells them how to charge and when to lower the charge current etc in realtime based on cell level information. This allows the batteries to last longer or that is the consensus as the BMS will make changes to/during every charging cycle as it sends commands to the system with target voltage and current every 200ms based on what the cells are doing. We combine REC with an active balancer after an initial top balance.
I am looking at doing something like you are talking about and would like your input, if you don't mind. I have twelve 3.2V, 310aH cells on order and have been trying to figure out configuration and a BMS for a 12.8V system. I am thinking about a 3P4S configured like the below with a Batrium Watchmon4 and four cell monitors. Also I am going to use Victron components (inverter/charger, DC-DC charger, and solar charger). Am I correct that this configuration will work and I can utilize four cell monitors? Thank you in advance for any advice you can provide.3P4S.jpg
 
Yes that is a correct configuration for your plans. What is the max amperage you may pull from your battery? If over 500a - get the Batrium 1000a shunt... if under 400a the standard 500a shunt will be fine (and preferred).

Also -make sure you have a Class T fuse.
 
Yes that is a correct configuration for your plans. What is the max amperage you may pull from your battery? If over 500a - get the Batrium 1000a shunt... if under 400a the standard 500a shunt will be fine (and preferred).

Also -make sure you have a Class T fuse.
Thank you! I want to design for the inverter, and I still need to verify what the max amperage is. Specs show peak as 5500W, but I want to be sure. It is this one. https://www.continuousresources.com...x120v-inverter-charger?variant=39385020530845
 
Open the owners manual (online) - Victron puts the spec’s of what amps it wants (and requested wire sizes) in the manuals.
 
In case he doesn't notice..
Yep, totally missed this.

I have twelve 3.2V, 310aH cells on order and have been trying to figure out configuration and a BMS for a 12.8V system. I am thinking about a 3P4S configured like the below with a Batrium Watchmon4 and four cell monitors.
Yes, that works fine, per @Rocketman's notes. For that many AH, I would recommend the REC Active BMS. It designed specifically for 4s Victron applications with a more advanced charging profile. The built-in 2A Active Balancer will be extremely helpful. You find out at some point that an added active balancer might keep the cells from drifting off if you are having issues with that.

They aren't the easiest to order from so I can process an order for you or get you a quote if you are interested. I'm processing several orders at the moment. Feel free to PM me and I'll get back to you as soon as I can.

500A is fine for a single 2x120V. And yes, we are back-ordered until June on those units as well. Have 300 coming in 6/25 to Victron's warehouse..
 
Yep, totally missed this.


Yes, that works fine, per @Rocketman's notes. For that many AH, I would recommend the REC Active BMS. It designed specifically for 4s Victron applications with a more advanced charging profile. The built-in 2A Active Balancer will be extremely helpful. You find out at some point that an added active balancer might keep the cells from drifting off if you are having issues with that.

They aren't the easiest to order from so I can process an order for you or get you a quote if you are interested. I'm processing several orders at the moment. Feel free to PM me and I'll get back to you as soon as I can.

500A is fine for a single 2x120V. And yes, we are back-ordered until June on those units as well. Have 300 coming in 6/25 to Victron's warehouse..
Message sent. Thank you!
 
Yep, totally missed this.


Yes, that works fine, per @Rocketman's notes. For that many AH, I would recommend the REC Active BMS. It designed specifically for 4s Victron applications with a more advanced charging profile. The built-in 2A Active Balancer will be extremely helpful. You find out at some point that an added active balancer might keep the cells from drifting off if you are having issues with that.

They aren't the easiest to order from so I can process an order for you or get you a quote if you are interested. I'm processing several orders at the moment. Feel free to PM me and I'll get back to you as soon as I can.

500A is fine for a single 2x120V. And yes, we are back-ordered until June on those units as well. Have 300 coming in 6/25 to Victron's warehouse..
Inverter Service Center had a 2x120V in stock, so I have one on the way.
 
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