4s3p 12v LiFePO4 500A BMS Help Needed

[A.Texas.Yankee]

Hello all,

I am new to the world of DIY Lithium and I just ordered :

12 pcs - 3.2v @ 300AH LiFePO4 cells

I plan to run a 4s3p configuration for my 5th Wheel Toy Hauler. I'll be running (2) 3kw Victron Multi-plus off this battery bank with estimated peak amps @ 500A.

I had originally planned to run 3 Daly 4s 500A BMS but when I went to order the BMS I was told by a Daly rep on Alibaba that they do NOT support parallel BMS at all. They suggested using (1) 500A BMS but in my limited knowledge of the subject, that doesn't seem correct? 5 leads to monitor 12 cells?

I looked on the forum and saw many paralleling BMS without issues, but none with my amp usage.

What is required to build my battery bank (4s3p 12v 900aH w/ 500A peak usage)?

 

[snoobler]

Welcome to the forum.

Do you have a life-or-death compelling need to use 12V? 6kW from 12V is borderline absurd. Even 24V is not optimal at 6kW. There's a reason you didn't find other users with your 500A peak usage. What size battery cables are you going to use with that? How many bus bars will you use to connect the cells, and how thick will they be? How big is your wire budget?

Terminology: 4S3P implies that you have 3 separate groups of 4 cells in series then paralleled., i.e., 3X 4S batteries wired in parallel. If that's the case, you need 3 separate BMS as very few BMS permit multi-cell monitoring in paralleled batteries (Batrium is the only one that comes to mind). If you meant that you are going to hook 3 cells in parallel and then put those 4 groups of 3 in series, then that's 3P4S, and you only need 1 BMS with 5 leads to monitor the 4 cell groups as the 3 parallel cells will all have the same voltage.

I would never personally choose to build a battery bank in your chosen configuration unless I had said life-or-death compelling reason to do so; however, if I found myself in that life-or-death situation, I would build 3X completely separate 4S batteries each with their own 200A BMS. I would also buy 2 spare cells, and I would rigorously test all 14 cells and top balance all of them before building the batteries.

 

[HRTKD]

I have paralleled two 280 Ah 4s LiFePO4 batteries, using the Overkill Solar BMS, without any issues. If I needed more Ah capacity or more amps, I wouldn't hesitate to add a third 4s battery and BMS to my system.

 

[snoobler]

One or two Overkills?

 

[HRTKD]

Each 4s battery has its' own BMS. The two batteries are staying balanced. When I test large draws, the amps coming through each BMS are very similar. I would say exact, but I can't see both BMS at the same time due to how the app works. If I used two devices (phone and tablet) I would see them at the same time. But what I'm seeing so far with just my phone is good enough.

 

[snoobler]

I thought so, but the way you worded it "using the" vs. "using two" made it ambiguous.

Old android phones are prolific in my house - at least 6 decent ones. I'd probably make dedicated displays running nothing but the app and leave them connected all the time...

 

[HRTKD]

Lately, I don't connect to the BMS that much. I checked it daily when camping the first two times and then weekly for a couple months. The cell balance was good. Now I just look at the Victron BMV-712 display on the wall and call it good.

 

[A.Texas.Yankee]

Welcome to the forum.

Do you have a life-or-death compelling need to use 12V? 6kW from 12V is borderline absurd. Even 24V is not optimal at 6kW. There's a reason you didn't find other users with your 500A peak usage. What size battery cables are you going to use with that? How many bus bars will you use to connect the cells, and how thick will they be? How big is your wire budget?

Terminology: 4S3P implies that you have 3 separate groups of 4 cells in series then paralleled., i.e., 3X 4S batteries wired in parallel. If that's the case, you need 3 separate BMS as very few BMS permit multi-cell monitoring in paralleled batteries (Batrium is the only one that comes to mind). If you meant that you are going to hook 3 cells in parallel and then put those 4 groups of 3 in series, then that's 3P4S, and you only need 1 BMS with 5 leads to monitor the 4 cell groups as the 3 parallel cells will all have the same voltage.

I would never personally choose to build a battery bank in your chosen configuration unless I had said life-or-death compelling reason to do so; however, if I found myself in that life-or-death situation, I would build 3X completely separate 4S batteries each with their own 200A BMS. I would also buy 2 spare cells, and I would rigorously test all 14 cells and top balance all of them before building the batteries.

Thank you for the welcome. There's a LOT on this forum and have been reading for weeks.

I wouldn't say life or death, but it's a 12v system in a place now and I cannot rewire (anything touched past distro panel voids warranty and on a $140k rig, warranty is pretty important. Basically it will be a mobile work/living station (i.e. full time living 5th Toy Hauler family of 3 & 2 fulltime jobs) where I will need full power while traveling and will not always have access to generator or shore power for a few days at a time. Dual 3k inverters off 12v is common in RV industry and becoming more and more common. They're almost exclusively using a minimum Battleborn 12v 600AH (6p) set up with Dual Victron Multi-plus 12v/300va/120 (some with solar and some with gensets, and some with both). I know 3000va isn't quite 3k watts, but it's my round up calculation needs I work off of. I just didn't want to spend $6k minimum just in BB batteries. I know I'll need to start with the cells so I ordered them and the rest in in planning stages while I await the 2 month trek of the batteries to Texas from China.

Why would you use 200amp BMS for your set up? Am I wrong in thinking 500 amp BMS units?

I will be using 4/0 cables that will run about 3' max length from bank to inverter(s). I know it's a lot of amps and have looked into a 48v system but there's a lot more adaptation required and there's even less documentation going that route.

 

[A.Texas.Yankee]

Also, what are the pros/cons of

Option "a" of 4s3p with 3 separate BMS

OR

Option "b" of 3p4s with a single BMS

 

[WA5IDX]

There is another option that I have used for my electric powered boat. It's a 5 hp ( approximate) electric motor - that's circa 3,780 watts). Running large conductor cable was not an ideal solution so I have a 48v battery bank (currently AGM) for the motor and then use a 48V to 12V DC-DC power supply for my 12v needs. The DC to DC power supplies come in all sorts of power capabilities and it would allow you to use a 48V/120v inverter. You could then use a much smaller BMS...... Just a thought.

 

[A.Texas.Yankee]

There is another option that I have used for my electric powered boat. It's a 5 hp ( approximate) electric motor - that's circa 3,780 watts). Running large conductor cable was not an ideal solution so I have a 48v battery bank (currently AGM) for the motor and then use a 48V to 12V DC-DC power supply for my 12v needs. The DC to DC power supplies come in all sorts of power capabilities and it would allow you to use a 48V/120v inverter. You could then use a much smaller BMS...... Just a thought.

I've looked at going 48v, but the problem is I have the house power that runs off 12v, plug in solar panel that is 12v, 12v supply from 7-pin, generator on board that in
I'm already trying to figure out how to with with, etc. I think if I were starting starting from scratch I'd be 100% 48v.

 

[WA5IDX]

Yep , it's always the details to trip you up. Be careful with the 7 pin connector power as you alternator will likely not like the Lithium batteries much. I'm just disconnecting my "charge" wire on my 7 pin plug (Airstream) and using the Solar, Shore or gen set to keep the lithium batteries charged. I don't use the genset for 12v charging (it's only 15Amp for 12v DC) but to supply 120v to the 75A charger in the Inverter. My 12V "House" loads are less than 45A which could be supplied by DC-DC converter but.............................................

Similar to you, I'm installing 544 Ahr of Lithium in a 4S2P (aka 12v) configuration (each "pack has a BMS) fed by 600W of Solar but only 3KW of inverter. Very similar to HRTKD set up.

 

[A.Texas.Yankee]

Yep , it's always the details to trip you up. Be careful with the 7 pin connector power as you alternator will likely not like the Lithium batteries much. I'm just disconnecting my "charge" wire on my 7 pin plug (Airstream) and using the Solar, Shore or gen set to keep the lithium batteries charged. I don't use the genset for 12v charging (it's only 15Amp for 12v DC) but to supply 120v to the 75A charger in the Inverter. My 12V "House" loads are less than 45A which could be supplied by DC-DC converter but.............................................

Similar to you, I'm installing 544 Ahr of Lithium in a 4S2P (aka 12v) configuration (each "pack has a BMS) fed by 600W of Solar but only 3KW of inverter. Very similar to HRTKD set up.

Have a 400 amp alternator that will be wired back so technically not the 7-pin, but you get the drift. Genset is going to be my primary way to recharge off grid. I really don't think I'll be going full solar other than plug in panel. With 60 gallons of fuel on board and really only running the Onan 5500 genset to recharge bank that should last plenty. At most I'll be 2 weeks out before having to refuel/refill and dump tanks. We'll see if I can stretch it that far.

After researching and getting feedback from Daly seller I'm thinking I'll end up single 500A BMS running a 3p4s set up. I'll monitor cells individually and may look into a stand alone cell balancer as well. Not sure if that can be run with the BMS, but that's another quest.

 

[wmills_92105]

500 amps is a lot. Multiple 4/0 runs. Serious fuses/breakers/etc.

Then possibly adding complexity later to try to balance individual cells?

Is that really a win in cost over building 3 separate 200A capable packs? Overkills only do 120A on the 12V ones. Maybe Daly isn't the best choice, but your phrasing makes me wonder if they thought you were going to try to run 3 BMS in parallel on the same pack? Did you ask about 3x Daly 200 on 3 separate 4s packs? That should work. Then you are running 3 separate 4/0 runs to the power panel and probably put a breaker/fuse on each pack.

 

[snoobler]

Thank you for the welcome. There's a LOT on this forum and have been reading for weeks.

I wouldn't say life or death, but it's a 12v system in a place now and I cannot rewire (anything touched past distro panel voids warranty and on a $140k rig, warranty is pretty important. Basically it will be a mobile work/living station (i.e. full time living 5th Toy Hauler family of 3 & 2 fulltime jobs) where I will need full power while traveling and will not always have access to generator or shore power for a few days at a time. Dual 3k inverters off 12v is common in RV industry and becoming more and more common. They're almost exclusively using a minimum Battleborn 12v 600AH (6p) set up with Dual Victron Multi-plus 12v/300va/120 (some with solar and some with gensets, and some with both). I know 3000va isn't quite 3k watts, but it's my round up calculation needs I work off of. I just didn't want to spend $6k minimum just in BB batteries. I know I'll need to start with the cells so I ordered them and the rest in in planning stages while I await the 2 month trek of the batteries to Texas from China.

Why would you use 200amp BMS for your set up? Am I wrong in thinking 500 amp BMS units?

I will be using 4/0 cables that will run about 3' max length from bank to inverter(s). I know it's a lot of amps and have looked into a 48v system but there's a lot more adaptation required and there's even less documentation going that route.

3 separate batteries each with its own 200A BMS wired in parallel could provide 600A.

Multiplus comes in 12/24V variants only, so 24V would be the other option. No trailer rewiring needed.

As was mentioned, there are DC-DC converters that make providing 12V to the trailer a triviality. They cost about $50.

There are 12-24V chargers for alternator charging.

You'll need to run double 4/0 each with its own fuse. A single 4/0 cable isn't rated for 500A. Consider that 4/0 cable isn't rated for 500A. You think an alleged 500A BMS will really handle that?

 

[A.Texas.Yankee]

500 amps is a lot. Multiple 4/0 runs. Serious fuses/breakers/etc.

Then possibly adding complexity later to try to balance individual cells?

Is that really a win in cost over building 3 separate 200A capable packs? Overkills only do 120A on the 12V ones. Maybe Daly isn't the best choice, but your phrasing makes me wonder if they thought you were going to try to run 3 BMS in parallel on the same pack? Did you ask about 3x Daly 200 on 3 separate 4s packs? That should work. Then you are running 3 separate 4/0 runs to the power panel and probably put a breaker/fuse on each pack.

I originally asked them about running 3 separate batteries each with individual bms running in parallel. I did not ask about your 3 separate pack set up although I have seen some use a common bus bar but seemed like additionalw wiringand failure points. Daly rep said no BMS in parallel at all, under any circumstances. In searching through the forum and other forums, there have been others told the same. Cost isn't the reason between the single vs 3 BMS units. My original plan was to go with 3 units until Daly rep said no paralleling of bms. Which is why I originally thought thought something was lost in translation and lead me here. Daly seems to be the only choice within my budget unless there are others with similar amp rating I haven't discovered.

 

[snoobler]

It sounds like a translation thing to me. Battery manufacturers like BB and SOK with built-in BMS allow paralleling batteries. I can't imagine why Daly wouldn't allow it.

There are other options. Some BMS work via external relays. Chargery has a version that functions that way. The downside is the relays have a constant draw consuming power all the time (0.3kWh/day). Electrodacus works by sending signals to the charge controller and inverter for LVD/HVD as well as low temperature protection. In that case a single 3P4S battery would be used.

 

[the_colorist]

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)



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.

 

[Rocketman]

With 2 Multiplus- you may have issues with the 30amp vs 50amp shore connection.
You generator is probably single phase(can be 2 phase). And when connected to a 15/20/30amp shore power that is single phase. When connected to 50amp that is dual phase. Your ATS (auto transfer switch) probably puts the same phase on both power legs with 15/20/30 amp connections.
The 2 Multiplus’s can be set for either single phase or dual phase. There are several workarounds- just wanted to make sure you knew about this problem.

if you decide on one big battery with a contractor 3p4s, look at Batrium Bms (also OrionJr & Rec-bms were also ones I looked at).

I choose Batrium because I will be able to connect the Can-bus into my Victron system (CCGX) and have the bms control the charging and discharging.

 

[k3nny]

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.

@the_colorist In this case (3p 4s) would the voltage stay 12v?