BMS for 4S2P?

HRTKD · May 8, 2020

I'm in the very early design phase for upgrading my RV. Due to space considerations and a need to stick to 12v, I was thinking about using a 4s2p battery arrangement using Will's recommended Fortune 100Ah Lithium Battery. What I don't know is which BMS should be used for the battery layout.

Does each 4s bank of batteries get its own BMS? Or, is there a BMS that understands the 4s2p layout? I'm open to other battery configurations. The 4s2p configuration gives me more flexibility in how I arrange the batteries in the available space, which isn't much.

MisterSandals · May 8, 2020

HRTKD said:
Does each 4s bank of batteries get its own BMS?

Yes

Personally, i like 2p4s.
I lose the ability to monitor individual cells, only pairs. I did spend a little thought, time and effort to make the pairs equal to each other.

HRTKD · May 8, 2020

What's the difference between 2p4s and 4s2p?

Ampster · May 8, 2020

HRTKD said:
What's the difference between 2p4s and 4s2p?

2P4S means you have one pack consisting of groups of two cells (2P) assembled into a pack of four of those groups in Series (4S).
4S2P means you have two packs each consisting of four cells in series. It means you need two BMSs

HRTKD · May 8, 2020

I could get by with just one BMS for 2p4s? I'll have to look up that configuration. I was not aware of it.

Ampster · May 8, 2020

Yes you can use one BMS. That is one of the big advantages of 2P4S. The other advantage is you don't have to worry about each pack getting out of balance with each other which can happen because the interconnects to the packs often have different lengths and therefore slightly different resistance which adds up over time in less current getting to one.

Bob B · May 8, 2020

you just do 4 parallel pairs of cells .... and then put those 4 pairs in series with each other. That is how I am doing my RV battery.

MisterSandals · May 8, 2020

Download the doc, excellent diagrams:

Cell Configurations for 12V 24V and 48V LiFePo4 Batteries

This short deck shows 1P and 2P cell configurations for 12V, 24V & 48V LiFePO4 batteries. To get the deck, click on the orange button at the top of this page. Note: Reviews, Comments and corrections are welcome Document Revision History...

diysolarforum.com

HRTKD · May 8, 2020

MisterSandals said:
Download the doc, excellent diagrams:

Cell Configurations for 12V 24V and 48V LiFePo4 Batteries

This short deck shows 1P and 2P cell configurations for 12V, 24V & 48V LiFePO4 batteries. To get the deck, click on the orange button at the top of this page. Note: Reviews, Comments and corrections are welcome Document Revision History...

diysolarforum.com

Thank you! For all the reading I've done of the various threads, I missed that one.

tsenator · Jan 23, 2022

Ampster said:
2P4S means you have one pack consisting of groups of two cells (2P) assembled into a pack of four of those groups in Series (4S).
4S2P means you have two packs each consisting of four cells in series. It means you need two BMSs

They make single BMS 4S2P BMS's out there. BestWay makes one. Here is its spec sheet and manual, it can even be monitored with Bluetooth Go to the end they show the smartphone showing all 8 cell voltages

HRTKD · Jan 23, 2022

tsenator said:
They make single BMS 4S2P BMS's out there. BestWay makes one. Here is its spec sheet and manual, it can even be monitored with Bluetooth Go to the end they show the smartphone showing all 8 cell voltages

I skimmed through the PDF. I don't see where it shows how to setup for two separate batteries.

If it can manage two separate batteries, then it might be something that @Will Prowse would be interested in testing.

tsenator · Jan 23, 2022

HRTKD said:
I skimmed through the PDF. I don't see where it shows how to setup for two separate batteries.

If it can manage two separate batteries, then it might be something that @Will Prowse would be interested in testing.

I'm pretty sure Will is very well aware of 4S2P BMS's they are out there. These batteries are being sold out there too for example - https://www.alibaba.com/product-det...670.html?spm=a2700.details.0.0.12f26bc6FjCnMn

Horsefly · Jan 23, 2022

HRTKD said:
I skimmed through the PDF. I don't see where it shows how to setup for two separate batteries.

If it can manage two separate batteries, then it might be something that @Will Prowse would be interested in testing.

Yeah, I agree. Nothing in that PDF (at least the English part) suggests that this single BMS can manage two separate 4S batteries. If you think about it, that would be a very abnormal thing for a BMS to do. It makes way more sense to have a single BMS manage a single battery, IMHO.

tsenator · Jan 23, 2022

HRTKD said:
I skimmed through the PDF. I don't see where it shows how to setup for two separate batteries.

If it can manage two separate batteries, then it might be something that @Will Prowse would be interested in testing.

No its there , yes I agree hard to follow . But it isn't really "2 separate batteries" its 8 Lifepo4 cells and it monitors all 8 cells but in a 4s2P configuration. So the great thing is that it will try and keep all 8 Lifepo4 cells "balanced" . Instead of hooking up 4 leads for 4 cells you would connect 8 leads for 8 cells (but it would be a 4s2P) . The cool thing is this device can do 4S4P and connect up to 16 cells and balance & monitor them . Here is a pic of the 16 leads (plus ground) to connect to cells -- Also a pic of the computer screen showing monitoring of 16 cells with voltage levels

Horsefly · Jan 23, 2022

tsenator said:
No its there , yes I agree hard to follow . But it isn't really "2 separate batteries" its 8 Lifepo4 cells and it monitors all 8 cells but in a 4s2P configuration. So the great thing is that it will try and keep all 8 Lifepo4 cells "balanced" . Instead of hooking up 4 leads for 4 cells you would connect 8 leads for 8 cells (but it would be a 4s2P) . The cool thing is this device can do 4S4P and connect up to 16 cells and balance & monitor them . Here is a pic of the 16 leads (plus ground) to connect to cells -- Also a pic of the computer screen showing monitoring of 16 cells with voltage levels View attachment 81023 View attachment 81024

Nothing in that shows that it works with 4S2P. I am even more skeptical than I was before. I really want to see how it handles the jump from Battery 1 cell 4 to battery 2 cell 1. It requires 5 leads for each 4S battery being monitored. What you have shown kinda proves that a 4S2P is NOT supported.

MisterSandals · Jan 23, 2022

That looks like a 16S battery

Screen Shot 2022-01-23 at 8.53.49 PM.png

tsenator · Jan 23, 2022

People might think its an " abnormal thing for a BMS to do" but its a very smart thing to do . People are always trying to make sure Lithium battery banks in parallel are "in balance" and it takes a lot more intervention in case one or two cells go out of balance in 2 different parallel battery banks . This is one place monitoring them all ! . And its not that unique. I've seen numerous 4s2P (or more P) BMS's out there

time2roll · Jan 23, 2022

If such a BMS exists.... does it protect both batteries as one unit or individually?

tsenator · Jan 23, 2022

I'm ordering one of these batteries soon, So I will report back. But its 200 AH bank using 8 100 AH Gotion Cells so we should know soon https://www.alibaba.com/product-det...670.html?spm=a2700.details.0.0.12f26bc6FjCnMn

tsenator · Jan 23, 2022

time2roll said:
If such a BMS exists.... does it protect both batteries as one unit or individually?

From the specs I read it protects it as one 200AH unit. If you want two separate 100AH batteries and the ability to just shut down one if it goes bad then you need two BMS's

BMS for 4S2P?

Boondocker

Participation Medalist

Boondocker

Renewable Energy Hobbyist

Boondocker

Renewable Energy Hobbyist

Emperor Of Solar

Participation Medalist

Boondocker

New Member

Attachments

Boondocker

New Member

Solar Wizard

New Member

Solar Wizard

Participation Medalist

New Member

Solar Wizard

New Member

New Member

Similar threads