4P8S Cell Configuration

[Shock-tower]

Greetings,

I finally received my 32 Lifepo4 Navitas prismatic cells from Battery hookup the other day. I'm planning on building a 4P8S pack with a Daly BMS.

This is the first time I have configured this type of pack and I wanted to make sure I have the cells connected correctly. I want to keep the cell form factor to 4x8 so that I can fit them into the battery bay of an old electric wheelchair base.

Can someone tell me if the pack layout in the attached image is correct or am I going to blow something up?

Thanks!

 

[sshibly]

Op, look at the very end of the strings, does not look kosher to my eyes.

Here what I would do, take 8 A4 size paper and mark + and 1 on opposing sides to mimic a cell and then put them next to each to to achieve you configuration.

After you have done with ONE cell, i.e. 8s1p, then add more cell to that configuration

 

[DerpsyDoodler]

Op, look at the very end of the strings, does not look kosher to my eyes.

Here what I would do, take 8 A4 size paper and mark + and 1 on opposing sides to mimic a cell and then put them next to each to to achieve you configuration.

After you have done with ONE cell, i.e. 8s1p, then add more cell to that configuration

His diagram looks like 4p8s, to me, which is not the same as 8s4p; nor would he be able to use 1 BMS for 8s4p. It would require 4 BMS in parallel.

 

[Shock-tower]

Hmm. I need to use one BMS. I guess I got the order of the S and the P wrong. Back to the drawing board.

 

[DerpsyDoodler]

Hmm. I need to use one BMS. I guess I got the order of the S and the P wrong. Back to the drawing board.

You can do 4p8s, but you lose the ability to monitor each cell individually. This just makes diagnostics (if/when) you have a cell problem a little more involved than just looking at a screen of info for each cell. Something else that influences this decision is the discharge and/or charge rate you desire or need. I’m going to step back at this point and let an EE take over. There are many people more knowledgeable than I on this subject matter, available here.

 

[Shock-tower]

You can do 4p8s, but you lose the ability to monitor each cell individually. This just makes diagnostics (if/when) you have a cell problem a little more involved than just looking at a screen of info for each cell. I’m going to step back at this point and let an EE take over. There are many people more knowledgeable than I on this subject matter, available here.

Thanks Derpsy. I'm okay with monitoring the 4 cells in parallel. I appreciate the help.

 

[DerpsyDoodler]

Thanks Derpsy. I'm okay with monitoring the 4 cells in parallel. I appreciate the help.

Recheck my post, I edited to add ”another factor of influence on this decision...”

 

[DerpsyDoodler]

Thanks Derpsy. I'm okay with monitoring the 4 cells in parallel. I appreciate the help.

Furthermore, the best thing for you to do is start with an energy audit. snoobler edit: @Steve_S has some good links in his signature and will get you started in the right direction.

 

[Vopezy]

Did these cells get restocked and I missed the last batch? Or did it take 3 weeks to get them?

 

[Shock-tower]

Did these cells get restocked and I missed the last batch? Or did it take 3 weeks to get them?

It took 3 weeks to get to Canada. They were sent back to BH because of incorrect labeling so that added a few days as well.

 

[Shock-tower]

Here's my new configuration. I think this might be correct now. 4P8S

 

[John Frum]

Hmm. I need to use one BMS. I guess I got the order of the S and the P wrong. Back to the drawing board.

Why do you need to use 1 bms?

 

[Shock-tower]

Why do you need to use 1 bms?

I just wanted to keep it simple and keep the cost down. I know I won't be able to monitor individual cell voltage within the parallel packs, but I'm okay with that unless it's a big no-no.

 

[John Frum]

I just wanted to keep it simple and keep the cost down. I know I won't be able to monitor individual cell voltage within the parallel packs, but I'm okay with that unless it's a big no-no.

Its doable.
There are some ins and outs though.
Your bms now has to balance virtual cells that are 8 times the size.
You should get a bms with lots of balance amperage.
The bms is also a single point of failure.
How much charge/discharge current are you planning to put through this bms?

 

[Shock-tower]

Its doable.
There are some ins and outs though.
Your bms now has to balance virtual cells that are 8 times the size.
You should get a bms with lots of balance amperage.
The bms is also a single point of failure.
How much charge/discharge current are you planning to put through this bms?

I'm getting a 125 amp Daly BMS, but I will rarely use that much. I'll likely be changing at 20 amps from a MPPT charge controller and discharging around 40 amps or less on average.

 

[John Frum]

I'm getting a 125 amp Daly BMS, but I will rarely use that much. I'll likely be changing at 20 amps from a MPPT charge controller and discharging around 40 amps or less on average.

Hope its a smart bms as the default cutoffs are too low in my opinion.
Also I would de-rate the bms by .33 to .5.

 

[Shock-tower]

Hope its a smart bms as the default cutoffs are too low in my opinion.
Also I would de-rate the bms by .33 to .5.

Thanks for that. The BMS is supposed to arrive tomorrow. Hopefully I can adjust those settings.

 

[Tim R]

I'm building an 8 cell setup using the Electrodocus SBMS. I looked and looked and looked and the more I looked, the more l liked the Electrodocus. I have my cells configured like this. I don't know if its a 4P4S or whatever, it is what they recommended at Electrodocus so I am good with it.

 

[Shock-tower]

I'm building an 8 cell setup using the Electrodocus SBMS. I looked and looked and looked and the more I looked, the more l liked the Electrodocus. I have my cells configured like this. I don't know if its a 4P4S or whatever, it is what they recommended at Electrodocus so I am good with it.

View attachment 37540

Nice! I hear good things about the ElectroDacus. I might get one for a future project.

 

[snoobler]

I'm building an 8 cell setup using the Electrodocus SBMS. I looked and looked and looked and the more I looked, the more l liked the Electrodocus. I have my cells configured like this. I don't know if its a 4P4S or whatever, it is what they recommended at Electrodocus so I am good with it.

View attachment 37540

2P4S

Why the offset?