Work in Progress - But it's alive!

[weirded]

Revived an old 400Ah 16S bank that had a rodent-damaged, unreliable BMS. Swapped it out with a Seplos BMS in order to be able to get it communicating with the other batteries on the wall.

It's alive and taking a charge. Still waiting on some beefier bus bars and need to enclose the BMS before I flip the switch and run the house off it...

 

[Culchee]

Looks like a good setup... hope it all goes well for you.. good luck..!

 

[weirded]

Sun came out today, got a first charge into it. Looks like the cells have gone out of balance quite a bit. Now shopping for an active balancer...

 

[Culchee]

Sun came out today, got a first charge into it. Looks like the cells have gone out of balance quite a bit. Now shopping for an active balancer...

View attachment 184613

Hi Weirded...
So I’m wondering about the balancing... is the Seplos not suitable for balancing..?

 

[weirded]

Hi Weirded...
So I’m wondering about the balancing... is the Seplos not suitable for balancing..?

The Seplos BMS does passive balancing, which has a number of drawbacks compared to active balancing from my understanding - especially given that these cells are a few years old and seem to have drifted, I am hoping it'll make a difference. It also just sounds fun/interesting

 

[Culchee]

So active versus passive...I shall have to enter the balancing rabbit hole... ?

 

[Culchee]

What’s your understanding Weirded may I ask...?

 

[Quattrohead]

95 mv isn't that bad at all, put those beasts to work and don't worry about it.

 

[weirded]

95 mv isn't that bad at all, put those beasts to work and don't worry about it.

Bad enough for the BMS to not let me continue charging (at least unless I start messing with BMS settings). Given the history of these cells, they can use a good balance. I’m not even sure the old BMS did any balancing.

 

[weirded]

What’s your understanding Weirded may I ask...?

This is the video that convinced me to pick up the active balancer:

 

[hwy17]

Active balancing is the funnest controversy in DIY battery building.

Afaik the DIY EV building scene does not use them and they deal with larger packs with many more cells.

 

[Culchee]

This is the video that convinced me to pick up the active balancer:

 

[Culchee]

This is the video that convinced me to pick up the active balancer:

Andy’s great... will def watch this.. thanx

 

[weirded]

Active balancing is the funnest controversy in DIY battery building.

Afaik the DIY EV building scene does not use them and they deal with larger packs with many more cells.

Interesting. The TL;DR that convinced me: the Seplos BMS is apparently limited to 115mA of balancing current, and only balances when the pack is essentially full. For my 400Ah cells that’s not a recipe to reach balance.

I’m sure there are BMS that balance better, but I decided to stick with the Seplos (because I have 4 others).

 

[hwy17]

Interesting. The TL;DR that convinced me: the Seplos BMS is apparently limited to 115mA of balancing current, and only balances when the pack is essentially full. For my 400Ah cells that’s not a recipe to reach balance.

I’m sure there are BMS that balance better, but I decided to stick with the Seplos (because I have 4 others).

115mA/400Ah is pretty skinny. But the AB detractors would say balancing is only a very fine nudging at the top. The cells will be unequal in capacity but no balancer can help with that.

 

[weirded]

115mA/400Ah is pretty skinny. But the AB detractors would say balancing is only a very fine nudging at the top. The cells will be unequal in capacity but no balancer can help with that.

Fair enough. At this point, for my setup it seems to be a (possibly lazy) way to improve things with little additional effort - and they’re not that expensive in the bigger scheme of things. Was able to grab the NEEY 4th gen open box for $110 shipped from the US.

 

[Q-Dog]

Cells don't have to be identical, they only have to remain within acceptable parameters while they are in their working range.

 

[weirded]

Cells don't have to be identical, they only have to remain within acceptable parameters while they are in their working range.

Understood. I suppose this is a bit of working around limitations of the Seplos BMS. It cuts off charging as soon as one cell exceeds 3.5V even if the others are well below.

 

[Quattrohead]

It cuts off charging as soon as one cell exceeds 3.5V even if the others are well below.

This is adjustable. I feel like the default settings are pretty bad on the Seplos BMS. And the documentation leaves a lot to be desired too.

 

[weirded]

This is adjustable. I feel like the default settings are pretty bad on the Seplos BMS. And the documentation leaves a lot to be desired too.

Yeah definitely. Still trying to figure out what they mean with “pressure” in the app.