new bms features that I would like to see.

[John Frum]

1. status light with momentary switch that indicates the status of the bms. could be a simple "OK" and "ERROR".
2. EZ button to reset a tripped bms.
3. parralel mode for top balancing a set of cells, disconnect the cells when one of them reaches 3.65 then the resistors kick in to balance them. Momemtary switch and led could indicate whether the cells are sufficiently balanced or not.

 

[BiduleOhm]

I'm obviously very interested by this thread

But I'm not sure I understand the 3. correctly, can you explain more please?

 

[John Frum]

But I'm not sure I understand the 3. correctly, can you explain more please?

Usage model:
User gets raw cells to build a 12, 24 or 48 volt battery.
They purchase the BMS that I describe.
It has a modal switch for top balancing.
Mode 0 = top balance mode(all cells connected in parralel)
Mode 1 = serially connected cells
With the switch in top balancing mode they parallel their cells and connect the balancing leads to the cells.
Now they can top balance their cells through the bms and the bms will disconnect the charge source if/when one of the cells hits the configured upper limit.
That upper limit is typically ~3.65 volts for lifepo4.
At this trigger point the bms can start using its resistors to balance the cells.
For bonus points the bms can have a momentary switch and led that shows the user status information related to the top balance.

 

[Dzl]

Adding to your list, something I greatly crave:

1. Well written and detailed manual and technical datasheet.

 

[Craig]

Hmm well without the parallel mode this is what the Chargery does. You can set it to balance the cells at any voltage you like. It has a switch that will reset it. I use the lights on the SSR to know the status.

Over the years I have pondered a way to have batteries switch from parallel to series but it's really complicated especially if you have 12 or 16s or more.

 

[cass3825]

Over the years I have pondered a way to have batteries switch from parallel to series but it's really complicated especially if you have 12 or 16s or more.

I did something similar with a DIY 3-phase wind turbine which had 24 coils per phase. On startup, all 24 coils were in series. As RPMs increased coil arrangement transitioned to parallel in order to increase load on the turbine. Options were 24s1p, 12s2p, 8s3p, 6s4p, 4s6p, 3s8p, 2s12p and 1s24p. Relay switching nightmare.

 

[BiduleOhm]

Usage model:
User gets raw cells to build a 12, 24 or 48 volt battery.
They purchase the BMS that I describe.
It has a modal switch for top balancing.
Mode 0 = top balance mode(all cells connected in parralel)
Mode 1 = serially connected cells
With the switch in top balancing mode they parallel their cells and connect the balancing leads to the cells.
Now they can top balance their cells through the bms and the bms will disconnect the charge source if/when one of the cells hits the configured upper limit.
That upper limit is typically ~3.65 volts for lifepo4.
At this trigger point the bms can start using its resistors to balance the cells.
For bonus points the bms can have a momentary switch and led that shows the user status information related to the top balance.

Ok, now I understand 100 %. The main problem I see is that the BMS would need to work on only one cell voltage. Even if it would be possible it greatly increase the complexity (and so cost). I don't think the RoI would be interesting at all, especially as it's basically a one time thing you can even skip with not totally out of balance cells and letting some time for normal balancing to do it's job.

Switching the cells wiring would be hugely impractical and expensive (think the FET/SSR/Relay thing but dozens of them...).

 

[John Frum]

I don't think the RoI would be interesting at all, especially as it's basically a one time thing you can even skip with not totally out of balance cells and letting some time for normal balancing to do it's job.

Reality is a harsh mistress.

 

[svetz]

Love that list!

...Adding to your list, something I greatly crave:

2. a light that indicates when the battery is fully charged while charging

 

[Sparky]

Adding to your list, something I greatly crave:

1. Well written and detailed manual and technical datasheet.

Oh, now you're just talkin crazy!