Stuart Pittaway diyBMS combined with Active Balancing

[G€€RT]

Hi,

I was wondering if some of you already try a Passive Balacing combined with an Active Balancing ?

For now I'm using Stuart Pittaway diyBMS which works very nice.

Any information is welcome.

 

[mandrews44]

Most of the shelf BMS's have passive balancing which dissipates an overcharged cell to balance the pack. I've added an active balancing board that moves power from overcharged cells to undercharges cell(s). In theory, when a pack has only one cell with a lower voltage, the passive or dissiapative BMS blanancer will start dissiapting 3 higher voltage cells while the active balancer takes power from higher cells and transferes it to the one lower voltage cell. The end result, in theory, is they meet in the middle with the least power turning into heat. This also depends on the voltage difference and how far into the knee of the charge you are.. > 3.3v to 3.65 (max). I've also done testing with manual balancing and discovered the cells don't accept much current when the start voltage is 3.450 and target is 3.5v.. it charges at a whopping 450ma.

 

[G€€RT]

I think there is also a down site on Active Balancing, you wil never notice a dead cell as it wil charge up.
Therefore I was thinking to use a combination of the two.

I already found a (still in devellopment) solution called ActiBMS, this is the best of both worlds of balancing.
It is a fork of Stuart Pittaway diyBMS and the authors name is hitec95.

The monitoring software is great and runs on a WeMos D1 mini.

 

[mandrews44]

I already found a (still in devellopment) solution called ActiBMS, this is the best of both worlds of balancing.
It is a fork of Stuart Pittaway diyBMS and the authors name is hitec95.

This is an awesome idea but what makes it unattractive for me is if it is like diyBMS, they are using relays for charge / discharge control. If the new one is using MOSFET's instead of relays, I'll be interested. Once thing I've done with higher power relays, (only up to 30a) is the inverse of what I have seen so far. When the circuit is 'ON', the relays is not energized and just uses the NC connection. When it needs to turn the circuit off, it energizes the relay for the reset time and then turns it back off. For high power relays, that is the only way I can see a BMS working with relays instead of the MOSFETS.

Under extreme loads during battery protection, you are risking welding the contacts together and not having any protection you thought you had.

 

[G€€RT]

Under extreme loads during battery protection, you are risking welding the contacts together and not having any protection you thought you had.

Yes, you are right !

Just an idea, can't we moddify the relay outputs with an array of high amperage mosfet's instead ?

 

[mandrews44]

Yes, that would work. I did something similar with with an H-bridge to replace a relay used for motor control (forward / backwards) that was controlled by a RPi