I know this is an old thread, but the topic was valid for what I wanted to post.
I've been a fan of active balancing. I've tested charge and discharge cycles with both the QNBBM and Heltec (capacitor-based) active balancer, and seen very good results. However, after watching
@Off-Grid-Garage YouTube videos and watching his opinion evolve, I think my position has changed just a bit.
It seems to me if you have a situation where the system is cycling every day and perhaps cycling fairly deeply, an active balancer that balances all the time (QNBBM and Heltec) may actually cause cells to drift out of balance as
@Off-Grid-Garage saw. The cells are spending enough time closer to the bottom knee that the balancers are trying to balance there, which can undue a top balance. Then when the cells rise up closer to the upper knee the balancers are working to get them back in (top) balance again. This can go on forever, and over time I'm guessing it isn't good.
On the other hand, if you have a system that spends a bit more of its time close to fully charged or in float, a good active balancer can successfully preserve the top balance. This is the case for our cabin system, which is normally only in use when someone is visiting the cabin: 3-4 days per week during the May through November time frame. The rest of the year the cabin is not used. This means that during the days when no one is using the cabin the active balancer can get the cells back to a good top balance.
I currently have one 8S 24V system and two 4S 12V systems, all using the Heltec active balancer. The two 12V systems will probably be cycled pretty heavily for 2-3 months every year, and periodically the rest of the year.
So now I'm thinking I want to leave the active balancer on the 24V system for our cabin, for the reasons stated above. For the two 12V systems, I want to be able to use the active balancer selectively. Not just at certain points in the charge cycle as
@Off-Grid-Garage argues, but rather to enable it when the cycling is either not happening or is shallow.
To this end, I'm thinking of putting in a switch or relay control to turn the Heltec active balancing ON or OFF. The solder pads that
@curiouscarbon pointed out above seem to be made to order for this.
See that spot where it says "RUN"?
That's actually two separate electrical connections. You can simply remove the blob of solder there and wire in a physical switch instead. This will allow you to control the active balancer manually.
So has anyone actually used these pads to turn the balancing on and off?