I have a completely different project (Halloween displays) that all use leftover 20700’s from old esk8 builds.
I’d like to find a multi-position charger like the eFest LUC V6 that will allow me to set the charge termination to an arbitrary percentage that I can choose in a menu. Like 60% or 75%.
I do understand these are unprotected cells, but the amount of power the displays use is very small, so at the end of the night they won’t have lost more than about 15 to 20%.
About the charger though? Sorry, I don’t remember which round cell chargers have what features. I’m pretty sure all use voltage though, not percentage (which is too unreliable an indicator of charge level).
The question was whether there is a charger that will terminate at a user-selected voltage (or percentage). like if I wanted to terminate charge at 4.00 volts.
These are individual cells used in Halloween displays, so there is no BMS involved.
It’s a pretty arcane ask, I admit. It has more to do with my OCD than actual battery health
I ordered the MC3000. I looked through the manual - it’s obviously translated from chinese, or maybe it’s AI generated, but it’s mostly gibberish. I’m hoping once the device arrives I can walk through the menus until I find what I’m looking for.
Ok, well, I should have known, but this has now turned into a full project. I sent the MC3000 back and went down the bench supply path.
Which works but the problem is as the battery approaches the target voltage the charge process slows down tremendously.
I chose 3.9v as my target voltage because it’s about 65%. This is sufficient capacity for the displays but if I don’t use the cells and just throw them in a box for the winter it is low enough that they won’t take damage from being stored with too much charge.
What I’ve found is that if you set the bench supply to the target voltage the cell will charge up to that voltage, but will continue to draw current for a really long time as it tapers off to full charge.
So then resting voltage comes into play. What I really need is a system where I can charge to a higher target and then the cell will fall back to my desired V.
for instance, if I charge to 4.0 then pull the thing off the charger as soon as it hits that voltage it should fall back to 3.9 resting. I just pulled that number out of my ass.
This will make the charging process much faster. Finding the magic charge-to resting V number is just experimentation. I have no doubt that there’s a table on the internet but I couldn’t find it.
The other issue is that some number of cells are over 3.9. So I would need to discharge them to the correct resting voltage.
All of which leads to my new project to automate this whole process. I’ve started by 3D printing a battery box. That’s as far as I’ve gotten
