Simple balancer for lipo, will it work?

Hey, I have been away for a few years(like 4-5 years!! jeez) ever since my lipo battery got overcharged due to my dumb charging setup. I got the urge to get the bike back in operation and wanted to run an idea past you guys.
Looks like the bulk charging for 20s lipo packs has hope now that lunacycles is stocking an affordable charger and grin has that sick satiator. My dead 20s pack was charged with a supposedly modified SLA charger that over charged it when I forgot to take it off charge soon enough. The BMS scene doesn't seem to have progressed much though, but I use the CA for protection while in operation, and I had an idea for a 20s DIY balance charger, and wanted to seek more intelligent feedback.

My thought is to wire up 20 single cell modules and power it with a 5v 20a supply.

I would link all the modules in parallel on the Vin side, I know that will work. Where my mind bogs down is can I wire the charge modules like a battery balance lead? Or would I need a pair of wires coming off for each cell group? Or is there a smarter cheaper better way I am missing?


On the battery front, sounds like the 18650GA Sanyo cells are well liked, I am watching tumich's thread with interest. I was happy with my hobby king lipo pack before I ruined it, and some of the packs that didn't get ruined still power my robomower just fine. What are diy battery makers doing these days? I'm working on building a spot welder in case I want to do 18650 cells, though from reading sounds like I might be better off just soldering with a larger iron.

You cannot have outputs connected in serial as I don't believe that outputs are isolated from supply line (usually negative is common).

Easiest and probably cheapest would be to just buy a cheap 20s bms, remembering that the standard charge rate for the GA cell is 0.5C. Or a simple to understand method would be to bulk charge using 4 battery medics to balance.

You cannot use those boards. It will 100% cause total destruction.

The only thing that can make this work is if you put each of them on a isolated dc-dc converter or use a 4.2v isolated dc-dc converter but those dont exist.

flippy said:

You cannot use those boards. It will 100% cause total destruction.

The only thing that can make this work is if you put each of them on a isolated dc-dc converter or use a 4.2v isolated dc-dc converter but those dont exist.

Click to expand...

Lol thanks for setting me straight, I bought a few, I'll just use them as single cell chargers. Guess I'll just do the same thing and expect different results (buy lipos,and bulk charge)

flippy said:

You cannot use those boards. It will 100% cause total destruction.

The only thing that can make this work is if you put each of them on a isolated dc-dc converter or use a 4.2v isolated dc-dc converter but those dont exist.

Click to expand...

You can put 5V isolated DC/DC converter in front (on 5V side) of each board, but then it will be much more expensive than to buy decent BMS and charger...

Peter.bp said:

flippy said:

You cannot use those boards. It will 100% cause total destruction.
The only thing that can make this work is if you put each of them on a isolated dc-dc converter or use a 4.2v isolated dc-dc converter but those dont exist.

Click to expand...

You can put 5V isolated DC/DC converter in front (on 5V side) of each board, but then it will be much more expensive than to buy decent BMS and charger...

Click to expand...

that is what i said.

Sorry flippy, now I see that you said about DC/DC converter in front, I missed that detail.

My favorite bulk charger is only for 48v, and came from EM3ev.

Not as adaptable as the satiator, but it has the three way switch that's oh so handy. One position is storage charge, about half full. The other two are full, and 90%.

But I opened it up, and set them differently, the 100% setting is more like 95%. or 4,15v per cell for 14s. This way my bulk charges can avoid ruining a cell by overcharge, even if it's out of balance by .15v, it wont go over 4.3v.

The majority of charges are to 90%, unless I plan a very long ride. Or I charge to 90% in the evening, then to 95% just before I ride.

On the discharge, I just stop when I must, based on a CA whole pack voltage. Usually I stop by 3.5v per cell. Most of the time, 3.7v.

Balancing I do by hand, I find it quicker than using an RC charger. Without unplugging anything, I can single cell charge or discharge a low cell with an RC charger. I use the balance wire to charge a single cell. Out in the wild, I can discharge a single cell with a light bulb.

I carry a big enough pack so that the c rate is low, strain on each cell minimal. I don't ride the lipo daily, but only have to actually balance the packs about 4 times a year, because I'm not hammering them hard enough to go out of balance every cycle.