Tech Tricks: Homemade Balance Charging Cradles.

[Nisei]

The charger may internally have a common "ground" either on the positive side or the negative side of the batteries. You cannot tell without looking.

You can, just use a multimeter to measure if either the positive or negative terminals are connected.
and if neither of them are I'd suggest using a 4-pole TRS connector. They are quite common nowadays since a lot of headsets with built in mic are using them.

 

[Nisei]

Just finished my cradle which I've built using a dead Nitecore i4.
I wanted a nice looking unit without loose wires I had to attach using magnets and I've always liked these spring loaded chargers that can take different sized batteries.
When looking at the back I thought perhaps it would be possible to fit the balance ports in the same space where the mains connector was and when measuring it it turned out to be the exact same width as a 2S and 3S socket next to one another and the exact same height as 2 sockets on top of each other; perfect!
So the first thing I did was strip most parts from the PCB and making sure all terminal points I was going to use were isolated from the rest of the board. I did this by scratching away any unwanted board traces with a hobby knife.
I then took a couple of sockets and soldered them onto a piece of perfboard and hot-glued that to the main PCB. Then it was a case of soldering all wires into place and triple checking if everything was in the right place and there were no shorts. I then popped all parts into place, added some labels and it was finished. When charging less than 4 batteries at a time I'm using dummy batteries in the remaining slots. It's working like a charm.
Thanks for all the info in this thread!

 

[Nisei]

OK so that was the last time I make an effort of taking pictures and posting.

 

[Aahhyes68]

OK so that was the last time I make an effort of taking pictures and posting.

No,no, no,no,no....... You did a great job ! I've asked questions about doing this same thing with an i4 but it never came to fruition. I like it !! I just revisited this thread so your work is NOT going unappreciated !!

Thanks for posting !!!

 

[spencer]

Nesei, I really like what you did. It is very clean. I have also converted an old spring load but I don't have it set up for balance charging because I only just got a balance charger. I was parallel charging up to 4 cells at a time.

Something I noticed is that there is a very significant amount of resistance in the springs. At higher charging currents this resistance translates into a voltage drop. As a result, when the charger is putting out 4.200V and goes into CV mode, the battery voltage is really only about 4.050V. As a result I have to charge quite a bit at the end at a very low current. I have to reduce current to about 500mA to make the voltage drop negligible. When charging 4 18650's this way, it takes a very long time to top up cells (125mA per cell).

Nesei, have you noticed any negative effects in terms of any additional resistance added by the wire? It is possible that your wires are of a lower gauge than mine and have less resistance. Looking at how it is hooked up and some intuition, the effect should not be as pronounced in a series situation. I could also be totally wrong on that point.

Does anybody have any suggestions to counteract this effect in a spring load charger? Right now I'm thinking about just throwing the whole unit out and making a setup similar to the one in the OP. I don't really need to charge anything other than 18650 cells right now and I do like his second version. Decisions, decisions...

 

[Nisei]

Thanks for the feedback Aahhyes68 and spencer.
Yes spencer, the resistance in the springs is a b|tch when it comes down to discharching. I haven't noticed any side effects when (balanced) charging though. Everything's fne when charging either 1, 2, 3 or 4 batteries but discharging is a no-go as voltage seems to drop to sub 3V within seconds after pressing the enter button. I'm gonna do some measuring with my Fluke to see what's actually going on.

 

[keefd]

Ok, I know this is an older thread, but I'm a bit confused on the wiring. I'm not a total electronics novice, but I could use an explanation.

I get how power flows when the cradle Nisei built is loaded with 4 cells, but isn't the V+ in broken when using less than 4 cells? It looks like you'd load starting from the left going right, but say if you did 3S1P, what takes the positive voltage from the top right terminal to the V+ terminal to the left when there is no fourth cell to carry the voltage? The orange wire normally wouldn't act as V+ in a 3S arrangement, you'd unclip the red wire from the 4S position and clip it to the 3S position.

Or is the charger's original circuit board still functional? I assumed that the board was completely bypassed. Or is the i4 charger completely functional with the hobby charger supplying 12V, but how? My 106b+ won't send out even close to 12V in a 1S or 2S confuguration, unless the charger doesn't need +12V. I'm also a little confused as it looks like the balance wires are also pulling double-duty as power and neutral wires. Unless the cut traces on the underside are to disable not only the AC, but to disable the +12V as well.

I got mostly confused as I ordered a similar holder to this: https://highdesertvapes.com/products/4X-18650-Battery-Holder.html (link as an example) and I wondered how to wire it up so that I don't have to move the power leads around when doing less than 4S.

(sorry for the long post!)

 

[Nisei]

Ok, I know this is an older thread, but I'm a bit confused on the wiring. I'm not a total electronics novice, but I could use an explanation.
I get how power flows when the cradle Nisei built is loaded with 4 cells, but isn't the V+ in broken when using less than 4 cells? It looks like you'd load starting from the left going right, but say if you did 3S1P, what takes the positive voltage from the top right terminal to the V+ terminal to the left when there is no fourth cell to carry the voltage?

It's covered in one of the last sentences of my post:
When charging less than 4 batteries at a time I'm using dummy batteries in the remaining slots.

 

[kreisl]

Great thread i must have missed it before.
I used to use diy solutions too.



Not anymore. Some ppl know why

 

[Nisei]

I've been neglecting certain hobbies for a while (I've got too many) but I really would like this thing to become useable.
Is there a technical person here who can explain why my cradle (see above) won't work? All I can think of is that in the original i4 charger they've taken the resistance of the springs into account when the charger is measuring the cells.

 

[Gauss163]

If it were due only to resistance of the the springs then presumably you'd see a symmetric effect when charging. Are you sure that you cut enough traces to take all original components our of your circuit? It shouldn't be that difficult to troubleshooting using a DMM.

 

[Nisei]

Yup, all traces are isolated. If you look at spencer's reply (7 posts up) he was having the same problem.
Probably also the reason why they've started using these metal rails in the newer versions of the charger.
I guess there's not much I can do about it.