11/18/2025 8:36 PM - Some research and design thinking to establish design rules

I begun researching the current market. And I was able to find VIFLY 1S Series Charging series.
After that I was able to find all the different connector types on OscarLiang.
I know a little bit about PH2.0 and XT30.
Found out that BT2.0 is the best for tiny whoops. So I'll use it on my tiny whops if I get one.

I love modular and Open-Source designs! So as a base I'll use 6x XT30 on the two sides for it's robustness. I'm also thinking of putting the BT2.0 connectors on top.

I would love to charge 18650s and FPV 1S batteries. For FPV batteries I'll use BT2.0, either as a module or as connectors on top.
Main focus on being able to use my RC charger to charge 18650 as it has a lot of interesting features like calculation of internal resistance. Ehm When I was a little baby maker I tried to measure Ir with my multi meter.🤣

11/18/2025 8:57 PM - Drawn the schematic.

I've started with the power and balance input. I thought that finding the horizontal XT60 connector would be difficult, but thankfully I was able to find in footprints and LCSC.
next was wiring the balance port to a sub schematic with connectors.
I begun with wiring a unique pin to each other but I was short of 3 connectors which was weird. But then I remembered that the batteries should be in series not each wired to a unique pin.

after that I added a placeholder rotary switch.
When searching for these kind of switches I've stumbled on this one from aliexpress which seems to be the one from VIFLY. It would be cool if I could make some kind of electronic circuit to switch it automagicaly. I probably shouldn't over kill it.

The balance port is a standard 7 pin JST XH with 2.45mm pin pitch.
For the XT60 there is already a footprint in KiCAD. When seeing that there is a horizontal one I knew I need to use it. Same for the XT30!
As for the BT2.0 I wasn't able to find anything in KiCAD. So I'll have to make my own.
Here is the drawing:

Next up -> Routing the PCB!

11/19/2025 - Drew a footprint for BT2.0 connector

Started with creating a new library and footprint named BT20.
After finding the dimensions I was able to add one hole as a starting point as its going to be mirrored.
After setting it to the right place and as circular hole it was obvious that the leads are super close to each other. So I made it oval. But something still seemed wrong. So I've searched for a 3s step model to use as a reference. Thanks to Riley.
In FreeCAD I was able to export just the one connector that was needed.

It seemed to be OK.
I took inspiration from XT60 connector already in KiCAD.

Added it to the schematic symbol.
After that it's finished.

11/25/2025 - Finished up the main 1s charging board

I've started with deciding on how to select the voltage.
I was thinking of using a selector switch but I didn't find any on LCSC and aliexpress doesn't have any info regarding them. After that I thought of using mosfets but I made a purpuse built PCB with it there would be a lot of issues getting it up and running.
So I choose a 2x07 pin header so I can use a jumper to select and I can also prototype with it.

After that was routing.
My first thought was to use a KiCAD plugin called "replicate layout" but it didn't do exactly what I wanted.
So moved the top left most XT30 to x0y0 and thought about spacing as I would like to be able to use 18650 holder directly attached to the PCB.

added the XT60, selector and balance connector to the right side as there was GND and highest potential.
And there it is.

11/28/2025 - Made the XT30 to 18650 battery board

For today I whipped up a 18650 extension board.

First thing was the schematics.
I firstly duplicated the xt30 from main board schematic.
After that I went on LCSC to find the 18650 holder. I was able to just find ones with SMD pads.
Then I looked in KiCADs footprint library to find available 18650 holders. There were 5 of which one seemed to be a close enough match. So I compared the two datasheets and they seemed to be compatible.

Then I went on layout and routing. I began with placing the XT30s in 20x20 grid as it is on the main board. Then added the 18650 holders with sufficient spacing. Routed it all up and added some graphics. And done

1/24/2026 2 PM - Finished it

It's all soldered together. I'm so happy with the result. It looks super professional, and I can use it as a 18650 to xt 30 adapter for my projects, neat. And it gives me a funky vibe.
And I was able to test it with one 18650 cell, and I found that the cell is super soft.
More testing coming soon.

1/24/2026 8 PM - Tested it on the charger

So I was super thrilled to try the board on my stash of 18650 cells. I found that a pack of four I bought has Ir around 200mR. And the cells in the picture are from a dead parkside battery. I managed to charge it from 3V3 to storage without any problems.