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Leaving the BMS at home

So I’m putting this here because I believe there is merit to this approach but since I’m just hacking away in my garage, maybe someone else has a better way. I’d like to create discussion around this topic, so please chime in with any experience you have.

I lurked for a long time here and other places before I charged headlong into battery making. I have professional experience with electronics, specifically running them in the ocean, down to depths of up to several hundred meters. After soaking up what information I could find, I decided I would try and route the balance leads off the board and be rid of the onboard BMS altogether.

I’m not going to cover the actual battery building here, but other threads have done better than I ever could.

40 30q’s (±$150, depending on market conditions)
7 Pin waterproof connectors male/female panel mount ($35 or less/pair)
10 ft 12g silicone wire series connections, discharge leads ($11/10ft red+ 10 ft black shipped)
10 ft nickel strip ($5 shipped)
14g charge leads ($5)
20g silicone wire balance leads ($14/20’ spool)
JST 2.0 connector and crimps ($35/kit)
Adhesive Heat shrink tubing, assorted ($15/box, enough for several more projects)
60/40 electrical flux core solder ($10/spool)
Fish paper ($10)

Total just under $300 if it’s your first battery, after buying the spot welder and the soldering iron. I had some of this stuff already, so actual cost was lower.

My first board, I would simply open the enclosure to charge through the JST connector. If you run your boards with lipo packs, you’re probably doing this too. I basically built 2 5s 3p packs and wired them in series for a 10s 3p. I’d have to take it all apart to charge. Not the most elegant, but it worked, and more importantly, I found out that I freaking love commuting on a esk8 and it was very practical way to get around when combined with the trolley system here in San Diego. I present Frankenboard :

The second battery was much more refined in that the balance connections were routed off the board. Basically just routed the balance wires through a waterproof 7pin plug. I’ll post a link but others have found arguably better or undeniably cheaper plugs.

For this one I routed the balance wires and the leads for the series switched series connection into the deck and out a wooden panel. I did this to keep the enclosure free to pop off whenever I needed to dig into it.

Very scientific way of testing the water resistance of the assembled board.

not done here, but I have some lessons learned if you’ll take my word for it while I salvage my pics


  1. great way to get more info from the battery pack.
  2. If you already have a hobby charger, it’s probably cheaper.
  3. Leaves more room for batteries
  4. Fewer failure points onboard


  1. very tricky soldering work involved. that middle pin is hard to solder without touching the neighboring pins.
  2. Relatively inconvient to charge. Either charge one side at a time (safe) or charge both sides at the same time with two separate chargers. Duo chargers do not work, I killed 2.
  3. The jst end of the charging adapter can be finicky, especially if cheaper wire is used. I’ve had to fix that part every few months for a cable that was made with fake silicone wire. Another one I made for a 12s (2x 6s in series) I made with nice wire and corformalled the crap out of it and it hasn’t broken yet…

more to come
(PSA: save your esk8 pics to the forum before your phone dies on you and takes them all with it :green_heart:)


Sooo one 6s chargers and you’re charging half the pack at one time?

yeap. ever since I smoked my duo by plugging both sides in without severing the series conmection. poof.

Untill then charging both sides on the duo charger worked great

now if I want to charge both sides at once, I need to get another charger out. then the series connection can be closed, no worries

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You can get this charger which will do 2 x 6-12s batteries at the same time

I just did a trampa 12s8p liion as a single pack and routed a massive balance plug through the monster box

A lot of fiddly soldering and crimp work because I wanted the battery to be removable from the monster box and also needed to make an adaptor to suit the charger. But it’s an excellent charger and I really like this solution.

You can get smaller ports and plugs like the GX20, but they would definitely be harder to solder

My next approach will be for my Madness build, already have a BMS and charger for it, so I will combine those two together with a gx20 port.


heck yes, I would love one if those. I saw that when you posted in the battery builder club thread and suddenly believe in true love

buuuut… an Imax B6AC is 30 sheckles and works fiiiiine…lol

I went with the split pack method because of how easy and cheap it is to get 1-6s chargers

also, I had to find a connector that was less than the thickness of the enclosure so the smaller plug fit better

Did that on my board with a GX20, it’s not too hard to solder as long as you start with the middle pins, TS80 with the pointy tip works great for that.

Wanted to eliminate a failure point from the board, but ironically, my D140 arrived semi-dead. :sweat_smile:

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Round of applause for Bestech QC everyone, not 1 mistake in 10 years.

Update with salvaged pics (first post)

Also, I lurked around and found @visnu777 's beautiful builds


and Blutstern

Question for @visnu777: Do you have the same charging cable for the two boards? Same charger? I’d love to hear more about your experience with this type of charging since you’ve been at this longer :wink:

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(Left side 10s (12pin, WF28, cable for the Blutstern, on the right the new Grünstern connector for 12s (14pins, SP28,
I use the Graupner Ultramat 18. It is currently shipped for repair but overall I love it. I drive it with an external power supply with 3.8A@12s charging current. Recently I ordered an active balancer out of curiosity since balancing with the Ultramat takes some time :slight_smile:

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What balance charger are you using?

Preparing for a group ride later, carefully monitoring the cells manually.

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