26650 A123 Battery Pack with parallel/ series Switch selector

Hi everyone

Recently the lipo battery pack on my eMTB (15Ah 12S 2P) started to develop some issues and i decided to change it. i choose A123 battery cells for the new one. i like the life cycles ( 1500 +), the discharge rate, not like the lipos but still pretty decent, and like the abuse tolerance of this cell. http://www.a123batteries.com/product-p/anr26650m1-b.htm

For the enclosure will be using a UK 409 Dry Box, this will waterproof the system and will provide space for the volt meters, connector and series/parallel switch. http://www.uwkinetics.com/products/409-dry-box

For the assembly of the pack i like to use hot glue because once it has harden and the pack is enveloped it provides mechanical reinforcement to the structure of the pack.

Once glued and spot welded just need to solder the Discharge wires and balancing wires.



Pack specifications: Single Pack 10Ah 6S4P

One of 2 finish pack with discharge wires for parallel/series switch set up.

i really like to use the convenience of being able to charge the batteries in 6S and using it in 12S setups, just by flipping a switch without having to disconnect anything.

The instruction of the parallel/ series DPDT switch are in this post

This is the final Product:

in the Drybox i included: XT-90 loop key 2 Volt meters with alarm 2 on/off switches for the volt meters XT-60 charging port 2 balancing ports DPDT switch for charging (6S) and discharging (12S) configuration.

not visible in the pic. is the Ubec and 2.4Ghz transmitter.

all this is installed in a ABS enclosure inside the DryBox.

The wires i used Flat braided wire equivalent to 12 AWG to run it under the bindings. the look it’s more clean.


This is truly a nice build and I’m just excited that there is finally a thread about something that hadn’t been covered a thousand times.

That is a clean build, keep it up!

cool, first A123 battery Ive came across! :open_mouth:

I build a very similar form factor for my trampa, but thats a 60A max battery for a more touring oriented trampa. not sure if I did the right thing, trampa seems more like a fun/trick machine, long tours didnt work out so well so far, since the stance wasnt too comfortable. :no_mouth:


Holy S**t dude, that thing looks like its going to blow up both your legs on an unlucky day.

That is unlikely to happen, since lifepo4 is known for their safety feature (part of the reason why Boosted are using them for their boards). I might be wrong, but I don’t think they are going to to explode even if they are overcharged or shorted, at least not to the extent of lipo and lithium ion.

The stance takes some time to get comfortable but once you do and get a hang in the bindings this boards are super fun for carving, tricks and going on any terrain.

this is awesome! i love to see people trying some variations in their eboard builds…

can you tell us more about the specs of this pack… what is the constant current it can output safely? how many WH?

This are super safe battery.
I drop one of this packages ( 80% SOC) and the cell that hit the floor got crush and leaked electrolyte fluid this ting did not even heat up or produce smoke. I just replace the damage cell, I put the cell out side in the backyard and monitored for about 4 hr during this time no smoke or over heating, no other lithium chemistry can tolerate abuse like this.

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This is a double configuration pack by using a DPDT switch to change from parallel to series without the need of connectors just a flip of the switch.

In 6S the capacity is 20 Ah @ 19.8V and in 12S is a 10 Ah @ 39.6V.

beast mode… what are these cells C rating?

20C continuous and 48C burst Here’s link to spec http://a123batteries.com/v/vspfiles/images/pdf/26650.pdf

Going off topic a bit. Are those straps any useful for stopping the momentum when you do a hard brake? I’m thinking about building an all weather

Yes the straps help with the braking. It takes getting use to the strap and the stance but once you are comfortable with them they are so much fun you can take tight turns at faster speed and can carve harder because of the extra support.

Hey Kaly,

Your post is awesome. Do you know the specs of the DPDT switch you used for series/parallel selection? I want to run two 6S LiPos in series (12S) during riding, and charge them in parallel at 6S, just as you are doing. However, I can’t find a switch with an adequate current rating. The best I can find is 20A, but my motor can pull up to 70A. Did you have this same problem? Thanks!

I use the 20A switch. Here is not the Amps that you need to check but the watts.

20A x 125V = 2500 Watts 10A x 250V = 2500 Watts

i have used this switch with all my builds with no problem at all. from 12S lipos to 12S lifepo4 all good. http://www.homedepot.com/p/Gardner-Bender-20-Amp-Double-Pole-Toggle-Switch-GSW-16/100210997

just a WARNING make sure you label with a sticker the position for charging because if you mix that up when connecting the balancing lead in parallel will fry the lead.

where do you get those wide battery weld straps?

So is there a reason that a single pole switch with the same rating couldn’t be used as a power switch for the board?

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A single pole switch can be use for 6S to 8S but for 10S to 12S you’ll need a anti spark loop key, in order not to damage the switch.

At what point did you put it in you circuit? Directly connected to the batteries?