Servers by jDrones

Make your own Li-Ion battery pack

(Hugues) #1

Hi guys,

Did you know you could build your own Li-Ion battery pack ?

Li-Ion batteries have the highest energy density per unit of mass available to us.

In comparison with LiPo batteries, you get 30% less weight for the same mAh capacity, which translates into direct endurance or increased flight autonomy.

Ready made LiIon batteries for dorne users are not mainstream (they are not sold on hobbyking, nor any other main RC online shops), and are quite expensive.

A DIY assembled pack is a fun project and will get you a much cheaper LiIon battery made to your custom requirements.

You can select individual cells based on their total capacity, based on how many amps they can continuously discharge.

You can then add them up in series to get the tight S voltage, and add them up in parallel to get the right minimum amps continuous discharge rate.

In the video I show how I’ve built a 4S battery which is able to output 30 amps continuously, with a 10 500 mAh capacity. It will be used on my 300 class folding quadcopter for an endurance test.

(John DeVere) #2

Basically 3C, right? Pretty good, the 10C MultiStar comes in at 804g and roughly 184Wh/kg.

Yours is about 270Wh/kg

There are LiPo’s available under 5C, but they are not very popular, so they’re hard to find… you’d likely still need to assemble into a larger back, but might be easier with a Y-harness.

It’s definitely a challenge to find the sweet spot under 10C.

(rmackay9) #3

Haven’t seen people do this before!
Not trying to add scope creep but it would be interesting to make it a “smart” battery. I hear there are boards out there that can add that ability (and ardupilot supports some varieties of them).

(Andras Schaffer) #4

Sorry to ruin the party, but this pack is a disaster waiting to happen.
Never ever omit the protection paper ring from the positive side of the battery cell. The top sides of the cell is negative and only covered with a thin layer of heatshrink. This heatshrink is stressed when you solder the tabs and creates a potential short point. (The blue plastic ring does not covers the sides of the cell casing !)

(Hugues) #5

Hi Randy,

Actually the same cells exist in a “smart” protected version that makes it impossible to overcharge or over-discharge. But they are heavier too, so you loose a bit on endurance (heavier pack for same capacity).

(Hugues) #6

Sure you have to be prudent. I build packs like this since 2015 and never had any issue, even with my fixed wing crashing a few time with such battery on board.
Additionnally, the chosen cell model is a “button top” one, which isolate mechanically the +/-, contrarily to “flat top” ones.

(Hugues) #7

Yes, the 18650 GA cell model from Sanyo is a 10A continuous discharge cell. This is much improved over the mythical Panasonic 18650 1C model.

(Andras Schaffer) #8

Well, I tought the same till this happened :

Be wise, and use that .05 cent paper ring.

(Kikislater) #9

Woaohhh ! I build mine like you eosbandi : with diy spot welder …
What is causing your problem shown un picture ? Do you have link to this 0.5 cent paper ring?

(Perth UAV - Sam) #10

I think PLA/ABS is better than paper. :slight_smile:

We’ve been using these 3D printed cell holders in competitions since 2014:

Another way is to use custom PCB’s with openings for the solder tab spot welding. Both versions are physically stronger than just the tab welding, and simplify assembly. The 3D printed clip only weighs about 4-5g, so not much added mass.

We’re also looking at making some smart battery version using something similar to the ISDT BattGo and using the XT60i connectors.

Regarding C rating there are a few options out there now, including 30A rated cells from Sony/LG and of course the newer 20700 cells that are slowly trickling through with decent, and even better specs.

Basically we try to use 18650’s if max average draw is under 2C, or 30 minutes of flight time, with minimal peaks to 4C. Like in QP’s etc.

(Joe Breznai) #11

(Hugues) #12

nice find, thank you

(Hugues) #13

PCB linking cells by soldering tabs is an excellent idea. Thx for sharing.

I investigated the NCR20700B 4000mAh 15A Battery cell but it is bigger and much heavier (63g vs 47g) than a 18650 cell of same mAh capacity. In my case I do not need more than 30 amps continuous discharge for a 3P pack. This cell however would be interesting for someone who would need more continuous amp discharge (15A per cell versus 10A for the 18650GA), at the expense of a more voluminous and heavier pack.

(Andras Schaffer) #14

Missing paper ring, and soldered balance wire which melted the shrink wrap under the tab. It catched fire in my hand during magneto calibration. I hold the Guiness record since then for “a man who was the quickest to throw a 4kg quadcopter” category…:smiley:

The paper ring linked above is just fine…