I'm currently building a Talon (v3), mainly waiting for parts.
While looking for high capacity batteries I found out two things; There are a lot of brands, and prices are still steep in the high-cap regions.
I've also seen a few people on the Tube using 18650 cells, but none of those explain why.
Does anyone here have experience with these custom 18650 packs?
And which 'cheap' brands of standard 5~12A 4S seem to work best?
I'm going to use an Emax GT3526 710KV swinging a 13x6.5 prop, which should draw no more than 47 amps at peak load. I'm aiming to stay under 3 kg AUW, expecting about 4~5 amp draw at cruise speed. Or is that not attainable?
18650s have higher energy density by weight.
They have low power output compared to LiPo batteries, but 4-5 amp at cruise is easy.
I used them for my long distance flights
Very impressive flight, Moglos.
Did you buy a ready made pack, or DIY with individual cells?
I was thinking of getting tabbed cells and stringing them together, should be fairly easy combining four cells in a cluster and stringing a few of these together.
But how about charging such a pack? Is there a way to make a balance lead for charging?
The motor is rated for 5S, would this have a big impact on drain? I noticed you tested a 25% increase from 4S to 6S..
I couldn't find tabbed cells so I bought a cheap welder and welded them myself.
I wrapped the cells in heatshrink and made small cuts near the ends of each cell so I could insert a custom made balance plug. It was a regular balance plug with the individual leads pulled out of the plug molding. I inserted the exposed plug wire and the pressure of the heat shrink held it in place. It wasn't beautiful, but it worked and was super light weight.
I did some research on Li-ion 18650 cells if anyone is interested:
NCR18650B cells have a nominal capacity of 3350 mAh (advertized as 3400), 2C discharge rate (6.5 amps to play it safe and a 12 amp burst for 5 seconds), 46 grams per cell, and can be drained to 2.5V per cell
NCR18650GA cells have a nominal capacity of 3450 mAh (advertized as 3500), 2.8C discharge rate (10 amps certified and 30 amp bursts are allowed), 48 grams per cell, and can be drained to 2.5V per cell
18650VTC6 cells have a nominal capacity of 3120 mAh (advertized as 3000), 6.4C discharge rate (30 amps continuous and burst), 46 grams per cell, and can be discharged as low as 2V per cell (though I would stick to 2.5V to be safe)
When using these cells, you can safely add the C-rating per 'pack'. so when you make a 4S with 3 packs in series, you can safely draw 30 amps continuous at 14.8V using NCR18650GA cells. This would result in a 10.3Ah pack at less than 600 grams. Adding a balance plug is just a matter of connecting the 'dots'. One lead from the main + and - (red and black), and one lead for every 'bridge' in the pack(s).
The cells can be found (with tabs) on Ali for around $30 per dozen (=4S3P) and don't forget some wire, XT60 connectors, shrink wrap and some balance leads (which would set you back another few bucks). Another benefit is you could power all other electronics besides your motor and servos from a seperate LiPo without much extra weight (a 10 Ah 4S LiPo weighs at least 850 grams).
There are several vendors of quality lithium ion battery packs with integral battery management systems (BMS). A good vendor is https://uavfpvbattery.com/. I prefer custom battery packs from http://www.novoxypower.com/. You can specify the batteries, form factor, connectors, and BMS parameters. For small planes with 3S or 4S you can make 18650 packs using spring clip battery holders. I get them from AliExpress. Purchase the battery holder with leaf springs, not coil springs.