If you're like my buddy Simon who dumpster dives at the recycling center for discarded laptop and cordless drill battery packs so he can harvest 18650 cells, it might be time to change your habits. Getting to the recycling center is harder for me because I don't drive much these days. That's because She Who Must Be Obeyed usually has the car (except when it needs fossil fuels). But I'd like to visit the dump more, so I am preparing to make my own Tesla style electronic vehicle because I can't afford the real thing. I hatched that plan when I read that Tesla is using 21700 cells in the Mark 3. Like many others, I happened to have a few kicking around, so I decided, if you can power a Mark 3 with it, how would it fare in an electronic Chinese handwarmer that is sold with grossly overstated claims of 10 amp capacity (a claim that is tested in this video BTW). I have successfully used these same cells to build a 20Ah 52V battery pack for my eBike. At a real 5 amp capacity per cell (as opposed to the anaemic 2,300 MAh that Simon may get if he's lucky), they truly are the pre-eminent Li-Ion cell of our time. In light of this, SWMBO, after checking Quora, remarked that if all goes well and once I convert 2,208 Chinese electronic handwarmers to the 21700 cells and wire them into the trunk, I could be the first North American to power my vehicle using Chinese powerbank/handwarmers with the added bonus of a vibrating seat. (According to SWMBO, the Tesla Model 3 long-range battery pack contains 4416 lithium-ion 21700 battery cells.) But, if you only have a pedestrian interest in the possibility of making up a better electronic handwarmer, this demonstration may be on-target. The style of handwarmer in this video ship with, on average, a real capacity of 5400 MAh derived from 3 18650 cells wired in parallel (not the 10,000 claimed). Each side of the handwarmer draws about 1.25 amps per hour (at the highest setting of 60C for heat). So that roughly translates to an expectation that this style of electronic handwarmer will provide heat for 2 hours. Ripping out the OEM battery pack and installing 21700 cells should double your effective heating period.
In spite of the expected grossly inflated capacity claims, there was a surprise with respect the the apparent quality of the other components, especially the battery pack. The first pleasant observation was: there was no soldering on the terminals, the prime leads were spot welded on to the nickel strips. Both ends of the battery pack were then insulated, and the entire pack shrunk wrapped. The solder pads on the PCB for the connections have 20mm of separation to provide better protection against the possibility of an arc, or a disconnected lead wire, shorting the battery pack. The circuit also has a thermal sensor to provide temperature regulation to prevent the possibility of overheating and consequent thermal runaway. On the downside, although this device also claims to function as a power bank, it does not do the job very well. As soon as you load it's circuit with a meaningful current, there is a significant voltage drop.
Summation: The OEM Handwarmer/Charger that is depicted here claims a capacity of 10,000 MAh, but falls well short of the mark. It is possible to modify the unit to achieve the capacity of 10,000 MAh and get reasonable results for heating your hands for up to 4 hours. This still does not make it recommended as a power bank. And as far as the other feature of this unit, the vibrator? Well, that is simply a very sad reflection on the mentality of the entity that brought this forward with the hopes that this feature would be a selling point. SWMBO remarked that if they had made a docking interface to place an electronic toothbrush head into it, at least then perhaps they could generate momentum for some optional consumable items as well.
Timeline:
00:05 the 21700 batteries
00:12 size comparison 18650 vs 21700
00:21 cut away diagram illustrating why the 21700 can achieve more power with minimal weight increase
00:36 why Tesla drove the transition to 21700 cells
00:47 more cars than Tesla using it: McLaren and the 2018 Lucid EV
01:05 current end user pricing for 21700 cells
01:52 overview of the 10,000 MAh handwarmer/powerbank
05:15 time lapse of modifications to handwamer in order to fit 21700 cells into it
05:45 preparing new batteries for spot welding
06:36 results of capacity test on original battery pack: 5400MAh
06:46 Time lapse of the spot welding process
07:09 thermal sensor shut-off function test
09:10 testing the power bank function
11:15 Coming soon: Preview, a look at a small handwarmer that surpasses 60C by using ceramic wire wound resistors, and uses an external power source such as a power bank.
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