Handwarmers S04E09: Chinese Electronic Handwarmers, making them effective, making them safe!
Channel: Mountain Parameters
Date: 30/01/2020

There is an appeal to the thought of a heat source you can put in your pocket that does not need oxygen, does not need stinky fuel, does not need to have the catalyst replaced in the burner, and does not require that you go to a website run by an impecunious senior with poor people skills to get your replacement parts. Of course the Chinese have thought the same thoughts, but in the true spirit of value added dynamics, have even built one with a built-in vibrator. For the first time in years, when I casually mentioned this to SWMBO, she seemed to develop an apparent interest in my vocation as a Handwarmer Influencer, and ordered me to source one and do a video on it. Of course, I obeyed, because like Lord Varys, I am nothing if I am not obsequious (and without scruple). Perhaps we'll look at supercharging that one with a 21700 cell in a future video.

The one in this video lacks the vibrator, but as evidenced in Big Clive's previously referenced tear down of the vibrator version of this handwarmer, is very similar. However Big Clive noticed a few deficiencies, so, to be truthful, I thought I could also jump on the Bandwagon and, for emphasis, flag them as well. 

In the resultant video I try to make it appear as though other people's ideas are mine, take a rather sketchy Chinese electronic handwarmer, and demonstrate how to use your DIY skillset to make it into something you might actually want to use (as long as you do not place it near you testicles).

Timeline:
02:30 Start of teardown of handwarmer: view of the PCB and removing the native sub-par 18650 cells
03:00 Start of capacity test of native cells @ 2A load
03:45 Test results, MAh of cells: 1000MAh per cell (not 5,000 as claimed)
04:10 Notes on deficiencies of internal wiring
04:30 Image of the heating pad these use
05:00 Questioning the suitability of the wire guage to handle the current
06:40 Fast forwarding through the process of hot glueing and spot welding the cells with nickel strips (never solder onto the terminals of Li-Ion batteries, you MUST spot weld).
07:30 Soldering the mains onto the Nickel strips
08:00 Capacity test of the new Panny battery pack: load of 2 amps, low voltage cut-off 3V
08:25 Results of test with new battery pack installed. 3 hours to reach low voltage shut off, with capacity of 6100 MAh @ 2A load. Verified, 3 times more run time for this handwarmer by replacing better cells and wire guage.
08:40 Installing the new battery pack into the handwarmer case.
08:55 Will the operating temp of 60C damage the Li-Ion cells? Apparently not, as illustrated by this chart from "The Battery University".
09:25 Preview of upcoming video: If Chairman Mao did not issue Zippo's to the Red Army, which handwarmer did they use? Secrets of the Red Book will be revealed.

Conclusion: There is no free lunch. Batteries do not store as much energy as you may think (an average candy bar has 10 to the 6th power of Joules equivalent, whereas a AA battery has ten to the 3rd). If you want temps as high as 165F that will last for 12 hours or more, then there is no alternative to a liquid fuel handwarmer. If you just need something for a couple of hours for a quick bike ride, XC-Ski, and you are happy with a device that cannot sustain heat above 135F for long, then an electronic device may have it's place (you'll recall in a previous video we looked at how a flashlight in your pocket that can draw 3 amps will get as hot as an electronic handwarmer). But perhaps not with the batteries and wiring they send them from China with, be prepared to spend some coin on decent Li_ion cells, and make some of your own modifications.

Resources referenced in this video:
Big Clive measuring amp draw of unit:
https://youtu.be/o7IvYsPYiFA?t=514

Wire gauge current ratings:
https://www.engineeringtoolbox.com/wire-gauges-d_419.html 

Safe discharge temperature for Li-Ion batteries:
https://batteryuniversity.com/learn/article/charging_at_high_and_low_temperatures  

Join the discussion on handwarmers at:
https://handwarmers.forumotion.com/