Disposable e-cigarette Teardown - Part 2

I seem to be inadvertently gaining a new hobby. A short cycle ride last week yielded 3 more 'disposable' e-cigs.

DANGER: 

There is a really good chance that the battery is still holding quite a lot of energy. The fluid runs out first. So if, during disassembly, the unit triggers (quite likely), then a big current will flow and the heating element will get hot. Similarly any accidental short between the leads to the battery could easily cause a fire.

Cut the leads to the element (one at a time) and to the battery (again one at a time) as soon as you can access them. 

Also have a contingency plan such as fire blanket (not a bucket of water) or open window through which the flaming device can safely be thrown in the event of it catching fire.

If in any doubt that you can do this safely, then don't do it.

This time, two ENG Legends and a more substantial R and M Tornado. The latter had a USB-C connector and although I couldn't see a way to refill it with fluid, looked like a reusable model. This turned up some interesting clues, as you will see later.

First, the ENG model. This is very similar to the models I took apart in my previous post.

Again, it's much the same arrangement with a thing looking for all the world like an electret mic insert switching the battery to the heating element. It has a nice useable 5.5Wh battery -- again without any protection PCB.

The insides of the R and M Tornado are altogether much more interesting. 

Not only does this board have a little PCB holding a LiPo charging circuit and USB-C socket, but also the PCB is nicely designed and silkscreen labels for the parts and terminals. A second PCB for the heating element has what I assume to be a SOT-23 MOSFET. The heater PCB receives power from the battery and a control signal from the first PCB,

This PCB has the USB socket and LiPo charging on one side.

The other side has a microphone that supplies the control signal to turn the heating element on.

This PCB is a handy little charging circuit. There is no obligation to use the 'puff sensing' feature. With the addition of a switch and a CREE LED bulb, you could make a great little USB torch. Maybe something for the next blog post.