Best way to power a 12V-2A load using 18650 Li-Ion batteries

Question

I would build a small present for my friend's child who has a 3D pen like this: 3D pen link

By now it only works with an AC-DC adaptor, so it always requires a wall plug. My idea is to build a battery pack to allow the use even when there's no AC plug.

Reading the "3D pen tech. details" I sketched some project requirements:

• voltage: 12V
• current: 2A (max I suppose)
• Li-Ion battery like 18650
• At least 3000mAh capacity
• Integrated IC for battery recharge and battery over-discharge protection
• Others IC to protect output and avoid overheating etc (if required)
• 3D printed custom case, so I'm not too dimension limited (smaller is better obviously).

My first idea was to use 4 18650 cells, to reach a voltage between 16.8V (full charged) and 13.6V. Then using a step-down board to level voltage to 12V.

Another solution will be using only 3 cells (12.6V - 10.2V) without any regulator, and using only a over-discharge IC. This solution is the simpler, but I have no idea if the pen would tolerate under/over voltage.

What do you suggest? There's any other solution to achieve that?

Answer 1

Buy a mini-UPS from eBay. They are cheap and some of them provide a 12VDC output as well as a 5VDC USB socket for emergency phone charging. They have internal Li-ion batteries.

Answer 2

Measure the actual current requirement of the pen, if you can, as the design may be simplified depending on it.

For a similar scenario (powering a WiFi router outside, far from any wall sockets), which also had the same power requirements on label (12V, 2A), I've used a powerbank + a step-up regulator board (which you can buy cheaply from Amazon/ebay, I used this one). However this relied on the case that the router didn't actually need 2A to operate, it needed much less - but this may be the case with the pen, too.