Work05GlidePower
USB-C charging for electric scooters.
01 · Problem
I rode an electric scooter to school. Its charger was heavy and bulky, and I was already carrying the charger for my Mac. Leave the scooter charger at home and I was stuck; carry both and my bag was half chargers.
Then I looked at what the scooter actually draws while charging: 60 to 120 W. My laptop charger does 100 W over USB-C. The phone, the watch and the headphones already charge from it. Why not the scooter?
02 · Idea
USB-C Power Delivery can hand over 20 V, but the scooter’s pack charges at 42 V. So the box does two things: a small trigger board negotiates 20 V from whatever USB-C charger is plugged in, and a step-up converter turns that into 42 V for the scooter’s charge port.
Around those two boards: filtering capacitors, because the converter switches at high frequency and the scooter’s battery management system deserves clean power, and fuses on both sides.
On paper: a power bank with a barrel jack would also work.
MineI didn’t want another thing to charge. The point was one charger for everything, and USB-C PD already carries the power. All the box has to do is change the voltage.
On paper: a purpose-built 42 V supply would be neater.
MineOff-the-shelf boards let me test the idea in a week. The smaller step-up module turned out to work as well as the big one; it just runs hotter, which is a cooling problem, not an electronics problem.
03 · Build
Bench first: converter set to the right voltage, multimeter on the output, a 100 W Apple charger and then a 65 W one. Both worked. Then a box for it, drawn to fit the two boards and their heatsinks, printed in PETG on the Ender 3 at home, with the name cut into the side.
04 · What broke
First test, I dialled the converter to 48 V, because that’s the nominal voltage of the pack, and plugged it into the scooter. It pulled 96 W and kept pulling. Nothing caught fire, and I’m still glad about that. Then I read the label on the original charger: 42 V. Reset it, and the current sat at 1.7 A and never went above it. The battery was already at 95%, which helped.
Two smaller ones. A 1000 µF capacitor on the output stopped the PD trigger from starting at all, because the inrush to charge it looked like a short; the fix is a resistor and a diode to limit that first surge. And the 65 W charger refused to start once the box was assembled, which the 100 W one didn’t.
05 · Result
The scooter charges from the same USB-C charger as the laptop. The heavy brick stayed at home.
06 · Today
Cooling. The converter needs a fan running the whole time, and the plan was a heat pipe from inside the box to a passive heatsink on the outside, so the enclosure stays sealed. And I’d never set an output voltage from memory again. Read the label first.
I also wanted to open-source it and make a video. I moved to India before either happened.