How to charge your Xiaomi Mija M365 scooter from car or power bank.
Actually this is about making quick (as quick to build – not fast charging) car charger for you scooter, but there is nothing (except timeeeeee 😉 ) that forbids using it with QC/PD power banks or chargers – it will work, simply it will take ages to charge it.
It should also work for every other scooter (not just Xiaomi) – just check the required voltage and current.
Few bites of theory… task should (and IS!) very simple, we just need to bump voltage from 12V to 42V – right? Well, yes and not exactly. So this is true, we need to provide 42V for our BMS (battery management system) to charge battery, but since out car is “kind of” unlimited current source (from BMS point of view), we also have to limit the current. Otherwise the BMS will simply shut off with overcurrent charging protection.
Luckily we don’t have to do much, it’s enough just to find proper DC-DC step-up board with current limiter (CV/CC). I’ve found two of those , but you can use probably many others.
The red one is 400W and with some wider ranges, white one is 250W. Both will be ok, I’ve started with the red one. You should find it on Aliexpress for around 4-5$ each – I’ve provided direct links above, but I don’t know how long they stay valid.
Anyway, you will also need a M365 charge cable – you can try to do it on your own, or buy it for 2$. The problematic part is the plug – it’s (or at least I haven’t found) nothing standard. You should also get car lighter plug – but that’s trivial.
After screwing (not screwing up 😉 ) everything properly – just remember about polarity – grab your multimeter and connect converter (ONLY!) to car. Measure with voltmeter on output terminal voltage and screw upper blue potentiometer (it’s marked as CV) until you get required 42V. Kind of counter intuitive is that you gain voltage turning counter clockwise 🙂 – so be aware.
Now twist few times (let say 8), also counter clockwise current limiter (marked as CC) – so you will lower current a lot. Now connect ammeter on positive cable (you should also have it, for 5A or 10A in your multimeter) and connect scooter. It should start charging – if not it’s ok – perhaps current is too low. Screw clockwise CA potentiometer until you will get around 1.9A on your ammeter. And that’s it – you car charger for M365 is ready.
Just pack it up in some case and enjoy!
Since this converter will try to always keep the 42V output voltage, you can connect it to 19V laptop charger or PD power bank – it will convert it to 42V every time. The only problem can be too big current drawn and some (most) power banks will shut down itselfs – in this case you will have to lower current limit to somewhere around 1A or even less. But it will work!
I’ve prepared also crude, printable case for red board – look for it on Thingiverse.