Charging an Electric Scooter with 12V


I bought an electric scooter, pretty happy with it, it's good to go shopping and carry laundry.

I used it a lot when on my sailboat, now that I found some foldable bikes around 200-300€ I think a foldable bike that doesn't need charging would have been better. But back then I thought an electric bike was 600-3000€ and takes up more space. The space thing is still quite applicable, the charging though that was our topic for today.

Ok so let's begin with what I have, a electric scooter charger rated on the label 220-240V, 2A input with 42V, 1.7A output. 

Remembering physics basic that would put it to around 480W consumption for around 80W output, not sure what the 400W became in that process, heat/magnets ? Did I miss something?

Anyways, what I have on board is a 400W (peak 800W inverter) so when I tried to plug in the charger the LED overpower turned RED and then the power when out, after I insisted for a couple of minutes...

So... My socket is protected with a nice dashboard fuse, just press the button and it's done.

The inverter was protected with a 3A fuse, 3A*12V equals 36W so I was not going to reach that power peak consumption. I tried with a 3.75 slow blow that I had on board and it blew again, now I have a 15A fuse so 15A*12V makes for 180W, that was the most they had in the store. But since I could feel the wires getting hot, instead of going through my box of fuses I just made the above and below calculations...

So my inverter (400W) could power the charger but not for sustained high consumption (480W), at 400W the inverter might need 400W/12V = 40A, 40A is a lot for me. I'm ignoring the inverter efficiency here.

So it got me thinking and that's the current situation :


(Figure 1)

Now that's a lot of power conversions.

This would be better


(Figure 2)

Turns out the formula for the step up converter is :

Iout = Iin *(Vin/Vout)*(1/efficiency)

Which should be equivalent to

Iin = Iout Vout *Efficiciency / Vin

Iin = 1.7 * 42 * .9 / 12 = 5.4A

So compared with my original 40A that's a 10X reduction, is that right ? Only experience can tell me, and I'm still trying to resist buying yet another gadget.

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Kirby 3 months ago

Wonderful views on that!

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Everettsheni 3 months ago

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