Another Portable Charger Build

I am building a portable charger for my onewheel, but the same principle could be used for any PEV. I will be making a 3D printed enclosure for the whole thing, will post it here also if anyone is interested.
List of parts below. Need to start the CAD work this week, then I could mount everything and start wiring. Going to use a 10s battery that I have laying around. It already has a charge/discharge BMS. I will put an anti-spark XT90 on the output. Does anyone think I need to put one on the input as well? Plan was to plug in the battery first, then the onewheel second. Might need someone to double check everything before I plug it in.


Made some progress this weekend. Did some CAD work and 3D printing. With a bit of file work, all the components fit. Looks like there will be plenty of room for when I start to wire this up. Might make version 2 with a smaller enclosure later on.


Made a little bit of progress today. I don’t trust those screw type connectors, so I took them off. Going to just solder everything on. Hoping for more progress this week.


Did about a third of the soldering today. Went super slow and triple checked everything, then once again before plugging in the battery. Plugged in the battery and did not let any magic white smoke out. Just got the input volt meter working and soldered the anti-spark xt90 to the board. Also found some hardware that works.


Got all the wiring done. Only thing left now to is wire up the connector to the onewheel. Then set the output voltage and amps. I will upload the enclosure STL if anyone is interested.


You’re scaring me testing it with those semi exposed ends my dude :eyes:


No need to fear. Those where just some extra wires laying around under the towel. Thanks for looking out though.


Can anyone confirm the wiring in the image below? I am getting pin 1 as negative and pins 2 & 3 are positive. Do I need to connect both 2 and 3 to positive? This is for a onrwheel xr.

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@mariocontino would possibly know

Thanks, just watched @mariocontino video on youtube and it confirmed the pins.


This is awesome! I love the output meter, what’s the max input voltage on in? I was planning on building another one of these since my first one kinda sucked.

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Very cool project! I love these little magic boxes :slight_smile:
Compliments on your wire routing as well. It takes deliberate care to get things the right length and affixed correctly. You even have service loops! You obviously have some experience.

Can you explain what the function of the large (ground bus?) bar is on the left side?

Hopefully the two button head screws through the lid are not live

Thank you. The bus on the left is what the current runs through for the amp/volt meter. The two screws out the top are not technically live. They are both negative. But you are right, I should just cover them.

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Current shunt for the wattmeter.

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OK, finally got all the soldering and wiring done. Triple-double checked the polarity. Plan now is to plug everything in and start charging. Setting the correct voltage is easy. But for the current, my plan is to turn the pot to min current while charging, then turn it up slowly while reading the meter.

Question. For our typical battery chargers, the charger either stops charging or trickles once it gets to the desired voltage. With this set-up, I would have to manually stop the charge, correct?

Since the battery I am using has a charge and discharge BMS, I dont need to set the shut-off voltage, correct?

This is the XR wiring (Pin 1 negative and Pins 2 & 3 positive):

This is the current pot:


You’re using a power supply as a charger versus using a dedicated charger that has the extra “smarts” added in to monitor the charging current and stop charging when the current has dropped down to a certain level (indicating that the pack has been “topped off”).

Your power supply will continue to charge your pack indefinitely, which is bad for the cells in the pack. If your pack is well balanced you could probably stop the charging about an hour after it reaches your set charge voltage.

Check the cell balance occasionally and leave the supply on for a few hours if additional balancing is needed. Or, you can sometimes tell the BMS to balance even if not charging.

If everything is set up correctly, that is true. You would get a almost-full charge by just having the BMS cut off when the pack rose to the right voltage. I recommend setting the charger to the correct voltage though anyway.

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Thanks for the information. Have you setup one of these boost converters before? Still kind of confused about setting the voltage cutoff. But I assume most times these units are used with a power supply. In these cases the voltage is constant. In my case as the onewheel charges, the charger battery voltage will start to drop. I still want it to charge when the battery voltage is dropping. I am using a 10s to charge this, so 42 volts. I still want it to charge all the way down to 32 volts. I think the cutoff on this when set correctly will cut off near 42 volts. But I could be wrong.

Fully charged up my 10s and set the output voltage to 63 volts. Now the scary part, need to plug it into the onewheel to set the current.

Matches my onboard volt meter.


Input voltage: 10-60v
Output voltage: 12-83v

Sorry, I do not know how to adjust the input low voltage cutoff for that boost converter. I don’t even know if it has that feature or not.