How To: Motorcycle Cell Phone Charger

(Send me the photos and I’ll get them put in here, don’t know why it won’t let you, but wanted to get this up at least since it is such a cool mod)

I’ve been overcome by the desire to contribute, so here goes. This is how I built cell phone chargers for everyone’s bikes during the Epic Trek II. First, you need to buy one of these:

Image Here.

That is a Hobbywing 3A-UBEC. It’s a BEC (Battery Eliminator Circuit) made for RC cars, but it’ll work just fine as a voltage regulator for a cell phone charger. You could use any BEC with a 5V output, but this one is cheap and readily available. Just Duck it, you can buy them almost anywhere. Before you begin, I recommend reading all the instructions, so you don’t screw up and complain to me. Here are the tools you will need.

Soldering Iron


Heat shrink tube – various sizes

wire cutter / strippers

wire – 20-22 AWG

1 3-ft cell phone charging cable. This may be standard micro USB or Apple style, whichever one fits your phone.

multimeter (optional)


Now for the Instructions:

Step 1: Cut off this thing here. There’s only one of them so you can’t get confused. Remember,  the wires wrapped through the green donut are the output. If you’re using some other BEC without the green donut, mark your wires so you don’t get confused.

Image Here

Step 2: Cut off the USB end of your charging cable. Cut it so the wire attached to the plug that goes into your phone is longer than you think you need it to be.

Step 3: Now strip off a few inches of the sheath and isolate the power and ground wires. Like this:

Ground ( – negative) = Black

5V ( + positive) = Red

If you’re really confused right now because you don’t have red or black, that’s because you’re color blind, but I can help:

Orange = Red = 5V (+ positive)

White = Black = Ground ( – negative)

The remaining wires are data and shielding. Cut them off. You don’t need them.

Step 4: Slip some shrink tube over the wires before you connect them. I’d recommend putting a fat piece over both wires and skinny pieces over each individual wire. Splice the wires together like this. Connect the positive 5V wire to the red output of the BEC and the negative ground wire to the black output.

Step 5: Once you’re sure you have the wires connected properly, solder them. Wait for the solder to cool and slide the shrink wrap over the solder joints and shrink it.

Step 6: Now you need to connect wires to the input of the BEC, so figure out how long those wires need to be. Keep in mind that the positive wire needs to reach the positive terminal of your battery, but the negative wire only needs to reach a ground point anywhere on the chassis. They need not be the same length.

Prepare your shrink tube. Solder the positive wire onto the red input wire of the BEC. That’s the one not wrapped through the green donut. Solder the negative wire to the black input on the BEC. Shrink the tube over them.

Step 7: There’s one last thing you need to do before connecting the completed charger to the bike. If you’re using the Hobbywing 3A-UBEC, it has a jumper to switch between 5V and 6V modes. Make sure the jumper is set to 5 volts, and put a big piece of shrink tube over it to prevent tampering. Your cell phone battery is most likely a single cell Lipo with max charge of about 4.7 volts. Putting the Hobbywing in 6 volt mode would risk overcharging the battery and setting your phone on fire. Presumably, the phone’s internal charging circuitry is designed to prevent this, but I’m sure you don’t want to find out the hard way that it isn’t.

Image Here – finished product

Now that you’re done, turn off your soldering iron. You might want to connect a voltage source up to the inputs and check the output with a multimeter to make sure everything works. Or just wire it to your bike and plug it into your phone and see if it charges. Read the useful notes below. They aren’t absolutely necessary to complete the task of building the charger, but they’re… well,  useful.


Useful Notes:

Make sure your battery and ground connections are tight. If they shake loose, the charger will obviously not work.

If you’re going to leave your bike unattended for a long time, disconnect the BEC from the battery. It will slowly drain and kill your battery. For the same reason, don’t leave your cell phone charging when the bike is not running.

I built this for a Honda CT 110. As far as I know the CT 110 doesn’t charge the battery at idle rpm, so you have to rev the engine or keep moving to avoid draining your battery.

Your cell phone battery is much lower capacity than your bike battery so 10-15 minutes of charging while the bike is off is probably harmless, depending on the health of your battery.

It’s generally not a good idea to connect the charger to your alternator circuit. The voltage outputs there are high enough they could damage the BEC. Connecting on the battery-side of the bike’s voltage regulator is the best idea.

Three guys used this thing for more than 1000 miles of riding each. It works.


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