Mobile Power Supply / Jump Starter

I had to charge my motorcycle in a garage, where usually there are no working electrical outlets.

I also had an old motorcycle battery, still usable for less demanding purposes than always reliably starting an engine. Also I had a DC/DC step-up converter amongst my electronic gadgets.

The idea: Let's build a mobile power supply/jump starter. It don't have to be strong enough to start a bike, but it can give a refreshing shot of charge to a little or moderately depleted battery.

• An old, used motorcycle battery (not strong enough to always start the engine, but still good for less demanding purposes)
• A DC/DC boost/step-up converter
• Main switch
• 3-way push button for switching Voltmeter input
• Volt- and Ammeter
• L-shaped metals from a furniture accessories shop (also used for shelves)
• 10x15 cm 3 mm thick MDF sheet (any wooden or plastic sheet is good - but don't use conductive material for this!)
• M3 and M4 screws, nuts and washers
• A terminal block for output cables

I've used L-shaped metal parts from a furniture accessories store to join the battery and the front panel.

I also use them as the major GND and VCC rails.

First I've drilled up the 4 mm holes on the L-shaped metals to fit for the M5 screws of the battery terminals. (Leave the rest of the holes at 4 mm.)

Then fastened the metals to the battery, then marked the holes for the M4 screws on the MDF sheet.

Note: In my case the distance of the terminals is 12 cm, and the total width of the battery and thus the width of the needed MDF sheet is 15 cm.

Placing the components required some experimenting. Suggest to place them and play around, then mark the positions with a pencil. Pay attention on required clearance of components on both sides, also the clearance for the battery itself.

I've cutted the wooden plate with a Dremel and a mini cutting blade. Note that MDF is surprisingly tough, so use a stronger Dremel.

Let's mark the position of the DC/DC and the output terminal block and drill the 3 mm holes.

Connect battery negative terminal to GND of the DC/DC, the Voltmeter and the black wire of the Ammeter. Connect the red wire of the Ammeter to the output terminal block. (Yeah, I know it would be better having black there.)

Connect battery positive terminal to the main switch. Connect the other terminal of the switch to the Vin of the DC/DC with a thick cable, to the red wire of the Voltmeter and to the NO (normally open) terminal of the push button with a thin cable.

Connect Vout of the DC/DC to the output terminal with a thick cable and to the NC (normally closed) terminal of the push button. Connect the COM terminal of the button to the yellow (probe) cable of the Voltmeter.

Almost all cable connections are done with screw terminals, so it's pretty easy to wire it up.

If you've connected all cables to screw terminals, only 2 things remained:

Terminals of the 3-way push button require some soldering, and ring tongue terminals require crimping.

Once, everything is connected, tighten all screws and ready to go!

If you need to charge the battery of your mobile power supply, simply grab the L-shaped metal profile with the clips of the charger. These are directly fastened to the battery terminals, and pretty easy to reach.