750 Watt Human Powered Battery Charger

This instructable will follow the same design of my previous pedal generator, with a couple modifications, making it capable of charging a wide range of batteries, limited only by the strength and stamina of the the person pedaling the bike.

Supplies

Bike trainer

3 phase bridge rectifier

140kv motor

750w charge controller

Tools:

Metric hex key wrenches

Digital Calipers

Utility Knife

Optional but recommended:

Assembly

Follow my previous instructable, but replace the RC motor with a 140kv model.

In this build, I mounted a 35 AMP 3 phase bridge rectifier to the frame of the bike trainer, using the metal to metal contact to assist in cooling the rectifier.

From the rectifier, I ran a pair of 12 gauge wires to a project box that I mounted to the handlebars. I used velcro cable ties to secure the wire to the frame to keep it out of the way while pedaling. Inside the project box I cut a hole for the charge controller management console, and drilled a couple holes for wires to enter and exit. To cut the rectangle shaped hole, I put some masking tape on the box, measured and and drew the shape. I then used a utility knife to slowly trace the shape repeatedly, angling the blade over time to remove some of the plastic material. Once through the material, I whittled and sanded the hole for final fitting. There's probably an easier way to do this, but that's the approach I took.

Add the mount to the box, and affix to the handle bars. I soldered ring connectors on the ends of the wires to connect the in and out positive and negative inputs and outputs on the charge controller. For my setup, on the output wires, I added spade connectors to connect to a battery or battery bank. Use whatever connectors are appropriate for your use case.

Charging Batteries

First I tried charging a small 12v AGM battery. I found that the battery would only take less than one amp of power at 15 volts. I was supplying plenty of voltage and power from the motor, so I think the battery just self limits how much it will absorb.

Switching to a LiFePO4 battery worked much better. This battery has a peak input voltage of 14.6 volts and will take up to 10 amps. With that I was able to put over 140 watts into the battery.

Doubling the battery bank, with 2 LiFePO4 batteries, in theory, I would be able to put 29.2 volts x 10 amps = 292 watts in. In reality, it seemed I could only get to about 284 watts going into the battery bank. This is more than enough for me - in fact, I'm happier at 150 watts or so.

Stepping up the battery to the next size up 16Ah LiFePO4 would bump up the input current allowed to 16 amps (but controller is limited to 15 amps output), so with 2 of those, you should be able to get over 430 watts of resistance, for those looking for that level of a challenge.