Honda FL250 Odyssey Lighting Coil Mod For Charging Battery

The Odyssey that we worked on had the Goki Electric Starting kit added, probably many years previously. Electric starters need a battery, and the FL250 had nothing setup to charge the battery needed for powering the electric starter...so we had to figure out how to add that.

 

The Odyssey 250 is actually an AC system, including an AC ignition coil and AC lighting. Since the original did not have a battery, there was no need to convert any of that energy to DC. Unfortunately, this also led the engineers to save some wire and use the frame as the 2nd leg of the AC circuit. But....that single-wire AC made it quite tricky to make a charging system for the battery setup. 

Scouring internet forums and consulting various Honda wiring diagrams, we decided that the best solution for good charging of the battery is to use the lighting coil as the charging circuit, but the coil needs to be modified so it has 2 wires instead of only the existing single wire AC.  That way, the power from the lighting coil can be run through a voltage rectifier and converted into DC for the battery.

This shows where the original lighting coil winding was attached to the magneto plate. Remove this screw and cut off the copper wire from the terminal beneath.

This is the copper wire that is the end of the lighting coil winding, ready to be soldered to a wire and run out of the engine case. Remember to use heat shrink or another insulator to prevent the wire from touching anything else in the case.

Here you can see the wire soldered and wrapped with heatshrink so that it is no longer in continuity with any metal from the engine. This way it can be run, with the other existing lighting coil wire, into a 4-wire DC voltage rectifier (2 AC wires in, a power and ground DC out). We used one from a Honda CB350 and got a charging voltage of 13.7-13.8v, enough to recharge the battery after using the electric start.

Here you see the modified coil on the magneto plate, about to be bolted back into the engine. The lighting coil is the copper colored coil, the other large coil is for the igntion and the small coil is the pickup for the electronic ignition. 

One other thing to keep in mind: we kept the original AC taillight, so that the taillight is on when the Odyssey is running and turns off with the engine (since there is no keyswitch), To do this, simply make a 3-way connection in the wiring from the lighting coil and have one branch go to the light and the other to the rectifier. Hope this helps, good luck!