Hello,
I asked this question some time ago, and it's still "awaiting moderation". This comment might also get lost, but I wanted to share with the group what I ended up building.
I used (4) 2n2222 diodes to make a full wave rectifier, directly connected to my AC source (the headlight circuit on the bike). I then had DC. I sent the output of that to a relay. I used a 220 ohm current limiting resistor at the input of a board mount relay to provide the closure. I now had a dry closure when the engine was running, and I could rev the engine all the way up and the diodes not get hot. I fried a few until I got to the 220 ohm resistor. It was more or less trial and error. It was kind of a messy way to do it, but the calculations are part of what I was looking for help with. Anyway, I then needed a 5Vdc source to charge my GPS, and I butchered a cigarette lighter charger and strapped that thing to the board. I wired the input of that to the battery (using a 5A fuse), sending the + side through my newly built relay secondary contacts. The output of that powers the cigarette lighter charger circuit, and the output of that is now the 5Vdc I need to run my GPS. I sealed it up, and velcro'd it to the inside of my headlight housing. I've had it out on 3 rides so far, and it works like a charm.
I asked this question some time ago, and it's still "awaiting moderation". This comment might also get lost, but I wanted to share with the group what I ended up building.
I used (4) 2n2222 diodes to make a full wave rectifier, directly connected to my AC source (the headlight circuit on the bike). I then had DC. I sent the output of that to a relay. I used a 220 ohm current limiting resistor at the input of a board mount relay to provide the closure. I now had a dry closure when the engine was running, and I could rev the engine all the way up and the diodes not get hot. I fried a few until I got to the 220 ohm resistor. It was more or less trial and error. It was kind of a messy way to do it, but the calculations are part of what I was looking for help with. Anyway, I then needed a 5Vdc source to charge my GPS, and I butchered a cigarette lighter charger and strapped that thing to the board. I wired the input of that to the battery (using a 5A fuse), sending the + side through my newly built relay secondary contacts. The output of that powers the cigarette lighter charger circuit, and the output of that is now the 5Vdc I need to run my GPS. I sealed it up, and velcro'd it to the inside of my headlight housing. I've had it out on 3 rides so far, and it works like a charm.
