Not aware of anything that turns off when the ignition switch is on but you can do what you want by adding a diode in series with the solar cell. That's a one-way valve for electricity that will allow current to flow from the solar cell to the battery any time. You do not have to disconnect the solar cell just because the engine is running but system voltage does go up a little from 12.6 volts to as high as 14.75 volts. If that 14.75 volts is higher than what the solar cell produces, the diode will prevent current from flowing backward through it.
If you really want the solar cell to be disconnected when the ignition switch is on, you can use a relay. When the ignition switch and relay are off, you use the "normally closed" (NC) contact to connect the solar cell to the battery. Turning the ignition switch and relay on makes that contact go "open circuit" which disconnects it. I can draw you a diagram if you want to do it that way. Relays like that are real common and you can find them in lots of cars in the salvage yard. I used a lot of Chrysler relays for my radio display at old car show swap meets. The relay must have 5 terminals. Those are more common than those with only the four terminals that are always needed.
Please consider a to help us answer more questions.
Thursday, November 15th, 2012 AT 2:55 AM