The fan control modification I have detailed to the left served me well for a long time... but, one problem I found a nuisance was the need to switch the fan off again when you switched the bike off. What I mean is, each time I would get home, I would have to flip the fan override switch off again, otherwise the fan would be on the next time I started the bike... no big deal, just a nuisance for a very lazy person! :-) With the introduction of the tank top control panel mod, I took this opportunity to create an electronic fan control mod. This meant replacing the toggle switch with two momentary switches, one for on and one for off. The circuit is designed such that when the ignition is turned off (power is interrupted) then the fan circuit will also switch off. This is achieved with an SCR, or Silicon Controlled Rectifier. An SCR is basically a simple "switch", where once the switch is turned on then power continues to flow until the power is interrupted. Once power is returned, the SCR must be triggered again to go "on". The current fan control circuit is shown below:

The "ON" switch can really be any switch you want. I used a small industrial tactile key switch (similar to the ones used on a computer keyboard) on mine. The switch only has to conduct the signal power to the SCR to switch it on, it does not have to conduct the current that is supplying the fan itself. In the circuit above the switch can only conduct a maximum of 0.01 amps due to the 1.2kilo-ohm resistor. This would be further reduced due to the resistance of the fan itself.

The "OFF" switch however must conduct the full fan current, and as such should be of a reasonable rating. I used a 3A momentary double-pole double throw (DPDT) switch with the contacts wired in parallel (effectively making a 6A switch). I have never had any problems with this arrangement, and while I have never measured the resistance of the fan I would suspect a single 3A contact would have sufficed.

The SCR could be any of very many, the BT151 was simply readily available when I built the circuit. Any with a reasonable rating would do.

@ Sean Flanagan, 2004. All rights reserved.