Simple Voltage Controlled Fan Switch

[Resqueline]

Yep, 120W on 12V is 10A. Thus you can use the internal relay, enhancing the current capability of the PCB by adding some thick stiff wire between the solder points.
There's not much to be improved about my circuit other than to build it and try it out in practice, seeing how easy it is to adjust, perhaps tweaking the adjustment ranges.
One of the challenges in making your own circuit is how to get it onto a circuit board. Layout & etching requires gear, whereas Veroboard is easier but more breakable.

 

[fatdaddy]

Hi.
I went with the Jaycar kit and have completed it.................I'm glad I went the kit route having done it, as a first time it was enough identifying the components from a bag that I knew they were all in to start with!

Anyway I have bench tested it as per in structions and have a reliable switch on point at 0.45 but I cant get the turn off point to below 0.64 (that is the limit of the travel on VR2).
Is there anything I can add/alter to alter the range, I would like it at 0.59.

Thanks

(FYI, the kit I have is lablled "revised" , but I think the only difference is that the moveable link is now just a wire link and the D3 diode is given alternative places to be mounted)

 

[Resqueline]

Ok, then the hysteresis is too large, and you'll just need to increase the value of VR2 or the resistor that is in series with it.
Their total resistance will need to be at least 36% higer than it's now (guesstimate).

 

[fatdaddy]

thanks, That did it.
(470k)

 

[Terrano93]

Where did you put the 470k res?

 

[fatdaddy]

in series with the standard resistor. I can check on the diagram if you need me to be more accurate but it will be a few days till I am able

 

[Terrano93]

in sereis with the 10k, or in series with the vr2

 

[Terrano93]

yep worked it out the 470k res in between vr2 & d3,
works a charm,
in need to very low therhold as i have 2 of these units to work together to give me 2 speed fans.
Thanks