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Three Speed Electric Fans

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After a wander round the scrappy in the sunshine today I bagged a twin fan setup from an Audi that is a perfect fit for my radiator. It had a pressed ali resistor pack attached to it so I pulled that too, on getting it home it turns out to be a resistor pack that offers three fans speeds.

So, given a standard X-Eng fan switch, which has two temperature switch points, can anyone see a useful/practical/simple way of using the full three speeds?

I'm not sure I can be bothered with making a three-level adjustable fan switch sensed from the coolant but it may come to that, if only for the bling value :lol:

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Freelander td4's have three speed fans but there controlled from the ECU I think but surly DH can coble somthing together.

Saw his truck down at stunning yesterday, Mike did a very nice job ot the Ibex's roof.

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John, are the resistor values arranged such that it would form a digital to analog converter (resistor ladder)?

If so, your thee speeds actually give you 8 combinations.

You could put a little keyboard on the dash and play tunes on your fan - think how you could impress the girls with that!

Apart from that, can't see the point myself - I'd just go with single speed.


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Simon, no they're in series so you have:


So if you apply 12v to the "slow" point it passes though two resistors, the "MED" point only one and for full speed you connect directly to the fan. I suppose using Ian's twin fan wiring you could get another three speeds but that may be overkill :unsure:

If I wanted to play tunes I'd use F/V converter and PWM drive, got some big power darlingtons here (ESR6065) begging to be used for something silly :rolleyes:

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I see what they're doing and it would be easy to implement with MegaSquirt, you just steal the PWM drive for the idle valve and add a power transistor to the end. Or you could do the same with a 555 timer for about 50p:


Obviously you may need to beef up Q1 a little :unsure:

If I ever get round to putting in the electric water pump I may well do something like that, if the MS can't do it all on-board by that stage...

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