owain
Post #1
Right. Imagine I was ripping out the standard blower and bits to stick in proper in-line 12v fans instead. This is all fine. However, when it comes to controlling the speed I'm not really sure what's best - back in t'day when I did my Electronics GCSE we only really dealt with low-current stuff, where you could use potentiometers and variable resistors to change the brightness/speed of a component.
However these fans draw about 3A, so nearly 50W of power - far more than you can push through a standard variable resistor.
So what can I do instead? Get a rotary switch and wire in a selection of big fat resistors or am I missing something obvious? All cars do this, so it can't be that expensive or difficult a thing to do. I'd keep the standard electrics but I want to pull all that stuff out and do it more neatly myself.
Can anyone with more knowledge of electronics lend me some ideas? Also I can't really remember how to calculate the resistances I'd need to run at two or three different speeds.
Anyone?
Ta people.
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Posted 31st Dec 2010 at 19:19
much easier and saves faffing about. 
) to generate a square pulse which can vary between say 10% and 100% duty cycle and use this output to drive them. Potentiometer adjusts the oscillator rate (so pot can be nice & low current), use a MOSFET transistor to do the heavy lifting/high current switching.
