# Sizing a Potentiometer



## Fat Bastard (19/2/14)

I've bought some M012 speed controllers for my pumps from http://www.kemo-electronic.de/en/Light-Sound/Effects/Modules/M012-Power-Control-110-240-V-AC-1200-VA.php on the advice of the pointy-heads at Jaycar. On the advice of the sparks at work, we replaced the stock 500k pots with nicer units. 
The problem I'm having is that the pump motor only starts 2/3 of the way through the range. It still varies the speed, but through a limited range. The pots are linear. Would swapping for a logaritmic, reverse logaritmic or larger or smaller pot help?

I know very little about wires n stuff.

Thanks in advance.

FB


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## Ducatiboy stu (20/2/14)

Try a 300k resistor in series with a 200k pot.


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## Fat Bastard (20/2/14)

Cheers Stu!

It was my thought to do that at first too, but then I thought if it's not starting until the resistance is down to halfway, why not use a pot with half the resistance?

And bugger me, it works. With a lamp anyway. Which it didn't with the 500k pot. The bright sparks at work confirmed it's ok to do this, so it looks like the controller is now all systems go!


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## law-of-ohms (20/2/14)

next time, get one of these....

http://www.stilldragon.com.au/diy-controller-kit/


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