It is a cheap 20 Amp motor speed controller that goes from zero to full power, might be good as Ralph suggests for heater fan use (and much cheaper than the normal 3 speed switch and resistor set-up) or even infinitely variable windscreen wipers
CovKid wrote: have complete control (any speed you desire) for under £4:
http://www.ebay.co.uk/itm/Universal-DC1 ... 2ed90035b7" onclick="window.open(this.href);return false;
Then I found a very cheap circuit that could be used as a device to provide optimum charging voltage to a leisure battery. It takes your system voltage and can boost it to a preset level, say 14.5 Volts for a modern type leisure battery. It's only 10 Amps, but I bet there are heavier duty ones available. Ebay link to DC voltage booster
Then there is this Car Temperature / Thermometer / Clock / Voltage / Meter thingy, like this one I bought
It is rubbish This is my review on Amazon :-
Having now had this fitted for a few months I find my review less than complimentary, but it was cheap !!!!
The Voltmeter on mine reads about .8 of a Volt low
The outside temp sensor reads all over the place. I suspect this is due to moisture on the unsealed contacts in the sensor (I might try and seal it).
The "icy road" alarm is a damn nuisance as you cannot turn it off. Even worse when I had the unit wired permanently on, it woke me up at 4am one night! (it's in my VW camper van)
The "icy road" alarm actually stopped working recently. Good news or bad? At least it won't pee me off on a long journey at minus temps outside.
The clock re-sets itself to 12:00 whenever the inside of the van gets very cold (most nights recently)
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So what is your best, or worst van "gadget" purchase?