'L' Question pwm Fan control

[randolph57]

I m just finishing off fitting a new blower motor after original partially seized and randomly blew fuses. I decided to go with the PWM upgrade (thanks Cov Kid )
I was going to use the original 12v supply to the switch as the ignition conrolled supply to the controller (red/black wire) but it is only 1.5mm and seems to be at the limit of the potential 20 amps the motor can draw.
VW in there wisdom increased the wire size (2.5) after the original 3 speed switch on the wires to resistor banks and also the yellow wire direct to the blower so basically will I be ok with the original red/black wire or should I access the 'snake pit' behind the fuse box to find another 'switched' 12 v supply?

Thanks
Chris

[CovKid]

I found the original wire was fine. It only really becomes a problem with an old motor. With a new one, the surge draw is much reduced - it is more incremental. However, if you really want to beef up the cable, use a test meter and checkout which fuse is live in fusebox with ignition on and piggyback on the reverse of that with a suitable inline fuse. Worth noting ofcourse, that with PWM there is no sudden surge due to the way PWM works. This is not true of resistors, and the reason why PWM is a better solution.

Mind you, PWM no good for wipers - unless you want incredibly slow ones

Eventually I'm going to bump into someone at a show with a rollered camper, kawasaki silencer, PWM blower, and beefed up main cables.....

[randolph57]

Original red/black it is! Thanks for the speedy reply.......Now to get the dash back in

[CovKid]

For anyone reading this that has no idea what we're on about, see: http://wiki.club8090.co.uk/index.php/VW ... ol_Upgrade" onclick="window.open(this.href);return false;

[ash1293]

While Ive got dash out and sorting a load of other things I thought I'd go down the same route. Been out this morning as just found my PWM in the recyling bin - thank you postie for not leaving a card - and had a little play with it.

While it powers fan as expected I was a little surprised to find there is still a measurable 12v output even when turned to its minimum. Not enough to power fan but enough to register on a multi meter. Do you think this is something to be concerned about, enough to add a separate on/off switch or just leave it powered by ingnition fed live?

[tonytech]

The "measureable 12v" is probably a very short pulse (a few milliseconds every 200milliseconds or so) digital meters dont measure pulsed voltages or currents very well.
Personally I wouldnt worry too much, I rarely drove my van with the fan off.

I have a PWM module controlling a motor for a Physics demonstration.
I swapped the variable resistor out for on with a built in switch (like the old style radio volume knob)
I used the switch to operate a relay in the main supply (but after the switch)
T

[CovKid]

Seconded, the output is virtually nothing at minimum. That said, ideally the fan controller should be devoid of power with ignition off. Alternatively, if the PWM unit has an LED (some do) - you could extend this to show near control knob if you wanted to. I had intended to do just that with mine but as its off when ignition is off, I didn't bother. By then I'd moved on to more exciting projects.