A odd one, low amp cooling of a welder.

[.RC.]

I have a bit of an odd one here and am looking for ideas.

I have an old generator with auto idle.   I have an older mains powered transformer mig welder (no microprocessor anywhere in it).   What I would like to do is make the generator go to auto idle when the mig welder is not welding.

I can get the engine/generator to auto idle by simply disconnecting the cooling fan.  The welder has a 240V cooling fan that runs all the time on it.

The welder has a small transformer on it that outputs 24V, 36V and 110V all AC.  I have connected a 24V computer fan to it via a bridge rectifier and it will run and the engine will auto idle  as the computer fan must draw so little current of course they slow down when the engine is at idle.

The welder also has a thermal cutout mounted on the welder diode rectifier so if the diodes get too hot it should cut power to the wire feeder.

My plan was to connect two computer fans via a bridge rectifier to cool the welder rectifier diodes.  Also add a 70 degree?? thermal switch to the welder rectifier connected to the main fan, so should it get that hot the main fan would cut in.

Can you run three 12V fans in series off a rectified and smoothed 24V AC supply (so you get around 34VDC.)

Anyone have any other ideas?

[Phil1977]

It´s definitely better to use a small DC DC from the smoothed transformer output.

Computer fans are usually brushless, that means they have a lot of logic between their DC input and their motor windings. These drivers want stable input voltage, and if you put them in series this is not stable at all.

Beside that it seems perfect to just use a thermostat for the main fan. So the generator stays only active if the welder got hot - and in this case it´s probably also good for the generator to run a few minutes longer.

[.RC.]

Thanks, I did try a buck converter, but the generator saw that as a load and would not idle down.

My other idea was install some computer fans, but power them by a power tool battery.

[Phil1977]

Did you try to underpower the fans by reducing the output voltage of the buck converter? Did you use a buck with low idle power?

You could also charge some supercaps while welding and feed the fans with them.