On-demand fan for Syncrowave 350?

There are temperature switches that you can buy that would let you do what you want, easily.

I would also look into replacing the fan with something a little quieter.

I had a Dialarc 250HF that had this problem. The Syncrowave 250 that I replaced it with has the fans on demand and it is most excellent!

You probably want to watch heatsink temperature for the SCR's and the transformer iron temperature. I looked at the docs for my Syncrowave 250 and it shows the two main fans controlled from a relay driven off the main board. It does not show what controls the relay.

If I was going to thermostatically control the fans myself, I would probably try about 50 C for the switch on point for the fans. Higher would probably be safe, but it seems like the main thing you want is to have the fans off when you are just sitting and setting up or thinking about whats next. As Iggy mentioned, you can get fixed temperature thermo switches cheaply enough. That would be a simple (maybe too simple) approach.

BobH

In my own experience, on these big machines with fan on demand, the fan barely ever comes up during "normal" welding of 130 amps or so. I remember that when welding a trailer with stick, it came up maybe twice. Out of abundance of caution, I would use 40 C switches. As BobH said, fans and SCR heatsink are excellent locations for thermostat switches. You probably need a relay and have the switches wired in parallel.

You may be able to get a quieter fan, not all fans are created equal.

Thanks, Bob and Iggy; you guys got me pointed in the right direction. I was not aware that 250's had on-demand fans. So I went to my archive of Miller tech manuals and pulled out the one for the 250. Turns out that early 250's (1995 and older) have the same set up as my

350; an overtemp thermoswitch that shuts down the welder when the transformer windings hit 125 deg C.

Starting in 1996, Miller added two more thermoswitches; one on the SCR heatsink (50 deg C) and one on the transformer (80 Deg C). These are normally closed at lower temps, wired in series with the 24VAC power to a normally closed relay that switches the fan. At lower temps, the switches are closed, which opens up the fan relay. If either the SCR or Transformer switch hits its temp and opens, this allows the fan relay to close, powering on the fan.

I looked up the price for the two switches as Miller replacement parts, one is about 10 bucks, the other 20 bucks. However, I can get

50 and 80 degree C thermoswitches from Newark for under 5 bucks each. Since I need to buy a 24VAC relay anyway, I probably will just order the whole set from Newark.

Thanks again, Jeff

Make sure to get thermal paste, for good contact between thermoswitches and heatsink or transformer. I would use a lower threshold switch on the transformer, but it is just me.