Electrical Question for EL Tech Guys

I just recently finished my DIY TIG cooler. It came out real well. I'll be posting pics once I get back from a road trip. The question I have has to do with the capacity of the circuit feeding the gas solenoid on the 250 EX. I was thinking that it would be nice to have the cooler set up so that it comes on automatically anytime the torch is on. The easiest way I can see to do that is to control power to a 110V receptacle using a relay and have the cooler plugged in to it. There are fairly inexpensive industrial grade relays that will handle a 25A inductive load @ 110V (my cooler draws 7A @ 110V). The one I'm looking at only needs 10mA, 220V to trigger it. I was thinking it would be easy enough to tap into the wires going to the gas solenoid and use that to trigger the relay, that way, I'd have water flow anytime there was gas flow. Normally, I wouldn't sweat drawing an additional 10mA from a circuit, but the wires going to the gas solenoid are pretty small - they look to be around 22 or 24 gage. So, woulld anyone know if that circuit could handle an additional 10mA? Has anyone tried this?
-RP

Isn't there outlet on back of welder for a water cooler. Seems to you would want cooler running when welder is turned on rather than off and on with gas. Just my 2 cents.

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Originally Posted by RP62

I just recently finished my DIY TIG cooler. It came out real well. I'll be posting pics once I get back from a road trip. The question I have has to do with the capacity of the circuit feeding the gas solenoid on the 250 EX. I was thinking that it would be nice to have the cooler set up so that it comes on automatically anytime the torch is on. The easiest way I can see to do that is to control power to a 110V receptacle using a relay and have the cooler plugged in to it. There are fairly inexpensive industrial grade relays that will handle a 25A inductive load @ 110V (my cooler draws 7A @ 110V). The one I'm looking at only needs 10mA, 220V to trigger it. I was thinking it would be easy enough to tap into the wires going to the gas solenoid and use that to trigger the relay, that way, I'd have water flow anytime there was gas flow. Normally, I wouldn't sweat drawing an additional 10mA from a circuit, but the wires going to the gas solenoid are pretty small - they look to be around 22 or 24 gage. So, woulld anyone know if that circuit could handle an additional 10mA? Has anyone tried this?
-RP

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I agree, the coolers and fans do not have to be running all day, sucking up power and making noise during idle times. I would throw a delay on break timer in the loop to get rid of residual heat.

Edit, I don't know the voltage to the solenoid, but I'm sure you could put a SSR in parallel, they draw almost nothing.

Yeah, but then if a ten cent part breaks, you're gonna toast your torch.. or do they boil over first, like all our cars used to? :O

I don't think the solenoid is 220V. I'll have to double check the exact requirement tomorrow.

To all the comments:
Why not plug it in to the back of the welder - The receptacle on the back of the welder is 220, my cooler is 110 and I though it was overkill to keep it running the whole time.

Use delay before break relay - I had considered that but there's really no residual heat so far (although I've been welding thin steel so the highest amps I've gone to so far is 125). So far the head of the torch stays cool to the touch and I never saw a temp increase on the coolant temp. If I decide to go that route, I'd probably build the relay driver circuit myself as I've done several similar circuits.

Use a SSR - I don't have experience with them, but was under the impression that they weren't designed for inductive loads and would slowly burn up in this application.

Trigger with a transistor - thats an option I hadn't considered. I may go that route if the verdict is that it won't handle the extra 10 mA. I'm really trying to keep it as simple as possible.

Thanks much guys, I appreciate all the comments.
-RP

How about an additional switch/relay, on the torch or wherever, and keep it independent of the rest of the unit?

I would be shocked if it didn't have plenty of excess capacity; on my LX225 the solenoid is triggered by a relay that's got a 5A contact rating. IIRC (memory) it runs 115VAC to the solenoid, which makes other solutions a little more complicated.

The post flow should take care of the residual heat I would think?

(Some SSRs will have inductive spike protection in them. If not and you want to use one, simply add a MOV (varistor) or back-to-back zeners across it's "contacts" for protection. SSRs would be pretty useless if they couldn't drive inductive loads.)