converting always "hot" mig to "cold"?

Date 02-10-2004 10:43

Hi Matt,
I don't know anything about your particular machine, but that does sound like a safety concern. Is there a contactor that is stuck? My machine is another brand but I believe there is a contactor that energizes when the trigger is pulled to make the wire hot and to open the solenoid to deliver shielding gas. I had a couple machines here at work that were hot all the time and they had some bad parts that had to be replaced. There are a few welding machine mechanics that monitor this forum and I'm sure they will know what you need to do to fix your machine.
John Wright

By bumpp Date 02-11-2004 02:41

thanks for the quick reponse. but no, the unit is working fine, its just that it never had the feature. the schematic that came with it just shows the transformer, and a rectifier, and thats about it. :) cost was a BIG factor in my purchase decision, now i think it worth my while to add this feature. i just need to know what to add where.

thanks,
matt

By sparx

Date 02-11-2004 17:25

the cost to change this machine to electrode cold or contactor controlled output could easily be more than the machine is worth. the way to do this is to aquire a relay that uses the same voltage as the machine (115v or 230v) the trigger wires will be used to trigger the relay which in turn will be used to trigger a contactor( another expense- probably the bigges expense of this project) that is wired between the output side of the transformer and between it and the output to the welding torch on your machine. (i have obviously excluded a fair amount of information on exactly how to do this, but if you have a competent electrician or electronics guy at your disposal, he/she should be able to handle this)

By dee

Date 02-12-2004 22:32

sparx,
I'm curious as to why you're switching the secondary and not the primary side of the transformer. I have a feeling the electrical parameters of the primary side would permit use of a less expensive relay.

By sparx

Date 02-13-2004 17:28

I guess the reasoning behind my idea is based on the contactors in the suitcase type welders. LN-25 for example has a hot line coming from the welding machine (secondary side) and is triggered at the wire feeder. I am not sure if the transformer in these wire feeders will last if you are constantly switching them on and off. A transformer does need a short period of time to become fully energized. I am not an electrician but I do play around with all things mechanical, which is why I replied to the post. You might have something there though with switching the primary side being a less expensive way to do this.
as always, my 2 cents worth.

side note: I am Canadian so maybe my 2 cents worth isn't actually worth 2 cents....probably more like 1- 1/2 cents in U.S. currency :)