Help - trying to rewire welder for 208v instead of 240v

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Well, I moved my ancient Silver Beauty 90175 Mig Welder to my new shop and have not been able to figure out how to switch it over for 208 volt service.  The data plate says 208/240v and I've never had any trouble with it before.  At my house I have 240v service, but since my shop has 3 phase the nominal voltage is 208.  When I tried to weld at the shop I'm not getting enough juice to pull the power contactor in.  Instead it just buzzes and the wire feeds slowly.  I have a manual for the welder, but there is nothing in it about switching the voltage over.  There are no schematics inside the welder anywhere, and the lower amp transformer that has all the heat setting taps is not marked either.  There are 4 posts on the input side of the transformer numbered 43 - 46 and 43 and 44 are currently used.  Any ideas on how to test the resistance in these coild and make a good guess at which ones to use for 208v?  I don't care to burn anything up just guessing at it!Thank you,Jason
Reply:I bet your welder is single phase only and will not play with three phase.  I think (but could be wrong) that the 208-240 is all single phase ratings.  If this is true, there is a bright side...now you can grab one of those cheap 3p mig units of ebay or some other equip auction and have a heck of a welder.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Well, I am not trying to hook it up to all three phases.  It should be fine running it off 2 of the three legs - as long as I can get it set for 208 instead of 240.I really do need to find a nice wire feeder to go with my XMT-304 CC/CV power supply.  This welder I am trying to get to work right now has a pitiful duty cycle, and I end up pulling the cover off and sticking a fan on it most of the time in the summer.  That gets to duty cycle up to just bad from pitiful.  But, it's all I have right now and I got work I need to do...Thanks,Jason
Reply:I wonder if there is any inexpensive way to transform the power a bit.Last edited by smithboy; 04-18-2006 at 09:24 AM.Smithboy...if it ain't broke, you ain't tryin'.
Reply:Ok, I pulled all the wires on the input side of the transformer and checked the resistance between the terminals that were being used.  I then found a pair that had the closest resistance (was about 5 ohms less if I remember right) and tried them.  Welds fine now...  Plus, I wrote down both combinations with a sharpie on the inside of the cover...
Reply:If I remember correctly (and I may not), the difference between the 208 & 240 has to do with the generator that supplies it, rather than the device that is powered.  That difference being whether the generator is a Y-type or Delta-type generator.  There is a difference in the angles of the windings, which gives a corresponding voltage difference.  I BELIEVE that a device rated 208/240 will work on either.I'm not an electrician, but I used to work for a company that sold gensets.  I've slept since then.
Reply:That electrical stuff still gets me every time.  Sometimes I think I know something...other times I KNOW I don't.  I thought that 240 and 208 were completely different animals (1 and 3 phase).  Well, they are in a sense...but, when you are only using two legs off the three phase, the voltage difference between the two systems comes from the angles between phases 180 vs 120.  You still have two hots just like single/split phase.  I read that before, but just now understood a bit more about it.  Panozeng, I appreciate the question...I got more from it than you did, I bet.Smithboy...if it ain't broke, you ain't tryin'.
Reply:On most equipment of that type that are designed for 208 and/or 230 volts you are doing a couple of simple things by changing straps or moving to different lugs but both equal out to setting the range that the machine is expected to run on and permform the best. The more PCB (control board) dependant the machine the more critical this can be. With a machine set for 230/240 something as low as 212 might be looked at as low voltage by the machine and things can happen if it gets run on an extended basis. I'm talking about more gismos than welders here and it does make a big difference where the control boards (if any) derive their input power, off the main source through and to their own power supply or off the machines transformer, things like that. But the crux is you are setting the ground rules for the input voltage and what happens after that. I just barely stmble through with this kinda stuff so take everything with a grain of salt. I'm sure there are better ways to explain it. Awright can probably teach a class on it. Maybe he'll jump in here later. You are lucky to have a piece of equipment that is strappable. I've known of rectifier/chargers that got cooked because no-one realized that there were such things as straps and also assumed that 220 was "220".