Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Hood on April 17, 2007, 06:42:23 PM
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A bit off topic ::)
Just wondering if anyone could tell me if an oil cooled welder could be used as a power supply for my servos. I have an Oxford 140Amp Oil cooled welder that I never use, it has a 50V and 80V output terminals, I am needing 50V so that would just be perfect. However there must be somthing different in a welder compared to a normal transformer as the current is selectable on a welder.
Anyone have thoughts on this?
Hood
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You sure are thinking Hood. Better be careful, might see some smoke from your head. :D I think it should work. Put your meter across the terminals and adjust until you get 50vdc. Then set you meter on ac and that will give you an idea of the ripple it is going to have. Not sure but it sounds like a good thing to test.
Brett
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No chance of that, thats why I have no hair, its a form of air cooling ;)
Not sure I follow what you are saying , mind you theres nothing unusual in that as its quite hard to follow a rednecks train of thought :D
The welder is AC and I will need to rectify it. The outputs are 80V and 50V both AC, the adjustment is for amperage.
Hood
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Hood, If you can get the voltage you need and it is clean, it should work I would think. As long as you have enough amps. Their is no such thing as a power supply being too big unless it makes your power meter spin off of the wall or is supplying too much voltage. If you can get the right voltage and enough or more amps, I think it will work.
Brett
Edit,
I meant to say, you should be fluent in Red Neck by now.
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Well these things weld at 140Amps all day long so that wont be a problem, I am just worried that it cant be like a normal transformer as the voltage varies as you go between different tappings on a transformer.
Will eat my porridge tomorrow and go fetch it from the old workshop and see what its like, well I know what its like, its green and its flippin' heavy ;)
Hood
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I would check it with a scope just to be sure its clean DC. Otherwise I think it should work.
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Thanks, the DC should be OK once I rectify/smooth it but will make sure I check before I hook things up to it, dont want to let any more magic smoke out :D
Hood
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Once rectified and smoothed, the AC voltage of 50 Volts will become 70 Volts DC.
This is caused by the full wave rectification. I assume you know this ?
You multiply the AC voltage by 1.4 to establish the DC voltage.
EDIT : When AC voltage is measured, because it has waves with peaks, the peaks are not measured, but an average is measured. (RMS) (Root Means Squared) one you are converting both sine waves to one side and you then smooth between the peaks, the average Voltage becomes a constant voltage. Hence a little higher than AC
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I did this a few years ago and always look for an excuse to replublish old works :-[
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Ha ha, thanks Benny, yes I did know but it does no harm to post it.
I am looking for 80v dc so 55V ac would be better for me but 50 will have to do :) My mains is about 440 across phases so I might get nearer the 80V that I am seeking.
Hood
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Hey Benny, think the guy that wound that transfomer was on the *********x ;)
Hood
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I can see why you say that, because the winding are not around the core, however its based on the transformer symbol http://www.kpsec.freeuk.com/powersup.htm#transformer
Or are you commenting on my limited freehand skills.
BTW, we used to have a brand of beer here called *********x ( 4 EX) is that what you meant ?
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Yes Benny, you have got me right on both counts, just looked like you had been sipping a bit too much of the castlemain(sp?) when you drew the windings, no offence was meant.
Hood
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Oh forgot to say I got the transformer hooked up today, with the 440 instead of the 415 across the phases I am getting 54V ac which once rectified and smoothed is giving me 80V dc no load and putting a bulb accross it drops it to 78v which is perfect. Only thing I am wondering is whether it will drop further with a bigger load, time will tell.
Put the scope on it and and there doesnt seem to be any ripple whatsoever so it should be ok. BTW sorry for poor quality pics, my phones camera isnt very good but for £6.50 I cant complain :D
Hood
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An AC arc welding transformer is designed to give a reasonably constant current at any particular setting. If the arc length is varied, the volts go up or down to control the current. The set is said to have a drooping characteristic (oo-er!). So the output is not regulated, unlike a close coupled power supply transformer, where a good design will hold the voltage within about 10% for any current drawn within its rating. Rectifying and adding capacitance will smooth the output but if the load drawn is varied the voltage will also vary. If your load current is reasonably constant you should be OK. It will be very interesting to see the results of your experiment. I am not an electronics expert but did sell welding equipment a long time ago.
Good luck!
Ian
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Thanks Ian, knew it was too good to be true. I would think the volts required will vary quite a bit as it is the voltage that gives the speed of the servo. Oh well, will give it a go and see but looks like it wont work too well :(
Hood