Using A Welding Machine As A Power Supply?

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Hi all, I am working on a science project where I've got a load with very low resistance (more or less a short circuit) and I need a continuous DC current of around 30a. I'm trying to avoid using resistors because I don't want so much heat dissipation. As I understand it, a welding machine is capable of limiting current with minimal energy wasted as heat.So I was wondering if an electric welder power supply would be able to function as a power supply for about 3 hours at a time? I won't need more than 50 amps continuous. The voltage can be fixed and the circuit doesn't require high voltage or amperage precision.I'm not particularly familiar with welding power supplies, so my main concern is that by allowing the machine to function as the sole current limiter in the circuit, it would overheat, because normally when welding I assume that the electrical arc is a source of resistance, which would lighten the resistive load on the machine.So far it seems I will need100% duty @ 30aDC110-120V standard input Thank you for your input!
Reply:I use mine all the time for anodizing larger parts. Works great.
Reply:Try one of the Harbor Freight #91110 "toaster" welders.  Cheap enough on sale.  If it doesn't work or burns up, take it back.http://www.harborfreight.com/welding...der-91110.html"USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:I can't remember the welder model number, but Omnimax theater projectors use a pair of Miller 300 amp DC welders to drive the projector lamp. A DC welder should be a good choice for your project if you size it correctly for the load. Too big isn't a problem. Just don't go with a welder that is just barely rated for the current that you need. If the welder will never be used for anything else after your project a Harbor Freight welder will probably be adequate. If you think you may want to re-sell it or learn welding afterward, then get something better. If it's going into a science fair you will also need to be careful about your project's power requirements as most shows are not prepared to supply more than about 5 amps per exhibit at 120 volts.  Make sure that they can supply what you will need.CharleyMiller MM252Miller Bobcat 225NTMiller DialArc HF / DIY Cooler2 Victor O/A TorchsetsMilwaukee 8" Metal SawMilwaukee Dry Cut "Chop" Saw 5 Ton Wallace Gantry Various Grinders, Benders, etc.
Reply:Keep in mind that when you have zero resistance across the welding terminals that the amps out will probably be higher than what the setting on the dial says. You will want to verify your amps with a DC ammeter.
Reply:Originally Posted by OldendumTry one of the Harbor Freight #91110 "toaster" welders.  Cheap enough on sale.  If it doesn't work or burns up, take it back.http://www.harborfreight.com/welding...der-91110.html
Reply:Most most welders today do not like to be short circuited.  Remember most have a duty cycle and most have thermal overload protection.  I have used engne drives to thaw frozen pipe but never an electric welder.
Reply:Contact the different welding manufactures sales reps. is your area. you might be able to borrow a demo machine for your project. Go to welding supply stores and ask for help in contacting them.Tell the store what you are up to and they may even help. You will never know unless you ask.If you have access to transformers and large diodes and the right test equipment. It may be possible to build a simple power supply out of borrowed parts. Welders and diodes and transformers can get pricy for school projects.One more thought, ask around your extended family, neighbors, Clubs, church for help.You might get lucky. Be careful with electricity and don't get shocked.
Reply:Just what is your load resistance?  A welder may not like it as they are designed to put out a current at a voltage high enough to sustain an arc."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Originally Posted by OldendumTry one of the Harbor Freight #91110 "toaster" welders.  Cheap enough on sale.  If it doesn't work or burns up, take it back.http://www.harborfreight.com/welding...der-91110.html
Reply:Load resistance is basically 0 ohms, or too low to measure with my multimeter. The entire circuit is just copper wire and a small segment of lead, and I'll be measuring temperature changes. High current is actually better, so 40a @ 100% duty isn't a problem.http://www.millerwelds.com/resources.../glossary.htmlI looked around some more and it turns out CC welders all have a maximum short circuit current (Under "Constant Current (CC) Welding Machine"). I'll probably have to ask the manufacturers to get that info.
Reply:Originally Posted by shortfuseThe lowest setting on the dial on the HF 91110 is 40 amps.
Reply:Originally Posted by weldbayI have used engne drives to thaw frozen pipe but never an electric welder.
Reply:Most of the older Lincoln and Hobart styles had a 75 amp setting where you could thaw frozen pipes. Remember limited input welders were originally for the Farm market and local handyman.Not everyone had one in his garage.As far as the science project, I have an older battery charger with a timer, no electronics in it, just brute charging power.This could be an option also?
Reply:If you are really looking at 30a at >.5 ohms of resistance,you are looking at a fraction of a volt across the circuit.A welder would work,but you would need to drop about 15v across a resistance of some sort.The resistance would need to be adjustable. The small 120a welders seem to have about a 450w output at a 100% duty cycle.
Reply:One guy rewired the secondary of a microwave transformer for high current output, then used a Variac on the input for control."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Originally Posted by OldendumOne guy rewired the secondary of a microwave transformer for high current output, then used a Variac on the input for control.