3 phase mig help.

[bleach]

3 phase mig help and one more Q on a tool(a mill).

i bin finding 220 3 phase welders for very cheap lately. so what makes it 3 phase and can i get it to nom 220 30amp power? or is this a very dumb Q??

(i'am asking this cause i have bin finding that the new welder is not doing what i would like it to.)

just to give you guy an idea i can get a 140-250 amp for 500-800 or i can get 250 amp 3 phase for 300-500.


thanks again guy's this web site has bin very useful.

 

[shenion]

Think of single-phase welder like a single piston compressor. The valves let air flow only one way the same way as a rectifier converts AC to DC. This single-piston compressor produces a pulse of air on each cycle.

Consider a 3-phase welder like a 3-piston compressor; each piston 120 degrees apart from the others. As one piston is going down, another is coming near the top of its stroke. So when the 3 "rectified" outputs are connected together it becomes almost a constant flow.

3P welders produce a smoother arc, also for a given output, there is less current on the input side as it is split between the 3 wires.

Look at one wire on 3P and compare it to the other two. One will be ahead in phase by 120 degrees and the other behind by 120 degrees. Compare that to single phase where the two wires are always 180 degrees out of phase.

There is no way to generate 3 phase from single phase simply and efficiently. For welders the only option is use a 3-phase motor with a static phase converter (produces a low-current 3rd phase to start the motor), this is called a rotary converter. The motor acts like a motor and generator. You end up running a 10+ HP motor all the time. Figure the kilowatts used by the welder and you will need a motor of about 1 and 1/3 (i.e 12KW welder needs 16HP motor).

You can modify a 3P welder to run on single phase. I Have run two different ones here for testing. They worked OK; one better than the other. It depends on how the input and output sides of the main transformer are wired. Also, the reactor (smooths weld current) is set for the 3P near constant DC from the rectifier. When used on single phase, it will not work as well as there is now huge ripple (100%) in the power.

Some welders can be used by just using two of the lines and leaving the 3 phase unconnected. You will get 2/3 the rated power of the welder. Others need the third phase disconnected internally and bypassed.

You need to have the schematic of the welder, understand wye and delta configurations, be able to calculate voltages/currents and do the right connections without burning things up.

 

[bleach]

so your saying it's a pain in the **** and maybe not worth it to save some money. thank you for that very easy to under stand post. funny i own a 3-piston gas powered air compressor. it all so look like you have it do the same thing i do in computers.


well i have one more Q on tools i saw a cool looking deal on a nice old looking mill but it has no motor do you guy's think it would be a good buy?(other than the ad saying it has no motor i got no more info for you.)

there is some thing i like to do. i was going to get a milling table put it on a nice old drill press and maybe change the motor out. and it would cost me as much for that stuff as i would for the mill.

thanks for all the help.

 

[oddball90]

Best bet is get a single phase welder then. In the UK it is the same 3 phase welders can be got for silly money £25 to £250 secondhand, but a good make 180 amp single phase can go to nearly it's new price £250 to £400.

 

[bleach]

^ thank guy's. it silly that 3ph is cheap and 1ph is not.

also if you guy's don't mind someone is trying to sell me an cheap mig welder it a bluepoint MB135 has any one heared about this one? (maybe i should make a diff tread for my Q but i dislike doing that.)

any thoughts on the mill?

thank you for all the help this site is great.

 

[shenion]

Never heard of Bluepoint, probably rebadged. Someone here may recognize it.

You should be able to get a motor for the mill. You will need to know the RPM, horsepower and shaft size.

 

[bleach]

^thank you for the very fast reply.

cool so the mill look good from the pix. well i have bin takling to the the guy who owns it he going to give me the motor spec.

well i look at the mig and it looks ok, i have looked on-line and found that it's snap-on tools or century welder and on the back it's says this:

but the web site say it has a 100% D C @ 135 amps???!?

 

[shenion]

Looks like 85A max. Would be good for body work.

How much does he want for it?