Dual voltage machines-NEMA confusion

[Owen]

It's been a while since I was here last.

I have a new plasma cutter which advertises "120/240V auto sensing dual voltage". That's fine and dandy but theres no way (that I know of) to use 120 or 240V off the single plug...aside from splicing in a 120V cord. Or having some sort of physical conversion box (6-50 to 5-15...actually 5-20).

For home use, it'll stay in the 6-65 250V receptacle, but if a friend wants to borrow it...Using Nema10-30 is not an option for me.

Any one ever splice in something like this?
Owen

 

[Stuart in MN]

Do you have a make and model number? With that we could maybe find the owner's manual online and figure out what they're doing.

 

[bluesman2a]

Why can't you run it off the same plug? Both use the same three wires. Both have a ground. Only difference is that for 220 you swap the neutral for another hot leg.

I had a Miller Spectrum 375, same deal. Just build a 1-2 foot adapter pigtail. Appropriate plug for your plasma on one side (female) and appropriate plug for the wall on the other (male). When you're done, just unplug the adapter pigtail. I mean is there something simple here that I'm missing in your setup? If not seems pretty straighforward to me.

It only takes about $10-15 in parts depending on what you have laying around. Works fine. After a while of carrying th thing around to different friends' places, I had a collection of pigtails. Now with my new 80 Amp unit, there's only one plug and it doesn't travel.

 

[Owen]

Do you have a make and model number? With that we could maybe find the owner's manual online and figure out what they're doing.

It's a Thermadyne Cutmaster 38. The plug it came with is a 5-20.

I was wondering how the auto voltage thing worked. I was actually expecting to see the unit with two pigtails when I opened the box!
Thanks,
Owen

 

[Owen]

Why can't you run it off the same plug? Both use the same three wires. Both have a ground. Only difference is that for 220 you swap the neutral for another hot leg.

I had a Miller Spectrum 375, same deal. Just build a 1-2 foot adapter pigtail. Appropriate plug for your plasma on one side (female) and appropriate plug for the wall on the other (male). When you're done, just unplug the adapter pigtail. I mean is there something simple here that I'm missing in your setup? If not seems pretty straighforward to me.

It only takes about $10-15 in parts depending on what you have laying around. Works fine. After a while of carrying th thing around to different friends' places, I had a collection of pigtails. Now with my new 80 Amp unit, there's only one plug and it doesn't travel.

I didn't know I could do that! So I just build pigtails for whatever receptacle I want? Any suggestions on wire sizes, etc.?

Thanks guys

 

[the intimidator]

I would just watch out for a old dryer at the side of the road 2 minutes and you have a couple feet of heavy wire with a male plug on one end if you don't need that then cut it off and attach whatever male female plugs you need at most this would be 10$ and 15 minutes of you're time

 

[Tscott]

All you need to do is make pig tail addapters, When I set up my stick welder (it didn't come with anything on the pig tail) I put on a 220vac male twist lock plug and then made up a longer chord that had a female 220vac twist lock recepticle and on the other end I put a standard dryer plug head so I could run off the dryer curcuit in my old house. I kept the amps low on the welder to keep from tripping out the 30Amp breaker.

As for how the unit tells what coltage it is operating on, thats a bit more difficult to figure out. In my stick welder I just hook it to 120VAC instead of 220VAC. The transformer does not know the difference it will still bump up the voltage the same ratio (i.e. voltage X the ratio of turns on the primary to turns on the secondary) ( for a more in depth anexpalnation google how transformers work). So I get about half the power out of the stick or stinger, the transformers in most welders of this type are about as tough as a concrete block so there isn't much you can do to hurt them aside from applying to much voltage and arcing through the insulation.

All plasma cutters use solid state electronics to bump the voltages way up, these boards are probalby equiped with a current sensing device of some kind that can differentiate between 120vac and 220vac.


Hope this helps

Tom

 

[bluesman2a]

I didn't know I could do that! So I just build pigtails for whatever receptacle I want? Any suggestions on wire sizes, etc.?

Yep, that's all you do... No problems. For wire, for the effective length of the pigtail, you won't need to consider it much. I would probably not do anything less than a 10 or 8 just on general principle.

As for how it understands the voltage, my Miller had a switch inset inside a grate inside the machine, check your manual for something similar. If there is not one, then it's autosensing which is not unreasonable.

 

[Stuart in MN]

The owner's manual is available online here:
http://www.thermadyne.com/uplFiles/litLibrary/thermaldynamics/0_2888.pdf

It does say the plasma torch automatically senses the input voltage, no switching required.

The power connection requirements are on page 18:

INSTALLATION 3-2 Manual 0-2888
3.3 Primary Input Power Connections
CAUTION Check your power source for correct voltage before plugging in or connecting the unit. The primary power source, fuse, and any extension cords used must conform to local electrical code and the recommended circuit protection and wiring requirements as specified in Section 2.

Power Cord and Plug
This power supply includes an input power cord and plug suitable for 120 VAC, 20 Amp, Single - Phase input power. For 208 / 230 VAC input power, replace the supplied power plug. Use only an approved replacement input power plug with ground. Replace the plug as follows:
1. Cut the original cord close to the plug.
2. Strip back the outer cord cover as needed to connect the inner conductors to the replacement plug.
3. Connect conductors to the plug contacts according to the plug manufacturer's instructions. All three conductors must be connected to the plug.

Connect the input power cord as follows:
1. Check the power source for correct voltage before plugging in the unit.
2. Connect the input power cable (or close the main disconnect switch) to supply power to the system.

Could you put in a 120vac 20 amp receptacle at your place? Then you wouldn't have to mess with the cord. As you mentioned it does have a 20 amp plug so you (or your friend) have to have the correct receptacle.

Otherwise, I suppose you could cut the cord off and make a couple pigtails. I'd suggest using a twistlock connector so no one can accidentally plug it in to the wrong type of receptacle.

 

[PAToyota]

Hmmm... Seeing those machines I just always assumed that they furnished adapters... If you have 220V available, there is no way I'd downgrade it to 120V. I just feel a bit weird hacking the plug off of things like that...

 

[Owen]

Yes, I already knew it was auto sensing which I mentioned in the second sentence of my post. Exactly how it's done, I'm not sure.

Anyway, I went and got some connectors and appliance cord and made up a pigtail to connect the 110V plug to my 220V receptacle. This way I'm not limiting myself to just 110V or 220V (although I'll have to make another pigtail for the 110V, we don't have any receptacles like that in our house). Or...I'll just let whomever borrows it make the pigtail!

Thanks guys! Machine is working beautifully and sliced through 1/2" steel tonite no problemo.

 

[bluesman2a]

although I'll have to make another pigtail for the 110V, we don't have any receptacles like that in our house

All that plug is, is a 20 amp 110 outlet. If you have a place you commonly use it at home (i.e. garage) you can replace your standard wall receptacle for about $5-7 each. Something I did, when I made my extension cord for the shop, I put a 2 gang (quad) metal box with a strain relief on it. In the box I put the 20 amp outlets, so my extension cord serves as the "adapter" and I can still use normal drills, grinders and such.

 

[Owen]

Nah, I'll just have someone else make it!

I had all the 110V parts in my basket at Home Depot but thought, "i don't need this stuff..." so I put it all back.