240V electrical question
#11
  
I'm not in a position to do this at the moment but I am curious.  My access to shop space is usually limited, especially when it comes to electricity.  So right now all my tools are 120V.

If I ever got a 240V tool (possibly a thickness planer) could I power it using a regular wall plug and a small gas generator together.

Here's my reason for wondering if this would work. I know that a 240V plug is two 120V hot lines, one negative line, and a ground.  Could I wire a plug to take a hot from the wall outlet, a hot from the gas generator, and either the negative back to the wall or splice it where the negative goes to the wall and the generator?  While finally having the ground go to the wall outlet?

I know that this isn't up to code.  I was thinking that if this was safe then It is fairly easy to run two extension cords to a box or plug.  Plug in the two lines, one to the 120V wall socket and one to the 120V running gas generator.  When done unplug everything and put the cords away.

I know that this is probably a long shot but I just wanted to ask.

Thanks
Peter

My "day job"
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#12
  Re: 240V electrical question by Peter Tremblay (I'm not in a positio...)
That won't work for a slew of reasons, I'm afraid.  

BUT, if you have two circuits in your work space or can get to a second with an extension cord, and if they are on opposite poles in the panel, and if they are both not on a GFCI, then you will have 240V between the two hots.  

I once designed a combiner to do that safely, then found that one is already being sold commercially, so I never took it any further.  It's not something you want to build, as it takes three relays to prove each 120V leg, then prove that they're 240V between them (it's that, or it's 0V between them), then join them if all is right. 

You can also make your own, without relays, but that's a bit like making a suicide cord for a generator, and not something I would detail on an open forum.
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#13
  Re: RE: 240V electrical question by TDKPE (That won't work for ...)
(03-04-2021, 12:28 PM)TDKPE Wrote: That won't work for a slew of reasons, I'm afraid.  

BUT, if you have two circuits in your work space or can get to a second with an extension cord, and if they are on opposite poles in the panel, and if they are both not on a GFCI, then you will have 240V between the two hots.  

I once designed a combiner to do that safely, then found that one is already being sold commercially, so I never took it any further.  It's not something you want to build, as it takes three relays to prove each 120V leg, then prove that they're 240V between them (it's that, or it's 0V between them), then join them if all is right. 

You can also make your own, without relays, but that's a bit like making a suicide cord for a generator, and not something I would detail on an open forum.

One of the slew of issues is keeping the frequency in sync as the generator will vary a little in frequency plus having the sine wave in sync.  At the very least the plainer may let the smoke out.  Anything you rig up is libel to cost more than running a few wires from the panel.   Roly
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#14
  Re: RE: 240V electrical question by TDKPE (That won't work for ...)
(03-04-2021, 12:28 PM)TDKPE Wrote: That won't work for a slew of reasons, I'm afraid.  

BUT, if you have two circuits in your work space or can get to a second with an extension cord, and if they are on opposite poles in the panel, and if they are both not on a GFCI, then you will have 240V between the two hots.  

I once designed a combiner to do that safely, then found that one is already being sold commercially, so I never took it any further.  It's not something you want to build, as it takes three relays to prove each 120V leg, then prove that they're 240V between them (it's that, or it's 0V between them), then join them if all is right. 

You can also make your own, without relays, but that's a bit like making a suicide cord for a generator, and not something I would detail on an open forum.

Thanks Tom,

If I could get to two outlets on different breakers would that count for different poles?
Peter

My "day job"
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#15
  Re: RE: 240V electrical question by Roly ([quote='TDKPE' pid='...)
(03-04-2021, 12:41 PM)Roly Wrote: One of the slew of issues is keeping the frequency in sync as the generator will vary a little in frequency plus having the sine wave in sync.  At the very least the plainer may let the smoke out.  Anything you rig up is libel to cost more than running a few wires from the panel.   Roly

I thought that that would be an issue but I don't know enough about it to be certain.
Peter

My "day job"
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#16
  Re: 240V electrical question by Peter Tremblay (I'm not in a positio...)
Don't most genertors include a 240v circuit? If not, you could limit the search for a generator to one with appropriately sized 240v. Might as well run the full 240 from a generator as long as you're burning fuel.
earl
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#17
  Re: RE: 240V electrical question by greenacres2 (Don't most genertors...)
(03-04-2021, 01:45 PM)greenacres2 Wrote: Don't most genertors include a 240v circuit?  If not, you could limit the search for a generator to one with appropriately sized 240v.  Might as well run the full 240 from a generator as long as you're burning fuel.
earl

I thought only the big ones did but I'll certainly double check.
Peter

My "day job"
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#18
  Re: 240V electrical question by Peter Tremblay (I'm not in a positio...)
Many motors are wired to use 120 or 240. The machine will work the same on either voltage. the 120 volt will use twice the amperage as the 240. The only draw back is many motors will draw more than 20 amps on the 120 voltage.
Treat others as you want to be treated.

“ You only live once, but if you do it right, once is enough.” — Mae West.
20 year cancer survivor
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#19
  Re: RE: 240V electrical question by Peter Tremblay ([quote='TDKPE' pid='...)
(03-04-2021, 01:35 PM)Peter Tremblay Wrote: Thanks Tom,

If I could get to two outlets on different breakers would that count for different poles?

If you have access to the panel, and if there are empty spaces, and if it's remotely close to your work area, adding a 240V receptacle is quick and easy and the safest way to do this.  A long extension cord to your machine is preferable to trying to combine two circuits into one.  

As to a generator, for the record, my 4kW running, 6kW starting Generac portable won't start my 3 hp Unisaw which takes 70-80A at 240V to start.  The magnetic motor control drops out due to low voltage as soon as the main contactor closes, since the voltage drop is huge and well beyond what the generator can produce.  Even if it didn't drop out, it would take a theoretical 18kVA to start it at line voltage, and will a grossly reduced voltage, I doubt the motor could develop the torque to overcome even the bearing and belt friction.
Tom

“This place smells like that odd combo of flop sweat, hopelessness, aaaand feet.”







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#20
  Re: RE: 240V electrical question by lift mechanic (Many motors are wire...)
(03-04-2021, 02:11 PM)lift mechanic Wrote: Many motors are wired to use 120 or 240. The machine will work the same on either voltage. the 120 volt will use twice the amperage as the 240. The only draw back is many motors will draw more than 20 amps on the 120 voltage.

Yeah, my 2 HP bandsaw has that option.

But the thickness planer that I'm tempted by is a 3 HP 15" and I don't believe those have the option to switch to a 120V

I did see a used 15" grizzly with a 3 HP motor and thought that I might swap out the motor for a 2 HP one that can run on 120V  But that's would be a fair bit of work and not inexpensive. 

I normally take light passes on my planer so I think a 2 HP could handle it but I'm not sure.

My dream planer is a 15" with a helical carbide head.  That might not ever happen though.
Peter

My "day job"
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