3 phase problem

   / 3 phase problem #11  
Bill -

After posting that I'd never heard of such an animal as a 115V 3-phase motor, I poked around on the internet until I found one. I tried to find some info on how the heck one works when wired to a typical 3-phase panel, but came up blank. Can you shed any light on how the heck such a motor works, and how it is wired to a 3-phase panel?

Thanks, John
   / 3 phase problem #12  
I'm all wet on electrical advice occasionally too, but I see no reason you can't go with an idler motor like plenty of people do with 240V single phase.

I've seen pages with better drawings; also, discussed here before too I think, but this one looks to describe it pretty well:

3ph idler

It does mean you'd need another 3ph 120V motor.
   / 3 phase problem #13  
A three phase motor will run on single phase, you'd just have to rope start it when you want to use it. May not be the best solution but it doesn't cost anything.
   / 3 phase problem
  • Thread Starter
   / 3 phase problem #15  
John, I believe that these motors are used for speed control with the use of an inverter. Baldor makes an inverter that converts 480V 3 phase to 115V 3 phase. Inverter duty motors are much more rugged and can be ran down to 15 hertz where a normal motor shouldn't be ran below 30 hertz (if I remember correctly). Not a good explanation but it's all I have.
   / 3 phase problem #16  
Bill - Thanks, that sounds very reasonable, and is a whole lot more info than I had before. /forums/images/graemlins/smile.gif Makes good sense now that you've got me outside of the little "box" I had my thinking stuck in; namely, that the motor was somehow going to be wired directly from a service panel. Couldn't quite wrap my pea brain around that one! /forums/images/graemlins/tongue.gif

Thanks again, John
   / 3 phase problem #17  
That converter would be sweet.

I have no idea how much power that fan takes, but if it's a fraction of the motor's rated output, RedRocker's suggestion would be the simplest. I think you lose about half your torque in this mode [I know logic says 1/3; maybe that is the case /forums/images/graemlins/confused.gif] It's rated continuous and you're looking at a few hours here and there, so I wouldn't worry much about too much current for the windings.

If you don't mind the "jumpstart", the next simplest would be to get another identical motor, or any 3Ph 115V motor larger: wire all three leads to the respective one between motors and your hot and neutral lines to two 2 of them. You wouldn't need any fancy capacitor wiring like the link I posted, but might need to spin the idler motor to start it.

Disclaimer /forums/images/graemlins/tongue.gif /forums/images/graemlins/grin.gif : I've always found another way around it, so never actually tried this; second hand info and a few web sites, but it does make sense, also all the web sites I'ved searched at one time or another have the same basic premise; just variance on how to start the idler.

Good luck whatever route you choose! /forums/images/graemlins/cool.gif
   / 3 phase problem #18  
Soultion 1: Abondon the blower and look for another source of air - leaf blower or vacuum cleaner?
Well, if I had to get a bigger blower for one project I'd use my echo PB2000 leaf blower. It also is a teriffic shreader cleaner. A $5 garage sale canister vacuum cleaner might also work.

Solution 2: Inverter
A small variable speed drive would give you the ability to dial in your desired blower rate. Many small drives can also run off single phase. You must check the instructions, as some drives have loss of phase protection and will shut off if it detects one phase leg is missing. You mus "derate" the drive, which meqans buy one larger than your motor nameplate rating. A rule of thumb would be to make sure to double the drive hp rating. 120v 3 ph .6 amp = 125 watts = 0.17 hp. If you got a 1/2 hp rated drive you would be fine.

The next problem is that 120v 3 phase drives are not common. You would have the best luck with getting a 240v drive and stepping the voltage down to 120v using a 480/240 transformer. When you connect the 240 to the normal 480 v input 9primary), the output (secondary) will be 120v. This must be a three pahse transformer which is not as common as 120v control transformers.

By code you should also have an overload relay. Most important, make sure the forge and blower are well grounded. This will make sure the breaker trips should something short.

Overall, the alternate blower would be an easier solution. You can't beat an Echo PB2000 blower. It does have a variable throttle.
   / 3 phase problem #19  
I just hate the thought that you may end up throwing good money after bad.Borrow the wife's hair drier...
I have welded 1' square with charcoal and a Sunbeam.
   / 3 phase problem
  • Thread Starter
Well i gave in and ordered a new blower, it wasnt that it was that expensive just i hate having one that i cant use. How did you figure out the horsepower of the motor by knowing the v and amps. is there a formula?
thanks all for the help,