# best option for 3ph. motor



## chappellt (May 24, 2009)

I have a 7.5hp 3 ph Delta Invicta RT40 tablesaw that I got for $500 at auction. It is in excellent condition, but I do not have 3ph. power. Is my best option a phase converter? rotary or static? Or do you think I am better of buying a new single phase motor (5hp). Pros and Cons???


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## Tinstaafl (Jan 6, 2008)

We have a couple of guys who have been down that road and will probably be along with their recommendations, but what are you defining as your best option? 

Financially, rotary is hard to beat. Definitely cheaper than replacing the motor. Static costs significantly more, but has a few advantages over rotary while still not equaling motor replacement.

If there's any chance at all that you'll be getting more 3-phase equipment (and it's hard to stop once you've begun that slippery slope), it makes all the sense in the world to get a converter.


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## Inner10 (Mar 12, 2009)

Or get a 3 phase service installed if available. :thumbsup:


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## Speedy Petey (Sep 30, 2003)

Getting a single phase motor is by far the cheapest and easiest option.


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## Tinstaafl (Jan 6, 2008)

Actually, from what I've seen the price of a static converter is pretty comparable to a new single phase motor. By comparison, a rotary converter is dirt cheap if you build it yourself with a used 3 phase motor--and they're not hard to find.


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## WarnerConstInc. (Jan 30, 2008)

Speedy Petey said:


> Getting a single phase motor is by far the cheapest and easiest option.


That is actually wrong. 

First, I bet the motor frame is something that is unique and have you ever priced a 7.5 hp single phase motor?

Quick search shows the generic one's start out at 500 bucks and go way up from there.

Static phase convertors are pretty cheap but, in the long run you end up hurting the motor single phasing it and you only get about 1/2 the power.
I have a 4-8hp static sitting on of my cabinets in the shop.

All my equipment is 3 phase. I do not have 3 phase pole power.

I run a Rotary Phase Convertor. It is a 10hp and I can start a 7.5hp motor with it and run up to 30 hp worth of machines at one time with it.

I spent about 500 bucks for the RPC control panel and the surplus 10hp motor. 

You could also get a VFD but, that would be a hella expensive option too for 7.5hp.

My vote is go for a RPC, I see them used all the time in the 400-700 range.


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## WarnerConstInc. (Jan 30, 2008)

Tinstaafl said:


> Actually, from what I've seen the price of a static converter is pretty comparable to a new single phase motor. By comparison, a rotary converter is dirt cheap if you build it yourself with a used 3 phase motor--and they're not hard to find.


I think you are confusing a static with a VFD.

Link to static:http://andersonconverters.com/page3.html

VFD's for a 7.5hp motor when you have single phase power is going to be pricey.


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## Tinstaafl (Jan 6, 2008)

WarnerConstInc. said:


> I think you are confusing a static with a VFD.


Don't think so. I know a VFD is pricier. :thumbsup:


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## WarnerConstInc. (Jan 30, 2008)

Tinstaafl said:


> Don't think so. I know a VFD is pricier. :thumbsup:


Ok then but, a static is only 125 bucks, a VFD would be like 500-700 bucks.:whistling

And a new single phase motor with the right frame may be pushing the 750-1000 range.

Good luck finding a used one for that, not to mention you will probably have to change out the motor controls too.


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## Kent Whitten (Mar 24, 2006)

WarnerConstInc. said:


> That is actually wrong.
> 
> First, I bet the motor frame is something that is unique and have you ever priced a 7.5 hp single phase motor?
> 
> ...


Look at the brain Darcy is sporting!


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## Tinstaafl (Jan 6, 2008)

WarnerConstInc. said:


> And a new single phase motor with the right frame may be pushing the 750-1000 range.
> 
> Good luck finding a used one for that, not to mention you will probably have to change out the motor controls too.


I think you're a bit high on the new single phase, but I defer to your more recent research. :notworthy

My mention of a used motor was regarding the building of a RPC. :thumbsup:


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## WarnerConstInc. (Jan 30, 2008)

KentWhitten said:


> Look at the brain Darcy is sporting!


I was forced to learn this stuff, not many industrial electricians around these parts.

If you can't get pole power and you want to add a few more machines, a RPC is the best way to go. It is a one time investment and it opens your world up to a bunch of industrial grade equipment at bargain prices.

I do like buying stuff with large single phase motors though as I can usually sell the motor for more then I paid for the machine.


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## WarnerConstInc. (Jan 30, 2008)

Tinstaafl said:


> I think you're a bit high on the new single phase, but I defer to your more recent research. :notworthy
> 
> My mention of a used motor was regarding the building of a RPC. :thumbsup:


here are my results for a search on 7.5hp single phase motors:

https://www.google.com/search?q=7.5....,cf.osb&fp=5e558c29839c65f9&biw=1280&bih=903

a used or surplus 10hp 3 phase motor should run a person anywhere between 100 and 200 bucks. A pre-built control panel for a 10hp idler is right around the 250.00 range.

Now feeding that to a 3 phase panel with 3 pole breakers can get a little salty unless you have good friends or are patient looking for the parts.

I just picked up two 30 amp and two 20 amp GE bolt in's for my panel for 12 bucks each.


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## Speedy Petey (Sep 30, 2003)

WarnerConstInc. said:


> That is actually wrong.


It is certainly NOT "wrong". It is my opinion and IMO it is correct, or at least the best choice.

You say a motor is around $500, yet you spent that on just the converter alone? Sounds economical. :whistling

Let me re-phrase: If the motor can be had in the same frame and configuration in single-phase it is as cheap, or cheaper, and FAR easier to simply replace the motor.


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## WarnerConstInc. (Jan 30, 2008)

Speedy Petey said:


> It is certainly NOT "wrong". It is my opinion and IMO it is correct, or at least the best choice.
> 
> You say a motor is around $500, yet you spent that on just the converter alone? Sounds economical. :whistling
> 
> Let me re-phrase: If the motor can be had in the same frame and configuration in single-phase it is as cheap, or cheaper, and FAR easier to simply replace the motor.


Cheapest and easiest is getting a static converter at about 150 bucks total. I can't find the frame style of the motor on that saw but, I bet it is not an off the shelf option most places.

You could wire the RPC right to the TS and have the full HP and still have under 500 bucks in it.

Swapping in a single phase would not even make the list of options for me.


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## J.C. (Sep 28, 2009)

I would probably investigate the single phase option first. I would find it annoying having a RPC hooked to the table saw. I really dislike the noise from RPC's and wouldn't want to have to turn one on and off every time I want to use the table saw. I don't mind RPC's for most other machines but I use the table saw too often during the day to want to use one for the table saw. Of course that's just my opinion and I'm sure others will disagree.


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## WarnerConstInc. (Jan 30, 2008)

J.C. said:


> I would probably investigate the single phase option first. I would find it annoying having a RPC hooked to the table saw. I really dislike the noise from RPC's and wouldn't want to have to turn one on and off every time I want to use the table saw. I don't mind RPC's for most other machines but I use the table saw too often during the day to want to use one for the table saw. Of course that's just my opinion and I'm sure others will disagree.


I just turn mine on and leave it on.

I have been around RPC's that were horribly noisy and annoying.

Mine is whisper quiet, the only noise is from the fan on it.

I also got a remote control to turn mine on too.:whistling

Anyway you look at it, you will be spending at least another 500 bucks to get it to run.


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## Speedy Petey (Sep 30, 2003)

WarnerConstInc. said:


> Swapping in a single phase would not even make the list of options for me.


That's awesome! 
At least we are giving the OP some options and not saying anyone of them are "wrong".


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## J.C. (Sep 28, 2009)

WarnerConstInc. said:


> I just turn mine on and leave it on.


That would drive me crazy. They aren't loud, it's just a motor running but, I couldn't take listening to it for 10 hours a day. :laughing:


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## WarnerConstInc. (Jan 30, 2008)

J.C. said:


> That would drive me crazy. They aren't loud, it's just a motor running but, I couldn't take listening to it for 10 hours a day. :laughing:


Stick the motor outside under a little cover. 

A TEFC motor can handle the outside environment just fine without any sort of protection.


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