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Old 10-07-2008, 02:03 AM   #1
wareagle
 
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Default Converting Single Phase Power to Three Phase

There have been several discussions here and who knows how many elsewhere on how to squeeze that third phase out of a residential power system. For the purposes of this thread, I will outline what I feel are the three most practical options for converting single phase to three phase power. During the years, I have used each of these options in my shop, and will give you the results that I observed with each set up. This is meant to be a guide for someone exploring the options, and in now way will cover every situation. It is up to you to determine the best option for your needs and budget. Warning: Electricity is dangerous. Anyone looking to do any electrical project should either study the topic extensively prior to commencing any work on a given project, or better, hire the work out to a qualified electrician.

So on to the show:

So you have bought a new piece of machinery, and it has that dreaded three phase motor on it. Now what? Your options are changing the motor to a single phase motor, going to a DC motor, or converting your single phase power source to a three phase power source. We are skipping the first two as they are outside the scope of this thread.

What are the options for converting single phase to three phase?

_________________________________________________

Static Phase Converter:


These units do exactly what they say they do, and that is they magically give you that third power leg for your motor. They are inexpensive, and are easy to install. Don't expect stellar performance from one of these units. They will merely get you by.

Pros:
Inexpensive
Small
Easy to install


Cons:
Motor only provides 2/3 of HP rating
Lacks torque
Sizing is critical


In my experience, this unit worked when the motor was warm. If the motor was cool, I had to help it start by turning the spindle by hand. The motor would easily be overwhelmed with heavier cuts, and in the end I decided this unit did not serve my needs.

In summary, a static phase converter is suitable for applications that do not require heavy starting or running torque. If one were to have a need for three phase and can sacrifice 1/3 of the HP rating of the motor, then this is an option worth considering.
_________________________________________________
Rotary Phase Converter:


This is a unit that is designed to handle applications that require large motors (above 3HP) and heavy working torque. These units are heavy, bulky, and can be difficult to construct if you are doing it yourself. The manufactured units are easily installed.

Pros:
Can handle high starting torque requirements
Can operate multiple pieces of equipment (if sized appropriately)
Motors retain most of their rating


Cons:
Units are expensive - even if self built
Size & weight
Cost per hour can be high (a rough guess is $1.50 per hr per HP)


In my experience, I used a home built phase converter, but not for long. The electric bill broke me of that habit. With the RPC in place, my electrical cost went up over $100 in a month's time. I went back and figured for the amount of time I spent in the shop with the RPC running, that unit was costing me about $5.50 per hour to run. At that price, it doesn't take long to get SWMBO interested in the shop activities!

In summary, a rotary phase converter is the ticket when you have motor loads that require high starting or running torque. These units are expensive and usually are impractical in a home shop environment due to their initial cost, size and cost per hour to operate.
_________________________________________________
Variable Frequency Drive/Inverter:


If anyone has read my previous posts on the subject, then you already know this is my favorite option for the home shop environment. Having one of these devices gives a lot of latitude over the other options for just slightly more than the equivalent static phase converter. There is good reason for my picking these units.

Pros:
Inexpensive
Infinite control of spindle speeds
Superior motor protection
Motor retains most of rating


Cons:
Difficult to install
Programming is/can be tricky
Units are slightly bulky


In my experience, this has made my milling machine a totally different piece of equipment. I get better finishes, I have much better control of spindle speeds, speed adjustment doesn't require belt changes, and the VFD/Inverter slightly reduced my electrical consumption when compared to the static converter. When the single phase motor goes south on my lathe, at three phase motor will replace it with another VFD/Inverter!

In summary, the VFD/Inverter option is likely the best bang for the buck in 90% of the home shops. These units are inexpensive, and once installed and programmed, run like a dream. These units are finicky to get set up, but a little time and patience will yield capabilities beyond imagination.
_________________________________________________

Power conversion can be a black art of sorts. Regardless of what any company claims, you will never get 100% of a motor's rating when running on single phase power. There will be efficiency loss, it is a simple matter of physics. However, don't let the issue of power conversion stop you from pursuing the purchase of that mill, shaper, lathe or other equipment. There are options, it is a matter of choice as to which is best.

As I stated above, there are options outside of this discussion as well. There isn't any one of them that is right or wrong. Each situation is different, and having the knowledge to make a decision can be worth more than the equipment itself!

Hopefully this little post will take some of the Voodoo out of the equation and will help you make an informed decision for your needs, budget, and application.



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Old 10-07-2008, 02:53 AM   #2
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Default Re: Converting Single Phase Power to Three Phase

That's really an excellent write-up, summarizing the options available for a hobbyist. I converted my single-phase lathe to a 3-phase setup some time ago, utilizing the TECO FM50. I didn't find any aspect of it complicated, primarily because I closely followed the outstanding article on the subject, authored by John Pitkin. I have a large lathe than he does, but that wasn't really a factor in the conversion. If anyone's interested in his article, I'd be glad to email it if you'll provide me with an email address.



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Old 10-07-2008, 03:02 AM   #3
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Default Re: Converting Single Phase Power to Three Phase

GBB,
Email sent. I'd like a copy of the article, please.
I have ordered an FM50, should arrive here Wednesday.

Thanks in advance.

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Old 10-07-2008, 01:46 PM   #4
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Default Re: Converting Single Phase Power to Three Phase

W/E,

How long have you been using the VFD's? Reason I ask is they are strictly electronic, right? Now if it ever fails what would you do? Replace it with a new one, send it out for repair?

Just some questions. I won't think that the home hobby guy has the money to have some one trouble shoot the unit should it fail. He would have to buy a new one.

You said that your electric bill went up using a rotary converter? Is this used at the home shop or were you work? A bit confused here. It would seem that if you only use it occasionally that your electric bill would hardly change.

As you know I'm getting a 3 phase Bridgeport. It has variable speed option. Since I haven't started on my rotary converter yet I'm gathering info and have gone to the sight you mentioned to me in another thread. I'm kind of on the fence as to which way to go. I'd really like to build a converter just to see if I can do it. You say the cost is high in that direction. I'm a bit leery of the VFD since it's electronic and a bit scared if it decides to go south. I've worked with drives were I worked and have seen them just not work after a while. So the question remains weather to go rotary or VFD. A bit more studying might help.

Bernd

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Old 10-08-2008, 01:02 AM   #5
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Default Re: Converting Single Phase Power to Three Phase

Quote:
Originally Posted by Bernd
How long have you been using the VFD's? Reason I ask is they are strictly electronic, right? Now if it ever fails what would you do? Replace it with a new one, send it out for repair?
Bernd, I have had my unit online for a little over a year without one glitch. To the best of my knowledge, these units are all electronic. If my unit failed, I believe I would simple replace it. For the cost of a new unit, I can't see a repair being cost effective.

I will add that the power quality here is terrible. We have spikes frequently, and have brown outs and black outs far to often. I have lost a computer, a router and phone system to the power issues, but the VFD just keeps going.

Quote:
Originally Posted by Bernd
You said that your electric bill went up using a rotary converter? Is this used at the home shop or were you work? A bit confused here. It would seem that if you only use it occasionally that your electric bill would hardly change.
My electrical usage did increase substantially while using the RPC. The unit was a home build RPC, it was in my home shop. Your are correct in the occasional use scenario. However, my average usage is about 20 hours each month. With that level of usage, my electrical bill increased significantly. Once I was over the sticker shock and the interrogations from SWMBO were over, I figured my cost per hour at that time was about $5.00 per hour for the RPC alone. If one were using his RPC for only a few hours each month, then the cost increase would be negligible, but as usage goes up the electric bill will reflect it.

I think there is a general misunderstanding about RPCs in that people tend to think they run for free. There's no load on it, right? Actually, there is a load and it is substantial. You are using single phase power to turn the three phase motor, and it is inefficient. The thing to remember about any RPC is that you are adding another motor into your circuit, and that motor does consume electricity. The bigger it is, the more it will consume.

Quote:
Originally Posted by Bernd
As you know I'm getting a 3 phase Bridgeport. It has variable speed option. Since I haven't started on my rotary converter yet I'm gathering info and have gone to the sight you mentioned to me in another thread. I'm kind of on the fence as to which way to go. I'd really like to build a converter just to see if I can do it. You say the cost is high in that direction. I'm a bit leery of the VFD since it's electronic and a bit scared if it decides to go south. I've worked with drives were I worked and have seen them just not work after a while. So the question remains weather to go rotary or VFD. A bit more studying might help.
I have no doubt that you have the ability to build a RPC. The connections aren't complicated. As for cost to build one, they truly can be expensive. If you decide to build a self-starting RPC, the contactors, relays, capacitors and other components can add up in a hurry. I just built a 20HP RPC for a friend, and my cost in materials to build the controller was just shy of $600. The cost would be substantially less for your size of motor, but unless you have all of the components on hand or have access to them for cheap, you will easily see the $200 mark by the time it is done. As for a hand started RPC, that cost would be substantially less due to the reduction in needed materials.

Based on previous discussions regarding your situation, my suggestion would be to hook your motor up and get it to turn. Take a load reading on the feed circuit and see what it is pulling in Amps. With that information along with your electrical rates, you can figure out what the cost per hour will be for the RPC. Sorry, I don't have the formula handy at the moment. That will give you a good idea of what your best option will be.

Hope this helps!
W/E

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Old 10-08-2008, 01:21 AM   #6
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Default Re: Converting Single Phase Power to Three Phase

Wareagle,

Thanks for the insight. I'll do what you suggest and make a decision once I get some data gathered.

Regards,
Bernd

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Old 10-08-2008, 11:40 AM   #7
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Default Re: Converting Single Phase Power to Three Phase

There are a number of vendors on eBay that sell RPC panels for hookup to a motor. That might be a good solution if you don't want to go to the trouble of building from components.

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Old 10-08-2008, 02:59 PM   #8
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Default Re: Converting Single Phase Power to Three Phase

In regards to the query about the longevity of VFD's: The fellow that I got my original info from for converting my lathe has had his in operation for a little over 5 years without a hiccup. He spends quite a bit of time on his lathe as he's retired and it's his only hobby. Probably not as much as a 5day a week, 8 hour a day commercial operation, but it still speaks well for the longevity of the unit.

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Old 10-10-2008, 08:01 AM   #9
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Default Re: Converting Single Phase Power to Three Phase

Forgot one option. Phase Perfect phase converter. These units take single phase and convert it to true three phase electronically. Power quality of the three phase coming out of one of these is better than utility. And they do send power back into the grid so they will run equipment that cant be ran on a RPC. There are a lot of newer motor drives and some older ones that will just not run on a RPC.

Bad thing:

Cost. Looking at about $3k new. Still cheaper than having the power company come in and install 3 phase. But you really need to have it to justify it.

Good things:

Provides true three phase. You can hook anything you want to it. Route the output to a distribution panel and run as many machines as you want up to the rated power of the unit.

Good option if you have a lot of 3 phase equipment. Or things like a CNC machine that wont run on a RPC.

I used to run a RPC in my garage to run my lathe and tool grinder. 15HP. That thing sucked power! Ended up putting a servo drive in the lathe and installed 3 VFDs in the cabinet of the tool grinder. Now the tool grinder runs on 120v single phase. The VFDs were given to me by a friend. They are 120v in 240v 3 phase out. Good for 1/2 hp each.


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Old 10-11-2008, 08:17 AM   #10
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Default Re: Converting Single Phase Power to Three Phase

Just worth flagging up that whilst this is all good stuff in the European world of 220volt single phase and 415volt 3 phase the decisions aren't quite the same (see the Boxford thread).

The first question relates to whether the motor in question is dual voltage (220/415) or fixed for 415volt only. If it's dual voltage you have the option of a 220 single phase in/ 220 3 phase out inverter or some potentially lower cost options like capacitors to "fake" a 3rd phase. If the motor is fixed at 415volt you normally either need to re-motor the machine or use a converter that boosts the voltage from 220 to 415 amonst other things.

To be honest the best bet if you're UK based is two buy the two books in the "Workshop Practice" series by V J (Jim) Cox. One is called "Electric Motors in the Home Workshop" and the other is simply "Electric Motors. With this second book be sure to get the recent (2006 edition) because it covers inverters. They do overlap a bit but they're only about £6 each on Amazon.

Armed with only these books and a dusty O level in physics I ran my 2HP Victoria mill from a homemade converter that cost £25. As far as a I know it's still running now almost 10 years later. I've subsequently used most variants of single to 3 phase conversion but still refer back to these books.
There's no substitute for reading up on a subject!

Charles



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