New 1 PH Motor or 3PH Converter?
Hi,
I’ve recently purchased a PM 66 and, in my haste to get this really nice old saw and a really nice price, didn’t ask the “3 phase or single phase” question.
Upon trying to change plugs, etc, I’ve discovered the 3 HP motor seems to be a 3-PH motor.
Once I’ve confirmed that it’s a 3-PH “for sure, for sure”, I need to decide whether to replace the motor OR purchase a phase converter..probably a rotary phase converter.
Does anyone have experience in deciding between the two options?
In terms of price, I’m looking at Phase converters in the $300-$400 range. Seems like 3 HP motors run between $500 – $600..for Baldor or Leeson motors. Cost-wise, all other things being equal, the Phase converter seems like the “right” decision.
However, if I replaced the motor, I could also be assured of having a new motor, no compatibility issues (if there are any) AND I could upgrade to a 5 HP in lieu of the 3HP Leeson.
Are there issues with phase converters that I should consider?
Noise?
Long-term damage to the motor?
Electricity costs?
Any loss of power?
Any recommendations on brands/sources?
Is the rotary vs. the non-rotary the best decision? I understand there is power loss with the non-rotary converters….
I see rotary phase converters that are advertised as “not kits….ready to go, in one piece”…how important is this? I’d like to make this a quick thing vs. mucking around for 2 months..if that makes sense.
If I bought another motor, presumably I could utilize the standard PM 66 magnetic switch, etc…correct?
Any advice based on real experience would be much appreciated…
Larry Pile
Replies
Get a new motor and new heaters for the switch if you want simple and fast. You will need to add a jumper wire to the switch for single phase.
Edited 11/23/2004 11:54 am ET by rick3ddd
Hi Larry,
If you are planning on getting another 3 phase machine then I would consider a phase converter. However the rotary phase converter you refer to has to be sized for the largest motor that it will service. So if you get a 3 hp converter for your tablesaw you are limited to getting only other 3hp 3 phase machines. If you get another 3 phase machine with a 7 or 10 hp motor then you will have to buy a separate converter for that machine. Unless you choose to invest in a larger hp converter to plan for the future.
I would buy a new single phase motor for the saw. The wiring is easier and the investment is much less considering the cost of phase converters and the additional wiring involved to install.
I am assuming that this is a not a professional shop situation where the saw will be run every day.
Essentially the phase converter is another motor that will generate the necessary power to start up the machine and there is no real noise problem that I can forsee.
There is no long term motor damage that I know of.
Not sure of electrical savings, I've heard some say that 3 phase motors are more efficient but the electrician I have dealt with said that the consumption is about the same.
If you go with an inverter instead if a rotary converter you will have a reduction in power but I can't say how much.
As I said before I would go for the new 5hp single phase unless down the road you are planning on purchasing more 3 phase equipment.
J.P.
You should keep in mind that 3 phase motors are more efficient than single phase motors and will cost less to operate. I would go with a non-rotary converter, but make sure the motor is compatible with it.
Get the info right.
An inverter gives full power but is programmed to run only one motor at a time. It' s other main feature is all the programmable bells and whistles such as reverse, doubling the motors rated speed, infinitely variable speed which makes it appealing for shapers, drill presses, bridgeports, etc.
A rotary will run multiple machines at full power also and of different hp ratings.
A static gives about 1/2 to 2/3 of the rated power. The static cinverter only starts the motor then it's job is done. The 3 phase motor will run on the two legs once it's up to speed and the momentum keeps it going past the missing third leg hence the loss in power.
Been dealing with phase conversion for over 20 years and have used all methods. Going the single phase route is his best bet and 5 hp is really overkill.
Edited 11/23/2004 11:57 am ET by rick3ddd
My mistake. I was referring to the static converter and said inverter.
J.P.
Larry, I was in exactly this position a few years ago. Bought a PM66 at auction for $1. Someone picked it up with a forklift by lifting the table. It snapped the bolts holding the table to the cabinet. Other than some broken bolts it was in great condition. It had a big 3 phase motor on it.
I was faced with the same choice. I chose to go with single phase 3HP baldor. Cost something like $350. I've pushed it pretty hard and never wished i had more power.
Look on ebay for motors. A year or so back some guy was regularly selling big, maybe 3 HP, single phase delta motors new in the box for a song.
Let us know what you choose and how it works out.
dave
Larry,
Unless you have other 3 phase machines or plan on getting them, I'd swap the motor. I ran my shop with a rotary converter and it got real old starting the convertor first. Kind of took the spontanaity out of using a machine.
I sold 3 removed 3 phase motors on an auction and got a $1 for bunch.
Bob
My 2 cents- Replace the motor. I have 3 phase and use a rotary converter hooked to a Long Ranger remote to turn it off/on. As everyone else said, if you plan on getting more machines you can find used 3 phase for cheap- Nobody wants them. If the tablesaw is your only 3 phase change the motor.
John
I have done the same thing as you for running my rotarty converter. Ihave a 60amp 3pole magnetic switch powered by a 220 single phase Long Ranger. Paid about $100 for the long ranger and a surplus magnetic switch/contactor, plus the the 4x4x6" box
I highly recommend it to anybody considering a rotory converter.
I bought a PM66 with a 3 phase motor. I bought a variable frequency drive on eBay. This converts single to 3 phase. It provides for braking when the power is turned off. It also allows for changing the frequency so that a 3 phase can be run at different speeds. I like this because I sometimes cut aluminum plate.
BJ
Larry... Electronic phase converters will give you a yield of 2/3 the original horsepower. If you add in an idler motor you will achieve full horsepower. The PM66 is designed to run with a 3 or 5 hp motor. Running it a 2hp would work but would degrade the saw. 3 and 5 hp single phase 230 volt motors are readilly available. I'll check the trunion mount points and let you know if you can swap one for the other.
Sincerely;
The Tool Guy
THAT help would be most appreciated.
I've learned more about 3-phase than I ever thought I'd need...but isn't that true for all of us?Thanks to all for great advice and a terrific sense of community.
Thank you, thank you, thank you. I only hope I can repay your assistance with quality advice for the next person.
Larry Pile
The modern electronic inverters run the motor at its full HP, the older static converters cut the available HP, the two units are very different in design.
John W.
As the price comes down on variable frequency drives (also known as VFDs or inverters) they are getting more popular for converting single phase to three phase power. I'm an electrical engineer and we use them for this purpose when three phase power isn't otherwise available. One thing to remember is that the VFD generally needs to be derated when it's used in this way - a rule of thumb is 50%, so you'll need a 10hp drive to run a 5hp motor and so on. This does vary from one manufacturer to the next so check before you buy.
You can buy static phase converters that will work, one commercial brand I've used is the Ronk Add-A-Phase. http://www.ronkelectrical.com/pages/home.html
There are also plans floating around out there for home built phase converters, here's one web page that discusses them. http://www.homemetalshopclub.org/projects/phconv/phconv.html
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