3-phase motor experts

[Jack Briggs]

I have a Delta (Invicta) RU-50 pin router, which I acquired last June. Previous owner used it on 3-phase power up until I bought it from him. Not having 3-phase in my basement, I consulted with American Rotary and bought one of their static phase converters. The converter is rated at 4-8 hp heavy duty for my 3 hp motor, because it's Brazilian made and supposedly hard to start. This was an engineer's recommendation.

Fast forward to today. I finally got the 240 wiring in my basement shop to run this and it won't turn over. Starts to turn for a half second, then stops - then repeats, about every second or so. On one occasion it tripped the overload on the switch.

Could I have a bum motor? Or should I try a different phase converter? Rotary? Any help appreciated as I needed this up and running today.


Cheers,

[Bruce Page]

Jack, does the spindle on the pin router spin freely by hand? I run a static on my 3hp mill and my 5hp lathe, the only time I have had a problem was when the spindle bearings on the mill got tight and needed replacement.

[Jack Briggs]

Bruce,

Spindle spins freely. I wonder if there's a way to test a 3-phase motor without actually applying 3-phase power to it? Maybe with a meter, let's say.

[Bruce Page]

Bruce,

Spindle spins freely. I wonder if there's a way to test a 3-phase motor without actually applying 3-phase power to it? Maybe with a meter, let's say.

I don't know. Maybe one of the sparkey's will chime in.

[jim sauterer]

i do not know much about converters.but you might want to disconnect the leads from the converter and make sure you are getting 240 volts between each leg l1 l2 l3 .a 3 phase motor will single phase and not start if it does not have 240 to each leg.single phasing increases amp draw on 2 legs and tripped the breaker.hope this helps

[Eric Commarato]

Jack,

I would send the static phase converter back and build yourself a rotary phase converter. I bought a kit on the bay for about 80 dollars. I was a very well documented kit with all the parts for a 10 horsepower rotary phase converter. In my case, I had to run a 5 horsepower Tannewitz table saw, so I needed a big converter. With the 10 hp kit, I had to get a 7 1/2 hp three phase motor for the idler to generate the third leg in phase with the other two legs. I found a 7 1/2 hp Baldor pump motor at a local motor shop for 100 dollars, so all in all I built my rotary phase converter for 180 dollars. It has worked great for the last 4 years, I can run my Tannewitz and my Oliver 144 BD jointer at the same time off this converter. It provides clean 3 phase power for up to 10 horse power 3 phase motors/machinery.

Good luck in what ever you decide.

Eric

[Jon Dieterlen]

Hi Jack. I have 240v 3 phase in our shop. There are 2 lines that are 120v to ground and 240v between them. These are just like 240v single phase. The third line (wild leg) is 218v to ground. Your voltage coming out of the converter should be similiar. Could your motor be wired for 440v 3 phase? There should be a diagram showing how to connect for high voltage and low voltage. You need to connect for low voltage.

AC (alternating current) alternates at a rate of 60 cycles per second. If you plot this on a graph, it creates a sine wave with ground being in the center of the graph. The way I look at it is the voltage goes from 120v above ground to 120v below ground 60 times per second. In single phase, the two 120v lines are spaced 180 degrees apart so that they are 120v to ground, but 240v apart. Three phase has a third line that is 60 degrees from the other two. This is why three phase motors will start w/no help from capacitors etc. The phase converter manufactures this third phase from single phase by shifting the voltage by using capacitors.

Someone correct me if I am wrong, but I think that sometimes this shift is not 60 degrees. If the votage is not shifted enough, the motor will not start. The phase converter needs to be sized to the motor load for it to correctly shift the third phase.

Hope this helps, Jon

[Brian Weick]

I agree with john-you could have either inadvertantly wired it for 440 or do not have the proper couplings between the winding wires as specified in the diagram. throw an electric meter on the converter output to check the voltage. I am not a big fan of static converters~ Variable frequecy drives are capable of large loads and have eplenty of options on them- just my opinion. Here is some info for you. there is a phone# for technical help.

PHASE CONVERSION TECHNOLOGIES & HOW THEY WORK
Investing in a three phase utility supply can be very expensive, especially in areas off of the main
grid. With utility estimates averaging $40,000 per mile to install, many three phase equipment
users are forced to turn elsewhere to find a three phase supply. Phase Converters are the
economical option, however power quality is often compromised with poor voltage balancing and
for most equipment loads, an oversized converter must be specified to enable motor start-up.
These inefficiencies lead to increased energy consumption and eventually may cause damage to
the three phase equipment, especially digital or electronic machinery.
We have outlined the various phase conversion technologies and points to be aware of when choosing a
phase converter. If you have any further questions please contact our friendly staff at 1-877-266-7823 for
service and advice.
How Does a Static Converter Work?
The Static Converter is made up of two small components:
A voltage sensitive relay and a standard capacitor (Cs) connected to
your motor application (Red Box). The capacitor delays waveforms (or
shifts the phase) during the start-up of your motor application. The relay
disconnects this start capacitor after the motor has started. From this
point, the motor will continue turning on the single phase supply. The
performance of such a motor is fairly poor and can be compared to a car
motor running on only a few cylinders
Motors operated on a static converter will produce about 50-60% of their
name plate power. When you add another low cost run capacitor (Red
Dotted Box) to the simple design, rated power goes up to around 70% of
the motors name plate power.
To help with understanding, the Start Capacitor (Cs) is used only to start
the motor and then it is switched out completely. The Run Capacitor (Cr)
is always in the circuit and is carefully sized to balance the voltages at
one load rating (generally around 50% full load). Since Cr is fixed the
voltage balancing at either end (0% and 100%) is quite poor.
How Does A Rotary Converter Work?
If you add an idle running motor to a static converter, you have a rotary
converter (Blue Box).
The added motor will compensate for some of the static converter
weaknesses and help extend the range of motor sizes and loads.
The internal motor is inactive at average load, but works hard when
loads don’t match the value of the chosen run capacitor (Cr).
Rotary converters are clearly somewhat better than static converters.
They can run several motors of different sizes. Large motors will produce
up to 90% of their nameplate power, small motors (motor being much
smaller than the converters idling motor or pilot motor) a bit more.
If manufacturers oversize these motors, the output symmetry is
increased as well as start capability and performance.
This is why manufacturers ask you so many questions about your
applications. When in doubt, they will offer a converter with a larger pilot
motor or suggest a larger converter altogether.

Hope this helps,
Brian

[Gary Falls]

why not just convert it and put in a single phase motor with a new switch if its the only 3 phase machine youve got? Deale can be found on motors. Just find what the frame # is on the motor and start searching.

[Josiah Bartlett]

I would skip that and get a nice variable speed drive for that motor, the Teco/Westinghouse 3 HP FM-50 drive will set you back about $150 and provides all the switching, speed control, overload protection, and phase conversion you need. I don't know why anybody bothers with rotary phase converters these days with the inexpensiveness and versatility of these units available these days.

You might just check to make sure the motor is wired right, maybe you don't have the taps wired right on the motor.

[Jack Briggs]

Thanks for the info guys.

The motor is correctly wired for 240, not 480. I've double and triple checked this.

The face frame motor is a unique size and no replacement motor can be found, at least with the 10 or more hours I've spent researching.

Eric, I'm starting to agree with you that I need a rotary converter. I'm calling American Rotary to try to get them to give me full credit on the staic for a rotary.

I will test for the voltages as per Jon's suggestions. Are there any other tests I can do in the meantime?

[Rob Russell]

I agree with the suggestion of a VFD. Unless you're planning on adding other 3-phase machines to your shop, a VFD for a 3HP motor is an ideal solution.

Check out Dealers Industrial Equipment, aka Dealers Electric for the VFD. It'll cost you $129 for the micro - $150 for a 3HP VFD would be a Real deal.

[Ryan Bess]

Let me start by saying that I am not an Electrical Engineer or an expert on 3 phase, I can only share my experience.

I have a 1932 Yates-American bandsaw with a 3HP, 3PH motor. I called on the expertise of my friend Mike, who IS an EE. The advice I'm giving you was passed down from him.

Please do not use a VFD. You may have trouble finding a VFD that will even start your motor. A 3HP rating on your tool motor does not allow you to simply buy a 3HP rated VFD and "hook it up". Starting the motor may be very difficult if not unlikely, as you're finding out with a static. Since 3PH motors do not have starting caps, getting a 3PH motor started is where it's at.
Another note on VFD's. In the words of my EE friend, "When VFD's fail, they do not fail gracefully. You will likely ruin your 3PH motor in the event of a VFD failure."

After much mewling and puking, I called American Rotary in Wisconsin. Very helpful staff that worked with me to find the correct rotary phase converter for my old bandsaw. BTW, my local saw mill uses a rotary converter for their 24 inch planer - it has been running 8-10 hours a day for 20 years!

Good luck.

[Rick Christopherson]

....... I called on the expertise of my friend Mike, who IS an EE. ........Please do not use a VFD. You may have trouble finding a VFD that will even start your motor. A 3HP rating on your tool motor does not allow you to simply buy a 3HP rated VFD and "hook it up".

This is incorrect. If a VFD is rated for single phase input, then it will give you your 3ph output without the need to derate the VFD. The FM50 has a 3hp model that is rated this way. You only need to derate the VFD when it is rated for 3ph input only. So contrary to what your friend said, yes, all you have to do is hook it up.

Starting the motor may be very difficult if not unlikely, as you're finding out with a static. Since 3PH motors do not have starting caps, getting a 3PH motor started is where it's at.

This statement alone causes me to question the knowledge of your friend, as it is completely the opposite of 3ph motors. The reason why 3ph motors do not have starting capacitors is because they do not need them. 3-phase power provides the rotating magnetic field necessary to start motors, as-is. 3ph motors start far easier than single-phase motors for this reason.

Your friend was telling you that it is hard to start a 3ph motor on single-phase power, which is true. However, this is not applicable to motors being powered from either rotary converters or VFDs. They start quite easily and quite smoothly.

Another note on VFD's. In the words of my EE friend, "When VFD's fail, they do not fail gracefully. You will likely ruin your 3PH motor in the event of a VFD failure."

In the unlikely event that a VFD fails, it will be the switching transistors on the output. This will either be a dropped phase, or DC injection. In either case, the motor will not be destroyed so long as the operator notices that the motor is not turning. Your friend's statement is based on unmonitored systems without motor feedback control. That's not applicable here since there is an operator controlling the VFD/motor and not a PLC.
==================================
For the original poster, a store bought static converter (including American Rotary) is just a motor starter. Capacitors are used to create the rotating magnetic field, but once the motor starts, the converter drops out of the circuit and the motor runs from single-phase power.

For your application, the cost of a rotary converter will be much higher than the cost of a VFD (unless you build your own converter). As was mentioned, a VFD is the best solution for your system.

[Rick Christopherson]

I will test for the voltages as per Jon's suggestions. Are there any other tests I can do in the meantime?

I read this thread yesterday but was too tied up at the time to respond. I recall reading someone suggesting to check the voltages, but I can't find it now.

Measuring the voltages on an unbalanced static converter will not tell you anything. The converter is active only when the motor is not running at speed, so the 0-speed readings will only give you a meaningless voltage across a capacitor, and the full-speed readings will only give you voltages across the motor (without converter).

The idea about measuring voltages probably came from my article on Building a Phase Converter, but this relates to balancing the converter. Your static converter does not have the run capacitors, so you would use this procedure to add the capacitors to turn it into a Balanced Static Converter.

P.S. Balancing your converter will not change how it starts, so this is not suggested as being a solution to your current problem.