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nc ks | Explain a rotary phase converter to me. When would you use one verses other phase converters? I have single phase service, but I have several 3 phase motors on conveyors in my seed equipment so I can vary the speed, soft start, and reverse. I don't have a rotary phase converter, not sure what kind of converters I have for sure. |
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| kb ag - 12/22/2015 23:00
Explain a rotary phase converter to me. When would you use one verses other phase converters? I have single phase service, but I have several 3 phase motors on conveyors in my seed equipment so I can vary the speed, soft start, and reverse. I don't have a rotary phase converter, not sure what kind of converters I have for sure.
My understanding is that rotaries break it back down and static phase converters don't so you have a good one if you can vary speed. |
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nc ks | Whatever I have are in an 8" deep panel on the wall, so they are not very big. |
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Faunsdale, AL | Rotary converters are basically an unloaded 3 phase motor run on the single phase supply and acting as a rotary transformer to create the 3 phase needed. They can be used to run one to several different motors or just idle along when they are all stopped. The rotary converter cannot vary the frequency or soft start etc. The best thing about them is they are simple and reliable delivering good 3 phase without any distortion.
The small units that allow speed changes, soft starting etc are variable frequency drives. These convert the incoming power (can be single phase if the unit is oversize) to DC and then the AC 3 phase voltages are synthesized from pulses of that DC power delivered at the correct instants in time to the 3 output lines that run the motor.
Commonly one VFD runs each motor or a group of similar motors and can be programmed to soft start, follow a speed reference signal from an onboard keypad or a remote controller or even respond to a feedback signal to control a parameter like pressure etc.
The cost of these has dropped dramatically in the last 20 years or so, even as the features and capabilities have been improved. A VFD can be equipped and programmed to do things like make a motor hold a load stationary and then rotate in either direction at a predetermined speed or accelerate at a predetermined rate etc. They offer very good torque at slow speed where the old fashioned reduced voltage soft starts had much less than normal torque at low rpm. Truly an amazing machine that we mostly use for some its simplest capabilities....variable speed, converting single phase to 3 phase and soft starting.
VFD does produce 3 phase with lots of distortion, so in some cases, they can be tough on motors. There are motors (probably most motors any more) that are designed to stand up to the spikes the VFD creates.
The cheapest converter that will run a 3 phase motor on single phase is a static converter that uses capacitors to synthesize 3 phase. These typically cannot be used to run a fully loaded 3 phase motor. Usually safe to run a motor at about 2/3 of full 3 phase power rating when using a static converter. They also don't allow full torque starts.
Edited by ccjersey 12/23/2015 00:21
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Jackson, MN | What does a VFD cost for say a 30 hp motor? |
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NW Central Ohio | ..unless you can find used ones...it's going to be about the same price as the cost of the motor. |
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nc ks | yup, vfd's is what I have. Couldn't think of it even though Ive had the panels open tons of time tracking down other gremlins. Does a rotary phase converter take a lot of power to start? I don't think I have enough single phase service to start a 50 hp 3ph motor, but could I run a 50 hp rotary phase converter to run some 5 to 10 hp motors? |
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| We have 2 "Anderson Converter Co.", converters. One 15 HP and One 40 HP. They use used electric motors to make the converters, so make sure they use a sealed motor to avoid dust build up and fire hazards. Our electrician says they are excellent quality and we have had very good luck. They will help size a converter for your needs. Make sure to put the converter in another room or a near by building, not near where your are working, because they are noisy. Contact number is 480-988-2804. |
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Chebanse, IL..... | We have several phase convertors. Ronk is the brand we have. If I understand your question correctly, the convertor itself takes very little power (amps?) to start & run. But, from what I know, the motor that you plan to run draws the same start load (amps?) whether it's 1 ph or 3 ph. So yes, the power load does spike considerably for the "start". Phase convertor doesn't act any differently though during a motor start. It just sits there spinning away. |
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Portland, ND | We have a couple converters, and they are very bulletproof. You can start large motors, it all depends on the size of Phase converter you purchase. The converter always starts with no load, and then the 3 phase is added to the running converter. I have a 30/80 that will start 2-30hp axial fans on my dryer, and a 20/60 in the seed plant that runs a couple 10-15 hp and several small motors. It runs about 90 hp of 3ph motors.
I don't have any experience with VFDs, but they seem very effective also. |
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North Central Indiana | KB
Rotary phase converters are usually rated by the largest hp motor you can start and then the total hp running at one time.
There are many great rotary phase converters made. I have an Arco Rotophase HD30. In my situation the largest motor I have to start is 25 HP. I could start a 30 HP if I wanted to. My total HP capacity is 100 on this converter. I do run run as many as 9 motors at the same time but their total combined HP is 90.
Additionally I have a VFD on my pit auger. It is 25 HP and I have a 50 HP VFD since I'm converting single phase to three phase. For those that already have three phase the converter doesn't need to be oversized like it is in single to three phase.
Whatever you do pay close attention to the power requirements of your phase converter as these units do not create power just convert and sometimes there is a loss of power in the conversion process.
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Sac & Story county IA | Here is a 60 hp drive.
http://www.automationdirect.com/adc/Shopping/Catalog/Drives/DURApul...
You need to have 5 amps of power on the line for each horsepower no difference of single phase or 3 phase. |
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Leesburg, Ohio | ccjersey gave the best explanation above that I have seen on VFD's and converters.
One thing I might clarify on the rotary ones, at least as I understand it... Electric motors use windings that produce magnetic fields to "pull" the shaft around. Single phase motors use two groups of windings, and three phase motors use three groups. The rotary converter uses the normal two legs of single phase power to run the converter on just two of these groups of windings, similar to a single phase motor. The two winding groups in a single phase motor are offset by 180 degrees of rotation. In a three phase motor, the three groups are offset by 120 degrees. That "unpowered" third group of windings in the converter generates power as it is turned by the other two groups. That power being generated is tapped, and becomes the power source for the "third leg" of three phase power to run your other three phase motors.
We have two rotary converters, one at each of two grain facilities. The only work done on the first one in eight years is replace the bearings in the converter. The other one was just installed in a new leg project this year, so only one season on it. But so far, all very reliable and economic source of three phase power. One is on the end of a rural electric line, the other is near an investor-owned utility substation. |
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Delaware | I can't explain a rotary phase converter, but I do know we went with VFD's on our irrigation systems, which are capable of varying speeds as well as converting single phase to three phase.
I also think I was told a rotary phase converter is only 80% efficient, while a VFD is somewhere around 97%. Our VFD's have been very reliable for the 3-4 years we have had them. I think for 30-40HP motors the VFD costs around $4-5,000. Cheaper if you go smaller. |
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Delaware | I actually found a newsletter about the Electric Co-op we work with that started introducing VFD's to us. An informative read for someone (like me) who doesn't completely have their head wrapped around 3-phase electricity.
http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=...
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Monroe City, MO | I've got a 40hp drive on a 20 hp motor. It cost north of $5k. It's a Toshiba. |
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| Rotary converters output and unbalanced three phase sine wave. They work well for some older equipment. As electronics get more sensitive, they need balanced three phase. There are phase converters that output balanced voltage. They are way more efficient too. However a bit more expensive than a rotary. Quieter too. www.phaseconverting.com has them. It is true three phase sine wave. Guys run sensitive CNCs off of them. They also have VFDs that do the phase conversion for pumping water. |
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rotary phase converters vs. others?
