single phase to 3 phase conversion 1

[JPR01]

sorry, this is long

I have been reviewing all the information I can find on the subject, but still have a couple of questions.

I have a 7.5 hp 220v 3 phase motor on a recently acquired machine. The motor has a unique mounting plus the replacement cost and the need for reversing direction, prevent replacing with a single phase motor.

I have looked at using a separate 10 hp motor as a single phase to 3 phase convertor and using a VFD. Since this is for my personal use and not for a large company, cost is an issue.

First the VFD, at this size and voltage, all the VFD's I have found are three phase input. Even if I step up to 10 hp unit, I am concerned about the running single phase to the VFD. The soft start of a VFD would be a plus. Variable frequency is not needed. I have located a 10 hp 3 phase 240 VFD for $700.

When using single phase power to the VFD, it would appear that 4 of 6 diodes would not be used for powering the dc bus. What about moving the diodes so that all are powered by the single phase? Not sure I have the courage to open up the drive and start reengineering the drive. Also it would seem that if the drive was designed for three phase, that the dc bus would not be very smooth using single phase.

The rotary converter, I was planning on a 10 hp motor with the necessary start and run capacitors. My concern is efficiency and starting current. Having located a used 10 hp dual voltage motor, the total cost would be less than $300.

Your input and advice is appreciated.
Jon

 

[Skogsgurra]

Hi,

There is a discussion on this in thread 237-94610.

A 10 HP VFD on a single phase mains will be very difficult. I would say impossible. Single phase supply VFDs are not easily available above three HP.

If you rebuild a three phase unit by changing the rectifier, you will have at least two problems: 1) The inverter will probably report the missing phase and refuse to operate. 2) The current drawn from the mains will be higher than the highest fuse you are allowed to install. The current also has a very bad form factor, and that aggravates the situation.

A 10 HP motor HP on a three phase 400 V grid (as an example) would consume 16 A and needs at least a 50 A slow blow fuse (high starting current). A single phase inverter with 230 V input voltage (if available) would need 32 A if the power factor were 1. Taking the bad power factor into account, it seems more likely that a 63 A fuse is needed for reliable operation.

It looks like you will have a problem running your machine off a single phase supply. Are you going to run that machine at top speed and/or maximum load? If not, you may be able to reduce the power needed so that you can find an inverter that can be used.

 

[Mstrvb19]

JPR01- Is this for home use? Depending on where you are, if you are really considering spending 300 to 700 dollars, it might be just as easy to ask the electric company to run three phase from the pole to your house (no conversion necessary!) This is assuming that there is three phase available there-some housing areas are only run with a single phase line. If, however, it is present, you might want to look into what they would charge for a three phase line to your house. Then all you need is a three phase panel that you can get at any electric supplier and some home improvement stores.
What kind of control do you need-does the machine you are speaking of have a reversing starter with it, or is your supply expected to perform that function? If you only need something simple (i.e. no fancy functions or capabilities) the cheapest thing would be to build it, as the net cost of the devices would far less than any of the options you are currently pursuing, assuming that the inverter portion of the device is a simple square wave inverter.

 

[Mstrvb19]

JPR01- aside-many manufacturers offer the main portions of an inverter as a single unit, with its own heat sink, for sale, sometimes called an H-block. You can get one for pretty cheap, then all you would have to do is perform the rectification of your single phase, a power supply, and supply a control input (you will need three set up with oscillators at 120 degree shifts). It wouldn't be too difficult, but, as skogs pointed out, the load might be a bit heavy at single phase, and any inverter that you build on your own will not be the most efficient. Plus, you have to be careful to supply your own filtering, otherwise you will put DC and HF AC components into your home power supply, which can cause lots of problems, not only for any electronic devices in the house but also for your power supply transformer.

 

[ischgl99]

You can use a three phase VFD on single phase with derating (I've been doing that for over a year on a 1 hp drive), I checked with Toshiba last year and was informed any of their 230v units can be used on single phase with 1/3 to 1/2 derating. You can call tech support and they will tell you what size drive you would need for your motor.

Getting 3 phase installed at your house will be expensive if they power company would even do it. You will also most likely be charged industrial instead of residential rates. A better alternative is a phase perfect unit.

http://www.phaseperfect.com

This unit takes single phase and creates a clean third phase. You will not have variable speed or soft start capabilities with this, but if you need three phase, this might be the way to go.

Mike Bensema

http://www.dutchmenservices.com

 

[busbar]

These seem extra groovy…

http://www.aseapower.com/products/ac45-3.htm

 

[JPR01]

Thanks for the suggestions and thoughts.

Since I am in the middle of a buried electrical service area, three phase power is not possible.

I am going to contact Phase Perfect on Tuesday since this seems to be the best solution I have seen so far.

 

[blutfort]

If you do consider the VFD route, most VFDs have a paramet that lets you de-select incoming power monitoring. Factory settings will shut down the drive if you loose a phase, but if you turn this off the VFD will continue to assemble a three phase output if only two of the three incoming legs are powered.

 

[edison123]

Hi Mike Bensema,

That was an interesting ref on phase converter (

http://www.phaseperfect.com).

Do you have by any chance used this product and if so, how would you rate it ?

Kumar

 

[dpc]

Another option is an Add-A-Phase unit by Ronk Industries. These are used all over the place to provide three-phase power to irrigation pumps from single-phase service. It's a magnetic/capacitive device with only passive elements. It works best if motor load is relatively constant.

 

[busbar]

Sporadically, this is a fairly active topic at Eng-Tips.

Assorted information/products…

http://www.gwm4-3phase.com/

http://www.capacitorconvertors.com/staticinstructions.pdf

http://home.earthlink.net/~ojmsmith/indexd.html

http://home.att.net/~waterfront-woods/Articles/phaseconverter.htm

Some threads are…
thread237-88925
thread238-85149
thread237-75783
thread237-74389
thread237-68085
thread237-62718
thread237-66357
thread237-61099
thread237-58717
thread237-57678
thread237-57678
thread237-53938
thread237-50067
thread237-40497
thread238-37887
thread237-28750
thread237-26789
thread279-25652
thread238-25659
thread238-18786
thread237-12936
thread237-11842
thread248-11407

 

[ischgl99]

I haven't used a Phase Perfect yet, but have talked with a couple people who have. One complained of a squeal from the unit, but he is sensative to any noise. One disadvantage of the unit is it can't be paralleled at this time, so if you needed more capacity later, you would have to isolate each unit from each other. The units worked well for them and overall are happy.

My preference is to use VFDs since you can usually easily find one on ebay for a good price. I like the variable speed capability and the PP is a bit expensive. But if you have several 3 phase motors that need to be run, then the PP would be an easy solution.

Mike Bensema

http://www.dutchmenservices.com

 

[dk18]

I recently have run into an application for a 10hp single phase VFD service on a 3 phase variable torque loaded motor. On initial start up the drive tripped out on supply phase loss. This was due because the drive had an internal protection that tripped the drive with a DC ripple greater than 17%. In this case on initial start up the DC bus would oscillate from 350VDC to 240VDC, with 327VDC steady state bus voltage with drive not running. Once the motor reached a steady state speed to DC bus would only oscillate +/-10%. I was able to go into the advance parameter settings and disable the supply phase fault. The drive has been running fine for amount a month, but per the VFD manufacturer the larger the ripple in the DC bus the shorter the life of the drive.

As mbensema had indicated drive must be de-rated 1/2 to 1/3 the three phase sizing. Really you’re looking at a 20-25hp 230V drive. Your cost is going to approx double, it may not be practical if you do not require variable speed.

 

[aolalde]

Hello JPR01 (Mechanical)

My opinion is that an electronic device solution is not necessarily the best for your problem. Single phase AC input rectification will be limited, reducing the power capacity of a standard drive. Add a phase devices could be a solution but check for real balanced 3-phases.

I suggest an old technology M-G set. Couple an old 15 HP single phase motor with an old Synchronous Generator. Recondition the generator from a junked Standby unit.

This will provide a pure generated 3-phase AC power.

 

[Marke]

hello JPR01

Using a three phase input inverter on single phase is not a problem provided that:
1) The single phase voltage is equal to the three phase voltage, i.e. 220 volt three phase inverter used on 220 volt single phase supply.
2) The inverter is sufficiently oversized. This is necessary as the ripple current through the capacitors is much higher on a single phase inverter than a three phase inverter plus the current through the rectifiers will be higher. Generally, I double the inverter size. i.e. for a 7.5KW motor, I would use a 15 KW inverter.
3) The inverter does not have an input phase loss protection system.

Best regards,

Mark Empson

http://www.lmphotonics.com