HELP! Dual voltage AND dual speed

[triphase]

Hi I need to fill a strange application. Application is for a piece of mobile equipment that is capable of operating at any speed. It is currently running with a dual voltage single phase capacitor 115/230 motor running 1800 rpm synchronous induction motor approx 1.6HP continuous duty rated. Draws approx 15A at 115V, and 7.5A at 230V. We need to take full advantage of the 230V line when available. So what we want to do is get a dual voltage/dual speed motor that can be reconfigured on the fly (contactors). So desired result when running on 115V would be 1800rpm at 15A load, when running on 230V motor will run 3600rpm and produce the SAME torque as running at 115V, double power output (~3HP?). How do I go about this?

My first thought was exactly what I said, single phase induction motor with multiple windings and contactors, preferably no variable frequency drive. Second thought was a 3 phase motor with VFD, but without using 2 VFD's or step up/down transformer, not sure best way to handle dual voltage without making it really complicated.

Any help greatly appreciated.
Thanks
Brian

 

[jraef]

If you had the VFD, why would you need 2 VFDs? Use a single VFD rated for 240V single phase input, 230V 3 phase output and a 230V 3 phase 3600RPM motor of the appropriate size. Then put in an isolation transformer with 120/240V-240V 1 phase windings, a selector switch to select the 120V or 240V primary windings, then hook the 240V secondary to the VFD input. If you have 240V available it just goes 1:1 though the transformer but gives you some isolation, never hurts to have it.

Or you could forgo that and just have a 120-240V transformer for the 120V input and have the selector switch put the 240V input direct to the VFD.




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[triphase]

If I did that I would not need a VFD, only a dual speed motor, and use an autotransformer (don't even need isolation). The reason for the second VFD is to eliminate the need for a transformer that has to handle 3kW (using a dual voltage 3 phase motor). I am trying to eliminate these extra components!

 

[jraef]

Well then your options are limited, I don't know of anyone that makes a standard 1 phase motor that is 3600RPM 2 speed and dual voltage, in fact I don't know of anyone that makes a 3600/1800RPM 2 speed 1 phase motor period. So you need to find someone to make you a custom motor in my opinion. I've used these guys for that, great to work with.

http://reuland.com/index.html

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[ccjersey]

Are you sure that the load you are dealing with really has the same torque at 3600 rpm as it does at 1800?

Is there some amperage limit on the supply? 15 amps at either voltage? Why is this? Could you get 30 amps at 115 volts? Are you trying to ensure that you can connect to any 120 volt receptacle anywhere and not trip a breaker?

 

[triphase]

the load is relatively contstant torque at any speed.(air compressor) The reason for this arrangement is to be able to take advantage of a 220v line when it is available (more output via double rpm) as opposed to a regular dual voltage motor which will not produce more output at 220V, just draw less current, same power. Since most 115v lines can be counted on for 15A or so, I would like the unit to be operating in a "high compatibility" mode that will pretty much guarantee operation anywhere, but when 220V power is available, I would like to be able to reconfigure for "high power" mode to get higher output.

 

[zlatkodo]

1. - Two-speed, 2/4 poles ,single phase motors, up to 2.2 kW are used in a dental laboratory and jewelry-manufacturing etc, for polishing.
There are many manufacturers and you need to ask for a double-voltage version. As an example you see:

http://www.buffingandpolishing.com/buffing-jacks.htm

2 - It seems to me that such an motor, according to your requirements, can be made, but I doubt someone will try if it's just one motor.
Zlatkodo

 

[wayne440]

Use two 120 volt compressors. Run one if you have limited 120V power available, two if you have 2 120 volt circuits or 120/240 with a neutral. No VFD needed, and you have a more reliable source of air, albeit at a lower volume if one compressor should fail.

 

[triphase]

That solution would not only double the cost by duplicating every component, but would double the physical size as well. Everything would have to be duplicated, interstage cooling, driers, etc. It is not a compressor issue, the compressor is well within it's ratings running at 3600rpm, it's purely a motor issue.

 

[wayne440]

I suppose it shows that I am used to having plenty of money and space available.