Single Phase Motor VFD
Single Phase Motor VFD
(OP)
Hi,
I have been following another thread "help slowing down electric motor" which got me wondering why single phase VFDs are not available. Given that there are millions of single phase motors why has it taken so long for someone to manufacture a universal 2 phase (90 degrees apart) VFD to match the start and run windings of single phase motors. (I have looked at INVERTEK)
Why not discard the start capacitor and switch and power both windings 90 degrees apart?
Roy
I have been following another thread "help slowing down electric motor" which got me wondering why single phase VFDs are not available. Given that there are millions of single phase motors why has it taken so long for someone to manufacture a universal 2 phase (90 degrees apart) VFD to match the start and run windings of single phase motors. (I have looked at INVERTEK)
Why not discard the start capacitor and switch and power both windings 90 degrees apart?
Roy





RE: Single Phase Motor VFD
But, with small developers looking for "Niche" markets, we may someday see VFDs such as you describe.
OEMs wanting to incorporate VFDs into their products may use 3 phase motors at about the same price or less than single phase motors.
You may have a good idea whose time has not yet come
Bill
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"Why not the best?"
Jimmy Carter
RE: Single Phase Motor VFD
Also, once you add a VFD then there are much better motor types that can be used. Once you create the DC buss you can create any type of output you want so, for example, you can create a 3-phase output and use a 3-phase motor.
RE: Single Phase Motor VFD
Waross "I don't see small motor manufacturers spending any money to produce VFD friendly motors" I don't either, it would take a VFD manufacturer, perhaps a 3 phase drive could be adapted with different firmware. You are correct OEMs will always pick a 3 phase, so would I but what about the millions of single phase motors out there, home hobby market etc.
LionelHutz "you would need to know the start winding capability" OK, so you need to take a few measurements, I immagine that there is some sort of formula motor manufactures use to figure out the wire size / turns for any given motor size.
Wouldn't the motor develop more torque with the additional field energised rather than just taking up space?
Thank you both
Roy
RE: Single Phase Motor VFD
This means a lot of buyers of 1p VFDs are going to be end users like our doughboy. This would mean lots of phone calls, miss applications, warranty issues, lawsuits, etc.
Technically you are correct. I think it's the non-technical that is preventing it.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Single Phase Motor VFD
Yes I looked at the Invertek manual, their drive applies to a limited number of VFDs Shaded pole and capacitor run. The output is single phase, not 2 phase.
I sketched out the output for a typical 3 phase drive (6 transistors). I think ideally you would need 4 transistors per phase however the regular 3 phase configuration might be workable. It's a while since I opened a split phase motor but from memory the start winding has approx the same No of turns.
Roy
RE: Single Phase Motor VFD
RE: Single Phase Motor VFD
Then you would have some product logistical issues to contend with. Small VFDs are no longer made with discrete power components. Now they are all made with what are called "IPMs", Integrated Power Modules, which contain the diode bridge, DC bus, and 6 output transistors complete with firing circuits ready for TTL connection directly to your mP. To offer a different configuration would mean trying to do it with discrete IGBTs again, which I'm not even sure you can do any longer in a cost effective way. So if you end up with a 1 phse - 1 phase VFD that ends up costing the OEM even 10% more than a 3 phase unit, why would he buy it? But without the volume of the OEM market, your product would be relegated to the end-user / retrofit market. Although you see it as "millions" of installations, they are not all applicable to variable speed, in fact only a small percentage would be. So the market is severely limited before you even get started.
Just because you can, doesn't mean it's a good idea.
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RE: Single Phase Motor VFD
Look at standard squirrel induction motors used today. The IM is designed to start and run at a fixed speed and designed to withstand the rigours of a DOL start. It means the physical size and material content (iron, copper etc)have to be considerably more than actually needed.
Fit an VFD on a standard IM and you suddenly realise the losses in the motor could be avoided.
Motor manufacturers such as Siemens, ABB, Emerson etc manufacture motors that can only be operated by VFD. The base frequency will be anywhere between 50-70Hz, the material used in the motor is considerably less compared to a standard IM of equivalent power. It means the overall efficiency is higher.
High Efficient motors you see today are only High Efficient when running on fixed speed at full load.
Taking this on further, the development of Permanant Magnet motors means the overall efficiency of the system is improved considerably but this means that the motors are designed in conjunction with the VFD.
The IM hasn't changed much in nearly 100yrs but what has changed has been the technologies surrounding it. All technologies are predominatly restricted by the base design of the standard induction motor.
I'm not really sure where I'm going with this little sermon but to say that the technology of varying the speed of a motor does not just lie with the VFD.
RE: Single Phase Motor VFD
Keith Cress
kcress - http://www.flaminsystems.com
RE: Single Phase Motor VFD
I think that Roy's idea could be of good use in such an application where all components are cut to size and the reduction of motor complexity and number of power components can have a deep effect on cost and marketability.
I'll forward your thinking to those guys, if you don't mind Roy?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Single Phase Motor VFD
Some of you seem to suggest OEM as the main user of VFDs, is that really the case?
Is efficiency a factor when buying a VFD for a small motor? (I am thinking 1/4 - 1 HP).
I guess I was thinking about the 10s of millions of single phase motors already out there that might benefit from variable speed or soft start ability.
I hear you Jraef on the high cost of development, so I guess the answer is to use a 3 phase drive with a firmware change to suit 2 coils. I tried to sketch this out, the run winding is easy but start winding is a problem except that as the run winding approaches zero the transistors are on less and less whereas the start winding would be on longer, any thoughts on if that's workable?
It was an interesting idea anyway!
The evolution of VFDs has certainly been interesting, I remember being blown away the first time I saw one over 40 years ago, before that it was either DC or very expensive Schrage motors. Is it just me or are the modern VFDs much harder on motors than the early SCR based designs, I don't recall special motors or cable length as an issue even 20 years ago.
BTW, how many 3 phase VFD motors do you have in your house? I have a F&P washing machine with no gearbox. The 3 phase 28 pole permanent magnet motor directly coupled to the agitator swishes back and forth just like a regular washer only without all the mechanical clanking.
Regards
Roy
RE: Single Phase Motor VFD
If VFDs are tough on motors? You bet. The earlier thyristor designs and GTO designs had slow switches. The new IGBT ones are much faster and kill windings and bearings. It is so bad that that is my main occupation nowadays. I will even be running a seminar on bearing problems (EMD) caused by VFDs this fall (sorry, in Sweden - and in Swedish, so it won't of any use to you fellers).
You don't seem to have anything against my mentioning about the two-phase thing? Actually, that is how induction motors started. Tesla's first system was a two-phase, 90 degree system. So the thought isn't really new. But newish.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Single Phase Motor VFD
I expect IGBTs must have some advantage over thyristors otherwise why are we putting up with them "killing windings & bearings".
Yes I read several books on Tesla, what a facinating character. I wonder how he would utilize the advances we have today.
Go ahead on the 2 phase thing if it's got any merit at all.
Roy
RE: Single Phase Motor VFD
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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RE: Single Phase Motor VFD
Thats very interesting, I expect they will be recycled also by the home hobby market. The washing machine motor I mentioned is very popular for wind powered projects.
Roy
RE: Single Phase Motor VFD
RE: Single Phase Motor VFD
The harmonics issue is solved either by using a reactor (single phase - on reactor) or, better, with PFC circuitry. The EMI part is not an issue with the technology used. That also takes care about the insulation and bearing issues.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Single Phase Motor VFD
the goal of the 'old' company a few years ago was to have (in the future) all motors with variable speed control.
Quite a challenge when you consider the motors that Roy is talking about.
RE: Single Phase Motor VFD
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...