What 10HP VFDs have the best single phase rating
What 10HP VFDs have the best single phase rating
(OP)
I have need of a VFD to provide three phase 230v off of single phase 230v. The load will be in the range of 5-7 HP, however, from my experience with the A-B Powerflex series they get derated by 50-65% if run off single phase, depending on model so that's why I put 10HP in the title. I am shopping for one that will power this load and when they get that big, they don't have a simple single phase rating published any more so I am wondering if those that have experience in this area can tell me what the derating is likely to be. The ones I have come across are Saftronics, ABB, Hitachi and there are more, I am not picky. It is a hermetic scroll freon compressor.





RE: What 10HP VFDs have the best single phase rating
Single phase current for the same HP load will be higher by the Sq. Rt. of 3, or 1.732. So right there all drives in this application need to be de-rated by that factor. The diodes in the rectifier of a 10HP 230V 3 phase drive are suited to carry about 28A, but if you feed that with a single phase source, all of the motor's power will have to come from 2 lines, not 3, so those diodes will have to carry about 50A. In addition, the extra bus capacitance that you need to have in order to achieve a smooth DC bus voltsage to feed the transistors in the inverter is significantly more and corresponds to a drive rating of 2X the motor HP rating. So you need to be buying a drive with diodes rated for at least 50A and bus capacitance for a drive rated about 55A, which will end up being roughly a 20HP drive.
But you really must do it by current, doubling the motor HP is just a convenient shortcut that has a little bit of fudge factor.
So in you application, the difference between 7HP and 10HP is significant, you need to nail that down before proceeding, or just accept that you have to base it on 10HP 230V 3 phase and buy a 20HP drive.
Side notes:
A) Not all drives can accept a single phase input, not because it doesn't work, but because they have phase loss protection that cannot be disabled. You need to check that out thoroughly before purchasing.
B) Saftronics no longer exists, they are now Emerson, so you must be looking at used or surplus drives. Be very careful, old drives that have been un-powered for more than a few years can fail catastrophically when re-powered unless you go through what is called a "capacitor reforming" procedure first.
"Will work for (the memory of) salami"
RE: What 10HP VFDs have the best single phase rating
As jraef points out, there are numerous components that will be impacted by the high DC link ripple created by connecting one phase, such as the DC link capacitors, rectifier etc. However, how would you know (with all due respect) what is happening internally unless you had detailed analysis or knowledge of each and every component.
There are numerous methods proposed to de-rate but my thoughts would be, if you are interested in a reasonable lifetime on the drive, going with the manufacturer's advice. They should have tested the drives if they are going to recommend a drive running on a 1 ph, otherwise there would be no warranty on the product.
I know two companies, one of them I work for btw, who will specifically rate drives based on 1ph input:
Danfoss FC202 series
http://www.danfoss.com/NR/rdonlyres/2A0A46F2-339A-....
Yaskawa
link2: Aircraft engineering Links/NKOE-7GPJP8/$file/AN.AFD.15.pdf" target="_blank">http://www.yaskawa.com/site/dmdrive.nsf/link2: Aircraft engineering Links/NKOE...
RE: What 10HP VFDs have the best single phase rating
In this situation, I have a PF400 that would have been sufficient to carry the load (3 motors) but the installers neglected to consider the single phase derating. I have been wondering for some time now, how feasible it would be to simply open it up, see what kind of diodes and capacitors it has on the DC power supply, triple them, and run it at full power. I might have to build a second box to contain the extra parts.
RE: What 10HP VFDs have the best single phase rating
RE: What 10HP VFDs have the best single phase rating
So for sizing a PF400 to run from a single phase source and run multiple drives, add up the combined motor FLCs, divide by .65 (35% de-rate) and select a PF400 with an output current rating at least that size, then add separate motor circuit protection for each individual motor, tied back to the VFD run command so as to stop the VFD if any one of them over loads. For example if you have 3 x 5HP 230V 3 phase motors, each with a FLC of 15.2A, the total FLC is 45.6A so the PF400 that you need will be a MINIMUM of 70A (45.6/.65). The nearest size that you could use thn would be the 72A rated unit.
But what size external diode bridge components and external caps you would cobble together? You are on your own with that, you can't expect a factory tech to support that when the company's name is all over the base unit.
"Will work for (the memory of) salami"
RE: What 10HP VFDs have the best single phase rating
RE: What 10HP VFDs have the best single phase rating
Keith Cress
kcress - http://www.flaminsystems.com
RE: What 10HP VFDs have the best single phase rating
fi.uba.ar
"Fouled It Up Beyond All Available Recognition!"
Sorry, it just jumped out at me, been one of those kind of days today...
"Will work for (the memory of) salami"
RE: What 10HP VFDs have the best single phase rating
Thanks for the response. However, a minor correction: the drive derates not BY 35%, but TO 35%:
I'll keep my options open and see what the owner wants to do.
RE: What 10HP VFDs have the best single phase rating
Although it is often stated that you need MORE bus capacitors for 1ph input to help reduce the higher ripple, the fact of the matter is larger hp size vfds all have LESS capacitance than their smaller brothers.
So, although it is a good theoretical thing to have MORE cap in bus, the reality of it is you will get less - and it still works with the 1.73 derate for input diode circuitry alone.
RE: What 10HP VFDs have the best single phase rating
RE: What 10HP VFDs have the best single phase rating
If I upgrade the capacitor, then the conduction angle is shorter and the instantaneous rating of the bridge may be exceeded.
My plan, at this juncture, is to open it up and see what's in there as far as rectifier and cap. Then triple the capacitance and triple the rectifier rating. This will depend on how it is wired and space restrictions, and also cost. At some point, adding another drive becomes more cost effective.
RE: What 10HP VFDs have the best single phase rating
I would suggest that if you are going to do this; ensure all other 'sensitive' devices are not connected to the same supply, upstream protection is good, put on protective eyewear, keep small children and animals away but make sure the video is turned on in plenty of time.
I don't mean to be too sceptical but you could get a possible bang/pop at start-up or when the inverter section starts to switch.
Good luck..
RE: What 10HP VFDs have the best single phase rating
There's a bit more to this than simply adding a big rectifier and a big capacitor.
RE: What 10HP VFDs have the best single phase rating
RE: What 10HP VFDs have the best single phase rating
Do NOT forget to include a bleed resistor to discharge the caps. The ~330V DC will probably kill you if you accidentally touch it.
RE: What 10HP VFDs have the best single phase rating
A most excellent point.
Keith Cress
kcress - http://www.flaminsystems.com
RE: What 10HP VFDs have the best single phase rating