What 10HP VFDs have the best single phase rating 5

[JohnMcNutt]

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.

 

[jraef]

The de-rating issue is universal, not brand specific, it has to do with two main issues: 1) having the front-end conversion components sized properly to handle the increase in current from the single phase source, and 2) having enough bus capacitance to smooth out the additional DC bus ripple that results from haing a single phase bridge rectifier.

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"

 

[ozmosis]

I think I would be looking at a drive unit that has been tested and designed to run at the required motor current based on a single phase supply.
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...R0626_SinglephaseAQUADrive_FactSheet_highRes.

Yaskawa

http://www.yaskawa.com/site/dmdrive.nsf/link2/NKOE-7GPJP8/$file/AN.AFD.15.pdf

 

[JohnMcNutt]

Thank you for the help. I will be sure to look carefully and/or call the manufacturer.

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.

 

[JohnMcNutt]

I should add, I contacted Rockwell tech support about this idea, but the call taker's understanding of the subject in general left something to be desired, and did not exactly inspire confidence in his answers.

 

[jraef]

It's unfortunate that you got someone in tech Support that could not answer that question, but then again it is possibly the result of how you asked the question. The PF400 is fully capable of being fed with 1 phase power by using a 35% de-rate of current. But if you asked "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", then you have to understand that NO factory tech support engineer is going to support you in disassembling a VFD and rigging up some kind of external conponents to allow you to do something that is was not designed for. Sorry.

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"

 

[ScottyUK]

Evox-Rifa had a useful application guide for electrolytic capacitors - the sample calculations might be of use if you decide to roll your own. Doesn't look like Kemet maintained it after they bought Evox-Rifa, but here's a third party link:

http://materias.fi.uba.ar/6648/archivos/RIFA_electrolytic_appguide.pdf

 

[itsmoked]

Nice link Scotty!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

Tangential humor... I just had to share this. Look at the middle of the link provided by ScottyUK.

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"

 

[JohnMcNutt]

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.

Thanks for the response. However, a minor correction: the drive derates not BY 35%, but TO 35%:

Three-phase input provides full rating. Single-phase
operation provides 35% rated current.

I'll keep my options open and see what the owner wants to do.

 

[mikekilroy]

Hitachi is also a potential source - they have an op note on 1ph use of all their vfds also - just derate 50% of course.

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.

 

[ScottyUK]

It is usually possible to add additional capacitance to the DC link. The problem with this brute force approach is that it will over-stress the rectfiers due to the higher peak current and shorter conduction angle, so your next mod will be an external rectfier capable of dealing with the higher peak currents. It quickly becomes a messy business.

 

[JohnMcNutt]

Right, if I simply upgrade the bridge rectifier (not hard to find modules that do this, and are small) then I have to worry about exceeding the ripple current rating of the existing cap.

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.

 

[ozmosis]

hmm, interesting plan.
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..

 

[ScottyUK]

You should seriously consider using a soft charge circuit for that capacitor bank. A series resistor with a bypass contactor which closes after the DC link reaches, say, 80% normal voltage would be a reasonable starting point. If you don't then a firework show is entirely possible. You need to look at the high frequency ripple capability of the DC link capacitors as well as simply their bulk capacitance. There are plenty of design notes available which should allow you to design according to your requirements rather than just use rule-of-thumb calculation.

There's a bit more to this than simply adding a big rectifier and a big capacitor.

 

[LionelHutz]

If you want to experiment then try a 50A rated contator feeding a 100A diode bridge connected to about 800uF of 400V rated capacitors connected to the DC bus terminals of the VFD. Keep the cap to VFD terminal connection short and twist the wires. Then, run the contactor off the "ready" relay on the VFD. The precharge circuit in the VFD should be capable of charging the extra bus capacitance so power up the VFD terminals to pre-charge the caps. If you turn on power and the drive does not power up in a reasonable amount of time then add a couple of power resistors across the contactor.

 

[ScottyUK]

A 7HP motor on a 10HP drive will need a lot more than 800uF. I've got a similar arrangement on an old A-B 1336 drive to run my lathe in my home workshop. That's a 15kW drive running a 5.5kW motor, and there's about 6000uF of external capacitance. Under a heavy cut it still occasionally faults on bus undervoltage. It is not an arrangement I'd use in a 'professional' situation, but I can't justify the cost of a 400V TP&N service to my house.

Do NOT forget to include a bleed resistor to discharge the caps. The ~330V DC will probably kill you if you accidentally touch it.

 

[itsmoked]

Do NOT forget to include a bleed resistor to discharge the caps. The ~330V DC will probably kill you if you accidentally touch it.

A most excellent point.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

I probably looked at the caps on a 600V drive so add more caps. The internal bus of the VFD will have bleeder resistors so the caps will still discharge. It will just take longer with the added capacitance.