Using VFD on single phase source

[WiscElectrician]

I have a situation where we ended up not using a 480V 1.5HP in line fan and it's ABB VFD during construction of one of our buildings. Now I am going to donate the fan and drive to a good friend who is remodeling a local tavern he just purchased, issue is he only has 240V single phase power available (this will be kicked up to 480V 1Ph). I don't run into situations where I am using freak drives to run a 3 phase load from a single phase source, and that is where my question lies.

I know normally in this situation, you would double the size of the drive to handle the extra power needed to run the fan. The plan is to install differential pressure sensors in the smoking room and one in the bar area. We'll then be exhausting enough to meet minimum ventilation needed to keep the room smoke free plus keeping the room negative so the smoking room doesn't draft into the bar area. Mostly the fan will be running at minimum levels but may have times especially when doors open where it needs to ramp up to keep the negative state. Seeing as it will 95% of the time be running at far less than 50% of it's full load, any opinions on if the drive will work and if not how long it'll last?

Thank You

 

[ptonsparky]

I have a situation where we ended up not using a 480V 1.5HP in line fan and it's ABB VFD during construction of one of our buildings. Now I am going to donate the fan and drive to a good friend who is remodeling a local tavern he just purchased, issue is he only has 240V single phase power available (this will be kicked up to 480V 1Ph). I don't run into situations where I am using freak drives to run a 3 phase load from a single phase source, and that is where my question lies.

I know normally in this situation, you would double the size of the drive to handle the extra power needed to run the fan. The plan is to install differential pressure sensors in the smoking room and one in the bar area. We'll then be exhausting enough to meet minimum ventilation needed to keep the room smoke free plus keeping the room negative so the smoking room doesn't draft into the bar area. Mostly the fan will be running at minimum levels but may have times especially when doors open where it needs to ramp up to keep the negative state. Seeing as it will 95% of the time be running at far less than 50% of it's full load, any opinions on if the drive will work and if not how long it'll last?

Thank You

What does ABB say about this long term use? We have done the transformer thing but just for temporary to program and test the drive controls in the shop.

 

[Jraef]

There are two issues: the current flowing through the diodes in the bridge rectifier will pull 1.732x more current and the DC bus ripple is going to be much worse without the added capacitance afforded by de-rating the drive by 50%. The DC bus ripple is generally the worse of the two, and it is related to load. So at lower load there will be less ripple, but at full load (presuming the full 1HP of the motor), the ripple may cause damage to the drive. More likely however is that the drive will simply detect it and shut down.

One thing you could try (if your drive offers this option) is to program in a 50% current limit on the drive. How a VFD responds to that is (typically) that the PWM is folded back, despite the commanded speed; i.e. the commanded speed is overridden by the current limit function, because speed = current. That way whenever someone did open a door or something, the drive will simply go to it's maximum current limit setting and stay there. It may result in some loss of function in your smoke deterrence system, but only temporarily from the sounds of it.

 

[kwired]

Are you going to be powering a 1.5 HP motor?

That said many standard sizes for 480 volt drives I have come across we would be purchasing a drive rated for 2.0 HP to drive a 1.5 HP motor, so you possibly have some extra capacity from the drive if it was originally selected to drive a 1.5.

 

[zbang]

Wouldn't it be a lot easier, and more maintainable, to replace the motor (if possible) and let it run full-speed? Seems like a lot of work to re-use the fan & drive.

 

[Ingenieur]

Wouldn't it be a lot easier, and more maintainable, to replace the motor (if possible) and let it run full-speed? Seems like a lot of work to re-use the fan & drive.

He wants to modulate using the onboard pid to maintain a differential static pressure in the space

I doubt the spaces will be tight enough to do it
might be easier to put a small control damper on the fan inlet
get a small actuator/controller, may be able to get one with the dp sensor built in (used on a vav box) and just run sensing tubes
need a very small range <0.10" wc

probably run full speed or damper 100% anyways
the power saving nil

 

[kwired]

Are you going to be powering a 1.5 HP motor?

That said many standard sizes for 480 volt drives I have come across we would be purchasing a drive rated for 2.0 HP to drive a 1.5 HP motor, so you possibly have some extra capacity from the drive if it was originally selected to drive a 1.5.

Never mind about the motor, I first thought you had a left over drive after reading OP again you have a left over fan/motor assembly and the drive for it. Still could be a 2 hp rated drive though.

 

[Open Neutral]

There's a state that still allows smoking in a bar?

 

[ptonsparky]

There's a state that still allows smoking in a bar?

That entered my mind but I think I've been in area that still have two sections. Last summer in central Missouri, MDSW informs me.

 

[retirede]

There's a state that still allows smoking in a bar?

Yep - Mizzourah

 

[GoldDigger]

Also many states in "private clubs" smoking may be permitted.

Sent from my XT1585 using Tapatalk

 

[Besoeker]

Wouldn't it be a lot easier, and more maintainable, to replace the motor (if possible) and let it run full-speed? Seems like a lot of work to re-use the fan & drive.

That was my thought too. A 1.5HP fan seems like a lot for a vent fan.

 

[Besoeker]

There are two issues: the current flowing through the diodes in the bridge rectifier will pull 1.732x more current

All other things bein equal, and they rarely are, the three phase diodes will conduct all of the current for a third of the time. For single phase it is all of the current for half the time. So I'm not sure where yoi get your sqrt(3) factor from. Trivia I suppose. I just think a vent fan is the wrong application for a three phase drive. But I readily admit that it's not my area of expertise.

 

[kwired]

All other things bein equal, and they rarely are, the three phase diodes will conduct all of the current for a third of the time. For single phase it is all of the current for half the time. So I'm not sure where yoi get your sqrt(3) factor from. Trivia I suppose. I just think a vent fan is the wrong application for a three phase drive. But I readily admit that it's not my area of expertise.

They did want it to maintain a certain level of negative pressure when doors are opened.

 

[Jraef]

All other things bein equal, and they rarely are, the three phase diodes will conduct all of the current for a third of the time. For single phase it is all of the current for half the time. So I'm not sure where yoi get your sqrt(3) factor from. Trivia I suppose. I just think a vent fan is the wrong application for a three phase drive. But I readily admit that it's not my area of expertise.

The motor draws 3 phase current from the drive, the drive draws single phase current from the line. The difference is the sq. rt. of 3, 1.732.

 

[WiscElectrician]

Thank you for the feedback everyone.

Just following up to a couple of the reply's. It is a 480V 1.5HP 3phase in line fan with a 480V 1.5HP drive. The drive was not ordered with any "fudge" room. And my thought for the fan and drive was to 1) Meet minimum ventilation codes 2) keep the smoking area negative with differential pressure sensors by giving analog signals to the drive to ramp up and down the drive output.

JRaef, thanks for the 50% reply, not sure why I didn't think of doing that...... I'll program it in the parameters for a 50% max output. Without doing the calculations, I'm guessing this fan ducted properly will move 3-4K CFM, so I couldn't see us needing to move that much anyway.

As for the smoking part, it's one of only a few bars anywhere around here that I know of that meet the qualifications. The smoking room is only connected to the bar area with common hallway, and the smoking area is more than 75% windows, which meets the guidelines for a smoking area.

 

[Jraef]

Getting into the nitty gritty details of exactly how the current is drawn by the individual diodes is not actually helpful to the OP, who was simply asking for advice on feeding single phase power into a VFD that is driving a 3 phase motor. I've let it go this far because I apparently made a semantic error and was concerned that the direction that some responders had gone was causing confusion, but I really think this needs to be done with now. I don't think the OP is needing any more clarification and certainly would not really care about the semantic accuracy of what I said. I have removed the superfluous postings as best I could, it was getting too far afield and was not germane to the OPs question.

The "1.732" issue was only mentioned because frequently, I see people purport that this is the ONLY issue when over sizing a VFD for a single phase input, when in fact it is not, the DC bus capacitance is the bigger issue and requires a minimum of 2x over sizing, 1.732 is inadequate and risks compromising the VFD. Let's leave it at that now.

 

[gar]

170515-2000 EDT

Jraef:

The 1.732 factor should not be suggested in this analysis, it is not correct. The propagation of incorrect ideas occurs far too often and creates problems when the next person repeats the same error.

Besoeker provided the correct analysis that if 4 diodes are used for a single phase rectifier compared to 6 diodes in the three phase rectifier that a diode in the single phase circuit will pass 1.5 times the average current of a diode for the same output power in the three phase rectifier.

This also means that total diode power dissipation in the single phase circuit only goes up by a factor of about 1.5 because diode voltage drop is approximately constant.

You are correct that capacitance in relation to ripple is probably the more important factor.

.

 

[mike_kilroy]

So Gar you are good with 1.5 factor?

Try this: 10a x100v 3ph produces 10x100x1.73=1730watts. Agree?

How many amps 1ph for same 1730 watts?

Still want to stick with 1.5?


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[Besoeker]

The motor draws 3 phase current from the drive, the drive draws single phase current from the line. The difference is the sq. rt. of 3, 1.732.

We've been there, done that, and had sound technical posts being unreasonably deleted.
At the risk of the same action being taken again I will reitterate that you simply cannot apply a simple fixed multiplier. For reasons already given - but banished to the ether.