VFD's, Blowers and electric bill

[Axxlrod]

I have VFD's on my blowers at my wash. I have six 15 hp blowers from Sonny's. I have my look back feature on my controller set to look back to my pre-soak arch. This means that my blowers will stay running if another car is in the tunnel at all. Is this defeating the purpose of the VFD's? It seems to me that if the purpose of VFD's is to eliminate the start up spike, then wouldn't it be more effecient to remove the look back feature and have the blowers cycle on and off for every car?

Anybody with electric knowledge have a definitive answer?

 

[dclark3344]

I am NO expert and willing encourage any correction. I have also been trying to understand ways to cut my demand charge on my electric bill. What I was told is VFD are mainly to operate the same motor at different speeds. The starting and stopping of any motor is what spikes the demand charge and increases your electic bill. The main thing to save on electicity is to have capacitor start motors which have a little capacitor that jump starts the motors.

 

[MEP001]

A VFD is not just to operate a 3-phase motor at different speeds, it's also to "soft-start" the motor. If you're billed based on peak usage, having a 30-hp motor kick on will create as much as a 400-amp peak. Starting the motor with a VF drive can keep it within 50% of its rated operating amperage, thus reducing your bill by reducing those peaks.

 

[dclark3344]

MEP001,
I assume that you can not use capacitor start motors with VFDs?????
So how does a capacitor start motor compare to a motor with VFDs in electic usage????? I know that it is not cheap to replace VFDS, I have replace 4 in the past 12 months. Plus the VFDs. require a lot of panel space.

 

[MEP001]

I assume that you can not use capacitor start motors with VFDs?????

No, except for certain single-phase motors VFD's are mainly for 3-phase.

So how does a capacitor start motor compare to a motor with VFDs in electic usage?????

It's not the actual usage that's as important as the start-up load. As I said before, if your bill is based on peak usage, reducing the peaks also reduces your bill. A capacitor start motor may have a lower peak amperage than a 3-phase motor, but it's not controllable, and a VFD can be programmed to start slower and reduce that peak.

I know that it is not cheap to replace VFDS, I have replace 4 in the past 12 months.

If they are properly protected and not overloaded they should last at least as long as a contactor.

Plus the VFDs. require a lot of panel space.

The VFDs I've seen aren't any bigger than a contactor that would do the same job.

 

[Whale of a Wash]

I don't think you can lower your peak if you already have vfd's. In our area it is calculated by our highest peak. If one turned on all the equipment and then closed for the rest of the month, the peak has already been established. To have a lower peak you could not run the air compressor when the blowers are running , this could be done with relays. What about this scenario, using the look back feature to lower the blowers to say 20% of output, saving Kw's. Let's see if i can explain my thought here: If i am driving and encounter 25 yield signs, I would get better mileage than if I encounter 25 stop signs(this is what the VFd's are doing now) My idea is:: you are currently running 100%, if the lookback lowers it down to say 20%, The average will then be lower by a certain percentage depending on the time at a lower speed, thus saving KW's or getting better mileage. An eye closer to the blower would then ramp it back up. In our area the power co, will come out and give an audit and advice for free.

 

[JGinther]

If you plan on running at 60 Hz, I would just buy soft-starters. They are cheaper than VFDs and will provide the same purpose.

 

[washman9]

where can you find VFD's or capicators large enough to start big motors. i am think my auto pump motor and auto dryer motors.

 

[Turbo]

what is a soft starter and where do I get them? My knowledge is limited in this area. VFD reduce the frequecy (Hz) which make s motor run slower so when load occurs motor is already in motion. What does a soft starter do and why is it cheaper? Thanks

 

[washnvac]

I just added a second automatic at a 5/1; thus making it a 4/2. I have 400 amp service. One electrician told me I needed to upgrade to 600 amp service at a cost of $35,000. Total running amps would be less than 400 amps, though. Start up was the issue. So I did some research and found Allen-Bradley SMC-3 Soft Starters. I spent less than $10,000, and installed these on Six 7.5 hp dryer motors, and Four 15 hp dryer motors. They are working like a charm. They have programmable settings for start up which you can do by percentage of running amperage, or by lenth of time for start. They also have soft stop. They are worth looking into, for sure. Check any local electric supply store.

 

[JGinther]

A soft starter works like a vfd in how it lowers inrush current on motors by temporarily reducing the incoming AC frequency at motor startup. In other words, it "ramps up" a motors speed instead of starting immediately. This reduces inrush current, which is what the power companies bill your facility on. (They do this because they have to build their infrastructure to be sufficient everywhere when your wash is at peak demand.) The main difference with a soft starter is that it doesn't have large enough capacitors and DC bus or the volts/hz ratio controls to keep a motor running at a frequency other than 60 hz. It is cheaper because you get less capability.

Axxlrod, to answer your question, I think that you would be best off using a combination of both, and if you can adjust your step start time between dryers, increasing that as long as possible based on your conveyor speed and rinse arch distance. Yes, the VFDs should help avoid having to "look back" to the front of the tunnel, but you want to be able to keep your inrush current to a minimum. VFDs will not eliminate all inrush current, they will just pad it a lot. I would just make sure that I didn't have any overlap in my step starts, ramp them up as slowly as possible, and then call the electric company to do a demand test. I would set the look back at about half the tunnel length as a guess. To get an accurate location, you would have to do a whole lot of calculations.

 

[Ric]

I just added a second automatic at a 5/1; thus making it a 4/2. I have 400 amp service. One electrician told me I needed to upgrade to 600 amp service at a cost of $35,000. Total running amps would be less than 400 amps, though. Start up was the issue. So I did some research and found Allen-Bradley SMC-3 Soft Starters. I spent less than $10,000, and installed these on Six 7.5 hp dryer motors, and Four 15 hp dryer motors. They are working like a charm. They have programmable settings for start up which you can do by percentage of running amperage, or by lenth of time for start. They also have soft stop. They are worth looking into, for sure. Check any local electric supply store.

So you have 5 producers on each iba dryer? What/who's dryer are you using? Are you happy with it?

 

[washnvac]

My older unit is Worldwide, with four 15hp motors. My newest is from Nu*Star with six 7.5 hp motors. Both do a good job. I think I like the Worldwide just a tad better because of the five outlets on each side producer. This seems to blow the sides down real good. Worldwide is out of business, but someone else is making a similar unit....maybe Aerodry? I specifically went with the 7.5hp on the new unit to keep that inrush down.