VFD idle power use

I have an apple packing line that runs on three phase. It has four 3/4 hp.
motors and a hoist (1/2 hp) I leave the three phase ilder on 12 hours a day
seven days a week. I'm trying to trim my $600 monthly fall electric bill.
(mostly 5hp cooler) I get 7 amps usage while none of the packing line is
running. It would be nice to get rid of the motor hum also.
My question, would a VFD work well to provide three phase for this packing
line. Is standby power usage on a VFD near 0? I'd have to bring motors in
with the existing control logic and wire VFD so it always powers the output
legs.
Karl
Reply to
Karl Townsend
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VFD as 3P power source or controls for your motors?
Here's a stupid question...why not just turn it off when not in use?
"Karl Townsend" wrote in message news:Ph1Qe.2734$ snipped-for-privacy@newsread3.news.pas.earthlink.net...
Reply to
Eat at Sloppy Joes
I'd first check the no-load power consumption of the idler. If it's 7 amps at near 0 power factor, it doesn't cost much to run. Just watch the electric meter for a little while with the idler being the only load running. That (and a bit of calculation) will tell you cost per hour of the idler's overhead.
My problem with VFD's is that they're so danged complicated. There are a buncha settings to get right. Maybe some of them have "default" values you can invoke if all you want is 3 phase 60 Hz.
Reply to
Don Foreman
I get 15 cents per hour(7amp*220Volt*$0.10/KwHr), or about $54 per month, or $270 per season as my estimate. I've got no way to check power factor. Just watching the meter, you can see it turns way more than the load from all the lights being on in the barn.(1200 watts total). If the VFD has virtually 0 power use at no load, there is enough savings to install it here.
I've got VFDs on the mill and lathe. They both ran right outa the box. I agree there's a ton of parameters. Most all of them will run just fine at defaults.
To answer another fellow's question, we pack apples between each customer visit all day long. We'd be turning it on/off fifty times a day to shut it off when not running. Not practical. We turn on the lights and phase converter when we open the door in the morning, and off when we lock up.
Karl
Reply to
Karl Townsend
"Karl Townsend" wrote in message news:ZT9Qe.1263$ snipped-for-privacy@newsread2.news.pas.earthlink.net...
Karl
Your estimate of the idler's power draw at no load indicates that the idler might be consuming about 2 HP. How big is the idler?
Jerry
Reply to
Jerry Martes
"Karl Townsend" wrote in message news:Ph1Qe.2734$ snipped-for-privacy@newsread3.news.pas.earthlink.net...
VFDs don't seem to create much heat when idling, so I can't imagine they're using much power. I've never checked one with a wattmeter, though.
Reply to
ATP*
Do you have a power-factor correction capacitor on the rotary converter? What you do is connect AC run capacitors between the two sides of the 220V line as it enters the rotary converter, measuring the current in one of those legs (between the circuit breaker and where you add the capacitors), until you get a minimum current. Past a certain amount of added capacitance, you will start to increase the current again.
Anyway -- the current at the minimum will be pretty much the "real" current, and any above that will be "imaginary" current. (They add at 90 degrees, so you can't really just add them, but for most power services, the "real" current is all that you are charged for, and the benefits of tuning the power factor are mostly less heating of the wires and less chance of nuisance trips at the circuit breaker (if your "real" + "imaginary" current takes it close to the trip point.)
It does, indeed.
The problem with using a single VFD for driving several machines is that you are then tempted to switch the power to the individual machines between the VFD and the machine, instead of setting things up so the machine commands the VFD to apply power or not to the machine.
Switching between the VFD and the machine increases the risk of damaging the output circuits of the VFD with the switching spikes. I've gotten away with it when using a 1 hp milling machine on a 7-1/2 hp VFD, but I'm not sure how long I will get away with it even with that big a difference between capacity and load.
Enjoy, DoN.
Reply to
DoN. Nichols
I suspect that there is an easier approach to this.
How about
1) using a radio controlled switch or other switches to turn the RPC on. I have such a switch in the upstairs bedroom fan that we bought at Home Depot. The fan is controlled by a remote. Oher switches could be used.
2) Making a system that detects a no load condition (such as current below 1 amp) for X minutes and shuts the RPC down after X minutes elapsed.
That ought to get the place running sensibly. Workers would sometimes need to remotely start the RPC prior to equipment use, which is no big deal. They do no have to remember to shut it down after use, which is nice. RPC would not be running most of the time, saving bearings and electrons.
i
Reply to
Ignoramus4038
OK. So when should I visit to get some Honeycrisp apples?
Reply to
Don Foreman
...
I've got a monster crop this year. They'll start Sept 24 and go to Dec 18 (last day open) I've got discounts for Semi truck loads.
Karl
Reply to
Karl Townsend
5 hp. idler.
I've got a 5 hp VFD waiting for my Hardinge upgrade. I think I'll stick it in and try it for the fall.
Karl
Reply to
Karl Townsend
One VFD for each machine is really the right way to do it. Not really that expensive for the small motors involved. I wouldn't be surprised if the occasional nuisance fault shuts the line down. We found that out with heating circulators- all of a sudden you put a VFD on and you're dealing with another point of possible failure.
Reply to
ATP*
How were you measuring that 7 amp current draw?
With an amp-clamp meter, right?
Well it was giving you the number that you didn't need to know - it was giving you the total of both in-phase *and* out-of-phase current.
The phase angle for the current flowing an unloaded idler motor like that is about 90 degrees. It's not real current and won't spin your meter.
Get a proper test setup to measure the phase angle and compute the *real* power while it's unloaded, and you will see your idler runs between 200 and 250 watts, most likely. That's the result I found with my 5hp converter.
My estimation is that your converter is not what's costing you the money.
Jim
Reply to
jim rozen
OK, Karl. Don't forget the sack you owe me from a couple years back.
Bob Swinney "Karl Townsend" wrote in message news:qVhQe.1352$ snipped-for-privacy@newsread2.news.pas.earthlink.net...
Reply to
Robert Swinney

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