Trash

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
Getting to the end of a project and Trash has become a headache.

We have a holding bin that feeds corn into a small drag via gravity and a slide gate. The gate is manually positioned. The Drag has a 1HP VFD for speed control. The problem is stalks, cobs, etc. can restrict or block the flow of grain. I would like to change the drag motor from a 1750 rpm to a 3600 rpm. At the same time I would change the total gear and belt reductions from 44 to 88 giving me approximately the same maximum drag operating speed and torque as before, but being able to increase the size of the gate opening. Increasing the gate opening right now overloads the drag and the entire process.

Clean corn would have been the best solution but we need to deal with what is.

See any problems with this?
 
ptonsparky said:
Getting to the end of a project and Trash has become a headache.

We have a holding bin that feeds corn into a small drag via gravity and a slide gate. The gate is manually positioned. The Drag has a 1HP VFD for speed control. The problem is stalks, cobs, etc. can restrict or block the flow of grain. I would like to change the drag motor from a 1750 rpm to a 3600 rpm. At the same time I would change the total gear and belt reductions from 44 to 88 giving me approximately the same maximum drag operating speed and torque as before, but being able to increase the size of the gate opening. Increasing the gate opening right now overloads the drag and the entire process.

Clean corn would have been the best solution but we need to deal with what is.

See any problems with this?
Click to expand...
From your description you will have approximately same HP ability from the drag as you did to start with as well as about the same speed. You would still be doing the same amount of work with the same HP motor, with minor change in efficiency, opening the gate further would still overload it.

Unless I am missing something.
 
I don't think you used and accounted for all the variables that your dealing with.

While working on the electricial side seems fine you now dealing with mechanical aspects adjusting for the feed rates, flow ratios, belt ratio's, and other things I probably
didn't call out or called out incorrectly! Changing the pully wheels, and drives is also another critical calc. Corn husk or seed will only fall at some rate, I'd start there.

Maybe a good machinest handbook or some other resource(s).

Easy enough for me to comment from the arm chair! :D
 
kwired said:
From your description you will have approximately same HP ability from the drag as you did to start with as well as about the same speed. You would still be doing the same amount of work with the same HP motor, with minor change in efficiency, opening the gate further would still overload it.

Unless I am missing something.
Click to expand...

The more I think about it, the more I think an increase in horsepower is the first step. Ratio change along with the higher rpm of the motor and the vfd will give us better control of product flow.
 
I would also ask what range of speeds the VFD is running the motor at right now. If generally below 60%, then maybe a drive ratio change is called for to get the motor into a better area of its speed/torque curve.
Otherwise, I agree that more HP is the way to go.
 
The motor is supposed to be rated down to 6hz. My SEWAG for the project is between 20 and 40 hz during normal operation. Programing shuts it down when logic would call for less than 6. Low speed operation is a concern but we won't know how much until we actually make corn flakes.
 
Since it is on a vfd I do not think nema d will make any difference

As prev stated, change to double gearing and double motor rpm Does NOTHING - it is the same end result speed and torque.

But double gearing, keep motor the same, and run 40-80hz Doubles your torque with same end speed! No need for bigger motor yet!
 
ptonsparky said:
The more I think about it, the more I think an increase in horsepower is the first step. Ratio change along with the higher rpm of the motor and the vfd will give us better control of product flow.
Click to expand...

ptonsparky said:
The motor is supposed to be rated down to 6hz. My SEWAG for the project is between 20 and 40 hz during normal operation. Programing shuts it down when logic would call for less than 6. Low speed operation is a concern but we won't know how much until we actually make corn flakes.
Click to expand...

mike_kilroy said:
As prev stated, change to double gearing and double motor rpm Does NOTHING - it is the same end result speed and torque.

But double gearing, keep motor the same, and run 40-80hz Doubles your torque with same end speed! No need for bigger motor yet!
Click to expand...

ptonsparky,

There might be another option, (making some presumptions here). If your VFD is 480V and capable of 2 hp, and your proposed gearing change was to change the sprocket ratio on the output of the gearbox.

Reconnect the motor in the peckerhead for 240V, setup the VFD to deliver 240V at 60 hz and 480V at 120 hz. The end result of these changes will
1. Allow the motor to develop 2hp @ 120hz.
2. Approximately double the torque at the conveyor.
3. Double the turn down ratio of the setup.

Some precaution will be needed, a note or documentation to define why this was done, (think about the poor sparky that comes across this setup 240 V connection in the peckerhead and a 480 system)

This solves the problem of what happens to motor torque at speeds above 60 hz.
 
milldrone said:
ptonsparky,

There might be another option, (making some presumptions here). If your VFD is 480V and capable of 2 hp, and your proposed gearing change was to change the sprocket ratio on the output of the gearbox.

Reconnect the motor in the peckerhead for 240V, setup the VFD to deliver 240V at 60 hz and 480V at 120 hz. The end result of these changes will
1. Allow the motor to develop 2hp @ 120hz.
2. Approximately double the torque at the conveyor.
3. Double the turn down ratio of the setup.

Some precaution will be needed, a note or documentation to define why this was done, (think about the poor sparky that comes across this setup 240 V connection in the peckerhead and a 480 system)

This solves the problem of what happens to motor torque at speeds above 60 hz.
Click to expand...

I've read about doing this but...:? and cautious.

Ok. We are already thinking that in increase in HP is needed so the VFD needs increased in size anyway. The price between a 2 and 3 HP is negligible with little or no wiring change needed other than a bigger line reactor.

Keeping the 1 HP rated at max of 1750 rpm, changing the motor configuration and VFD parameter as you suggested, will allow me to run it at 3600 rpm while developing 2 hp?

I would still need to make the ratio changes to the input side of the gearbox. Sheave ratio now is 1.45 with a gearbox ratio of 30.9.

Using the same arrangements and changing the motor only I could use a 1.5 to get 3 HP.
 
ptonsparky said:
I've read about doing this but...:? and cautious.
Click to expand...

It is only possible if you have 480V power and a reconnectable motor. You may already be aware of loss of motor torque above 60 hz. To satisfy the needs of the motor the VFD needs to output 8 volts per hertz when the motor is configured for 480, obviously the VFD runs out of volts at 60 hz. When a motor is configured for 240 V The VFD now has the ability to provide 4 volts per hertz, so now it can go to 120 hz without running out of volts.

You had already mentioned a problem with the lack of torque. By doubling the gear ratio you would have twice the torque at 60 hz, but you would have half the speed. If you had the motor configured at 480 volts, then you would be in a constant hp mode above 60hz (higher speed but less torque).

ptonsparky said:
Keeping the 1 HP rated at max of 1750 rpm, changing the motor configuration and VFD parameter as you suggested, will allow me to run it at 3600 rpm while developing 2 hp?
Click to expand...

Yes. I'm only suggesting this if all the components are already in place, and a simple sprocket change on the output of the gearbox to driven shaft is possible.

ptonsparky said:
I would still need to make the ratio changes to the input side of the gearbox. Sheave ratio now is 1.45 with a gearbox ratio of 30.9.
Click to expand...

Depending on the capacity of your gearbox the preferred method is to add the extra ratio after the gearbox.
 
milldrone said:
Is only possible if you have 480V power and a reconnectable motor. You may already be aware of loss of motor torque above 60 hz. To satisfy the needs of the motor the VFD needs to output 8 volts per hertz when the motor is configured for 480, obviously the VFD runs out of volts at 60 hz. When a motor is configured for 240 V The VFD now has the ability to provide 4 volts per hertz, so now it can go to 120 hz without running out of volts.

You had already mentioned a problem with the lack of torque. By doubling the gear ratio you would have twice the torque at 60 hz, but you would have half the speed. If you had the motor configured at 480 volts, then you would be in a constant hp mode above 60hz (higher speed but less torque).



Yes. I'm only suggesting this if all the components are already in place, and a simple sprocket change on the output of the gearbox to driven shaft is possible.



Depending on the capacity of your gearbox the preferred method is to add the extra ratio after the gearbox.
Click to expand...
Gearbox is direct mount to load shaft. Sheaves at motor and input to gearbox are the option.

The only thing we supplied was the vfd but if something doesnt work it seems to we get to figure out how to make it work. We may give your suggestion a try. Can't more than let smoke out.
 
I question how long a typical general purpose 60Hz motor is going to last if applied with 120 Hz and double the rated voltage. Even if the stationary windings can take this what about the rotor, and the bearings?
 
ActionDave said:
I'll bet on the windings giving out first. I like my odds.
Click to expand...
I kind of thought that as well. I know you shouldn't run a motor over it's designed frequency, you may get away with say 80 maybe 90 Hz on a 60 Hz design but not all that certain on all the details as to why, but 120 Hz - probably not going to go so well
 
ptonsparky said:
It is a Vfd rated motor although the 1800 rpm max does give me pause.
Click to expand...

Then why not just double the gear ratio as you suggested but NOT change the present motor?

Double your torque, double or triple your output HP with no need to pause for concern? See my post #10 again....
 
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