VFD & two motors

[ptonsparky]

Customer has two identical auger motors that he wants to control the speed of.

One VFD, with only one of the two motors being online at a time. Product A or Product B. Never both. I anticipate interlocking a couple contactors or starters of adequate size so one or the other must be "On" before the VFD is allowed to start, and VFD "Off" before contactor A or B is allowed to open.

Is a HP rated GP contactor adequate or should I be using a Starter, minus the overload block?

 

[kwired]

Customer has two identical auger motors that he wants to control the speed of.

One VFD, with only one of the two motors being online at a time. Product A or Product B. Never both. I anticipate interlocking a couple contactors or starters of adequate size so one or the other must be "On" before the VFD is allowed to start, and VFD "Off" before contactor A or B is allowed to open.

Is a HP rated GP contactor adequate or should I be using a Starter, minus the overload block?

Take away the overload block and you are left with a contactor, did you mean to ask something more specific?

 

[ptonsparky]

Take away the overload block and you are left with a contactor, did you mean to ask something more specific?

No, just is one more suited to the task of load side VFD vs the other. GP contactors seen a bit whimpy.

 

[petersonra]

Personally, I would be inclined to use a reversing contactor for this. You would need to remove the jumper wires on the load side of the contactor and take off the overload. The VFD can provide the overload protection.The reversing contactor gives you both electrical and mechanical interlocks.

 

[petersonra]

No, just is one more suited to the task of load side VFD vs the other. GP contactors seen a bit whimpy.

as long as it does not have to make or break loads it won't matter any.

 

[Cow]

Personally, I would be inclined to use a reversing contactor for this. You would need to remove the jumper wires on the load side of the contactor and take off the overload. The VFD can provide the overload protection.The reversing contactor gives you both electrical and mechanical interlocks.

I was also thinking the same thing, a for/rev starter sounds like a good fit.

 

[kwired]

No, just is one more suited to the task of load side VFD vs the other. GP contactors seen a bit whimpy.

By GP do you mean a "definite purpose contactor"? Otherwise my point is there are NEMA contactors, IEC contactors, as well as definite purpose contactors, all can be ordered with or field fitted with a motor overload assembly which makes them "motor starters".

I have seen similar setup before for a belt conveyor that needed to be able to run both directions as well as had a need to vary speed.

Belt conveyors tend to not reverse all that well as you need to have the "pull tension" coming from the top side of which ever end you want to move material toward. So they fit a motor on both ends and isolated them with contactors on output side of drive - been long enough ago I don't recall many details but seems like mechanical interlock would be a good idea, as well as aux contact in control circuit arranged so that drive will not run unless correct contactor for the conditions is engaged.

 

[Jraef]

Leave the OL relays on the starters. The reason is, if one motor starts to overload, and you switch to the other motor, the drives OL circuit will have a thermal retention that will think the new motor is already hot and it might nuisance trip.

Use a NEMA starter with a melting alloy OL relay, they are insensitive to the harmonics on the output of the VFD, which can potentially cause no-metal OL relays to nuisance trip.

 

[kwired]

Leave the OL relays on the starters. The reason is, if one motor starts to overload, and you switch to the other motor, the drives OL circuit will have a thermal retention that will think the new motor is already hot and it might nuisance trip.

I'm assuming you suggest to set the overload setting of the drive to a higher level then you normally would or even disable it if the drive allows that in that situation?

 

[ptonsparky]

Melting alloy. Do they even offer them any more?

 

[ptonsparky]

Yes, GP should be DP. :ashamed:

 

[petersonra]

Melting alloy. Do they even offer them any more?

I don't know. Rarely use NEMA starters. The last one I bought came with an adjustable OL. I much prefer them since I almost never know what the NP FLC is going to be. heck, sometimes what turns up in the field isn't even the voltage they told me, or the HP.

 

[Jraef]

I'm assuming you suggest to set the overload setting of the drive to a higher level then you normally would or even disable it if the drive allows that in that situation?

Yes, if you have external OL relays, turn the OL in the VFD off or set it higher.

Melting alloy. Do they even offer them any more?

AB, Siemens (in the old Furnas line) and Sq. D still offer them on NEMA starters, I think GE maybe, but it's been a long time since I've had anything to do with GE controls.

I prefer SSOLs now, but for when you need an OL on the output of a VFD like this, the SSOLs usually dont work and eutectic alloy versions are actually better than bi-metal. It's not that bi-metal don't work, they do. But they tend to heat up faster than normal and nuisance trip, then the human response to that tends to be to turn up the dial, which leads to motor failure. If you can resist the temptation to turn it up, that's fine, but the next guy may not understand. Sure, you could install larger eutectic alloy heaters too and have the same problem, but it's harder to do, plus the eutectics don't nuisance trip in the first place.