VFD question

Possible? Yes.

Likely to cause a failure in the VFD? Yes.

Just install two VFDs.

They are no longer all that expensive anyway.

Many of them sense how the motor is performing and adjust phase and even voltage and current.
 
brandonmays said:
Can we use 1 vfd to control both the motors if we double the horsepower of the vfd?
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Yes, my teco Westinghouse vfd states that you add up all the hp for all the motors and that is the size vfd you need. I was running a surface grinder with a 1 hpspindle motor and a 1hp hydraulic motor with a 1 hp vfd, ran ok but would throw an overload fault on the vfd. Switched to a 2 hp vfd an no more overload
 
I've got the electrical expertise of a baboon....I can make a light switch work, most of the time.

I bought an old Bridgeport mill 220-440 machine and put a $135.00 VFD on it myownself and it's freakin' AWESOME!!!

Dunno about loading and burnout except to buy something heavy enough to accept the draw (the sell them rated in "horsepower" as in "what horsepower motor they'll run"....worked for me.

The only quirk I've found is that they "wind up" and "wind down" kinda slowly. I do not use the manual spindle stop on the mill but instead portion out my work to allow the spindle to coast to a stop. IMO they're the coolest addition ever for home-owner/hobbyist/prototype guys like I'm.


opinionby




al
 
Break out the manual for your vfd. You can reprogram the ramp up and ramp down times .
alinwa said:
I've got the electrical expertise of a baboon....I can make a light switch work, most of the time.

I bought an old Bridgeport mill 220-440 machine and put a $135.00 VFD on it myownself and it's freakin' AWESOME!!!

Dunno about loading and burnout except to buy something heavy enough to accept the draw (the sell them rated in "horsepower" as in "what horsepower motor they'll run"....worked for me.

The only quirk I've found is that they "wind up" and "wind down" kinda slowly. I do not use the manual spindle stop on the mill but instead portion out my work to allow the spindle to coast to a stop. IMO they're the coolest addition ever for home-owner/hobbyist/prototype guys like I'm.


opinionby




al
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You say two loads separately controlled. Does this mean you wish to switch either load (on/off, forward/reverse etc...) at the machine? VFD's in general do not tolerate switching the load.
 
WSnyder said:
You say two loads separately controlled. Does this mean you wish to switch either load (on/off, forward/reverse etc...) at the machine? VFD's in general do not tolerate switching the load.
Click to expand...

We switch them on everything we use them on. It's required by code to provide for a disconnect between the drive and the load. . On, forward, reverse is controlled in the drive.
 
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So you have a safety disconnect between the VFD and the load but you don't actually use it to switch the load on and off or reverse? You use (like most everyone) the VFD to control your load?
 
TRA said:
We switch them on everything we use them on. It's required by code to provide for a disconnect between the drive and the load. . On, forward, reverse is controlled in the drive.
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I don't know what "code" you are talking about, because last time I checked the NEC does not require a safety switch between the VFD and motor. You do need a lockable, fused disconnect switch or circuit breaker upstream of the VFD. Any kind of switch between the motor and VFD is risking damaging both devices if operated under load. Operating multiple motors on a single VFD is very poor practice and should be prohibited in a responsible commercial or industrial setting.

RWO
 
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WSnyder said:
So you have a safety disconnect between the VFD and the load but you don't actually use it to switch the load on and off or reverse? You use (like most everyone) the VFD to control your load?
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Yes that's how we do it with multiple motors that by application must be set to run at various speeds and loads. With large conveyor systems, if you have a big enough drive you can switch them. All of the motors need to be the same. You cannot mix and match. The small VFD's won't tolerate switching, and are best suited to one drive-one motor.

My comment was just that VFD's can be switched if they are big enough. That's all. Don't try switching Steppers.

I should have been more specific. Most of the low budget drives that are available are not very forgiving.
 
RWO said:
I don't know what "code" you are talking about, because last time I checked the NEC does not require a safety switch between the VFD and motor. You do need a lockable, fused disconnect switch or circuit breaker upstream of the VFD. Any kind of switch between the motor and VFD is risking damaging both devices if operated under load. Operating multiple motors on a single VFD is very poor practice and should be prohibited in a responsible commercial or industrial setting.

RWO
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For industrial applications the NEC is not the last word. There are others, one of which is NFPA 79 that deals with systems under 600v. Over that another takes precedent.

We have to build controls that take all relevant codes into consideration.

There are safety rated drives that are supposed to cover the disconnect issue, but they are not cheap.

Actually all motors in industrial applications have to have an approved fail safe motor disconnect. I don't mean the knife switch on the wall.

We use safety rated contactors, but they only come so large. If you have a large enough application you can use multiple contactors daisy chained together.
 
"If you have a large enough application you can use multiple contactors daisy chained together. "

In series will NOT reliably increase voltage.
The contacts will NOT open at the exact same time.
Whatever unit moves first sees the full voltage.
Arcing eats contacts in relatively short order.

Putting them in parallel to increase current capacity fails for the same reason.
The larger load on initial contact movement produces excessive pitting.


There still are some tricks to contact material though.

Choose carefully and life can be reasonable.
We used to aim for a five year maintenance cycle to R&R the contacts with annual inspections.
 
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brickeyee said:
"If you have a large enough application you can use multiple contactors daisy chained together. "

In series will NOT reliably increase voltage.
The contacts will NOT open at the exact same time.
Whatever unit moves first sees the full voltage.
Arcing eats contacts in relatively short order.

Putting them in parallel to increase current capacity fails for the same reason.
The larger load on initial contact movement produces excessive pitting.


There still are some tricks to contact material though.

Choose carefully and life can be reasonable.
We used to aim for a five year maintenance cycle to R&R the contacts with annual inspections.
Click to expand...

It's not meant to increase anything except the mathematical probably that the contactors will not weld themselves together all at the same time.

The requirement has nothing to do with MTBF or capacity. My reference was that safety rated contactors are not available for larger applications and the work around is to use multiple contractors to satisfy the code requirements. IE, multiple contactors that are NOT safety rated, chained together.
 
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TRA said:
It's not meant to increase anything except the mathematical probably that the contactors will not weld themselves together all at the same time.

The requirement has nothing to do with MTBF or capacity. My reference was that safety rated contactors are not available for larger applications and the work around is to use multiple contractors to satisfy the code requirements. IE, multiple contactors that are NOT safety rated, chained together.
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That is when I used to be hired to produce equipment that WOULD carry the load.

I designed controls for some enormous electric motors over the years. 50,000 HP.

They had to be spun up to near speed before connecting power to not droop the grid.
That is ONE of the ways you reduce contactor damage.

The equipment to OPEN their feed is nearly as complicated.
As the magnetic field in the motor collapses the voltages generated have huge voltage surges.
 
alinwa said:
I've got the electrical expertise of a baboon....I can make a light switch work, most of the time.

I bought an old Bridgeport mill 220-440 machine and put a $135.00 VFD on it myownself and it's freakin' AWESOME!!!

Dunno about loading and burnout except to buy something heavy enough to accept the draw (the sell them rated in "horsepower" as in "what horsepower motor they'll run"....worked for me.

The only quirk I've found is that they "wind up" and "wind down" kinda slowly. I do not use the manual spindle stop on the mill but instead portion out my work to allow the spindle to coast to a stop. IMO they're the coolest addition ever for home-owner/hobbyist/prototype guys like I'm.


opinionby




al
Click to expand...

I have a Taiwan BP clone that has a 3HP 220 3 Phase motor. So, could I use a VFD to replace the rotary converter and use that 5 hp motor for something else?
 
adamsgt said:
I have a Taiwan BP clone that has a 3HP 220 3 Phase motor. So, could I use a VFD to replace the rotary converter and use that 5 hp motor for something else?
Click to expand...

Yes, as long as the motor can be delta connected. If you have a 2spd motor connect to high speed
I am not sure you will gain a lot by doing so though. You actually may lose some functionality on a basic install. Of course this can be made to have all the same functions but this would involve some control and programming of the VFD
If you do go the VFD track a good companion is the MACHTACH speed sensor /display

Michael
 
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