How slow can VFD go?

[S'mise]

The drive has analog input scaling..
Look at
P60 Analog input Offset
P75 Analog input Min
P76 Analog input Max

P60 is only for Analog input whereas this uses a speed pot. Even If I supplied 0-20ma, I'm guessing it would keep min RPMs within safe boundaries for the motor.

 

[kwired]

Don't know what possible settings are but I'd guess you maybe can have a command input of zero but another minimum output parameter set higher. If so it runs at that minimum output anytime the input command is lower and you also have a run input signal.

 

[gadfly56]

It sounds like the proper solution is a new gear box with the proper ratio. Anything else is a kludge that risks the motor letting out the magic blue smoke.

 

[ptonsparky]

Doing some simple math with sprocket changes on the output side may be all that is needed.

 

[drcampbell]

P60 is only for Analog input whereas this uses a speed pot. Even If I supplied 0-20ma, I'm guessing it would keep min RPMs within safe boundaries for the motor.

It'll keep the frequency output within the programmed-in limits, which might or might not be safe for the motor.
The motor's safety is assured only if somebody does a top-to-bottom system review and sets the minimum frequency (and maximum torque/current) accordingly.

 

[RumRunner]

I have an old Allen Bradley 160 ba03nps1 frequency drive feeding a conveyor belt.

Speed is adjust by a potentiometer except it doesn't go slow enough for the conveyor.

Motor is a 3/4 hp induction that goes into a gearbox (No, I don't know the ratio.)

Minimum Speed set to 0hz and all other parameters look normal to me.

Now I'm wondering how slow can a simple drive like this go?

This is a classic example of “fighting fire while not being able to solve the problem.”

Another instance, that when you feel like you found the solution to this nagging problem—you find out one day that the problem still there.

Very frustrating.

Your hunch:

The problem is borne out of different motor from original, different motor control etc. All of this is legitimate.
I’m not going through lengthy gospel because I’m not having second thoughts about your ability—I think you are capable enough.

After having tried those “hard knocks” approach with no obvious result—its time to go back to BASiCS.

TORQUE is INVERSELY PROPORTIONAL to POWER, divided by SPEED.
Now what’s the possible approach?

The VFD (the modern design) is capable of handling this variation for a satisfactory operation, through external feedback signal from other supporting machine associated with the process).
You should not arbitrarily adjust the speed of that motor with VFD and expect it to operate smoothly through the process.
It is as if solving a problem in one area “while creating another problem downstream”.

All of this has to work in unison.
The result is greater than the sum of its individual parts.
Micro managing is an insidious ailment in managing a problem.

As with old adage in engineering. . . . when things don’t work as intended—go back to the drawing board.

I’ve done that a lot.. . . and I’ve learned something every time.

 

[Russs57]

Might not be relevant but I'll mention it.

The gear box may be splash lubricated. It may have a minimum speed requirement.