I have a 220v VFD that is being used to control a blower fan. The VFD has a potentiometer on it that controls the speed of the blower. I'd like to move that pot off the board (or over-ride) it to put the pot control knob on a control panel with the rest of the controls. I put my multi-meter on the center and outer pin and found the resistance to be 0k-2.85k. Does that mean I would go with a 3.5k resistor? The only options on mouser are 2.5k and 3.5k. This is what I found.

Also with the current VFD, the range that it adjusts the blower is very small, too low and it shuts down, too high and its full speed. Is that the fault of the potentiometer or the nature of the VFD? The VFD model is Delta VFD-L (25/40W 230V 1 Phase). Its being attached to a Orix MB1255-T Blower.

 

You really cannot check the value of the potentiometer in circuit. I suggest you look carefully at the user and operation manual as my read is many of their units have a provision for external signal for motor speed control selectable via internal dip switches. There are also provisions for high and low torque applications. Here is an example of one such manual. I suggest you contact the manufacturer as to remote control. That or remove the potentiometer and use some extension wires to relocate it.

Ron

 

You really cannot check the value of the potentiometer in circuit. I suggest you look carefully at the user and operation manual as my read is many of their units have a provision for external signal for motor speed control selectable via internal dip switches. There are also provisions for high and low torque applications. Here is an example of one such manual. I suggest you contact the manufacturer as to remote control. That or remove the potentiometer and use some extension wires to relocate it.

Ron

Hi Ron,

Basically I’m looking to replace the pot with a panel mount pot, that’s all. So I want to remove the current pot and extend it with wires but I want a panel mount pot. If that wasn’t clear I’m sorry. I’ve found schematics for other versions of this VFD and they have either a 3k or 5k pot. If one was to guess on a pot, what is the safer way to go, higher or lower?

 

If one was to guess on a pot, what is the safer way to go, higher or lower?

I'd spend a bit more effort finding the details of the existing pot. You may be able to read a part number off it, and of course measure it once you get it out of the circuit.

It's likely a linear taper pot but it doesn't have to be.

You can tweak a pot with external resistors if it doesn't work the way you like, but the closer you get with the replacement the less hassle it will be for you.

 

I'd spend a bit more effort finding the details of the existing pot. You may be able to read a part number off it, and of course measure it once you get it out of the circuit.

It's likely a linear taper pot but it doesn't have to be.

You can tweak a pot with external resistors if it doesn't work the way you like, but the closer you get with the replacement the less hassle it will be for you.

Got it! I'll remove the current one and see what I can come up with. There is some options to remotely control, but its all via modbus controls, which I don't believe will allow for me to use a potentiometer. I'd prefer to just use a pot.

 

Got it! I'll remove the current one and see what I can come up with. There is some options to remotely control, but its all via modbus controls, which I don't believe will allow for me to use a potentiometer. I'd prefer to just use a pot.

Remove the pot and let's see what you have. Then I would think about using a 10 turn pot if you don't simply extend the wires for the existing pot. Anyway, all here nor there till you know exactly what you have.

Ron

 

Okay, got the pot off. Two outer pins read 4.92. The only markings I can read, on the top it says 501F, underneath that it says 502B2.

Also, I have a bourns 10-turn 10k pot here, anyway to make that work?

 

That is a 5k ohm pot. (assuming the meter is in the k range)

You can use a 10k pot but you will have to place a resistor across it, and deal with the fact that it won't be the way the original was.

 

Well I’m in no rush, so I’ll just order a 5k 10 turn pot and a standard 5k pot.

 

Just make sure the replacement pot is the same or greater wattage. Should work out fine.

Ron

 

The manual states a 3k to 5k pot, ensure it is linear version.
Most have Modbus input and this allows precise frequency (speed) setting.
Max.

 

So I ended up taking one of my 10k 10-turn bourns pots and put a 10k resistor on it. The fan control works really well now, significantly better than the stock pot. The only thing I can't figure out is, one of the buttons on the control panel of the roaster (not the VFD) lights up very dimly when the VFD is powered up. I can't for the life of me figure out why that is happening. Should I be concerned?

@MaxHeadRoom are you familiar with modbus? I might try and set that up, the software I use for data logging also allows for modbus control and reading of VFD's. I've been reading about modbus and its all a bit foreign to me.

 

Modbus is a serial RS485 interface and you need to know the protocol used by the VFD, normally it is in the manual, if this is a higher end VFD.
Max.