Help with speed pot on my VFD

Wloch248

Wloch248

Joined
Jan 2, 2010
Messages
337
Hey guys,

So I went to sand off a little scale on my platen so I could put a ceramic liner on it and finally get to grinding. The grinder and VFD are all hooked up and had been running/operating fine.

The VFD is a Teco FM50. I got the 10k speed pot from Radio Shack and like I said it was working fine. Now it only stays at 10Hz. I have function 6 (upper limit) set to 60Hz and function 11 set to 1 for a speed pot input. Now I can't control motor speed with the speed pot. I changed function 11 back to 0 for keypad control and that works fine. None of the wiring was touched and the connections to the speed pot were soldered. No loose wire on the vfd end either. Also, everything was cooled down and hadn't been run in a little while.

So, is the pot bad? Can you test via impedance or something of the sort?

Any suggestions? Other than just getting a new one.

Thanks!

Nathan
 
I don't quite understand.


1.

Did you have the pot hooked up in the past - used to work using the pot and has now failed?
I agree with Brian - test the pot for open circuit - infinite resistance.


or

2.

The VFD used to work, but now since you installed the pot for the first time it is stuck on low speed ?

There are 3 leads on the pot.

05112.png



If you installed on the 2 outside leads, you eliminated the wiper contact and turned a variable resistor into a fixed 10k resistor.
Which would put you on lowst speed.

You want to use 2 of them, but not the outside two.

The left 2, or the right 2.

If you have an ohm meter,
turn full left = counter clockwise and pick the 2 leads that give max ie 10 k ohms for lowest speed
turn full right = clockwise and pick the 2 leads that give minimum or zeroish ohms.
These 2 tests should give you the same 2 leads.



and

There are 2 types of potentiometers, linear and Logarithmic
You probably want linear so the adjustment is spaced equally throughout the movement of the knob.
 
These VFD's actually use all 3 poles Count.

+10v, wiper, and a common.

+10V and common are the two outsides, with the wiper naturally being the center.

If the speed varies in the wrong direction, swap the 2 outside wires.
 
Fellhoelter said:
These VFD's actually use all 3 poles Count.

+10v, wiper, and a common.

+10V and common are the two outsides, with the wiper naturally being the center.

If the speed varies in the wrong direction, swap the 2 outside wires.
Click to expand...

That's different.

Well then I'm FOS
 
Not FOS, but just not correct in this instance. On all VFD devices I have used, the three wires are as Fellhoeter said.
The potentiometer acts as a resistor with a center tap. The tap ( wiper) gives a refference voltage which sets the speed program. Without the winding fully in the curcuit, it won't work.

If all three wires are connected correctly, I would suspect a bad potentiometer.

Only other thing is that the pot should be isolated from ground. Here is an excerpt from the KB manual:
WARNING!
Do not earth
ground any Main Speed
Potentiometer terminals.
Note: When mounting the Main Speed
Potentiometer, be sure to install the insulating
disc (supplied) between the potentiometer
and the panel.
 
Thanks for the replies guys.

It was previously hooked up with the speed pot and working flawlessly.

It is not grounded.

It just started this out of the blue yesterday. I just got home and haven't had a chance to look at it yet but I will be checking the resistance. I have a feeling that the pot is fried and I will just have to buy a new one.

Thanks again,

Nathan
 
If you do have to get a new one, be sure to look for Linear



Logarithmic is used for audio applications.
Radio shack is usually not great on the info they give you.
 
A quick test to see if its linear taper versus Log taper is the 50 % point of a Lin taper is 5k ohms. On a log taper it will be closer to 8k ohms.

Test this out of circuit.
 
I had done lots of research prior to hooking everything up and i was the linear taper.

I was passing a Radio Shack on the way home and decided to just pick up a new one considering they are only $3.

Hooked the new one up and working great, reconnected the old one and nothing. So it was busted.

Now I can get back to more important things like grinding :)
 
I don't know to much about VFD's but do know a little about electronics. Just thought I would toss this out as I did not see anyone else touch on this. A pot will have a specific wattage rating. I'm not sure what the circuit in the VFD is running through the pot but maybe your pot is a little under rated for the circuit, which would make sense as to why it was working fine and then just stopped working. Another thing is that Radio Shack is way over priced and I would suggest sourcing a radio component supplier or electronic component supplier in your area, you will probably pay half the cost of Radio Shack.
 
The one I bought was the same as the first one. It was rated for 500VDC 0.5W. I could fine no mention in the manual about wattage rating for the pot.

Another thing I had a question about was if everyone shuts down the power to their VFD when not in use. Mine is wired directly to the sub panel and I have been shutting the power off to it by flipping the breaker.

Is that a big no no? I couldn't imagine it would give a much bigger surge than if I had an inline switch installed.
 
Doesn't your drive have a power switch?

The On/Off switch on most VFDs and DC drives cuts the incomming power. The RUN/STOP switch turns on and off the power out.

The power switch should be just before the main fuse in the circuit.

It is always best to shut off the VFD RUN/STOP switch to stop the motor , and then shut off the power. Doing it the other way around can damage the drive.

Using a breaker for a power switch is a bad idea.
 
I don't know for sure but I have been told that using a breaker for a power switch will ruin the breaker in short time. That is not at all what they are meant for. And I guess it's could be possible that tuning the unit on and off from the breaker could be surging the pot circuit and causing you the problem, that would just be a wild guess formulated form the fact that using a breaker as a power switch is a no no, and can't be good for the VFD.

I have no idea what the circuit on that pot is running but .5W pot is pretty typical. You can find higher watt rating pots. You could just step it up. Although it should just be a signal type circuit, so there should not be any significant current going through the pot so I really don't see why a .5W would not be just fine. Have you tried calling the VFD manufacturer and asking them what pot should be used?

BTW, you said it was the same as the first one? So this is the second time a pot failed on your VFD?
 
ShadowsHamon said:
.


BTW, you said it was the same as the first one? So this is the second time a pot failed on your VFD?
Click to expand...

No this time was the first time.

Stacy,

I am not "starting/stopping" the motor by flipping the breaker. I usually just leave the VFD on because the drive does not heat up at all while just idling. I only use the breaker to shut it off for servicing like when I switched the pot. I have the motor wired to a start/stop switch.

I spent about 5 minutes trying to turn the VFD off via the keypad with no luck. There is no switch for this purpose on the VFD. Pressing the run/stop button once or holding it down does nothing. No other button pressing combo worked. I could find nothing in the manual about turning it on or off. It listed some of the other vfds as having a power switch but those actually have a switch on the front of the drive.

I will prob just keep it on.
 
Btw. Do you have the Teco protected from grinding dust? It doesn't have a NEMA 4 enclosure and can/will be fried by the dust. Many guys have no problems with theirs when they put them in another room, or build a box for it with filters for air flow. Food for thought! :-)
 
It is in a Nema 4 enclosure with some filters.

And I am having my buddy put a switch in.

Thanks,
Nathan
 
bladsmth said:
WARNING!
Do not earth
ground any Main Speed
Potentiometer terminals.
Note: When mounting the Main Speed
Potentiometer, be sure to install the insulating
disc (supplied) between the potentiometer
and the panel.
Click to expand...

Just got my pot this afternoon and there is no insulating disc in the pack. What would be something OK to use to insulate it ?? a business card ? real thin piece of wood?
 
You must log in or register to reply here.
Back
Top