R.S. Pot, low resistance for initial rotation.

C

Computer Prog

Guest
I bought a RadioShack 5K Linear taper pot for an adjustable power
supply I built. The pot has about 300 degrees of rotation. I
connected the wiper with one of the side terminals and I use the wiper
and the other side terminal to get the resistance. My setup allows me
to get increased resistance with clockwise rotation.

The problem is the first 40 degress or so of rotation stays at 1 ohm.
It then jumps to about 8 ohms and then gradually gets up to 5k. The
first 40 degrees of rotation are basically useless.

Is this typical of a pot?
 
Computer Prog wrote:
I bought a RadioShack 5K Linear taper pot for an adjustable power
supply I built. The pot has about 300 degrees of rotation. I
connected the wiper with one of the side terminals and I use the wiper
and the other side terminal to get the resistance. My setup allows me
to get increased resistance with clockwise rotation.

The problem is the first 40 degress or so of rotation stays at 1 ohm.
It then jumps to about 8 ohms and then gradually gets up to 5k. The
first 40 degrees of rotation are basically useless.

Is this typical of a pot?
Click to expand...
Not good ones.
--
John Popelish
 
I bought a RadioShack 5K Linear taper pot for an adjustable power
supply I built. The pot has about 300 degrees of rotation. I
connected the wiper with one of the side terminals and I use the wiper
and the other side terminal to get the resistance. My setup allows me
to get increased resistance with clockwise rotation.

The problem is the first 40 degress or so of rotation stays at 1 ohm.
It then jumps to about 8 ohms and then gradually gets up to 5k. The
first 40 degrees of rotation are basically useless.

Is this typical of a pot?
Click to expand...
Nope. I would guess you got a clunker -- take it back with the receipt for a
cheerful refund.

Good luck
Chris
 
I already trimmed the length of the shaft and I also soldered onto the
terminals. I doubt my part qualifies for a return. I'll buy another
and take readings off it before I install it. If it reads the same
I'll bring it back.

Nope. I would guess you got a clunker -- take it back with the receipt for a
cheerful refund.

Good luck
Chris
Click to expand...
 
Computer Prog wrote:
I already trimmed the length of the shaft and I also soldered onto the
terminals. I doubt my part qualifies for a return. I'll buy another
and take readings off it before I install it. If it reads the same
I'll bring it back.

Nope. I would guess you got a clunker -- take it back with the receipt for a
cheerful refund.

Good luck
Chris
Click to expand...
How did you cut the shaft? If you put the pot's body in a vice and
sawed it off, you damaged the pot.

You have to clamp the shaft, and make sure any opening is covered to
keep the metal dust out while you cut the shaft.

--
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida
 
I quickly cut if off with an air cut-off tool while the pot was
mounted in my power supply case. I am not sure how I could have
damaged it since the cut only took about 3 seconds. I'll try to blow
it out with compressed air.


How did you cut the shaft? If you put the pot's body in a vice and
sawed it off, you damaged the pot.

You have to clamp the shaft, and make sure any opening is covered to
keep the metal dust out while you cut the shaft.
Click to expand...
 
I took the back off the Pot and this behavior is by design. The
"resistor" area of the outer terminals does not start until about 30
degrees of clockwise rotation. In other words, when it starts in the
fully counter-clockwise position the first 30 degrees of clockwise
rotation has a metal connection under the wiper that looks like a
direct connection. The "resistor" starts after that and only runs for
about 225 degrees of rotation.

IMO a very poor design.
 
computer_prog@hotmail.com (Computer Prog) wrote in message news:<455714d5.0401131213.36667048@posting.google.com>...
I took the back off the Pot and this behavior is by design. The
"resistor" area of the outer terminals does not start until about 30
degrees of clockwise rotation. In other words, when it starts in the
fully counter-clockwise position the first 30 degrees of clockwise
rotation has a metal connection under the wiper that looks like a
direct connection. The "resistor" starts after that and only runs for
about 225 degrees of rotation.

IMO a very poor design.
Click to expand...
I wonder if the cutting off of the shaft may have over-torqued the
shaft and damaged one of the stops - allowing excessive rotation. I've
used quite a few RS POTs - and while not high quality - they've not
been that bad.

Arch
 
I wonder if the cutting off of the shaft may have
over-torqued the shaft and damaged one of the
stops - allowing excessive rotation. I've
used quite a few RS POTs - and while not high quality -
they've not been that bad.
Click to expand...
No, the shaft and the stops are all undamaged. This is the way the
POT was designed. I even went back to the store and popped the back
off a brand new one and I saw the same thing. The first 30 or so
degrees of clockwise rotation was no resistance under the wiper.
 
John Popelish <jpopelish@rica.net> wrote in message news:<4002DC6C.1564EC1A@rica.net>...
Computer Prog wrote:

I bought a RadioShack 5K Linear taper pot for an adjustable power
supply I built. The pot has about 300 degrees of rotation. I
connected the wiper with one of the side terminals and I use the wiper
and the other side terminal to get the resistance. My setup allows me
to get increased resistance with clockwise rotation.

The problem is the first 40 degress or so of rotation stays at 1 ohm.
It then jumps to about 8 ohms and then gradually gets up to 5k. The
first 40 degrees of rotation are basically useless.

Is this typical of a pot?

Not good ones.
Click to expand...
Could it be a design that at some earlier time had a power switch on
the end of the pot? That 30 degree rotation would be about right to
actuate the switch without raising the volume prematurely.

GG
 
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