Change or convert a potentiometer value from one to another (2K to 100R)

Thread Starter

JoeCK

Joined Mar 20, 2020
62
I don't think Pan's approach will work in this case. Looks to me like you're going to need the correct pot.

One thing that mod doesn't have is temperature feedback. In other words, setting the temperature depends on your ability to test the temperature at the tip independently. Perhaps a rotary switch with a number of resistors to give you the desired temperatures. That way you'll have a ballpark temperature in mind.

A four position rotary switch should give you enough choices, although a pot will give you infinite temperature choices over its total range. I'd opt for 480˚• 440˚ • 345˚ • 200˚ (Celsius). Being in the U.S. and more familiar with Fahrenheit; those temps covert to 896˚ • 824˚ • 620˚ • 392˚ (Fahrenheit).
Thanks Tonyr,

"four-position rotary switch" seems to be doable with predictable outcomes :)
If can not catch hold of any pot conversion methods, I will definitely take this route.
 

panic mode

Joined Oct 10, 2011
2,715
if you need 100 Ohm pot, get an 100 Ohm pot.
if you want to use some sort of substitute, better show the pot function in a circuit so one can see how it is to be used. only then one may offer alternative or workaround. btw pot has parameters other than resistance... power rating, linearity, max wiper current etc are some things to consider.
 

Thread Starter

JoeCK

Joined Mar 20, 2020
62
If you need a 100Ω pot you buy or scrounge a 100Ω pot.
Ok MrChips,
I want to learn how to work around substitute/equivalent pots in the process.
If no one here is able to figure it out,... then I will try to take your path :)
 

Thread Starter

JoeCK

Joined Mar 20, 2020
62
if you need 100 Ohm pot, get an 100 Ohm pot.
if you want to use some sort of substitute, better show the pot function in a circuit so one can see how it is to be used. only then one may offer alternative or workaround. btw pot has parameters other than resistance... power rating, linearity, max wiper current etc are some things to consider.
Thanks panic mode,

I have shown the pot location and it's use in the circuit in a video earlier. Here I'm concerned only with the resistance. (all other parameters are negligible in their use in this circuit)
 

MrChips

Joined Oct 2, 2009
30,707
Now seriously, if this is to control the wattage on a soldering iron, you take the 2kΩ pot wired to a 555-timer circuit and PWM the power on the soldering iron.
 

crutschow

Joined Mar 14, 2008
34,281
If no one here is able to figure it out,..
As noted, there is nothing to "figure out".
A small resistor in parallel with larger value pot will give a very non-linear resistance change with pot rotation.
Below is a simulation showing the non-linearity in the parallel resistance of a 2kΩ pot with a 100Ω resistor versus pot wiper rotation (Yellow trace).

1666378894135.png
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
7,852
Now seriously, if this is to control the wattage on a soldering iron, you take the 2kΩ pot wired to a 555-timer circuit and PWM the power on the soldering iron.
When I watched the video it looked like the board was controlling the wattage. The 0Ω resistor made the iron operate at (what I was assuming before seeing the video showing how to program the iron), made the iron operate at max output. Changing that resistor would change the output as was listed.

I don't think PWM being added to the system, which may already be PWM, I don't think that's the right approach. Now just because we disagree doesn't mean I don't respect you or your opinion (or answer). Just I think the PWB already is controlling the wattage of the iron. There is no feedback, so it's probably programmed to deliver a certain amount of wattage at whatever the internal programming is set for.

I still like the idea of a rotary switch with a set of resistors which can be selected to replace that 0Ω surface mount resistor. If you "Know" the temp with a certain resistor, and with each subsequent resistor, then you can simply switch to the desired wattage and away you go.
 
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