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

Thread Starter

JoeCK

Joined Mar 20, 2020
61
Hello Guys,

I have 2K ohms potentiometer (as well as 50K, 100K pots to hand if they any better) and would like to convert it into 100 ohms.
(found it very hard to find 100R pots, and have a few of the above-mentioned values to hand as well)

And hopefully, full turn rotation/range of the pot is usable.

Any help would be appreciated.
 

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Ian0

Joined Aug 7, 2020
6,706
Hello Guys,

I have 2K ohms potentiometer (as well as 50K, 100K pots to hand if they any better) and would like to convert it into 100 ohms.
(found it very hard to find 100R pots, and have a few of the above-mentioned values to hand as well)

And hopefully, full turn rotation/range of the pot is usable.

Any help would be appreciated.
It depends on the circuit.
In some circuits it can be directly replace with no other changes.
In some circuits a 110Ω resistor between the outer terminals will do the trick
In some circuits it just has to be 100Ω
 

ThePanMan

Joined Mar 13, 2020
520
Wonder if this would work: a 2K pot in parallel with a 100Ω resistor. The resulting value is 95Ω (105Ω ultimately will achieve 100Ω)

One thing for certain, you'll have to watch the wattage. Replacing any pot with a lower value is going to have to handle higher wattage. Depending on the final wattage, you could find yourself burning up your pots.
 

ThePanMan

Joined Mar 13, 2020
520
Depends on how you intend to use the pot. If it's as a voltage divider then you don't need 100Ω. If it's for some other reason, depending on how you intend to use it - that's important. Wattage is going to play a significant role in the application.
 

AlbertHall

Joined Jun 4, 2014
12,187
Thank you for the reply.

However, I have seen modifying values of pots by paralleling/serialising a resistor between the terminals.
There are some problems with that approach.

If it is used as a rheostat (wiper connected to one end of the track) then the resistance will indeed vary from 0 to 100 but all the variation being at one end of the rotation.

if it is connected as a voltage divider then when the pot is in the middle of the rotation then you gave a much larger output resistance. If the load resistance is low this could severely affect the output voltage.
 

Thread Starter

JoeCK

Joined Mar 20, 2020
61
It depends on the circuit.
In some circuits it can be directly replace with no other changes.
In some circuits a 110Ω resistor between the outer terminals will do the trick
In some circuits it just has to be 100Ω
Thanks Ian0,
I'm trying to mode a portable soldering iron circuit which has an internal option to add a potentiometer. (at the moment the temperature signal line is shorted with a 0ohm SMD resistor)
 

Thread Starter

JoeCK

Joined Mar 20, 2020
61
I don't see why 100 ohm pots would be difficult to find. What is the pot controlling?
Hello dl324
I'm trying to mode a portable soldering iron circuit which has an internal option to add a potentiometer. (at the moment the temperature signal line is shorted with a 0ohm SMD resistor)
 

Thread Starter

JoeCK

Joined Mar 20, 2020
61
There are some problems with that approach.

If it is used as a rheostat (wiper connected to one end of the track) then the resistance will indeed vary from 0 to 100 but all the variation being at one end of the rotation.

if it is connected as a voltage divider then when the pot is in the middle of the rotation then you gave a much larger output resistance. If the load resistance is low this could severely affect the output voltage.
Thanks AlbertHall,

This is exactly what I'm trying to do in the video;
 

Thread Starter

JoeCK

Joined Mar 20, 2020
61
Depends on how you intend to use the pot. If it's as a voltage divider then you don't need 100Ω. If it's for some other reason, depending on how you intend to use it - that's important. Wattage is going to play a significant role in the application.
Thanks ThePanMan,

Need to do exactly like in this video, however, I only have 2K, 50K, and 100K pots in hand.

 

Jon Chandler

Joined Jun 12, 2008
432
Big Clive has 2 videos on this soldering iron.

The first is a tear-down and analysis of the iron, including testing different resistor values versus temperature. If you can't get a 100 ohm pot, the best bet is a fixed value resistor. Please keep reading on the other side of the video.


Clive's second video shows an undocumented "calibration" mode. Click on the button to lower or increase temperature. The downside is that there's no feedback of what the temperature is, other than knowing the temperature changes by ~4° per click (most of the time).


The advice I can give you is to check out Tayda Electronics for parts. They are located in Thailand with excellent prices on quality parts, with reasonable prices on prompt shipping.
 

Tonyr1084

Joined Sep 24, 2015
7,199
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).
 

Tonyr1084

Joined Sep 24, 2015
7,199
Clive's second video shows an undocumented "calibration" mode. Click on the button to lower or increase temperature. The downside is that there's no feedback of what the temperature is, other than knowing the temperature changes by ~4° per click (most of the time).
Interesting video. Probably the best solution for when you plan on doing a lot of soldering at a given temperature. But again, you have to test the tip temperature to know for sure what temp you're working at. I still think changing the resistance in known increments will give you a better sense of the tip temp without having to test every time.

My soldering iron has three pre-settable temps. I can choose "Channel A" and set it to whatever temp I want and the iron (with feedback) will reach that temp. Channels B & C can also be set at any temp I choose and it will remember those temps until I make changes. So I can set three different temp's simply selecting a channel. A rotary switch will give you the same options WITH a known outcome once you've documented it.
 

Thread Starter

JoeCK

Joined Mar 20, 2020
61
Big Clive has 2 videos on this soldering iron.

The first is a tear-down and analysis of the iron, including testing different resistor values versus temperature. If you can't get a 100 ohm pot, the best bet is a fixed value resistor. Please keep reading on the other side of the video.


Clive's second video shows an undocumented "calibration" mode. Click on the button to lower or increase temperature. The downside is that there's no feedback of what the temperature is, other than knowing the temperature changes by ~4° per click (most of the time).


The advice I can give you is to check out Tayda Electronics for parts. They are located in Thailand with excellent prices on quality parts, with reasonable prices on prompt shipping.
Thanks Jon Chandler,

I have seen these videos. However, would like the "pot-adjust" way for the safer side.

"second video shows an undocumented "calibration" mode" - it seems to be not practical especially with hobby solderings using various temperatures.
 
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