Drop the potentiometer's resistance with resistors in series?

Thread Starter

LimoCitron

Joined Apr 15, 2021
7
Dear community,

it might sound obviously but I need a 2.6 kOhm Potentiometer but I could only find 2.5 kOhm and a 5 kOhm one.
Could I just put resistors with a resistance of 2.4 kOhm in series with the potentiometer to turn the potentiometer into a 2.6 kOhm one?
Of course I have to pay attention the the resistor's power rating.
Thank you for helping
 

Papabravo

Joined Feb 24, 2006
18,400
Dear community,

it might sound obviously but I need a 2.6 kOhm Potentiometer but I could only find 2.5 kOhm and a 5 kOhm one.
Could I just put resistors with a resistance of 2.4 kOhm in series with the potentiometer to turn the potentiometer into a 2.6 kOhm one?
Of course I have to pay attention the the resistor's power rating.
Thank you for helping
You could put an additional 100Ω in series with the 2.5K potentiometer, but the wiper will not be able to go to full scale or zero depending on which end you place it on. You could also place 50Ω on each end and you would not be able to go all the way to zero or full-scale. There might actually be some advantage to this approach.
 

crutschow

Joined Mar 14, 2008
29,768
Why do you think the pot needs to be exactly 2.6kΩ, since the wiper is adjustable?
Likely a 2.5kΩ pot would work fine.
 

sparky 1

Joined Nov 3, 2018
716
It is a good question, and the right combination usually makes improvement with finer adjustment of potentiometers.
There are calculators online for your convenience. What effect happens by turning the knob a 1/2 inch and what effect would you like to obtain by turning the knob a half inch? For example, my power supply reads 4.90V but when I turn the knob a half inch it jumps to 5.45V. I would like a half inch turn to increase output about one hundred millivolts making it approximately 5.00V.

I think that it is the mV/inch ratio that might be the problem. I could make it have a high and low range. That would be series or maybe switching in a parallel resistor might work as well? Going further I could purchase a 2 -1/2 turn pot so the ratio would be 200mV per inch.

Conversion Calculator Parallel and Series Resistor | DigiKey
 
Last edited:

Audioguru again

Joined Oct 21, 2019
4,666
Why do you need exactly 2.6k? is it for an LM317 adjustable voltage regulator or any other IC?
The LM317C has a range of reference voltage from 1.2V to 1.3V so the potentiometer resistance must match its -4% to +4%.
Other ICs also have ranges in their spec's.
 

MisterBill2

Joined Jan 23, 2018
11,875
Like others already, in order to provide the best advice we need to understand more than just one detail. What sort of circuit requires an exact value between the ends potentiometer? That is not a standard value and so it is not likely that you will find one, ever, although you might find a 2.5 K one that is a bit high.
So please describe what the circuit is so that we can provide more useful options.
 

Ian0

Joined Aug 7, 2020
5,077
Don't forget that the tolerance on potentiometers is usually ±20%, so a 2.5k potentiometer can be anywhere between 2k and 3k.
If your circuit requires it to be 2.6k, does it specify the tolerance?
It the circuit depends on a potentiometer with a precise value, then it's not a good circuit.
 

MisterBill2

Joined Jan 23, 2018
11,875
Dear community,

it might sound obviously but I need a 2.6 kOhm Potentiometer but I could only find 2.5 kOhm and a 5 kOhm one.
Could I just put resistors with a resistance of 2.4 kOhm in series with the potentiometer to turn the potentiometer into a 2.6 kOhm one?
Of course I have to pay attention the the resistor's power rating.
Thank you for helping
Resistances in series ADD, they do b not "average", and so adding 2.4 K ohms in series with 2.5 K will give a 4.9K total resistance.

So once again, I am asking about the application circuit and the reason for wanting a 2.6 K ohm resistance. Even if you can not provide a drawing, a detailed description will work, at least for some of us.
 

Tonyr1084

Joined Sep 24, 2015
6,884
Would this work? The 5.5KΩ resistor in parallel with the 5KΩ pot will give an overall resistance of 2.62KΩ. The wiper can go full rail. Of course we need to know the application. This solution might not be workable in all situations.
1648907176834.png
 

Papabravo

Joined Feb 24, 2006
18,400
Would this work? The 5.5KΩ resistor in parallel with the 5KΩ pot will give an overall resistance of 2.62KΩ. The wiper can go full rail. Of course we need to know the application. This solution might not be workable in all situations.
View attachment 264098
Its a "picky point", but the TS did say "resistors in series". It is also true that "resistors in series" will not drop the resistance of a potentiometer.
 
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