Hacking AC thermostat

skmdmasud

Member

• Jul 24, 2018

• #1

Hi.
I have a situation where the AC temperature control unit is fixed to a specific temperature. I want to control the temperature to some degree. the temperature sensor used is a thermistor rated 1.5k at 22C. Can i place a 1k pot in series with the thermistor to change the temperature. Please suggest.

 

alec_t

Well-Known Member

Most Helpful Member

• Jul 24, 2018

• #2

Assuming the thermistor is a NTC type, the pot in series should enable adjustment to a higher temperature, but not to a lower one. Is that what you want?

 

S

schmitt trigger

Well-Known Member

Most Helpful Member

• Jul 24, 2018

• #3

To complement Alec's reply, if you want to lower the temperature, then a pot in parallel with the thermistor will do the trick.
I would use a pot with a value at least 10X that of the thermistor. And put a fixed resistor in series with the pot, such that the total resistance value NEVER goes down to zero.

 

skmdmasud

Member

• Jul 24, 2018

• #4

Thanks Altech and Schmitt.
Can I place a resistor in parallel and variable resistor in series so that I get a wide control range by turning the variable resistor.

 

S

schmitt trigger

Well-Known Member

Most Helpful Member

• Jul 24, 2018

• #5

It will be a little hassle to fiddle with two controls, but yes you can.

 

skmdmasud

Member

• Jul 24, 2018

• #6

schmitt trigger said:

It will be a little hassle to fiddle with two controls, but yes you can.

Click to expand...

I mean a fixed resistor in parallel and pot in series. So that I will turn the pot to get desires temperature.

 

alec_t

Well-Known Member

Most Helpful Member

• Jul 24, 2018

• #7

That would work too. What temperature range are you interested in?

 

skmdmasud

Member

• Jul 24, 2018

• #8

alec_t said:

That would work too. What temperature range are you interested in?

Click to expand...

20c to 30c.

 

K

KeepItSimpleStupid

Well-Known Member

Most Helpful Member

• Jul 24, 2018

• #9

If you did a few measurements we could figure out the optimum values. initially measure the resistance of the thermister at the fixed temp. Do the parallel combination at 20 and 30. 1/Rt=1/R1+1/R2....1/Rn for a parallel combination.