some advice on a thermostat please?

[fuseblower]

hello everyone again,
I'm thinking of buying a thermostat for an incubator that iv'e built
here's the product in question>>

**broken link removed**

In the spec's it will cover a range of 5 - 30 degrees C (38 - 86 degrees F )
but i need at least 98-102 degrees F
i know some basics about electronics but im no where near you guys out there.
so my question is do i just need to replace the thermistor or is there anything else i should change any help would be appreciated

i found a schematic at>>
**broken link removed**
for this unit
i want to thank you all in advance and hope someone can help me out.
cheers paul

 

[mvs sarma]

you may consider the Universal Thermostat design published in Elektor UK magazine Summer 2008 (july/August 2008) by RUUD VAN STEENIS on page 82

 

[fuseblower]

ive never heard of that can i download it or something?
cheers

 

[crutschow]

In the spec's it will cover a range of 5 - 30 degrees C (38 - 86 degrees F )
but i need at least 98-102 degrees F

i found a schematic at>>
**broken link removed**
for this unit

From the schematic, you can either reduce the value of R5 or increase the value of R6 to raise the temperature that the relay trips. The NTC sensor resistance is reduced as the temperature goes up, raising the voltage at pin 13 of the op amp. So you want to raise the voltage a pin 12 of the op amp to raise the trip point.

 

[mvs sarma]

ive never heard of that can i download it or something?
cheers

YES. It can be downloaded by paying nominal charges on line

**broken link removed**
you may follow above link

 

[fuseblower]

so its not just a case of changeing the thermistor then ?

 

[mvs sarma]

so its not just a case of changeing the thermistor then ?

Crutschow appears apt. Nice suggestion. By changing the resistor above and below the setting pot, we can change the range.

What i suggested is a full design.

 

[fuseblower]

ok to change the operating range from 41-86 degrees F to 41-102 degrees F i need to increase the value of R6 is this true ????????
would you know by what amount or is this trial and error ( a bit at a time)
cheers paul

 

[crutschow]

ok to change the operating range from 41-86 degrees F to 41-102 degrees F i need to increase the value of R6 is this true ????????
would you know by what amount or is this trial and error ( a bit at a time)
cheers paul

If you measured the value the the thermistor at the desired temperature you could calculate the value required.

If you just want to do it by trial and error, I would try increasing the value of R6 by about double. Just use clip leads to connect different resistors until you find the right value. The correct value would give you the desired temperature trip point at about the midpoint of the pot.

Incidentally, that change would also raise the lower trip point above 41 degrees F.

 

[Willbe]

a range of 5 - 30 degrees C (38 - 86 degrees F )
but i need at least 98-102 degrees F

If your Δ is now only 4°F I'd look into a bridge circuit if the link doesn't already use one; this is a pretty tight range.

 

[fuseblower]

Thanks Carl
well im not bothered about the range i can get as long as i can maintain a 99 degree F
thats what i need
once the temperature goes above 99 deg F then it will switch of the heat, then switch it back on again once it drops below thats the general idea

 

[Andrew Leigh]

Try this

https://www.craig.copperleife.com/tech/thermo/

Cheers
Andrew

 

[fuseblower]

thanks Andrew thats very intresting
cheers paul

 

[Ruud van Steenis]

you may consider the Universal Thermostat design published in Elektor UK magazine Summer 2008 (july/August 2008) by RUUD VAN STEENIS on page 82

You can also download the design from my own server: **broken link removed**