Hi all,
Been bashing my head trying to figure out how to control a pwm using a thermistor. At present it is controlled by a pot. Some details:
Pwm is controlled by pot. Voltage running through it is 5v. 5v results in 0% duty cycle and 0 volts 100% duty cycle or wot which then allows the full 12v to flow to the pump.
Application: want to use the pwm to control 12v water pump in an intercooler system in my 4x4. Want to replace pot with thermistor that will operate the pump at 1/2 speed when @ 40°c (or perhaps 30, have to run further tests) and increase speed to wot @60°c. The actual temperature settings at this point in time are irrelevant as its just a matter of playing with resesitors.
Problem: tried replacing in the thermistor. I could only get a ntc type which are non linear which is not ideal but will do. Made more difficult because resistance decreases with temperature.
Initially created a dividing circuit resulting in about 5v going to the pwm which means its 0% duty cycle. To control the pwm the way I want I'm looking at an input voltage (to the pwm) of between 2.5 - 0 volts. I have a bread board which I have been playing with resistors etc but I am no good at the maths which would make it a lot easier than guessing and i have not come close at getting the outputs I need.
I hope it's clear as mud. Any help appreciated. I would draw a picture i knew how to add it.
Cheers
Mat
Been bashing my head trying to figure out how to control a pwm using a thermistor. At present it is controlled by a pot. Some details:
Pwm is controlled by pot. Voltage running through it is 5v. 5v results in 0% duty cycle and 0 volts 100% duty cycle or wot which then allows the full 12v to flow to the pump.
Application: want to use the pwm to control 12v water pump in an intercooler system in my 4x4. Want to replace pot with thermistor that will operate the pump at 1/2 speed when @ 40°c (or perhaps 30, have to run further tests) and increase speed to wot @60°c. The actual temperature settings at this point in time are irrelevant as its just a matter of playing with resesitors.
Problem: tried replacing in the thermistor. I could only get a ntc type which are non linear which is not ideal but will do. Made more difficult because resistance decreases with temperature.
Initially created a dividing circuit resulting in about 5v going to the pwm which means its 0% duty cycle. To control the pwm the way I want I'm looking at an input voltage (to the pwm) of between 2.5 - 0 volts. I have a bread board which I have been playing with resistors etc but I am no good at the maths which would make it a lot easier than guessing and i have not come close at getting the outputs I need.
I hope it's clear as mud. Any help appreciated. I would draw a picture i knew how to add it.
Cheers
Mat
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