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electronic heater help
electronic heater help
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Old 21st April 2003, 09:48 AM   #1
fezz is offline fezz  United Kingdom
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Location: milton keynes, UK
Default electronic heater help

i want to design an electronic heater that heats water to a certain temprature (lets say 60c) and keeps it there, the problem is i really have no idea how to do this so could anyone point me in the right direction.

i was thinking of some sort of comparitor using a set resistor the same value as a thermister at that temprature
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Old 21st April 2003, 06:32 PM   #2
Havoc is offline Havoc
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Location: Belgium
Something like a bridge and a comparator might do it, like you are proposing.

It all depends on what exactly you want. Are we talking about a plate to keep your coffee cup hot at the office, or to keep a swimming pool at temp?

Take a look at the TDA1023.
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Old 21st April 2003, 07:01 PM   #3
Ilianh is offline Ilianh  Canada
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Do not forget to use hysteresis on your comparator otherwise (depending on the use) it might start/stop/start/stop at unwanted speeds (hearing fast clicking relays is not fun).

I remember making a Thermostat for pcb etching thing I made some times ago. It could give the temp in Kelvin and Celsius, had variable temp control and variable hysteresis.

I used a Temperature controlled current source that gives 1 uA at each kelvin degree I think.

Thats the IC http://cache.national.com/ds/LM/LM134.pdf

I remember choosing it because of its precision.

Use a similar Ic (national gives samples) with something like a 1k presision resistor that way at 100uA you have 100mV , a opamp to shift from Kelvin to celsius and a comparator with variable hysteresis.

Do not forget to keep the tracks and leads very short on that kind of circuits.
Time is the best teacher; unfortunately, it kills all its students
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Old 21st April 2003, 07:17 PM   #4
fezz is offline fezz  United Kingdom
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Location: milton keynes, UK
this will be used to heat about a gallon of water, its to remove the crap from it (for other projects such as my computer water cooling)

i definatly need some sort of comparitor, ive decided that when the input is the same as the resistor value the output needs to be zero, but when the thermister value is different it gives a output of 1

seems like i need an or gate comparitor.

this wil be hooked up to a relay to control the temprature of the heater

is it possable that the temprature could go above the set temprature with this setup though?
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