Thermistor

Have knocked up a fan speed controller ... where temp control speed ... and hence cooling.

The temp sensor is a Thermistor - the cct board is inside a metal case, I'm thinking that it might not be responsive enough if the thermistor is inside the case.........

I could arrange to glue it to inside of case lid, or even onto outside of case lid ........ anybody done any thermistor based projects ... just wondered what is normal.

Reply to
rick
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The thermistor should be as close to the area you want to measure as possible. Not sure why it would be inside a case, unless it was the inside of the case's temperature that needs monitoring ....

Reply to
whisky-dave

I take it this is a classified project, since you give us almost no detail. For quick response a thermistor needs to go where you're measuring. For a glacially slow response it can go elsewhere when the temp there follows the temp to be measured.

NT

Reply to
tabbypurr

In message , rick writes

45 years ago:-(

We were not attempting close temperature control. The thermistor was potted inside a short length of metal tube and then clamped to the fins of refrigeration plant.

Reply to
Tim Lamb

ive got temp monitoring on this PC and in warmer weather the internal temps sorta track the outside with a couple of hours lag and the fans going anyway ;-)

seriously, in air, inside a sealed case? forget it. In air inside a case with airflow from whats to be measured going through it, fine.

Reply to
The Natural Philosopher

Are you sure this is going to work?(depends where and how you are using the fan) fans in a closed area don't usually cool,they add heat,(from the motor) unless they are moving cold air from somewhere else or moving hot air which is replaced by colder air. fans make you feel cooler by evaporating sweat, they don't actually change air temp much.

Reply to
F Murtz

Not sure why you think that .... this is a home build project to control the speed of a computer fan ... thus allow cooling of a comms cupboard that gets too hot in summer.

The circuit is based on the cct here:

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They use a bare board ... for safety & longevity building this into al aluminium case. That is why question of where to mount thermistor comes from.

Reply to
rick

Yes it will work ... it is not in a sealed box .. but in top of teh comms room cupboard. The fan will expel air out of the cupboard, fresh air coming in at bottom of cupboard. Ambient temp is fine ... just closed cupboard gets too warm in summer

Reply to
rick

well, you avoided giving us the relvant info, until now

It would work gluing it to the case, but woudl give a time lag in operation, resulting in poor temp control and wasted energy. I'd put it near top of cabinet in the airstream.

NT

Reply to
tabbypurr

Some good old classic components in that circuit :)

Andrew

Reply to
Andrew Mawson

I can't see anything on that page

NT

Reply to
tabbypurr

Basically a 741 op amp comparing a fixed divide chain to one with a thermistor in it - 'supose it could have been even more classic and used a

709

Andrew

Reply to
Andrew Mawson

It's the image from this article

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Reply to
Andy Burns

thanks you two.

That circuit contains no feedback, making it bangbang operation rather than proportional.

Using transistors as temp sensors is cheaper.

NT

Reply to
tabbypurr

Sorry guys referenced wrong cct ...

should be this one .... a fair improvement on basic 741 this gives full PWM control of speed.

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or

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The question is the same.

Reply to
rick

wrong link .... reposted

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Reply to
rick

wrong cct .... corrected

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If you have issues with drop box ... its the Thermistor version here:

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Reply to
rick

I can't see anything wrong with your idea. You need to get the thermistor somewhere near the top of the cupboard - it doesn't have to be directly in the airstream as what you want is to sense the cupboard temperature, not necessarily the airflow. If there is a lot of heat buildup I'd be tempted to duplicate R4, T1 & D1 to add a second fan. As larger fans are quieter and more efficient I think I'd use 2 150mm fans. They should cycle down to a point where there is very little noise.

Just a point - remember that if the thermistor doesn't sense changes in air temperature it can't work. That means you have to make sure that rising air passes it even without the fan(s) running otherwise it won't run them. It's surprising how easy it is to find "dead zones" where this can happen. :)

Reply to
mick

I posted wrong link. This is the correct schematic:

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Or the original article (cct option 3):
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Full PWM control

Same question though on Thermistor position

Reply to
rick

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