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.

On Thursday, 21 May 2015 16:05:37 UTC+1, rick wrote:
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.

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 ....

On Thursday, 21 May 2015 16:05:37 UTC+1, rick wrote:
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.

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

On 21/05/15 20:43, wrote:
On Thursday, 21 May 2015 16:05:37 UTC+1, rick wrote:
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.

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

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.


--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. €“ Erwin Knoll

On 21/05/2015 20:43, wrote:

I take it this is a classified project,

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 he
https://www.dropbox.com/s/rewcotpvkd...rcuit.jpg?dl=0

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.

On Friday, 22 May 2015 14:17:19 UTC+1, rick wrote:
On 21/05/2015 20:43, nt wrote:

I take it this is a classified project,

Not sure why you think that .... this is a home build project to control

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

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 he
https://www.dropbox.com/s/rewcotpvkd...rcuit.jpg?dl=0

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.

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

wrote in message
...

On Friday, 22 May 2015 14:17:19 UTC+1, rick wrote:
On 21/05/2015 20:43, nt wrote:

I take it this is a classified project,

Not sure why you think that .... this is a home build project to control

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

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 he
https://www.dropbox.com/s/rewcotpvkd...rcuit.jpg?dl=0

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.

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

Some good old classic components in that circuit

Andrew

On Friday, 22 May 2015 16:37:01 UTC+1, Andrew Mawson wrote:
wrote in message
...
On Friday, 22 May 2015 14:17:19 UTC+1, rick wrote:
On 21/05/2015 20:43, nt wrote:

I take it this is a classified project,

Not sure why you think that .... this is a home build project to control

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

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 he
https://www.dropbox.com/s/rewcotpvkd...rcuit.jpg?dl=0

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.

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.

Some good old classic components in that circuit

I can't see anything on that page


NT

On 22/05/2015 14:17, rick wrote:

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 he
https://www.dropbox.com/s/rewcotpvkd...rcuit.jpg?dl=0


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.




Sorry guys referenced wrong cct ...

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


https://www.dropbox.com/s/gjypepcuzn...IC502.pdf?dl=0

or http://tinyurl.com/nanzf8d

The question is the same.

In message , rick
writes
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.

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.

--
Tim Lamb

rick wrote:
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.

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.

On 22/05/2015 06:24, F Murtz wrote:
rick wrote:
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.

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.


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

On Fri, 22 May 2015 14:20:00 +0100, rick wrote:

On 22/05/2015 06:24, F Murtz wrote:
rick wrote:
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.

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.


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


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.