Thermistor Question

[Gaz]

Hi all
Can someone help me with a thermistor question, I have a USB dual
hard drive enclosure with two 1TB HD in it. It's a Ritmo and has a cooling
fan that runs (noisily) all the time.
I know it's 12v and draws 110mA and I want to put a NPT thermistor in the
box so the fan only runs when the HD's get warm to hot.
I see the thermisters are rated xx ohms @25C and I'm wondering how many ohm
thermistor I need to stop the fan on start up, that will start the fan as
the temp increases.
This is the link from a nearby supplier I might use-
http://www.jaycar.com.au/products_uploaded/RN3430.pdf
Thanks Gaz

 

[Phil Allison]

"Gaz"

Can someone help me with a thermistor question, I have a USB dual hard
drive enclosure with two 1TB HD in it. It's a Ritmo and has a cooling fan
that runs (noisily) all the time.
I know it's 12v and draws 110mA and I want to put a NPT thermistor in the
box so the fan only runs when the HD's get warm to hot.
I see the thermisters are rated xx ohms @25C and I'm wondering how many
ohm thermistor I need to stop the fan on start up, that will start the fan
as the temp increases.
This is the link from a nearby supplier I might use-
http://www.jaycar.com.au/products_uploaded/RN3430.pdf

** Have you considered that the current flowing through the NTC to the fan
will HEAT the NTC ?

Means once the fan is on, it will likely stay on permanently.

My advice is to leave well alone.



...... Phil

 

[Clint Sharp]

Hi all
Can someone help me with a thermistor question, I have a USB dual
hard drive enclosure with two 1TB HD in it. It's a Ritmo and has a cooling
fan that runs (noisily) all the time. Annoying isn't it.
I know it's 12v and draws 110mA and I want to put a NPT thermistor in the
box so the fan only runs when the HD's get warm to hot.

You mean NTC I think? NPT is a type of thermistor fitting I think.

I see the thermisters are rated xx ohms @25C and I'm wondering how many ohm
thermistor I need to stop the fan on start up, that will start the fan as
the temp increases.

That's not quite the way it works, most thermally controlled fans that I
have seen have the thermistor integrated into the motor control logic of
the fan.

Third party thermal fan controllers use the thermistor to control a
power transistor or IC that either varies a PWM signal or the voltage
applied to the fan (some fans respond better to voltage changes than PWM
and vice versa). You might strike lucky but I suspect it won't be
reliable and you're going to need to do some experimentation to get it
right.

Probably cheaper and better to buy a ready built fan controller or a fan
that is designed with a thermistor in place already. For the (rapidly
diminishing) cost of the two drives, I'd just buy something.

There are plenty of plans out there for thermal fan controllers if you
really want to build your own.

 

[Clint Sharp]

** Have you considered that the current flowing through the NTC to the fan
will HEAT the NTC ?

Means once the fan is on, it will likely stay on permanently.

If he ever manages to get it to turn on in the first place.

 

[Davo]

Hi all
Can someone help me with a thermistor question, I have a USB dual
hard drive enclosure with two 1TB HD in it. It's a Ritmo and has a cooling
fan that runs (noisily) all the time.
I know it's 12v and draws 110mA and I want to put a NPT thermistor in the
box so the fan only runs when the HD's get warm to hot.
I see the thermisters are rated xx ohms @25C and I'm wondering how many ohm
thermistor I need to stop the fan on start up, that will start the fan as
the temp increases.
This is the link from a nearby supplier I might use-
http://www.jaycar.com.au/products_uploaded/RN3430.pdf
Thanks Gaz

Probably cheaper and easier to buy a quiet fan.

 

[Franc Zabkar]

I have a USB dual
hard drive enclosure with two 1TB HD in it. It's a Ritmo and has a cooling
fan that runs (noisily) all the time.
I know it's 12v and draws 110mA and I want to put a NPT thermistor in the
box so the fan only runs when the HD's get warm to hot.

The HDs will become hot much sooner than the box will.

I see the thermisters are rated xx ohms @25C and I'm wondering how many ohm
thermistor I need to stop the fan on start up, that will start the fan as
the temp increases.

How are you going to detect the temperatures of the hard drive HDAs?
What happens if one drive runs hotter than the other? What happens if
one drive doesn't spin up and contributes nothing to the heat load?

- Franc Zabkar

 

[Gaz]

The HDs will become hot much sooner than the box will.

###Yes they will, but they are both crammed into this box with little room,
so the box would also heat up fairly quickly, so a thermister mounted in the
box will soon detect a temperature rise.


What happens if one drive runs hotter than the other.
one drive doesn't spin up and contributes nothing to the heat load?

###These HD's hold movies for a media player and as such, only one is in use
at a time.

BB