A resistor at 150°C...how?

  • Thread starter Francesco Piantedosi
  • Start date
F

Francesco Piantedosi

Guest
Hi all,
I have to buil a circuit to use a resistor as a heater; what I want is
to use this resistor to heat a surface at 150 °C.

My first problem is to choose right resistor(I have ONLY 15 mm diameter)
able to dissipate this heat power without crash!

The second problem is design ctemperature control circuit...the
sensor(LM35 or lm45) should be in contact with surface I have to heat
and give feedback to power supply of my resistor...any ideas?

Thanks
Francesco



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
 
Francesco Piantedosi wrote:
Hi all,
I have to buil a circuit to use a resistor as a heater; what I want is
to use this resistor to heat a surface at 150 °C.

My first problem is to choose right resistor(I have ONLY 15 mm diameter)
able to dissipate this heat power without crash!

The second problem is design ctemperature control circuit...the
sensor(LM35 or lm45) should be in contact with surface I have to heat
and give feedback to power supply of my resistor...
Click to expand...
http://www.iprocessmart.com/sunrod/sunrod.htm
 
On Wed, 24 Nov 2004 22:11:58 GMT, Rich Grise <rich@example.net> wrote:

On Wed, 24 Nov 2004 09:44:43 -0800, John Larkin wrote:

On Wed, 24 Nov 2004 16:57:16 GMT, Rich Grise <rich@example.net> wrote:

On Wed, 24 Nov 2004 10:41:38 +0000, Francesco Piantedosi wrote:

Hi all,
I have to buil a circuit to use a resistor as a heater; what I want is
to use this resistor to heat a surface at 150 °C.

My first problem is to choose right resistor(I have ONLY 15 mm diameter)
able to dissipate this heat power without crash!

The second problem is design ctemperature control circuit...the
sensor(LM35 or lm45) should be in contact with surface I have to heat
and give feedback to power supply of my resistor...any ideas?

I've been looking into something very similar to this, to warm a 5-10 l/m
air stream to 155 C. The LM35 doesn't go that high. The thermistors I've
seen aren't guaranteed at that temp. range. This leaves either a
thermocouple, which is a PITA, or an RTD, which I don't even know how to
search for - all I come up with is platinum and stuff, which cost more
than I'm budgeted for the whole project.


Several people make thinfilm platinum rtd's on little ceramic slabs,
and they cost a few bucks each. google "thinfilm rtd"
^^^^^^^^^^^

Like I said - more than I'm budgeted for the whole project. ;-)

Thanks!
Rich
Click to expand...
Good grief, are you Francesco Piantedosi too?

John
 
Given the limited budget, I wonder if it would be possible to
derive the temperature from the resistance of the nichrome wire.
It all depends on the tempco of the wire, of course. Just a thought.
 
[CUT]

Good grief, are you Francesco Piantedosi too?

John
Click to expand...

Absolutely NO! ;)
BTW Thanks for the answers!

Francesco





--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG
 
Rich Grise wrote:
On Wed, 24 Nov 2004 10:41:38 +0000, Francesco Piantedosi wrote:

Hi all,
I have to buil a circuit to use a resistor as a heater; what I want is
to use this resistor to heat a surface at 150 °C.

My first problem is to choose right resistor(I have ONLY 15 mm diameter)
able to dissipate this heat power without crash!

The second problem is design ctemperature control circuit...the
sensor(LM35 or lm45) should be in contact with surface I have to heat
and give feedback to power supply of my resistor...any ideas?

I've been looking into something very similar to this, to warm a 5-10 l/m
air stream to 155 C. The LM35 doesn't go that high. The thermistors I've
seen aren't guaranteed at that temp. range. This leaves either a
thermocouple, which is a PITA, or an RTD, which I don't even know how to
search for - all I come up with is platinum and stuff, which cost more
than I'm budgeted for the whole project.

For the resistor, I found some thin nichrome wire on Ebay, which has a
resistance of approx. 28 ohms per foot, which gives me a "blank check" as
far as what I want the heating element to look like, since I'm making it
from scratch. I also have a 7.5V 1A wall wart that somebody threw away -
one of these days, I'm going to see how hot a 3" piece of this nichrome
gets with the wall wart, but the bugaboo, of course, is sensing the temp.

The controller shouldn't be too hard at all - there are a lot of suggested
circuits that you could just copy. You could search on, say, "voltage
controlled dimmer" and such.

Good Luck!
Rich
Click to expand...
Please be advised that the LM35D may not be speced beyond 125C (or
whatever), but I have found that it is linear and as repeatable as a
scientific thermometer or calibrated thermocouple at least to 185 C.
One could use surface mount resistors for the heater, and surround the
LM35; mounting everything on a sheet of copper for good thermal
coupling.
**
How else do you think i characterize parts for high temp use?
I have designed a number of electronic circuits, and guarantee
parameters to 175 C and useable operation (at minimum) to 186 C.
 
On Thu, 25 Nov 2004 08:28:04 +0000, Guy Macon
<http://www.guymacon.com> wrote:

Given the limited budget, I wonder if it would be possible to
derive the temperature from the resistance of the nichrome wire.
It all depends on the tempco of the wire, of course. Just a thought.
Click to expand...
Minco makes flexprint stick-on things that are simultaneously heaters
and sensors. Of course, they only sense their own temperature, not the
temp of the thing they're stuck to, so there's a coupling error. You'd
have the same problem heating air... the heater itself will be hotter
than the exit air stream.

John
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top