I've been asking myself that same question, and I think the R-Theta group buy profile is 9012, so C/W/3" section is listed as 0.6:
http://www.r-theta.com/products_standards_aluminum_profiles.asp
I'm not sure about the math, but I think this means a 6" section will give you a (ideal conditions) C/W of 0.3 - 100W idle load will raise the heatsink temp to 30C over room temp. Double again to 12" and you should get 0.15 and 15C for a 100W load, so figure between 15 and 30C - closer to 30 under average heat transfer (that's 30C over room temperature) for an 8" section. Some will chime in with a link to the heatsink calculator/simulator and you can plot your heat points etc for a real simulation.
http://www.r-theta.com/products_standards_aluminum_profiles.asp
I'm not sure about the math, but I think this means a 6" section will give you a (ideal conditions) C/W of 0.3 - 100W idle load will raise the heatsink temp to 30C over room temp. Double again to 12" and you should get 0.15 and 15C for a 100W load, so figure between 15 and 30C - closer to 30 under average heat transfer (that's 30C over room temperature) for an 8" section. Some will chime in with a link to the heatsink calculator/simulator and you can plot your heat points etc for a real simulation.
twitchie,
Your assumption is incorrect. The thermal resistance is not inveresly related to length. The thermal resistance of a 6 inch section will be greater than 1/2 the resistance of a 3 inch section. My guess is it will be around .4. There is a link to the R-Theta calculator on the page you mentioned.
Your assumption is incorrect. The thermal resistance is not inveresly related to length. The thermal resistance of a 6 inch section will be greater than 1/2 the resistance of a 3 inch section. My guess is it will be around .4. There is a link to the R-Theta calculator on the page you mentioned.
So I can assume 8" section would be ~.3 C/W and since a lot of people have had success with the big conrad heatsinks listed at .21, but taking into account the 1.4 multiplier since they rate temp different, that makes it effectively .3 I should be fine.
Cool, well not cool, but not boiling either.
Cool, well not cool, but not boiling either.
hello
heatsinkers
let's sink the temp
Question 1:
---------------------------------------
Anybody know of a temperature monitor project?
Good if it is a project for monitor power amp heatsinks.
- 1 sensor at heatsink, close to Transistors
- some indicators: LEDs
or maybe
- measure millivolt per degree with multimeter at testpoints
- digital display (advanced monitor)
Question 2:
----------------------------------------
What would be a suitable sensor?
- LM35 is a dedicated IC, gives 1mV raise / each degree C
but I have been told it is very slow .. like 5 minutes to reach value
- BD139, TO-126 transistor could be used, ~2.2 mV / each degree
in change of VBE, volt base emitter
.. but would need some Op-Amp and some calibration to get a nice scale
Regards
lineup
heatsinkers
let's sink the temp
Question 1:
---------------------------------------
Anybody know of a temperature monitor project?
Good if it is a project for monitor power amp heatsinks.
- 1 sensor at heatsink, close to Transistors
- some indicators: LEDs
or maybe
- measure millivolt per degree with multimeter at testpoints
- digital display (advanced monitor)
Question 2:
----------------------------------------
What would be a suitable sensor?
- LM35 is a dedicated IC, gives 1mV raise / each degree C
but I have been told it is very slow .. like 5 minutes to reach value
- BD139, TO-126 transistor could be used, ~2.2 mV / each degree
in change of VBE, volt base emitter
.. but would need some Op-Amp and some calibration to get a nice scale
Regards
lineup
I asked a similar question 1 year ago.
I got this nice answer:
Arius said:
What Aruis tells me is:
1. I should use only like 10uA current flow in the BD139
if using it as temperature sensor
2. I will get ~ -2.3 mV / degree C in temp raise
----------------------------------------
Original Topic:
On Semi ThermalTrak - Power Transistors
Regards
Temperature Control Department
of
Lineup Audio Lab
-----------------------------------------
Another good topic on heatsink and temp control, temp tracking
where also Nelson Pass contributed some good advice:
MOSFET amp problem - Heatsink and Temp tracking
.
I use a water cooling system with a flow controller to monitor the coolant flow and temperature. This shuts the amp down if things get too hot, or if the flow fails for any reason.
I made use of a temperature sensor sold in the UK by Maplin. This may be OK for monitoring a conventional system providing it doesn't get too hot. It is certainly easier than messing about with Vbes, bandgap references, instrumentation grade opamps:
Temperature Module
This module will display up to 69.8 Celcius and can be rigged to alarm. You can connect an external temperature probe, and there is a display bezel for it too:.
I made use of a temperature sensor sold in the UK by Maplin. This may be OK for monitoring a conventional system providing it doesn't get too hot. It is certainly easier than messing about with Vbes, bandgap references, instrumentation grade opamps:
Temperature Module
An externally hosted image should be here but it was not working when we last tested it.
This module will display up to 69.8 Celcius and can be rigged to alarm. You can connect an external temperature probe, and there is a display bezel for it too:.
Hastur said:
dissipation ability is related to:
1) heathsink surface
2) Air speed flowing on this surface (and hence is dependent on mounting: vertical mounting allow more air flow to run on heathsink surface than horizontal).
Hi
Piercarlo
PS - "Bulkity" of heathsink is more related to its thermal capacitance rather than its surface. More fins act more efficiently of more weight.
lineup said:
Not so.. the chip reacts in seconds- it's the heated mass and your thermal coupling that sets the response.
I use it with good results for measuring internal temp's in sounding rockets!
Any DPM set to 0-1V gives you direct readout of temp. If you want alarms or switch off, use a comparator or a small dedicated DPM.
AuroraB said:
Thanks AuroraB.
This gives me the option to use LM35.
It is a nice and useful little chip.
As it outputs 10 mV for each degree C = linear scale.
Together with some Op-amps, one reference and your multimeter
it makes a not too difficult circuit to measure temperature.
With good precision, I think.
It should not cost very much.
http://www.national.com/pf/LM/LM35.html
lineup
For my DOZ I used the "bells & Whistle" circuit here
http://www.cpemma.co.uk/thermal.html
Using small good quality fans with ball bearings makes for very low noise.
Once the circuit is adjusted and supply voltage to the fans is tweaked the set up is reliable. Only during hot summer use could you hear faint fan noise My thermistor monitored air flow temperature.
http://www.cpemma.co.uk/thermal.html
Using small good quality fans with ball bearings makes for very low noise.
Once the circuit is adjusted and supply voltage to the fans is tweaked the set up is reliable. Only during hot summer use could you hear faint fan noise My thermistor monitored air flow temperature.
An externally hosted image should be here but it was not working when we last tested it.
Hi,
the Rth s-a of a sink is roughly inversely proportional to the square root of the length.
If the sink you know is 3inches tall and has Rth s-a =0.6C/W then an 8inch tall section will have an Rth s-a ~=0.37C/W
Rth s-a (8")=Rth s-a (3") / Sqrt(8/3).
Remember to apply the correction factor for delta T (the difference between the contact point/face temperature and the ambient temperature)
Remember also, that the sink only matches the manufacturer's data if the whole contact face (or the manufacturer's stated method) is at contact face temperature. A large sink that is too thin will not transfer adequate heat to the far extremities compared a to smaller sink. This results in the fins at the larger distances running at a lower temperature than the manufacturer's test method and the effective Rth s-a can be much higher than the the data sheet and WILL be at least some margin higher than the datasheet.
The result of these two factors is that the semiconductor runs at a temperature significantly higher than expected if these corrections are omitted from your model.
the Rth s-a of a sink is roughly inversely proportional to the square root of the length.
If the sink you know is 3inches tall and has Rth s-a =0.6C/W then an 8inch tall section will have an Rth s-a ~=0.37C/W
Rth s-a (8")=Rth s-a (3") / Sqrt(8/3).
Remember to apply the correction factor for delta T (the difference between the contact point/face temperature and the ambient temperature)
Remember also, that the sink only matches the manufacturer's data if the whole contact face (or the manufacturer's stated method) is at contact face temperature. A large sink that is too thin will not transfer adequate heat to the far extremities compared a to smaller sink. This results in the fins at the larger distances running at a lower temperature than the manufacturer's test method and the effective Rth s-a can be much higher than the the data sheet and WILL be at least some margin higher than the datasheet.
The result of these two factors is that the semiconductor runs at a temperature significantly higher than expected if these corrections are omitted from your model.
How about adding fan? On a website http://www.aavidthermalloy.com
there is wery friendly search engine There i can input LFM for forced convection. I put LFM for sunon 80x80mm fan that has 40CFM, in LFM it is about 584LFM. With this fan and 300mm long heatsink i get 0.3C/W. I wonder how to calculate with two fans? Will it be double LFM, 1168? If it is like that then i get 0,21 c/w just like i need for amplifier
there is wery friendly search engine
There i can input LFM for forced convection. I put LFM for sunon 80x80mm fan that has 40CFM, in LFM it is about 584LFM. With this fan and 300mm long heatsink i get 0.3C/W. I wonder how to calculate with two fans? Will it be double LFM, 1168? If it is like that then i get 0,21 c/w just like i need for amplifier - Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.