"Patatas de Goma" is a sound installation where I want control voltage of car horns and car light bulbs in PWM :
http://jeromeabel.net/en/art/patatas-de-gomaThe past experiences was pretty difficult, because the car horns have an inductive charge and it takes 12A and peak may be at 20 or 30A. The current electronic system is not reliable at all. It's a lot of intensity.
According to this very good tutorial (EEVblog #105 – Electronics Thermal Heatsink Design), I need to design the heat dissipation very carefully.
The method described in this tutorial is here :
http://jeromeabel.net/files/projets/patatasdegoma/EEV105_ThermalDesign.pngThe current schematics are here :
http://jeromeabel.net/files/projets/patatasdegoma/schematics/The datasheets are here :
http://jeromeabel.net/files/projets/patatasdegoma/materials_datasheets/.POWER TO DISSIPATE BY THE MOSFETS
If the MOSfet let pass all the voltage 12V and the horn take 20A : P = RDS(on) * I^2 = 0.041 * 20 * 20 = 16,4W
But if the MOSfet let pass 1V or 0.001V : P = (12 - 0.001) * 20A = 240 W !
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MATERIALS DATA SHEETS :
- MOSFET : FDP61N20, 200V N-Channel MOSFET, 61A, 200V, RDS(on) = 0.041Ohms @VGS = 10 V
Rtheta JC Thermal Resistance, Junction-to-Case : 0.3 °C/W
Rtheta JA Thermal Resistance, Junction-to-Ambient : 62.5 °C/W
Tj, Tstg (Operating and Storage Temperature Range) : -55 to +150 °C
- HEATSINK : ML33G
Thermal Resistance 8.50 Ohms
Rth = 10 °C/W
- FAN : kde1206phv2a 12 Vcc - 60 x 60 x 15 mm
Rate speed : 3800 RPM
FPM = RPM x Circumference
Circumference = 3.14 x 6cm = 18.84cm; 18.84cm x 0.033 = 0.62172 feet
FPM = 3800 x 0.62172 = 2363
According to the datasheet if FPM = 2356, the surface to ambient is 2°C/W
- Insulating Kit - VELLEMAN MOUNTING KIT FOR TO220
- PELTIER MODULE CP2 TEC1-12706
(Ceramic Plate Thermoelectric Modules) (plaque a effet peltier)
Intensity : 6 A
Power : 51,4 W
Dimensions : 40 x 40 x 4,7 mm
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THERMAL DESIGN #1 - NO DESIGN
, WITHOUT ANY HEAT COOLER DEVICES :
In the MOSfet datasheet, Rtheta JA Thermal Resistance, Junction-to-Ambient : 62.5 °C/W
I need to dissipate 240W => 62.5 x 240 = 15 000 °C !!! Am I all right ?
The MOSfet Tj, Tstg (Operating and Storage Temperature Range) is -55 to +150 °C. So It will crash, isn't it ?
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THERMAL DESIGN #2 - WITH A HEATSINK :
Goal : decrease the Rtheta JC
If I attach the MOSfet to a heatsink, the MOSfet Rtheta JC Junction-to-Case thermal resistance is 0.3 °C/W.
I need to dissipate 240W => 0.3 x 240 = 72°C. It is lesser than the temperature range maximum 150 °C, so it could work. Isn't it ? Or I have to sum all other thermal resistances Rtheta HA and Rtheta CH ?
Rtheta JC = 0.3 °C/W
According to the first thermal curve (rise above ambient / heat dissipated watts), the maximum value is 70°C/8Watts = 8.75 °C/W
It is close to the 8.5 thermal resistance of the datasheet. Is it the same ?
If we add 1/3 to be closer to the reality :
Rtheta HA = 8.75 + (8.73/3) = 11.7 °C/W
Let's say I have not a Silicone/Mica component between MOSfet and Heatsink, the common number seems to be :
Rtheta CH = 1.1 °C/W
Total = Rtheta JC + Rtheta HA + Rtheta CH = 0.3 + 11.7 + 1.1 =~ 13 °C/W
If I need 240W : 240 x 13 + 18° (ambient temperature) = 3138 °C !!
If I need 144W : 144 x 13 + 18° (ambient temperature) = 1890 °C !!
Hum, Am I all right ?
It is better than 15 000 °C, but I need less heat.
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THERMAL DESIGN #3 - WITH A HEATSINK, A FAN :
Goal : decrease the Rtheta HA
The fan cools the thermal resistance of the heatsink (Rtheta HA).
The first attempt is to see the second graph of the heatsink (Air velocity feet per minute / Surface to ambient °C/W )
The FPM of my fan is :
FPM = 3.14(Pi) x 6cm(Diameter of the fan) x 0.033(cm to feet conversion) x 3800 RPM = 2363
In the graph, after 800 FPM the thermal resistance is stick at 2 °C/W.
So, is it all right to say that the new Rtheta HA is 2 °C/W instead of previously 11.7 °C/W ?
New total = Rtheta JC + Rtheta HA + Rtheta CH = 0.3 + 2 + 1.1 =~ 3.4 °C/W
If I need 240W : 240 x 3.4 + 18° (ambient temperature) = 834 °C !!
If I need 144W : 144 x 3.4 + 18° (ambient temperature) = 507 °C !!
Whaaa, still hot.
It is better but I need less heat.
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THERMAL DESIGN #4 - WITH A HEATSINK, A FAN, INSULATING KIT :
Goal : decrease the Rtheta CH
If I add an insulating kit, how calculate the improvement ?
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THERMAL DESIGN #5 - WITH A HEATSINK, A FAN, INSULATING KIT, FEW MOSFETS :
An advice sent to me was to put few MOSfets in parallel to spread the power (not the heat).
How calculate the improvement ? Which thermal resistance will decrease ?
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THERMAL DESIGN #6 - WITH A HEATSINK, A FAN, INSULATING KIT, FEW MOSFETS, PELTIER :
Goal : decrease the Rtheta HA
How calculate the improvement ?
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Thanks for any advice
Jerome