Electronics > Projects, Designs, and Technical Stuff

My constant current load - 90W , 3A 30V

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blackdog:
Hi SeanB,

Uhm, the diode is only for reverse protection...
It is Not Mounted on a heatsink, just my way to mount it.
The diode has only to blow the fuse.

Regarts,
Blackdog

Spikee:
Leech , you were almost correct . Whit a 1 ohm resistor of 100w i will be able to pull 10A max.
My mosfet and heatsink can only handle around 120W max. At 12 volt i can utilize the resistors rating fully at 10 A.
In my application i dont need to test high currents at low voltage so the 1 ohm 100W resistor is perfect.

Thanks for the info , tomorrow i will recieve my parts and i can start testing the pc heatsink.

Gr. Spikee

Spikee:
So i just mounted the 100W resistor and the mosfet on the heatsink. I mixed the artic silver stuff , put the two TO247 package opposite side of each other (to utilize the heatpipes fully) . Then i clamped them on the heatsink and applied ~10W on the 1ohm resistor so the curing would go faster.
it was ambient temperature of 18 deg C here and now the heatsink is stable at 39 deg. C (no fan , upside down ) .
You immediately see the advantages of heatpipes. the whole heatsink is at the same temperature and the fins got hot before the mounting plate.
After a few mins the mounting plate and the fins get around the same temperature.

Pic:

Whole assembly:
https://www.dropbox.com/s/3dse7kpoq3tft5k/2012-12-09%2023.05.08.jpg

Mosfet and power resistor:
https://www.dropbox.com/s/v9hmkshzxbjd6d1/2012-12-09%2023.06.18.jpg

Spikee:
So i just picked up my components at college  ;D .
The 1ohm 100w resistors are huge , do i need to put them on an external heatsink ? or can they handle the 100W just mounted on the metal case.
Item number: WH100-1R0JI  maybe i can fit them on the top of the processor side.

pic:

50K ohm 10 turn pot
2x 1ohm 100W resistors
10x 0.1 ohm resistor 3W

T4P:
Check the given thermal specs (Tj-a and Tj-c) of the resistors as well as calculate roughly how much temperature rise you can tolerate on a heatsink (I would recommend not going over 85C if possible so)
Think of the voltage drop (1V in your case so if you're pulling a amp it's 1W but surely it can handle it right? Actually such a huge resistor is somewhat overkill)
If you're just pulling 3A, seriously it's only 9W
I recommend using a fan or a better fan because those heatsinks IMO optimum-ly can't do more than 115W at 80C (50C rise i think?) at least

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