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A question about one way resistors. - Page 2

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Posted by Eeyore on August 5, 2008, 10:10 pm
 


ukmp wrote:


3 questions.

1: Where do you buy 'one way' resistors ?

2: Did you never learn about P=V*I or P=I^2*R ?

3: are you heatsinking those resistors ?

Graham


Posted by maggoo1 on August 6, 2008, 11:47 am
 
On Tue, 05 Aug 2008 12:47:49 +0100, ukmp


Thank you for all your replies.
When I asked my question i didnt know if they were supposed to get hot
but apparently they are.
As for heat sinks,this thought had crossed my mind.I will try it.
Thanks again
ukmp

Posted by Eeyore on August 6, 2008, 5:41 pm
 

maggoo1@btinternet.com wrote:


It seems you meant diodes. When these conduct, there is a voltage across
them. That voltage multiplied by the current through them gives the number of
watts of heat generated. The data sheet for the diode will give you an idea
how hot that's likely to make it get but silicon diodes are surprisingly
durable. As long as the internal parts don't exceed 150-200 Celsius they
should not fail.

Depending on what you need, there are many styles and shapes of diode that
may operate fine in free air or require a heatsink.

For a 12V system you should also possibly be thinking about using Schottky
diodes since they have a lower voltage drop and therefore enhance overall
efficiency (lower losses).

Graham


Posted by Cydrome Leader on August 6, 2008, 9:39 pm
 
how hot it gets will depend on the size of the diode. figure the
dissipation to be around 0.6 volts (forward voltage) * amps. So figure
about 2.7 watts of heat in your case.

The larger the diode case, the cooler it may feel, and possibly longer
lasting it may be. In general, diodes take heat pretty good.

Posted by Eeyore on August 7, 2008, 2:46 am
 

Cydrome Leader wrote:


0.6 V is low for a diode forward voltage drop unless a Schottky type. At rated
current expect more like 1V for a standard silicon junction diode.

Graham


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