[Boatanchors] carbon resistor wattage ratings

[Lloyd KK7IZ]

Its obvious. Your finger is defective.
Thanx
Lloyd  KK7IZ
kk7iz at cox.net

Lloyd Godsey  KK7IZ
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----- Original Message ----- 
From: "Dick KF4NS" <kf4nsradio at verizon.net>
To: <boatanchors at mailman.qth.net>
Sent: Wednesday, February 14, 2007 3:26 PM
Subject: [Boatanchors] carbon resistor wattage ratings


> Can somebody set me straight on what is acceptable as regards surface 
> temperature related to wattage rating of carbon resistors?
> 
> After I calculate the proper rating using the standard power formulae, 
> I then choose the next higher standard wattage rating and after 
> placing the resistor in circuit I use a temperature probe to check it. 
> In a recent example, I found P=.196W so I needed a 1/4W resistor but I 
> only had a 1/2W and the temp probe gave me a reading on that resistor 
> of 50deg C (122deg F). To the touch, that feels too hot. I cannot keep 
> my finger on it for very long. I recalculated the I_ squared_ R and 
> again it came up with .196W so 1/2W should be fine.
> 
> Please enlighten me.
> Thanks and 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow! 
> 
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