[Boatanchors] carbon resistor wattage ratings

[Dave Brown]

While LLoyd may well be correct, I'm not sure how one measures 
'defectiveness' in a finger! Instead try measuring the actual voltage 
across the resistor when in circuit-and check its resistance again. 
Do these number stack up? And we are talking DC here? -or is there an 
AC component as well that your measurements/calculations may not be 
taking into account?   e.g. incompletely filtered rectifier output 
voltage, etc.  50 centigrade may be fine anyway, resistors are made to 
get hot-it's all a matter of degree (no pun intended!)
 73 Dave, ZL3FJ


----- Original Message ----- 
From: "Lloyd KK7IZ" <kk7iz at cox.net>
To: "Dick KF4NS" <kf4nsradio at verizon.net>; 
<boatanchors at mailman.qth.net>
Sent: Thursday, February 15, 2007 11:32 AM
Subject: Re: [Boatanchors] carbon resistor wattage ratings


> Its obvious. Your finger is defective.
> Thanx
> Lloyd  KK7IZ
> kk7iz at cox.net
>
> Lloyd Godsey  KK7IZ
> 1315 N. Udall Circle
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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
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