Re: [[EE] Resistor power rating

Hey Justin,

I have seen 5W ceramic resistors, fail without signs of damage, heat, 
cracking etc.

I have also even seen them measure correct, but fail.

These were when I was repairing various switch-mode power supplies, many 
years ago now.

Peter

------------------

On 10/12/2025 1:16 pm, Justin Richards wrote:
> regarding 5W ceramic resistors, the internet suggested checking and
> replacing 2 x 5W ceramic resistors that maybe the fault on a  (neighbours)
>   60" tv.
>
> To my surprise one tested open cct.  I have found failed resistors before
> but never 5W ceramic and not without any outward signs of stress, Replaced
> both and neighbour happy.
>
> justin
>
> On Wed, Dec 10, 2025 at 2:47 AM David C Brown <[email protected]> wrote:
>
>> I need to experiment a little.
>> Tune for maximum smoke as my compatriot used to say
>> __________________________________________
>> David C Brown
>> 43 Bings Road
>> Whaley Bridge
>> High Peak                           Phone: 01663 780582
>> Derbyshire                eMail: [email protected]
>> *SK23 7ND          web: www.bings-knowle.co.uk/dcb
>> <http://www.jb.man.ac.uk/~dcb> *
>>
>>
>>
>> *Sent from my etch-a-sketch*
>>
>>
>> On Tue, 9 Dec 2025 at 13:09, Alan Pearce <[email protected]>
>> wrote:
>>
>>> Just be careful though, I have had "concrete block" wirewound resistors
>>> smoke on me. I don't know exactly why but suspect it was something to do
>>> with peak current at switch on.
>>> The ones I refer to as "concrete block" are those in a 1" cross section
>>> ceramic package with a cermet mixture on on side where the element gets
>>> inserted.
>>>
>>>
>>> On Tue, 9 Dec 2025 at 08:55, David C Brown <[email protected]> wrote:
>>>
>>>> Thanks for that.   It seems that a 5w wirewound resistor wold easily
>> meet
>>>> my requirements
>>>> __________________________________________
>>>> David C Brown
>>>> 43 Bings Road
>>>> Whaley Bridge
>>>> High Peak                           Phone: 01663 780582
>>>> Derbyshire                eMail: [email protected]
>>>> *SK23 7ND          web: www.bings-knowle.co.uk/dcb
>>>> <http://www.jb.man.ac.uk/~dcb> *
>>>>
>>>>
>>>>
>>>> *Sent from my etch-a-sketch*
>>>>
>>>>
>>>> On Mon, 8 Dec 2025 at 22:22, Clint Jay <[email protected]> wrote:
>>>>
>>>>> Vishay and Bourns both have info on their wesbites about selecting
>>>>> resistors for pulse load applications:
>>>>>
>>>>>
>>>>>
>> https://www.vishay.com/docs/48516/_ms9702509-2401-vishaychecklistpulseload.pdf
>>>>> https://www.bourns.com/products/resistors/pulse-power-resistors
>>>>>
>>>>> On Mon, 8 Dec 2025 at 19:32, Jason White <
>>>>> [email protected]>
>>>>> wrote:
>>>>>
>>>>>> vishay makes some nice pulse rated 2512's that have some graphs
>> where
>>>> you
>>>>>> can look this up in
>>>>>>
>>>>>> On Mon, Dec 8, 2025 at 2:09 PM David VanHorn <[email protected]>
>>>>> wrote:
>>>>>>> Normally, resistor power ratings assume 100% duty cycle, so
>> 1/0.016
>>>>> would
>>>>>>> be a first approximation, but the part may not be capable of
>>>>> withstanding
>>>>>>> that much pulsed power.
>>>>>>> Unfortunately, the low duty cycle ratings are hard to find on
>> most
>>>>>>> resistors.
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Dec 8, 2025 at 11:37 AM David C Brown <
>> [email protected]>
>>>>>> wrote:
>>>>>>>> I am planning to use a 2R2 resistor to limit the current to a
>>>>> solenoid
>>>>>> to
>>>>>>>> 6amps.
>>>>>>>> Ohms law says that the power dissipation is about 80watts.
>>>>>>>>
>>>>>>>> But the duration of the current pulse is only 16mS.   Does that
>>>> mean
>>>>>>> that I
>>>>>>>> can get away with a lower power rating and, if so, how much
>>> lower?
>>>>>>>> __________________________________________
>>>>>>>> David C Brown
>>>>>>>> 43 Bings Road
>>>>>>>> Whaley Bridge
>>>>>>>> High Peak                           Phone: 01663 780582
>>>>>>>> Derbyshire                eMail: [email protected]
>>>>>>>> *SK23 7ND          web: www.bings-knowle.co.uk/dcb
>>>>>>>> <http://www.jb.man.ac.uk/~dcb> *
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> *Sent from my etch-a-sketch*
>>>>>>>> --
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>>>>>> --
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>>>>>
>>>>> --
>>>>> Clint. M0UAW IO83
>>>>>
>>>>> *No trees were harmed in the sending of this mail. However, a large
>>>> number
>>>>> of electrons were greatly inconvenienced.*
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