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Pulse rating of 3W wirewound resistor?

Flyback

Well-Known Member
Hi
Do you know what is the pulse rating of the resistor SMQW322RJT? (13.5 x 7.3 x 6.8mm)

SMQW322RJT

Can it handle the attached power pulse? (this is what it would see)


As a way of comparison the SG73 (size 2512 = 6.3x3.1mm) resistor can do 110W for 20ms...
...so, the SMQW322RJT, being much bigger, and wirewound, you would think it would be good for at least double that?

For more comparison, the AC03 (13x4.8mm) resistor is about the same size, and can do 200W for 20ms

Even the small MMB0207 (5.5x2.2mm) can do 15W for 20ms


..So surely the SMQW322RJT could do the shown ~30W for 20ms?
 

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The datasheet says the resistor can handle 5x the three-watt rating for 5-seconds. Thats all we can know for certain because it has been tested. Anything after that is on you to test. If you are asking because it is a fun experiment, try it and let us know. If you are using it in a power supply for a medical device that will be operating in a child's bedroom unattended, well, you'll need to have some support from the manufacturer or a certification from a third party testing lab and a contract with the manufacturer that they will not make any changes to the raw materials or manufacturing process.

Don't burn down your own house or anyone else's house.
 
Applying 5x the rated power for the whole chip in 5 seconds is not the same as 45 W or 15x the rated power for 40 ms that is only in the WW wire with a certain coefficient of expansion may cause unknown stresses. We don't know the wire gauge or current density or even the current.

NG.
 
One of the things I make is shunts. I use "non inductive" resistors because they must have low inductance. The other thing I look for is "pulse". Most resistors are not tested for high energy pulses. The pulse resistors are designed and tested for high wattage for a short time.
You need a resistor with a graph like this. This 0603 resistor can handle 0.7 watts for 1 second. 20 watts for 1mS.
1714883236257.png
 
Pulse rating is not directly related to average heating. In my case I have a duty cycle of 3uS in a minute. I am using a 0.5watt resistor and putting 100 watts in the resistor. Some types explode off the board and some will last.

Years ago, I used carbon comp resistor because they could take large pulses while metal film opened up. Yes, heat is the problem, but it is more how the resistor is built.
 
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