Pulse power rating of resistor?

Hi,

there are "pulse power rated " resistors, like CMA0204 or CMB0207...

Klaus

about 30 years ago, i had a document from Dale about pulse handling capability of resistors.
it specified the pulse energy handling capability of various resistors
it talked about joule stress - enough joule stress and the resistor would explode, rather than burn up

this is as close to what i had as i have been able to find

TE specs for SMQ: Short time overload 5 times of rated wattage for 5 sec
Thus P = 3 W @ 150 'C, E(5s) = 15 J max for so-called "long pulses <=5s."
But for short pulses, e.g. 40 ms Vishay Dale bases analysis and recommendations on the amount of energy required to raise the resistance element to + 350 ºC with no heat loss to the core, coating, or leads.

Integrating your curve ( using triangles) computes to 1.33 J in 0.04 s.

Using a formula for E(t) from Vishay** for a similar non-inductive wirewound (WW);

E(1s)=E(5s), but E(0.5s) = 50% E(1s) thus
E(500ms) = 50%*E(5s) and regressing this gives (I think)
E(250ms) = 25%*E(5s) = 3.75 J
E(125ms) = 12.5% E(5s) = 1.875 J
E(62 ms) = 6.3 % E(5s) = 0.9375 J
E(31 ms) = 3.1 % E(5s) = 0.47 J


Thus your energy plot of 1.33 J in 40 ms appears to exceed the max temp. rating, assuming my interpretation is correct (?)

So what do you think is the junction temperature rise and the relaxation time to room temp within 1%? This depends on convection cooling rate.

Also keep in mind reliability risks, as Vishay says in link below;

"Note that repeated pulses consisting of the short time overload magnitude are extremely stressful and can cause some resistor styles to fail."


**

https://www.vishay.com/docs/49076/_wirewound_resistors_pulse_handling_capabilities_vmn_pl0396_1604.pdf

Vishay Intertechnology's acquisitions include such top companies and businesses as Dale, Sprague, BCcomponents (former passive components businesses of Philips Electronics and Beyschlag), Draloric, Sfernice, Vitramon, Siliconix, the Telefunken semiconductor



Conclusion
V's specs for 22 ohms 3W implies 5 times rated current =15W in 5s max for DC = 370 mA and thus 5s long pulse spec is 1.846 A max.

You are looking for a solution to withstand a pulse starting at 45W or 1500% of rated spec. This could outgas and explode or fuse open or just tick like a voice coil and be OK once or twice. But there is no guarantee. Thermal shock is much worse than a slow ramp. If you smell anything, I suggest you keep looking.

There is no short pulse spec