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#11
November 25th 03, 09:30 PM
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In article , Bill Turner
writes: On 24 Nov 2003 22:50:40 -0800, (Jason Hsu) wrote: Can the 1W-51 ohm resistors handle this 50 RF volts 0-peak (about 50W PEP) for .007 sec? 50W over .007 seconds is .35 Joules. .35W for 1 second is also .35 Joules, which a 1W resistor should have no trouble handling. Can the resistors be damaged during that .007 seconds? _________________________________________________ ________ You really need to ask the manufacturer of the resistor. They are well aware of the problem - if you get to the right person. Having said that, here is a generalization: If the resistor's element is a solid block of material, such as in a carbon composition type, it will have very good pulse power ratings. On the other hand, if the element is a film, it may develop tiny hot spots during pulsing and eventually fail. Absolutely a good, pragmatic answer, Bill. MANY components can survive a very short power overload. Carbon Comps do. A "sacrifice" test can be done with a DC power supply, an electrolytic capacitor, and a switch. Charge up the electrolytic, then dump the charge through the resistor. It should be a trivial thing to calculate the "pulse" of the initial charge-dump through the resistor for any under- or post-grad engineering type...for a particular resistance, capacitor, and voltage. A rough time-constant of t = R x C yields the "pulse" time. Figure the "pulse" power as half the capacitor charge voltage across the resistor under test. Not precision, true, but pragmatic and quick. If it doesn't survive, well, too bad. [sacrifice] If it survives, try it several more times, noting appearance, resistance before and after each "pulse" test. ...or, everyone else can spend a lot of time at "intellectual arguments" in here without ever trying it out on the bench... :-) Len Anderson retired (from regular hours) electronic engineer person |
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