Resistor  can survive high peak power pulses? - Page 1
Forum section: electronics / general

author: ocset
author_rank: Super Contributor
timestamp: July 20, 2020, 10:32:41 pm
content: Hi,We are using the RSF300JB-91-100R resistor (100R,3W) in an inrush overvoltage damping circuit as attached. (LTspice also attached)Will this resistor be able to handle these power pulses several times per day for 20 years?As shown, the power pulse is 1700W peak and lasts for some 35us.RSF300JB-91-100R resistor datasheethttps://www.yageo.com/upload/media/product/products/datasheet/lr/Yageo_LR_RSF_1.pdf

author: David Hess
author_rank: Super Contributor
timestamp: July 21, 2020, 02:22:10 am
content: I do not see any reason that it would not; it's voltage handling capability is more than high enough.A ceramic composition resistor might be tougher.

author: D Straney
author_rank: Frequent Contributor
timestamp: July 21, 2020, 03:08:32 am
content: That's a lot of instantaneous power. Worked in lighting myself for a while, and we mainly followed one of two routes for this sort of situation:1. Use a resistor from a company like Vishay or KOA Speer (I like the MOSX series), which have pulse-rated resistors with very detailed datasheets and specs on just this kind of thing - likely going to be more expensive though.2. Use the attractively-cheap (esp. as LED ballasts don't lend themselves to "spare no cost" kinds of project) Yageo part but stress-test the shit out of it. You could build an accelerated stress-test fixture that just gives it a similar pulse at some high rate that keeps the average dissipation manageable (although some level of above-ambient temperature would simulate the stress of being in a running ballast?), but changes the "few times a day for 20 years" to "once every 30 seconds for a month". Make a simple, reliable, no-tweaking-required timer + triac circuit or something 10x side-by-side on a PCB, have some reasonable number of copies assembled that gives you maybe 50-100 RUT (resistors under test) and see how many fail by the end. Not a 100% guarantee, if manufacturing process changes or all of those 100 happened to be from a particularly good batch, but it's a surprisingly ok confidence check.

author: bdunham7
author_rank: Super Contributor
timestamp: July 21, 2020, 04:32:18 am
content: Your 'inrush event' is only that high if it occurs right at the very peak of the power cycle. If you were to repeat this every power cycle continuously you would be almost at the rated power dissipation of the resistor and it would likely go on like that for years. It's only a current of about 4 amps in a fairly large device. I would worry about something else, quite frankly.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 22, 2020, 12:57:22 am
content: Is the PRO-3 an option, or is it UL vs IEC type issue?https://www.vishay.com/docs/28729/pr010203.pdf

author: nctnico
author_rank: Super Contributor
timestamp: July 22, 2020, 08:29:43 am
content: Quote from: treez on July 20, 2020, 10:32:41 pmI'd go for wirewound resistors. These have a specified impulse handling capability. If there is no pulse handling in the datasheet then assume the resistor is unsuitable.

author: Gyro
author_rank: Super Contributor
timestamp: July 26, 2020, 12:55:24 pm
content: Carbon Composition (still manufactured) and more modern Ceramic Composition (bulk ceramic) resistors have very high (documented) surge ratings. Useful especially where resistance tolerance and TC aren't critical.https://www.eevblog.com/forum/projects/resistor-extreme-pulse-overload-experiments/

author: Electrole
author_rank: Contributor
timestamp: July 26, 2020, 02:02:24 pm
content: I would go for a resistor series with documented surge capacity. Take a look at the EP series from TE Connectivity, for instance. The EP3WS100RJ is a 100 Ohm / 3 W wirewound resistor which should withstand 2.5 kV for 50 µs. The EP series is not expensive, and I have used it occasionally. The tricky part is to find out how the waveform over the resistor in your specific case looks like. Then, I would check that the I2t integral of that pulse is below the I2t integral of the pulse in the data sheet, and with a good margin. That ensures that the energy absorbed by the resistor is acceptable.