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In Reply to: RE: Shunt resistor choice (possibly correct or incorrect math)??? JR?? posted by tweaker456 on August 11, 2020 at 15:41:45
You were off one decibel point.Its 0.0024amp.
Dissipation will be 0.228 watts ,I would use a 1(or more) watt part in that spot .
Edits: 08/12/20 08/12/20Follow Ups:
That's correct. I forgot a zero. I think your suggestion of 1 watt or more feels better than just a half watt. Even a 2-5 watter might be a good thing if it's in a box?? Thanks for the correction. Tweaker
"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe." Alfred E. Neuman
Edits: 08/14/20
Thanks, Brick527. Do you foresee potential failure of the resistor, or just inefficiency as a proper shunt resistor for the application? TIA
Hey Duster.The resistor will work fine for what you intend it to do function wise.I always try to over spec resistors by 3 to 4 times for dissipation.Their dissipation ratings go down as the ambient temperatures go up.Think sealed chassis.Pretty common practice as far as resistors go.
If you already have the 50k's you can put two in series to make a 100k with double the dissipation(1 watt). It will still serve the same purpose.
Thanks for the tips, Brick527.
BTW, that Vishay Dale Mil-Spec resistor was pricey when purchased in small quantity.
Any suggestion of a low-cost option that is appropriate for the task? What would be the ideal power rating and resistance value for the application?
Cheers, Duster
Duster ,a standard metal film at 1 watt between 50k and 1 meg would do. With such minor amounts of capacitance involved you don't need much current to discharge them.If you were talking about a hundred microfarads or more than you would need more current to discharge them in a reasonable time.
Alot of power conditioners don't use bleeders at all.
I've become more vigilant about the matter after following a fellow solder slinger who tends to be very careful when handling a device without a resistive load. I've fingered too many IEC inlets while swapping-out power cords on the back of an audio component to see which orientation the ground prong is located; I don't even wish to see what it might feel like to get even a minor zap if there are no power cords plugged into a power line conditioner/distributor. Sometimes it takes actually being shocked by AC current before one takes more care...
I agree with your reasoning.Just put it out there that not all adhere to that practice.
It's also a reason why it's safe practice that a DIY power cord with a 3-pole IEC connector should always have a ground wire, even if it's intended for an audio component with an ungrounded IEC inlet. On the other hand, if the entry hole for the ground prong is *permanently* blocked within the IEC connector, perhaps that's enough to ensure the safety of the power cord, if and when it might fall into the hands of an unsuspecting user in the future.
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