EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: nikodemus on July 04, 2013, 10:25:28 am
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I'm thinking of building a resistor decade box.
Something that confuses me is that the designs I've seen seem to use resistors of all-the-same power rating, typically around 1W.
I was thinking of speccing mine for up to 10V voltage instead -- so for dialed in 1 Ohm, that resistor would have to be able to handle 100W, for 2 Ohms the second series resistor would need to handle 50W, for 3 Ohms the third 33W, etc.
Seems that a fixed-voltage specced box would just be much easier to use when working on eg. battery powered devices.
Am I missing something? Is it just assumed that these boxes are used only with current-limited power supplies, or is there another reason why a max-power spec instead of max-voltage spec is typical one?
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Do you know how big a 100W resistor is?
The reason why you can get away with smaller resistors is that you generally only use it to set up low current devices. Setting up op-amps and voltage dividers, led brightness.
https://www.tindie.com/products/redrocketlabs/resistance-decade-box-resistor-substitution-box/ (https://www.tindie.com/products/redrocketlabs/resistance-decade-box-resistor-substitution-box/)
If you're looking for something that you can use to put a "load" on a battery - take a look at Dave's "dummy load" project. It's a easy and fun build for a beginner.
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Thanks for the response!
Even more pertinently, now that I actually think about it, ... no matter the size of the resistor, I really don't want to think about the heat sink something able dissipate 100W would need!