Author Topic: Resistor decade box, component power rating  (Read 1368 times)

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Offline nikodemus

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Resistor decade box, component power rating
« on: July 04, 2013, 10:25:28 am »
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?

 

Offline george graves

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Re: Resistor decade box, component power rating
« Reply #1 on: July 04, 2013, 11:25:42 am »
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/

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.

Offline nikodemus

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Re: Resistor decade box, component power rating
« Reply #2 on: July 04, 2013, 01:47:49 pm »
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!
 


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