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# Help: Determining What Resistor to Use

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Hi,

I am pretty knew to electronics but I am having trouble finding the calculation to know what amount of resistance to use. (Ex. I have 280V and would like to make it 100V, how much resistance would I need?)

Thanks,
awak3n

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A resistor reduces a voltage by dividing the voltage with another resistor.
Reducing voltage with resistors causes them to heat. The heat is waste. If the current is high then since you want to reduce the voltage a lot, the resistors will become extremely hot.

It might be best to make a power supply for 100V.

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• 2 weeks later...

awak3n,
Here is a voltage divider calculator. This makes learning the formula more fun.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

MP

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