Hi. I'm hoping someone can help me out with a pretty simple physics question. My electrical circuit skills are pretty rusty, so please bear with me.(adsbygoogle = window.adsbygoogle || []).push({});

I'm using a 19V DC laptop adapter to power a 12V DC pump motor. The pump is rated for 3.5A. I have an on/off switch between the power supply and the motor. I'm trying to figure out what kind of circuit I need to put in between to drop the voltage from 19V out of the battery to 12V at the motor.

By my (likely overly simplified) calculations I think that I need a 2ohm resistor rated for 25W+. Is it as simple as just putting a resistor in between the + side of the battery and the motor? Do I need anything more complicated than that? I have to think that I'm wrong here.

Thanks!

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# How to calculate resistance needed for voltage drop

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