# 16 volt motor and resistor

troy8143
Member - Posts: 3
Joined: May 18, 2011
Location: Florida, United States
Posted: May 18, 2011 at 10:54 PM / IP Logged

I race drag slot cars and I am trying to reduce the voltage of my motor from 16v to 1v.

To be safe im going to assume it pulls about 4 amps at 16 volts. (64 watts)  At 1 volt I am assuming it will pull about .85 amps

Basically i need to pick out a resistor (or multiple resistors) that will not burn up, I dont know much about different resistors in anything more powerful than a small pocket amplifier.

What ohm rating and wattage would i need? where do i buy resistors?

oldspark
Gold - Posts: 4,913
Joined: November 03, 2008
Location: Australia
Posted: May 19, 2011 at 2:52 AM / IP Logged
V=IR => R=V/I
R = (16-1)/.85 = 15/.85 = 17.6
Hence 18 Ohms (a preferred value).
P=VI = (16-1)*0.85 = 15*0.85 = 12.75W.
Hence 20 Watts (preferred size).
Hence an 18 Ohm 20W resistor based on your info.
(Likewise, the motor will have ~1.3% of the original ie, 1/75th the power from 1*0.85/16*4 = 0.85W/64W = 1/75)
troy8143
Member - Posts: 3
Joined: May 18, 2011
Location: Florida, United States
Posted: May 19, 2011 at 8:32 AM / IP Logged
Thank you very much. I appretiate you showing the math with it. Now if i can just find one locally for less than 5\$ ;)

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