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How would i do this? (electronics, simple?) Answered

i have a 540 size motor and i am running it with a 12v 4 amp power supply. is that too much? could i use 9v batteries? i also need to control it, does anyone know the rating for it? radioshack only. Thanks

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user
Tool Using Animal (author)2008-01-31

Running a 540 sized motor off of 9 volt batteries will give you run time measured in minutes. Running it at 12V 4amps most likely won't hurt it, as long as it doesn't get to hot. Used to play with rc cars with 540 sized motors, ran them at 9.6 volts 30+ amps, but only for 4-5 minutes at a time.

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user

you can only crank soo many amps through a motor...(resistance of the motor's wire)

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user

I'm not sure what your point is, but I assure you, you can crank 30+ amps through a 540 sized motor, esp. if it's been rewound. RC car ESC are rated up to 300 amps. kruser, don't use a pot. scrape up $10 and buy a pwm kit off the net.

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Patrik (author)2008-01-31

If you just need something up quick and dirty...

If we assume guyfrom7up was right about the stats, 1A @ 6V, you would need to drop 6V down from your 12V supply. Easiest way to do that (but by far not the most efficient!) would be to simply put a resistor in series with your motor.

Just like in calculating a limiting resistor for a LED, you just take the desired voltage drop, and divide it by the desired current: 6V/1A = 6 Ohm.

Important: note that this series resistor will dissipate 6 Watts of power! So don't just use a single 1/4W resistor. Get a chunky power resistor out of an ancient stereo or powertool, or wire 24 x 144 Ohm, 1/4W resistors in parallel. Or you could even use a pencil core as an improvised power resistor (take off all the wood - this will get hot!)

The reason why guyfrom7up is advising you *not* to step down the voltage with a resistor is because you're essentially wasting as much power through the resistor as you're putting into the motor (using a potentiometer would be even worse). It's wasteful, it'll get really hot and potentially burn out and/or you need resistors which can handle that much power.

But if you absolutely need to get something up and running in a hurry, it can be an option. Just don't be lazy, and make sure to replace it with a pwm solution or a different power source as soon as you can...

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user
guyfrom7up (author)2008-01-31

you could though, but it will get poor performance. what's the motor for? You volt de graff?

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guyfrom7up (author)2008-01-31

ehhhh it's not recomended

heres how to use pwm with a 555

http://www.uoguelph.ca/~antoon/circ/pwm555.html

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guyfrom7up (author)2008-01-31

supposedly they run off of 6 volts (i think). You could use 9 volts. It takes almost an amps, can a nine volt supply that much? I've run 1.5-3volt motors off of 9 volts before, if you don't do it continuesly it'll work. Might shorten the life of the motor though it goes much faster and harder. to control it use a 555 timer and a power mosfet.

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