# Society of Robots - Robot Forum

## Electronics => Electronics => Topic started by: cooldog on January 03, 2009, 07:45:17 PM

Title: 12v variable slide resistor
Post by: cooldog on January 03, 2009, 07:45:17 PM
okay guys i was wondering if i have a simple circut of a 12v motor and a car battery (12v) with a switch and i put a 12v variable slide resistor in the circut would i be able to control the motors speed?

if what i am saying is true does anyone know where to get a 12v variable slide resistor?
Title: Re: 12v variable slide resistor
Post by: TrickyNekro on January 03, 2009, 08:26:27 PM
yes there is....
Title: Re: 12v variable slide resistor
Post by: cooldog on January 03, 2009, 10:03:51 PM
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=497-3466-5-ND

do you think this is will work?
Title: Re: 12v variable slide resistor
Post by: Razor Concepts on January 03, 2009, 10:07:39 PM
Depends on how many amps your 12v motor will pull. The one you listed is good to 5 amps
Title: Re: 12v variable slide resistor
Post by: cooldog on January 03, 2009, 10:18:43 PM
would that be max 5 amps from the battery or that my motors draw
Title: Re: 12v variable slide resistor
Post by: Soeren on January 04, 2009, 09:42:26 AM
Hi,

The LD1585 will only do for a small('ish) motor.
It can handle around 2W un-sinked and with a large heat sink around 25W tops.

Regulating it to eg. 6V will make it drop 6V (actually a bit more, since the terminal voltage is more than 12V).
Un-sinked this equates to 2W/6V=333 mA
With perfect heat sinking it will be 25W/6V = 4,17A

Regulating the output further down will only worsen this to around 166 mA and 2,1A respectively.
(It's all in the datasheet).
Title: Re: 12v variable slide resistor
Post by: Trumpkin on January 04, 2009, 09:43:06 AM
Quote
would that be max 5 amps from the battery or that my motors draw
Title: Re: 12v variable slide resistor
Post by: Soeren on January 04, 2009, 09:45:04 AM
Here is something far better http://www.dprg.org/tutorials/2005-11a/index.html (http://www.dprg.org/tutorials/2005-11a/index.html)
Title: Re: 12v variable slide resistor
Post by: cooldog on January 04, 2009, 10:04:57 AM
Here is something far better http://www.dprg.org/tutorials/2005-11a/index.html (http://www.dprg.org/tutorials/2005-11a/index.html)

that looks like a good circut however i looks like it need a lot of external parts

Quote
would that be max 5 amps from the battery or that my motors draw
i think that i am moving more toward this option

The LD1585 will only do for a small('ish) motor.

thanks anyway but i would like to use something for a bigger motor so i can use it in future projects

Title: Re: 12v variable slide resistor
Post by: Soeren on January 04, 2009, 10:37:50 AM
Hi,

The LD1585 will only do for a small('ish) motor.

thanks anyway but i would like to use something for a bigger motor so i can use it in future projects
Then you really need a PWM circuit, as a linear solution has too much loss (i.e. heat).

You should be able to buy a ready assembled PWM solution, although it might be a bit expensive - perhaps you can advertise for someone here to build the circuit for you, so that you just have to connect power, motor and a potentiometer (eg. your variable slide resistor).
If you want to take that route, stating where in the world you live is not a bad idea.
Title: Re: 12v variable slide resistor
Post by: cooldog on January 04, 2009, 12:34:33 PM
well i live near toronto canada