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help with 12v to 3v regulated supply

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cbiblis

New Member
I have a gear motor that will run from 3v-12v. @ 75ma. It runs to fast for my application on my 12v supply and the gears are to noisy. What is the cheapest and safest way to drop the voltage from 12v to 3v? I have tried a pwm and it doesn't do well and i don't want to use more gears. 6v is quieter but still to fast. This is where i came up with the idea of using 3v to power the motor.
I did use a few of diodes in series and accomplished the 3v but it not only lost it's strength but wasn't regulated enough to make the full revolution under pressure of the tray that it's turning.
Just some suggestions will do. Thanks
 

MikeMl

Well-Known Member
Most Helpful Member
LM317 in the TO220 package mounted on a good sized heat sink. R1 is 240Ω. Make R2 a 500Ω or a 1000Ω pot.
 

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MikeMl

Well-Known Member
Most Helpful Member
Is this right?

Make R2 a pot so you can set the running speed of the motor. If R1 is 240Ω, the formula for calculating R2 = 192 * Vo - 240 , so if you want 3V, R2 = 192 * 3 -240 = 336Ω. A 500Ω pot will adjust the voltage from 1.25V (the minimum) to 3.65V. A 1000Ω pot will adjust the voltage from 1.25V to 6.46V.
 

cbiblis

New Member
i hate to ask a stupid question but i guess i have to. On a pot there are 3 legs which ones do i use?:confused:
 

MikeMl

Well-Known Member
Most Helpful Member
Middle and one end
 
i can't find the ld1117 anywhere but futurlec and I'd like to have it by Christmas. LOL

yeah i know, they're freaken hopeless aren't they.

I ordered a 2x16 LCD and 4x16LCD both with blue backlight,
and they sent the normall ones.
 
i hate to ask a stupid question but i guess i have to. On a pot there are 3 legs which ones do i use?

Just to try and teach you something...

Think of a 3 pin POT as 1 resistor (2 ends), with a sweaper arm (2 ends.. one to connect to, and the other end move along the fixed resistor.

If you have a 10KΩ POT for example,
(with a multimeter) You will have 10KΩ between the outside pins.

If the rototing knob is in the middle (50/50);
between the first and second pin you will have 5KΩ, and between the second pin and third pin you will have 5KΩ.

If the rototing knob is 25% one way (leaving 75% the other way);
between the first and second pin you will have 2.5KΩ, and between the second pin and third pin you will have 7.5KΩ.
Or the other way around depending on which way you turned the know.

Ok, i think i made that as complicated as i could.
lol...
 

mbarazeen

Member
since you have tried it with diodes and it didnt work, i beleive even if you have a good regulated 3V it may not work. you try to operate a 12V motor with 3V and for sure it may not deliver propper torque as you expect.

my sugestion is to go for another propper motor, preferably a step motor. you can have low RPM with good torque with step motors.

any how you can try as sugested by others, incase if it doesnt work you can move to this option.
 
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cbiblis

New Member
Here is the link
6VDC 3RPM Gearhead Motor-The Electronic Goldmine
And you are right, it states 4v is the lowest i can go.
I am looking for a egg turner motor for my incubators. The slower the better a 3 turn per minute would be the best does anyone have a suggestion?
I know i could probably work on a 555 timer circuit with the 4v regulator. But i really wants to keep my circuits to a minimum and i don't know a thing about 555's.
Can someone tell me what i should search for to find a schematic using a 555 that would turn a motor on for a variable time then turn off for a variable time?
 
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mbarazeen

Member
if you want to turn a plate of eggs, then you can choose the tray to have gears on its circomference and to be driven by the motor at one point. its like it will act as a big gear wheel coupled to the motor, so you will get slow rotation. also you would get a great torque to over come friction, etc.
 
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