# reducing voltage



## ithurt (Jun 23, 2008)

Can I reduce a 3.7 volt dc wall wart out put to like 1.5 volts? 
I am trying to slow a motor down for my laser vortex. The speed with one AA battery is perfect but I hate using batteries.


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## Scottzilla (Jun 13, 2007)

Probably the easiest way is to get a potentiometer. That way you can adjust the speed until it's just what you want.


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## Kurt (Sep 23, 2006)

A couple of options:
1) go buy a variable wall wart that can push 1.5v
http://www.ace4parts.com/Products/300-mA-ACDC-Adapter-15V-12VDC__BE226.aspx

2) Build a voltage divider using a 1.5/1.8v zener diode
http://en.wikipedia.org/wiki/Linear_regulator#Simple_zener_regulator

3) Use a voltage regulator 
One example that offers a 1.5v regulator: http://www.diodes.com/datasheets/AP130.pdf (you'd get an AP130-15-*-*

Depending on how long a AA runs, you might just consider using batteries.
(put several in parallel to get you longer running time)

Curtis


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## Fester (Sep 17, 2006)

I gotta go with Scotzilla with the pot. I haven't tried a wall/lamp dimmer on such low DC voltage, but if you have one lying around, give it a try. 

BTW I am also doing a laser vortex for this first time this year. I have it built, but after changing lasers I need to re-set the mirror to get the cone big enough again. What are you using for to spin your mirror? What kind of laser are you using?


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## Otaku (Dec 3, 2004)

Definitely use a pot. Grab a 1 Mohm linear pot from R-S. Remember, though, that using a pot to slow down the motor will decrease torque.


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## Fester (Sep 17, 2006)

Anybody know if you can use a dimmer on the input (110) side of a wall wart?


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## MansionHaunter (Sep 20, 2006)

ouch - you wouldn't want to use a potentiometer for a load like a motor; it'll fry the poor thing. A high-current rheostat will work, rated for like 3A, if you can find one. 

As for the dimmer... that might work, unless the wall wart has a built-in regulator, then it'll do no good at all.

You could also get a few high-wattage resistors at Radio Shack or somewhere, and test several values in the 1 to 100 ohm range.


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## Scottzilla (Jun 13, 2007)

MansionHaunter said:


> ouch - you wouldn't want to use a potentiometer for a load like a motor; it'll fry the poor thing. A high-current rheostat will work, rated for like 3A, if you can find one.


I just assumed it was a pretty small motor since it runs off an AA battery. It's true you don't want to run a very big one through a standard pot. Any idea what kind of current your motor draws?


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## Fester (Sep 17, 2006)

I too would believe that it is a very small load. I am using an old PC fan with a 3vdc ps to spin a 1'x1" mirror.


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## ithurt (Jun 23, 2008)

the guy at radio shack told me to use 2-10ohm resistors wired in parallel.
did nothing.
I hooked up a single AA batery to test it out. Started at 7:00 pm and was still running at 7:00 am, so this should work fine. way smoother.

Thanks for all the help!


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## ithurt (Jun 23, 2008)

update: The motor ran for 2days straight! It was still going when I unhooked it.
The motor is from a portable cd player. Not the main drive but the one that controls the laser movement, if any one is interested. 1 AA battery is the perfect speed.


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## NecroBones (Feb 10, 2006)

ithurt said:


> the guy at radio shack told me to use 2-10ohm resistors wired in parallel.
> did nothing.


Wait... two 10-ohm resistors in parallel?

Did you wire them in parallel with each other, but in series with the motor? If so, then of course that did nothing. That's a 5-ohm total, which is really practically no resistance. If he was saying to put them in parallel to the motor, it's very little resistance in a bypass around the load. The motor is still capable of drawing a decent amount of current if the power supply permits it. This is not very energy efficient.

Yeah, go with a rheostat or pot.


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## Scottzilla (Jun 13, 2007)

I wonder if the fellow from The Shack meant to wire them in series like a voltage divider? Then you would hook the motor to the point in between the two resistors.


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## Master__Gracey (Oct 16, 2008)

Scottzilla said:


> I wonder if the fellow from The Shack meant to wire them in series like a voltage divider? Then you would hook the motor to the point in between the two resistors.


I'm sure that's what he meant, then make the second resistor in parallel with the rest of your circuit. Google Kirchoff's Second Law for more info on dividing voltage if you're interested.


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## HauntedSFX (Nov 5, 2008)

I use the speed controller from my electric model train set!


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## DynamoBen (Nov 9, 2008)

Fester said:


> Anybody know if you can use a dimmer on the input (110) side of a wall wart?


You will burn up the wall wart. Phase-angle dimmers are designed to dim resistive load not inductive loads (fans, wallwarts, foggers).


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