# Controlling 28v DC Motor



## gilbequick (Oct 6, 2007)

This is DIY, it may belong in the off topic section.

I'm looking for a way to control the drive speed (RPM's) of a DC motor running off of 28 volts. The simpler the better to keep power loss to a minimum. I would even settle for a stepped control, what I mean is instead of controlling it to a precise RPM, it could be 25%/50%/100% power. 

Cost is a factor, I want to keep parts to a minimum, again the simpler the better.

OK guys, have at it. What are your thoughts?


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## MDShunk (Jan 7, 2007)

Buy a trigger from a Milwaukee 28V drill and use a c-clamp.

(Hey, you asked for cheap, right?)

Either that, or buy a variable DC power supply.

What size motor we talking about here?


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## RIVETER (Sep 26, 2009)

gilbequick said:


> This is DIY, it may belong in the off topic section.
> 
> I'm looking for a way to control the drive speed (RPM's) of a DC motor running off of 28 volts. The simpler the better to keep power loss to a minimum. I would even settle for a stepped control, what I mean is instead of controlling it to a precise RPM, it could be 25%/50%/100% power.
> 
> ...


MarlinPJones associates.Google...they have a lot of things and very inexpensive.


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## gilbequick (Oct 6, 2007)

Actually the stripping of drill parts isn't a bad idea.

This is a small motor, about as big around as a coffee can but only about 4 inches long.


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## wildleg (Apr 12, 2009)

slot car control ?


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## gilbequick (Oct 6, 2007)

RIVETER said:


> MarlinPJones associates.Google...they have a lot of things and very inexpensive.


Holy bajezzus, that place is loaded with parts. I'm wading through it but don't really know what I'm looking for.
http://www.mpja.com/


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## MarkyMark (Jan 31, 2009)

If you don't need precision, you could always just wire switches in series with the battery cells so that the motor is getting 14/21/28 volts.


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## RIVETER (Sep 26, 2009)

gilbequick said:


> Holy bajezzus, that place is loaded with parts. I'm wading through it but don't really know what I'm looking for.
> http://www.mpja.com/


They will send you a monthly catalog and it is kind of fun to wade through it. I can't believe the prices.


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## LJSMITH1 (May 4, 2009)

RIVETER said:


> They will send you a monthly catalog and it is kind of fun to wade through it. I can't believe the prices.


 
Imported....


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## RIVETER (Sep 26, 2009)

LJSMITH1 said:


> Imported....


Nah, probably from China.


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## Mr.C (Dec 20, 2009)

Ok you said cheap so here ya go but first understand in no way would I suggest this be your standard of operation for this. With that being said use the lead out of a lead pencil and tap it at various lengths for the voltages you are looking for, this is in effect a rheostat and will work for you but the problem here is that it wont be efficient because you will get a voltage drop across a series load (the rheostat) and the motor. The total power used will be a combo of the work done by the motor and the heat you created through the rheostat to drop the voltage. In other words you dont want to go the rheostat route. What you want to do is tap your voltages from a battery so your only using what you need, why dont you rip a 28volt rechargable battery apart and tap it at you various voltage increaments then use a selector switch to choose your voltages connected to the load. If you are careful when you tear the battery apart and have the wire leads coming out the bottom then you will be able to still recharge the battery when needed. Or grab 3 12v car batteries put them in series and open the water caps on them, then you stick a wire in the individual cells to tap the voltage where you want it. 
Please note I am having fun with this and would not endorse this as a industry standard. (this is where a smile face would be appropriately inserted if I knew how)


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## Introyble (Jul 10, 2010)

Here is a simple way:

Use a potentiometer (pot) as a rheostat by simply wiring the pot in series with the simple circuit. As you spin the shaft of the pot you vary total resistance and thus total current. The change in current likewise affects the speed of the motor.

Single turn 5k pot s hould do the trick. Use only 2 of the three wires always using the wiper terminal then either the cw or ccw terminal. 

So, connect the positive lead of your DC power supply to the CW terminal of the pot. Then connect the Wiper terminal of the pot to the either terminal of your motor. Connect the negitive lead of your DC power supply directly to the other terminal of the motor. Now turn the shaft of your pot.


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## McClary’s Electrical (Feb 21, 2009)

Introyble said:


> Here is a simple way:
> 
> Use a potentiometer (pot) as a rheostat by simply wiring the pot in series with the simple circuit. As you spin the shaft of the pot you vary total resistance and thus total current. The change in current likewise affects the speed of the motor.
> 
> ...


 


true, but a pot big enough to handle this kind of load would be about 150 bucks


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## Introyble (Jul 10, 2010)

How much of a load could a 28 VDC fan be carrying?

What is the horsepower, mA or the wattage of your fan?

Guessing what, maybe 1/25 HP?

Lets see, a 50 watt 5k ohm potentiometer is $12. 50 watts is plenty for 250 millamps.

$12 isn't a lot of money but maybe your fan is much larger than I imagined?


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## McClary’s Electrical (Feb 21, 2009)

Introyble said:


> How much of a load could a 28 VDC fan be carrying?
> 
> What is the horsepower, mA or the wattage of your fan?
> 
> ...


 
Actually, he just said 28 volt motor, he didn't say how big. I was picturing a big drill motor, and you were picturing something small


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## colinlesnar (Jul 13, 2010)

In other words, do not want to go the route rheostats. What you do is click on the battery module so that you only use what you need, why not rip each other 28volt rechargeable battery and touch will be a different voltage increments then use the selector to choose the voltage connected to the load. If you are careful to pull the battery and the guide wire that comes from the ground, then you can still charge the battery if necessary.


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## RIVETER (Sep 26, 2009)

Surely he's got this figured out by now.


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## McClary’s Electrical (Feb 21, 2009)

RIVETER said:


> Surely he's got this figured out by now.


 
I wouldn't bet on it!,,,,,,, there's a fish tank guy been at it for months on here. Is he gonna buy the software to write a program for a fish tank?


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## RIVETER (Sep 26, 2009)

mcclary's electrical said:


> I wouldn't bet on it!,,,,,,, there's a fish tank guy been at it for months on here. Is he gonna buy the software to write a program for a fish tank?


What was he wanting to know? How to bond the water?


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## Introyble (Jul 10, 2010)

RIVETER said:


> What was he wanting to know? How to bond the water?


We are not sure what he wants, I told him how to do it already. $12 is alot of money in his world. Tell him to wire 3 9 volt batteries in series and as the cells die, his motor will slow down! :thumbup:


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## Wingnut (Jan 31, 2010)

a sewing machine pedal ?


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## McClary’s Electrical (Feb 21, 2009)

Wingnut said:


> a sewing machine pedal ?


 

Good idea. Never checked on how one works. What's in one?


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