# Ac to dc



## Lapowers (Mar 20, 2014)

I was wondering if anyone knows how to wire a 115 volt dc motor to ac


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## John Hasler (Mar 20, 2014)

Lapowers said:


> I was wondering if anyone knows how to wire a 115 volt dc motor to ac



With a 115VDC power supply.  I could build one but I don't think I could guide you through doing it.  Are you interested in selling that motor?


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## Inflight (Mar 20, 2014)

Sounds like you need a motor controller that uses Pulse Width Modulation to feed the motor.  An inexpensive solution is to utilize a 2nd hand Treadmill Motor Controller such as an MC-60.  Readily available on ebay for about $35.  

What is your application?


Matt


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## David S (Mar 20, 2014)

If you just want single speed the cheapest what would be with a full wave bridge rectifier.  Would need to know the rating of your motor to select the appropriate rectifier.

David


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## DMS (Mar 20, 2014)

The problem with just using a bridge rectifier is that you are going to generate about 160V peak DC (no load). This may not be a problem, but it is something to keep in mind. The voltages listed for AC values are "RMS" values, which is an average of the AC wave. 


I have run small DC motors (a little 115VDC gear motor) with a combination of a light dimmer and a bridge rectifier. This allowed for pretty effective speed control. Those light dimmers are not rated for motor use, so I would not try them on anything over about 1/4hp.

If you do this, I would also highly recommend adding a fuse ahead of the rectifier, and putting all the bits in a box. 

There are also off the shelf DC controllers that use something called "SCR control". The good ones are expensive, but they turn up as surplus periodically. These allow very nice speed control.


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## John Hasler (Mar 20, 2014)

DMS said:


> The problem with just using a bridge rectifier is that you are going to generate about 160V peak DC (no load). This may not be a problem, but it is something to keep in mind.



Unless he adds a filter capacitor he will get 115V RMS which is what the motor wants.




> The voltages listed for AC values are "RMS" values, which is an average of the AC wave.



RMS is root-mean-square, which is the same for a sine wave AC signal and a full wave rectification of it. The average of the AC wave is zero.

I agree that he ought to get himself some sort of speed control, though.  Otherwise there's no point in having a DC motor.


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## TOOLMASTER (Mar 20, 2014)

Look up dc speed controls on ebay..


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## DMS (Mar 20, 2014)

John Hasler said:


> Unless he adds a filter capacitor he will get 115V RMS which is what the motor wants.
> 
> 
> 
> ...



It is true that the RMS value after the bridge will be 115V. This may not be a problem, UNLESS he trys to filter things by adding a capacitor, and that capacitor doesn't take the peaks into account (ask me how I know. Hint it's the same way I know that exploding capacitors are very loud and smell bad  The first time I tried this, I didn't take this into account; just trying to help others from having to air out the house.

The only reason any of this is pertinent to the OPs question of course is is if he has something on the line that can't handle that peak voltage. According to wikipedia, that is going to be about 1.4 times larger than the RMS voltage (around 160V)


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## Lapowers (Mar 20, 2014)

I bought a south bend lathe with a 1/2hp westinghouse 115v dc motor  4.7 amp the motor was disconnected and none of the wires where marked where they go I found a rectifier in with the wires now I'm just trying to figure out how to wire everything up if worse comes to worse I have 1/2 hp ac motor I could use


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## awander (Mar 21, 2014)

If it is a universal motor it will run on AC or DC.


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## David S (Mar 21, 2014)

If it is just a simple dc motor and rectifier with no other controls, then you hook the incoming switched ac line to the two terminals on the rectifier marked with a sine wave.  The two wires from the motor go to the two remaining terminals on the rectifier.  The positive terminal on the rectifier will be marked with a symbol and goes to the positive lead of the motor.

David


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## lngknife29 (Mar 23, 2014)

You can put a choke on the load side of the capacitor circuit--this will knock the voltage back down to what you need---if you can, check out the control circuit on those treadmill motors everybody talks about--they have the choke in there for the same reason.


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## Lapowers (Mar 26, 2014)

Ok I finally got my motor hooked up I had to purchase a new bridge rectifier I got it wired to go forward and reverse with a drum switch. Not being an electrician and knowing nothing about electric motors I was able to do this with help from the members here thanks


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## David S (Mar 26, 2014)

I am glad it worked out for you.

David


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