# 90vdc motor to 110 outlet



## marc (Oct 9, 2008)

I am lost. I am trying to wire a dc motor (90vdc) to plug into a standard home outlet. I have read about rectifiers and capacitors but cannot make heads or tails out of which one or ones would be recommended. Can anyone help explain this in simpler "laymans" terms. Any help would be so appreciated.:huh:


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## InPhase277 (Feb 9, 2008)

Marc, this isn't something you're going to get alot of help on here, except that you should not do it, etc. The reason being, no one wants to give the kind of advice that may lead to you really hurting yourself, or potentially others. Which is highly likely since:

1) You have already professed to have no understanding whatsoever of the subject. And ,
2) You are not only dealing with lethal voltages, both AC and DC, you are doing so in conjunction with a high speed piece of rotating machinery.

Having said that, I will say that what you want to do is entirely possible with the correct understanding. And I know that you won't simply stop your experiment because of my warning. Let me give you this advice. If you do proceed, make sure that take all the safety precautions necessary with an experiment like this. Secure the motor to your work surface. Wire your power supply to something you can switch remotely, such as a power strip or a simple light switch. You don't want to be standing near the motor or your "new" rectifier when you first put power to on it. And you don't want to make the connection by plugging in a cord, because if there is a short or heavy load, you will get a face full of sparks.

So have everything wired and plugged up, then push the switch. Have a fire extinguisher near by. When building the circuit, you want to use components rated for twice the amount of current you expect to draw. I'll set you on the right path to research the circuit. Four diodes can be arranged to convert AC into DC. See the picture. Now start surfing the web.


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## micromind (Mar 9, 2008)

There are two types of electricity, AC and DC. 

DC; this type has a positive pole and a negative one. Positive is always positive, and negative is always negative. Voltage determines just how much positive and negative there is. The higher the voltage, the greater the difference between the two. 

AC; this type changes polarity. The rate of change is called frequency, also known as cycles or hertz. In the USA, the power you get from the utility is set permanently at 60 hertz. It cannot be easily changed. This means that the polarity (positive and negative) will change 60 times each second. 

Some devices don't care about the type of current they use. An incandescent light bulb is one of these, it operates equally well on AC or DC. 

Others must have the right type of power to operate. Motors are an example. Some motors can operate with either type of power, while others cannot. If the motor is designed to operate on AC, it won't run on DC, and vice-versa. 

Changing AC into DC is easy, there are devices called diodes (rectifiers) that will allow current to pass in only one direction. If two of these are installed (one in each AC line), they'll operate in a push-pull fashion, and the end result is DC power. There are several other ways to convert AC to DC, the above is the simplest. 

Converting DC to AC is much more difficult. Basically, the DC power must be turned on and off at whatever frequency is desired. There are many ways to accomplish this, and not enough space here to describe them. 

The direction or rotation of a DC motor depends on the polarity of the input power. Change polarity, and rotation will change as well. If you connect a DC motor to an AC line, since the AC lines polarity changes, the motor will try to turn in opposite directions. If you convert the AC power to DC, the motor will certainly run. 

In the case of a 90 volt DC motor, you'd need 90 volts of DC or less to make it run. If you convert 120 volts of AC to DC, you'll have somewhere around 120 volts of DC. Placing a capacitor across the newly converted DC will actually increase the voltage somewhat. This gets complicated, if you'd like, I'll explain it further. 

A 90 volt DC motor is designed to be used in conjunction with a speed controller. 90 volt DC is almost always 120 volt AC input, 180 volt DC is 240 volt AC. The speed of a DC motor depends on its voltage, and its load. AC motors are different. A speed controller for DC motors is an AC to DC converter, and a variable voltage control all in one. 

I realize this is somewhat complicated, if you'd like, either me or a few of the other guys around here can explain it further.

Rob

P.S. 277 is exactly correct, I just type a little slower!


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## ScottR (Oct 6, 2008)

marc,

InPhase is 100% right. Especially the part about the fire extinguisher.

I'm just curious, what's your application? If it's a temporary application, you may be able to pick up a used bench-top variable DC power supply on the cheap on eBay. That would save you the trouble and risk of constructing a relatively high Voltage / Amperage power supply, though if the motor has a high Amp rating it might get expensive to find the right PS.

(BTW - I'm with you on your desire to make the power supply yourself. Can't say I wouldn't try it, and it's the best way to learn.. IF you're safe about it).

Scott


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## marc (Oct 9, 2008)

hey guys,
thank you so much for your responses, if it makes either of you feel any better I am an auto mechanic so DC makes sense to me. And i have enough home improvement basics that i am not totally in the dark (no pun intended) with AC. It is just putting the two together has me twisted. I have a fully variable speed control but I heard that if you turn the motor down without a capicator that it would get "jumpy". Is the rectifier something i am going to have to fabricate myself out of diodes or can these be found at radio shack or somewhere of that nature. And lastly car stereos have large capicators, will i need something that large or is there a rating i should go by?
Again Rob and 277, thank you for your time and wisdom.


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## marc (Oct 9, 2008)

Scott,
there was a game show on ABC that had a wall of boxing gloves that would come out of a wall and try to knock people off a ledge. If you didnt get to see it, it was hilarious. Anyway, in that spirit we are trying to set up an challenge course that would be fun to our 4x4 club but be safe for the whole family. The reason i was trying to fab this myself is that i will have to produce more that one and just to see if we can do something on a much smaller scale but still say that we ultimately did it ourselves.


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## ScottR (Oct 6, 2008)

LOL! OK, that is definitely not what I would have guessed. I have seen the show and know exactly what you're talking about. Once saw a guy take one glove right in the groin. Hilarious.

I do like how you combined 90VDC, boxing gloves, 4x4s, and "safe for the whole family" into one topic. :laughing::laughing:

And I'm sorry I'm not being more helpful here, but you'll be in much better hands with InPhase and Rob than me.. In fact, this just raises another question: I would think that as an auto guy you'd go for 12 VDC.. Why the 90 V motor(s)?

And off topic, where are you located? Just asking b/c I have a new Rubicon and nowhere to go offroad..


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## marc (Oct 9, 2008)

Scott,
I did try 12v first and the wiper motor i finally ended up with was a little slow, even on high speed. 
I am located in the beautiful ozark mountains in northwest Arkansas. 4-wheeling here is pretty easy, and scenic. It would be a heck of a drive in a jeep (been there) but if you are ever in the area....
I myself settled on an Early Bronco (1977 to be exact) for my off road pleasure. and at 8mpg's off road is the only road it sees.
-marc


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## InPhase277 (Feb 9, 2008)

Marc, it makes me feel better that you have some mechanical knowledge. I wasn't sure from your post if you could turn a screwdriver. I didn't want to tell an accountant how to build high voltage power supply to a motor that could jump off the bench and into his teeth:laughing:. I suppose from the description of your obstacle course that this motor is going to power a hydraulic ram? Cause I can't see a small motor being able to push 4x4s off a road with a mechanical drive.

At any rate, you will need to source components that can handle the current of the motor. Radio shack won't have them on hand, but they may be able to order them. Or you can get the largest that RS has and parallel them. The only problem is your motor will be operating at slightly more than it's rated voltage. This may not be a problem for short term use, but continuously may damage it. Of course, you could always use batteries. 8 12-volt batteries in series will be 96 volts. And you could have a high output charger connected to keep them up. I'm thinking lawn mower batteries. But that's pricey.

You need this thing simple. So, if you get some large high power diodes, or parallel some smaller ones, and build the rectifier circuit I posted, coupled with a smoothing capacitor and a 2000 W lighting dimmer, you may be in business. Look at this:


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## J. V. (Jun 1, 2007)

http://www.kbelectronics.com/ Under $100.00


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## swordfish (Feb 3, 2009)

*voltage*

do you buy different size rectifiers to get the proper voltage to match your motor. or does any rectifier that is large enought to handle the load sufficent. I assume the dimmer regulates the voltage thus also acts a a variatable speed control. This subject is not handled well anywhere I have found. I work with ac and dc but running dc from a wall socket is said to be simple. HA HA . If someone knows how to do a vari speed dc motor speed control with all things that make them work good . rectifiers capacitors regulators dimmer switches ect please post a good diagram and text. Thank you


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## J. V. (Jun 1, 2007)

J. V. said:


> http://www.kbelectronics.com/ Under $100.00


To operate a 90 volt DC motor from 120 volts AC is easy and safe.
A small DC drive is all you need. A chassis mount from KB electronics is very inexpensive. I mention KB as they are cheap and readily available.
You connect the 120 volt to the terminals marked input and you connect the DC motor to the terminals marked output. Add a potentiometer and you are good to go. Just plug in the ac and adjust the DC motor speed with the pot.


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## Yoyizit (Jul 11, 2008)

marc said:


> I am lost. I am trying to wire a dc motor (90vdc) to plug into a standard home outlet. I have read about rectifiers and capacitors but cannot make heads or tails out of which one or ones would be recommended. Can anyone help explain this in simpler "laymans" terms. Any help would be so appreciated.:huh:


How much current does it draw?
Does it start under load or drive a fan?
Do you want speed control?

120vac run through a full wave rectifier will give you 106 vdc. A half wave will give you 52 vdc.

Once you know the current you can calculate the heatsink size for the rectifier and the value of a voltage dropping resistor.

I wouldn't use a capacitor; the motor inertia smoothes out the 120 Hz pulses.


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## hychesee (Oct 31, 2008)

If your run 120vac through a filtered fwbr you end up with 160vdc. If you need any speed regulation at all you absolutely need a dc drive, the capacitor will not stop the motor from cogging at anything less then full speed.

The horsepower of the motor will also drop exponentially with unmodified reduced dc voltage, either use an ac series wound motor like a drill or vacuum and a $20 router control (dimmer may also work) or go to ebay and get a KB drive as mentioned earlier look up "DC Drive" (Minarik is also good).

If possible do what I am doing now and let the Chinese save you money and buy a cheap cordless drill with built in speed control. I am making automatic window openers and am using $7 cordless screwdrivers - build in gearboxes too.

You sound like me 30 years ago while attempting to make my first welding positioner, a 90vdc motor a couple a rectifiers and series bypass transistors later all I had was a jumping cogging turntable.

The questions that Yoyizit asks above also needs to be considered.


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