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Author Topic: AC motor speed controller  (Read 7951 times)

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Offline pomprockerTopic starter

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AC motor speed controller
« on: March 17, 2008, 05:53:39 PM »
Can anyone who is more familiar with electronics explain this circuit to me? Or tell me if they think it would work?

http://home.maine.rr.com/randylinscott/aug99.htm


From what I understand it plugs into a wall and then you can plug a hand held drill into it and it will control the speed with the pot if say the drill speed controller was full depressed.

Offline benji

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Re: AC motor speed controller
« Reply #1 on: March 18, 2008, 08:24:12 AM »
this circuit is totally wrong
reasons : 
1/the scr is used only as a switch ,on or off,so there is no control over the voltage at the load, maybe they wanted to put a power transistor

2/i dont see an ac voltage/current happening at the load,it doenst change polarity
usually in ac motor you control the speed by transforming ac to dc then back to ac again so you should use two scrs in reverse directions
and you control the amount of current they pass by making a pulse generator circuit that changes the phase of the gate clock
the more the degree is the less the current is

if you are interested in regulating spped of ac motors they are called inverters , search for em
good ol' BeNNy

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #2 on: March 18, 2008, 12:04:53 PM »
 :D I don't understand any of that yet  :P

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #3 on: March 19, 2008, 01:12:05 AM »

Offline benji

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Re: AC motor speed controller
« Reply #4 on: March 19, 2008, 09:06:32 AM »
i dont see a circuit schematic provided

by the way why do you wanna use an ac motor?
these ones are only used in idustry
and the speed controller circuit for such isnt an easy one to build.
good ol' BeNNy

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #5 on: March 19, 2008, 10:48:26 AM »
oh just thinking about building something  ;D seeing if i can piece it together.

Offline benji

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Re: AC motor speed controller
« Reply #6 on: March 19, 2008, 04:33:30 PM »
a good thing to build as a circuit if you wanna improve your analog circuits analysis is to try to build audio pre-amps
even those are turning to DSP processing by now
total analog circuits are shrinkin away
good ol' BeNNy

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Re: AC motor speed controller
« Reply #7 on: March 23, 2008, 08:42:55 AM »
Be careful if you are playing with AC . . .

I personally would never risk it. And if I had to, I'd go get certified first.

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #8 on: April 02, 2008, 06:08:24 PM »
OK, I've decided to go with a DC motor for my application.

BUT, I want it to be powered by AC. (using a rectifier, and capacitor, not sure what else)

AND, I want it to be speed controlled. (Either by SCR or PWM or VARIAC, I don't care)

The motor will either be 90VDC, 115VDC, or 130VDC.

I'm not really sure how to power a DC motor from AC, can anyone who knows electronics better than me help me.

Offline airman00

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Re: AC motor speed controller
« Reply #9 on: April 02, 2008, 06:20:25 PM »
OK, I've decided to go with a DC motor for my application.

BUT, I want it to be powered by AC. (using a rectifier, and capacitor, not sure what else)

AND, I want it to be speed controlled. (Either by SCR or PWM or VARIAC, I don't care)

The motor will either be 90VDC, 115VDC, or 130VDC.

I'm not really sure how to power a DC motor from AC, can anyone who knows electronics better than me help me.

just get a wall adapter and convert AC from an outlet to DC
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Offline michaelsane

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Re: AC motor speed controller
« Reply #10 on: April 02, 2008, 07:09:30 PM »
You don't power the AC motor from DC you convert ac to dc using a bridge rectifier.  All a bridge rectifier is is 4 dioes, that force all + one direction, and all of the - a different direction, so there is no oscillation.  If you want a different voltage than the one coming directly out of your wall you will need to use a power transformer.  The transformer comes before the diode bridge and smoothing capacitor.  However, since you are wanting to use a speed controller chances are you are going to need a 5v supply, so you could create a voltage divider and use a 7805 type regulator for that.  From here you could use an mcu connected to 4 mosfets to make an h-bridge.  Unless you are using logic level mosfets you will also need a driver ic.

Transformer------>Bridge Rectifier--------->Caps----------->motor load

Offline benji

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Re: AC motor speed controller
« Reply #11 on: April 03, 2008, 09:54:04 AM »
Quote
The motor will either be 90VDC, 115VDC, or 130VDC.
thats big voltage for a dc motor,, anyways use a trnasformer then a bridge rectifier and do their math..
now about speed control,
the idea is to make less voltage come across the motor, do it the way you find easier ,
if you need a simple speed controller just connect a pot serially with the motor, as the pot take higher values the voltage across the motor
will be less so reduced speed,,also reducing in current is gonna happen so torque will be less too,,thats the bad thing about this approach.

using the pwm method will be a little complicated because of the high voltages you have,,im not sure about it.
maybe you need a thyristor,,,
good ol' BeNNy

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #12 on: April 03, 2008, 12:49:35 PM »
So to get the 115/120 VAC from the wall to 130VDC of my industrial motor I need to get a grounded power cable, hook it up to a transformer (why do I need to do this instead of go straight to the bridge rectifier, and what kind of specs should this have?), then from the transformer to the bridge rectifier (what kind of specs would this rectifier have?), and then go to a smoothing reservoir capacitor (of what value? The motor is 1 amp), and then would I need a voltage regulator?

Thanks ahead of time for your expertise. I'm new to electronics.  ;D

Offline benji

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Re: AC motor speed controller
« Reply #13 on: April 03, 2008, 03:21:31 PM »
firstival you NEED the transformer to get the voltage you want im talking here ac/ac
then rectify it using bridge rectifier ,this should give you a dc voltage value very close to the input ac voltage amplitude(trans out)

about caps (smoothing and in rec bridge) you should get ones that can handle the voltage at the trans out.
about its capacitances it should be relatively big , about 3300 uF is used, im not quite sure about it , check for such a circuit
over the net i guess there are plenty.

what do you mean of voltage regulator? an IC like 7805? if the voltage you aim for is this low then its always good to get one of those as it outs
ya a precise voltage ,but watch out for their maximum current, the 7805 can handle no more than 1 Amp.
for high voltages im not sure you can regulate it better than a smoothing cap.
good ol' BeNNy

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #14 on: April 03, 2008, 05:36:47 PM »
All I can find on the net for a 130vac transformer is a Variac.

Could I go Variac -> Bridge Recitifer -> Capacitor?


Would a Variac control the speed of the motor?

Offline michaelsane

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Re: AC motor speed controller
« Reply #15 on: April 03, 2008, 06:13:39 PM »
You could, but I am willing to bet you can find a transformer.  Why 130VAC j/w?  But how many amps will your motor sink?

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #16 on: April 04, 2008, 01:17:05 AM »
the motor is rated 130vdc, 1amp

Offline michaelsane

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Re: AC motor speed controller
« Reply #17 on: April 04, 2008, 03:52:58 PM »
The easiest thing to do would just be to use the 120VAC from the wall, and you wouldn't even need a transformer.  Is there any reason you NEED to run it at 130V?  Then all you would need is a diode bridge and some caps and you have a psu that can power your motor.

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #18 on: April 05, 2008, 02:30:23 AM »
Yeah thats what I was hoping I could do. Thanks. Do happen to know what the specs on the bridge rectifier and the capacitor would be or how I figure that out?

Offline paulstreats

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Re: AC motor speed controller
« Reply #19 on: April 05, 2008, 06:41:35 AM »
for the bridge just use high voltage rectifier diodes

for the cap just use 200vdc 3300 - 10000uf electrolytic capacitor (try to stay above the voltage you require when buying the cap)

If you use a variac instead of the cap, it may offer some torque/speed control for you. If you do decide to use potentometers and scr's for speed control, you will have to get some heavy duty types because they are gonna get HOT HOT HOT

Offline michaelsane

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Re: AC motor speed controller
« Reply #20 on: April 05, 2008, 12:56:03 PM »
This would work fine for you.  http://www.newark.com/18C7016/semiconductors-prototyping/product.us0?sku=FAIRCHILD-SEMICONDUCTOR-KBP02M

(LOL the quantity is 1337)

As for a capacitor just fine one that is around 200v and 3300uF or more. 

If you are going to be powering mcu's then you are going to need some 5v regulators and resistors also.

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #21 on: April 05, 2008, 01:22:34 PM »
I'm lookin at the radio shack rectifiers because I dont wanna pay for shipping if i dont have to. What is the PIV that its talking about?

Offline superchiku

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Re: AC motor speed controller
« Reply #22 on: April 05, 2008, 01:33:37 PM »
woudnt it be better if u just make a bridge rectifier rather than buying one
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Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #23 on: April 05, 2008, 01:36:12 PM »
the time versus cost issue, its not worth my time making one.

Offline superchiku

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Re: AC motor speed controller
« Reply #24 on: April 05, 2008, 01:40:53 PM »
WELL MAKING ONE WILL TAKE A MAX OF 10 MINS buying one online 3 days
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Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #26 on: May 17, 2008, 01:44:52 AM »
I bought the motor speed controller from the surplus center above.

Here is the wiring diagram I get:

[img width= height=]http://www.surpluscenter.com/Wire/W11-2449.jpg[/img]


I am not really sure about hooking up the 130vdc motor and the AC inlet connector that I bought, its not very clear for n00bs.

the wires coming out of the motor are green, white, and black.


I wired all the grounds to the heat sink chassis that it comes with.

anyway, when i touched the pot, my hand started to tingle. I don't think thats right!

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Re: AC motor speed controller
« Reply #27 on: May 18, 2008, 11:57:49 AM »
You have a DC motor running at 130V with three unidentified wires?! :o

Hmmmm sounds dangerous!

No motor datasheet?

Offline pomprockerTopic starter

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Re: AC motor speed controller
« Reply #28 on: May 18, 2008, 07:07:18 PM »
Well I ended up getting it fixed and working yesterday. Turns out I had two wires coming out of the motor reversed. Turns out on Bodine motors that the green wire is ground, the black one is hot, and white is neutral.

 


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