How to controll speed on electric motor...

[Tags]

I know this isnt a tractor question, but, there is such a vast majority of knowledgeable people here I thought I'd give this a shot. I recently purchased a used Airflo MSS tailgate sander with an electric motor. It is turned on and off with a toggle switch but I want to be able to slow down the spinner/conveyor when sanding a driveway. I contacted an Airflo dealer and was quoted $650.00 for a speed control switch but I think that sounds a bit steep, anyone have any ideas??

 

[KYErik]

What type of electric motor is it? A drill/circular saw type motor (noisy with brushes) or a quiet brushless motor (like would run a bench grinder)?

If it is a drill type motor, you can likely pull the variable speed resistor switch out of another piece of equipment with a drill type motor that is rated for the same number of amps.

If it is a brushless motor, I think you will need a Variable Frequency Drive (VFD). Slowing down the cycles (Hz) of the line voltage will reduce the motor speed, but it may lead to overheating since the internal fan was designed to run at rated speed.

 

[Tags]

What type of electric motor is it? A drill/circular saw type motor (noisy with brushes) or a quiet brushless motor (like would run a bench grinder)?

If it is a drill type motor, you can likely pull the variable speed resistor switch out of another piece of equipment with a drill type motor that is rated for the same number of amps.

If it is a brushless motor, I think you will need a Variable Frequency Drive (VFD). Slowing down the cycles (Hz) of the line voltage will reduce the motor speed, but it may lead to overheating since the internal fan was designed to run at rated speed.

Sorry,didn't even think of mentioning that. It is like a starter motor, 12volts and and I think it is 1/4hp

 

[murphy1244]

You need a reostat and a darn big one at that.

 

[BobRip]

You might try running it off of a six volt battery. I think this would give you a little below half speed. Take the motor to an auto parts store and see if they will let you test this. Of course you would have to charge the battery periodically. You might try putting a car headlight in the battery to motor hot lead. Use two in parallel if it's too slow. You could actually use your vehicle lights. Just connect the motor between the battery positive and the positive lead of the lights. The motor will run when the lights are off. I have not tried any of this. I just know something about electricity.

 

[Soundguy]

rheostat? please.. how barbaric.

PWM for sure....

handfull of IRFZ40's and some perfboard and etchant will do ya...

soundguy

 

[BobRip]

rheostat? please.. how barbaric.

PWM for sure....

handfull of IRFZ40's and some perfboard and etchant will do ya...

soundguy

Please attach a schematic, parts list, and pcb layout. Easy for you.

 

[Tags]

rheostat? please.. how barbaric.

PWM for sure....

handfull of IRFZ40's and some perfboard and etchant will do ya...

soundguy

Soundguy, what you said sounds great to me....if I could understand it....I also forgot to mention I am not well versed in the ways of electricity. Could you explain what you are saying like you're talking to a two year old?

 

[k0ua]

You need an SCR (Silicon Controlled Rectifier) speed controller. Either build your own SCR based controller. or buy something. you need to know the current draw of your sander in AMPs. I am guessing about 10 amps but could be more.

Silicon-controlled rectifier - Wikipedia, the free encyclopedia

12 volt speed control | eBay

dc speed control | eBay

12V-40V 10A PWM DC Motor Speed Controller w/ Knob - Free Shipping

Do some research and get back with us..

James K0UA

 

[BobRip]

You need an SCR (Silicon Controlled Rectifier) speed controller. Either build your own SCR based controller. or buy something. you need to know the current draw of your sander in AMPs. I am guessing about 10 amps but could be more.

Silicon-controlled rectifier - Wikipedia, the free encyclopedia

12 volt speed control | eBay

dc speed control | eBay

12V-40V 10A PWM DC Motor Speed Controller w/ Knob - Free Shipping

Do some research and get back with us..

James K0UA

By the time you build this yourself you will wish you had paid the $250.

 

[k0ua]

Several of them were 10 to 20 dollars

 

[Soundguy]

By the time you build this yourself you will wish you had paid the $250.

i've HAND built the pc board and high current controller for a prototype electric vehicle using a handfull of mossfets setup as a pulse width modulator ( PWM ),

For the 2yrolds.. it essentially gives pulses of 'full voltage' to the load, instead of being a resistor inline like a rheostat..

there are PLENTY of circuits diagrams online...

as K0ua said.. these can be built cheap...

soundguy

 

[Soundguy]

HERE IS JUST ONE OF THE MANY PWM SITES..

PWM - Pulse Width Modulation for DC Motor Speed and LED Brightness - Robot Room

GOOGLE PWM AND GET 50,000 MORE.

DO THE SAME WITH scr

sorry about caps.. typing in t he dark..

 

[k0ua]

We just need to know the current in amps or Watts of the motor in question to control to reccomend a controller to buy. I am thinking 20 dollars and maybe an simple radio shack plastic box to put it in for another 10 or so, some hook up wire, fuses etc.. a little time and you are all set..

James K0UA

 

[Soundguy]

as I recall, the lil mini project books radio shack sells have both PWM and SCR basic diagrams in them.

soundguy

 

[Tags]

I knew I'd get answers here, thanks for all the replies.I'm gonna get all the details off the motor, check the amp draw, do some searching,and I'll report back!

 

[k0ua]

Soundgy, I was just thinking,(dangerous I know) Why could'nt you just build a simple pass transistor setup like you would for a regulated variable voltage power supply, like a 2N3055 for the pass transistor, and driving that with one of the simple 3 terminal variable regulators. Less than half a dozen parts, A heatskink and WaLa a simple voltage regulator for about 15 amps. and a few dollars.. wudduy think? Or buy one of those Pulse width devices ready made for $20

James K0UA

 

[Redneck in training]

Soundgy, I was just thinking,(dangerous I know) Why could'nt you just build a simple pass transistor setup like you would for a regulated variable voltage power supply, like a 2N3055 for the pass transistor, and driving that with one of the simple 3 terminal variable regulators. Less than half a dozen parts, A heatskink and WaLa a simple voltage regulator for about 15 amps. and a few dollars.. wudduy think? Or buy one of those Pulse width devices ready made for $20

James K0UA

That would not work well due to large heat generation when not fully closed. The answer is switching controller like Soundguy suggested.

 

[Soundguy]

depends on the amp drawn.. that 2n3055 won't like excess current.. adn you waon't parallel them without a lil more support cuircuitry to ballanve them ( if you are thinking series pass regulator )..

the mossfets on the other hand will parallel just fine... lower onstate resistance too...

i'd go field effect transistor before the older NPN.pnp any day.... for a motor controller anyway...

I just like fets... so many uses. buddy and me were building timer circuits for lamps.. he used a 555 platform.. I used a capacitive discharge gate biased fet... mine worked better.. .. had less parts too..

now all that said.. I've done some brute work in autio applications with 2n 3055 and 2955 silicon.. and some tip packaged drivers in a/b mode... or.. 2n3055 alone in straight class A...


soundguy

 

[Soundguy]

That would not work well due to large heat generation when not fully closed. .

yep.. they'd likely be cooking.

my first choice when i look at a dc motor controller is always to investigage a pwm.. and then go from there...