Elec motor voltage

Started by swoffer, February 07, 2018, 11:57:27 AM

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swoffer

Hi all ,

Wondering if anyone here can help me with a bit of advice .



I have a small electric motor that I have put on a rod turner . The motor is rated for 3v and runs thru a set of gears to reduce the speed at the output shaft .



Works fine at 3 volts but it runs to fast and i need to reduce the voltage to 1.5v to achieve the speed I need . The young "expert" at Jaycar today sold me a resistor to put in the pos lead to the motor to reduce the voltage to 1.5 . Problem is when I soldered the resister inline it let no power thru at all .

The numbers on the resistor are 10w27ohmJ .

Any ideas how I can reduce 3 v to 1.5 ?

Cheers Al

Tiddlerbasher

Don't use a resistor.

Instead use a PWM controller (pulse width modulation). I typically buy these from  Ebay.
I won't bore you with the details of these except to say you will get a continuously variable speed from your motor so you can dial in the right speed.
Units like this will do the job:

https://www.ebay.com/itm/DC-New-1-8V-3V-5V-6V-12V-2A-Low-Voltage-Motor-Speed-Controller-PWM-1803B/172785981506?hash=item283ad8d842:g:~z4AAOSwsMVZbwYQ
or
https://www.ebay.com/itm/3V-35V-12V-24V-5A-PWM-DC-Motor-Speed-Controller-Adjustable-Switch-LED-Fan-Dimmer/122943366971?epid=918271106&hash=item1c9ffee73b:g:VfYAAOSw7GRZKUR2

Anything like those will do the job. As you are only using 3v just make sure that your pwm controller can work with that.

swoffer

Awesome TB , how bloody cheap are they eh .

So just to be sure , if I get this one   

DC 1.8V 3V 5V 6V 12V 2A motor speed controller 30W PWM 1803b K7 L6

And say input 6v I will be able to turn it down to 1.8 v , do I understand that correctly ?

Thanks heaps .

Keta

Hi, my name is Lee and I have a fishing gear problem.

I have all of the answers, yup, no, maybe.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

Bryan Young

Quote from: swoffer on February 07, 2018, 01:23:07 PM
Awesome TB , how bloody cheap are they eh .

So just to be sure , if I get this one   

DC 1.8V 3V 5V 6V 12V 2A motor speed controller 30W PWM 1803b K7 L6

And say input 6v I will be able to turn it down to 1.8 v , do I understand that correctly ?

Thanks heaps .

AC and DC motors work very different.  A DC motor will not work if you reduce the voltage.  It will only work at the proper voltage rating of the motor (+/- tolerances).  What drives the motor faster or slower is the effective overall current provided to the motor.  Note that the motor will only take a maximum prescribed current and you cannot push more current to make the motor faster even if you wanted to.  What a PWM device does it controls the amount of pulse current going to the motor.  The closer the pulses are together, the faster the motor will operate.  The wider the time between pulses will slow the motor.  In short, the speed of the motor is controlled by the current, not the voltage.
:D I talk with every part I send out and each reel I repair so that they perform at the top of their game. :D

swoffer

Thanks Bryan , I think I get what you are saying . But in laymans terms for me , if I get this little gadget will it control the speed of the motor I'm using ?


Bryan Young

Quote from: swoffer on February 07, 2018, 02:28:21 PM
Thanks Bryan , I think I get what you are saying . But in laymans terms for me , if I get this little gadget will it control the speed of the motor I'm using ?
Picture one of those water wheels that use to turn machine back in the old days.  A directed stream, water goes into a trough.  The water is then emptied onto a water wheel with little buckets to catch the water.  The more water you put in the buckets, the wheel starts to turn due to gravity.  The faster or more water is added to the wheel, the faster the wheel turns.  Does this makes sense?  I may be explaining it all wrong.
:D I talk with every part I send out and each reel I repair so that they perform at the top of their game. :D

swoffer

Yeh ,nah , its clear as mud now  ;D

See , I'm even more confused now . When I picked up this motor it is clearly marked for 3v . When I ran 3v to it from a power supply it ran at about 50rpm . So I got a 1.5v d cell and wired it to the motor , it then ran fine and about 10rpm , which is what I'm looking for . But if I read your first post correctly Bryan it shouldnt have worked on 1.5v ?

I hasten to add that I am extremely tech challenged when it comes to electronics  :'( :'( :'(

Tiddlerbasher

Swoffer - if it's 3v motor (I assume DC) then apply the 3v to the pwm controller, don't use 6v, it's too much. The ouput of the controller connects to the motor. A pwm controller doesn't change the voltage so the output would still be 3v. What happens is the controller 'chops up' the 3v at a high frequency, typically 10kHz to 50kHz. When you adjust the knob it varies the duty cycle, ie it is swiching on and off very quickly. So it is either 3v or 0v. The more times it is at 3v the faster the motor goes. The motor averages it's speed dependant upon this duty cycle but still maintains high torque as if it were on 3v all the time. If you were to simply lower the volatge the torque drops - ie the motor ends up being 'gutless' and not able to do its job.
The PWM controller is the way to go ;)

Keta

After going through all the monkey motion you will still have a motor that you can not easily control the speed of without using your hands.  Reinventing the wheel seldom improves things.
Hi, my name is Lee and I have a fishing gear problem.

I have all of the answers, yup, no, maybe.

A man who carries a cat by the tail learns something he can learn in no other way.
Mark Twain

Bryan Young

Quote from: swoffer on February 07, 2018, 02:50:13 PM
Yeh ,nah , its clear as mud now  ;D

See , I'm even more confused now . When I picked up this motor it is clearly marked for 3v . When I ran 3v to it from a power supply it ran at about 50rpm . So I got a 1.5v d cell and wired it to the motor , it then ran fine and about 10rpm , which is what I'm looking for . But if I read your first post correctly Bryan it shouldnt have worked on 1.5v ?

I hasten to add that I am extremely tech challenged when it comes to electronics  :'( :'( :'(

Likely the D-cell voltage is within it's tolerance, but the current draw is significantly less...thereby slower running motor.
:D I talk with every part I send out and each reel I repair so that they perform at the top of their game. :D

Tiddlerbasher

Dc motor speed is voltage dependant for a given rotor/magnet combination. If you don't need torque, aka start up power, dropping the voltage will reduce speed. If your rod turner is just for drying epoxy you don't need much power. If it's for power wrapping/cork turning etc. you do need a bit of power. My take is - build a machine that will do both with variable speed - one machine many uses. Wrap your guides with speed - then turn down the revs apply epoxy and leave to dry. This is why I would go for a manual speed control - dial it up - leave it alone to dry.
As always your choice :)

oc1

If the rod turner is for wrapping then you need some torque and either a good slip clutch or a foot control like Lee has shown.  If the rod turner is for drying then you don't need much torque but fixed speed control is important to keep from flinging off the finish before it dries.  For drying, the modulator like Tiddler has shown may work best.  Trying to control it by varying the voltage never works well because the speed and the torque interact and it may take many attempts before you find the right voltage.

Personally, I'd just toss it and get a little 10 rpm gear motor.
https://www.ebay.com/itm/DC-12V-0-6-120RPM-Reversible-High-Torque-Turbo-Worm-Electric-Geared-Motor-USEFUL/122297766357?hash=item1c7983d1d5:m:mybqDXTYEleucwD9w5MtURg

Sorry, I'm posting on top of Tiddler.
-steve

Gfish

#14
So it's a DC(direct current, i.e. usually battery operated only)) motor? Or does it plug into household current(AC) and use a converter(a converter reduces volts("force or pressure" of electricity) and the amperage(flow of electricity as a rate i.e. # of Charged particals movin across a conductor/unit of time) and converts AC to DC.
That resistor they sold you, can it be installed one way only? Or maybe it dosen't matter?...
Good tool to have is Digital Multi-Meter. You can measure dc or ac volts, small volumes of amperage, resistance(ohms), etc., etc.
Gfish
Fishing tackle is an art form and all fish caught on the right tackle are"Gfish"!