Thread: Variable speed control.

Originally Posted by shooter74743

Mine is AC and is variable speed...

Yes, this DC motor setup runs on AC current as well. I expect an AC motor which is variable has many differences than one which is a single speed. Brother-in -law will know. I shall ask!

Keep in mind that my motor is 3 phase though...

Originally Posted by sharptonn

Yes, this DC motor setup runs on AC current as well. I expect an AC motor which is variable has many differences than one which is a single speed. Brother-in -law will know. I shall ask!

No. A variable speed AC motor and a fixed speed AC motor are the same. The difference is the drive needed.
AC engines are controlled by changing the frequency of the input signal. For this, a frequency convertor is needed, and decent ones cost money. Sometimes as much or more than the motor itself.

Got TWO 1HP DC motors in my shop and no controller. :/ Found one on craigslist the other day for $200...... It was more than I needed as it had a tach and some other crud I don't need for a belt grinder so I passed.

Tom, my motors came off bulk mail machines. Probably the same as the ones you refer to.

I have a similar lesson drive controlling a variable speed sander I built.
The input plugs into your wall @ 110 vac.
The output will drive either a 90, or 180 vdc motor. You can wire the output either way as its a two wire output plus ground set up. It will run both directions depending on how you wire it, white to white, or white to black wire.
You can get a used dc motor all over, just find the hp, and shaft size you want and you can build from there. Lots of threads from folks on ideas and such.
Just need to verify input and output connections by removing the cover. Make sure any jumpers are set to the desired voltages and voila.. Now, if you are not comfortable wiring a household lamp, get a bud to help. Ideally with a multi meter to verify everything before you connect your motor.
Cheers.

We need to find an electrical engineer and get him hooked on a straight razor and the forum :<0) Mine is a woman that is 150 years old ,ex navy, and passed on being the first woman astronaut. She takes the time to explain all the yada french yada yada Swahili, yada plain english and I forget it all as I walk away. Now I just ask " can I do this or not ? "

Are you sure about that? My electrician buddy who is also a hack knife maker told me that they are not in the sense that you cannot use a single phase/leg (?) AC motor with a VFD.

Originally Posted by Bruno

No. A variable speed AC motor and a fixed speed AC motor are the same. The difference is the drive needed.
AC engines are controlled by changing the frequency of the input signal. For this, a frequency convertor is needed, and decent ones cost money. Sometimes as much or more than the motor itself.

Both are right.
Your buddy is right that you can't use a single phase AC motor and dc vfd controller.
Bruno's right that a fixed or variable speed AC motor is basically the same. Usually, only three phase motors are variable, not single phase units,, and you vary the phase or hertz to change speed on AC motors, not the voltage like in a dc setup.
Hope that helps.

My buddy was telling me to never just go out and buy any old motor for VFD use. I got mine as a package. It was one of the early AC VFD setups from Beaumont/KMG after they had switch over from DC motors. What i was told was that the AC setup was more reliable.

Originally Posted by MikeB52

Both are right.
Your buddy is right that you can't use a single phase AC motor and dc vfd controller.
Bruno's right that a fixed or variable speed AC motor is basically the same. Usually, only three phase motors are variable, not single phase units,, and you vary the phase or hertz to change speed on AC motors, not the voltage like in a dc setup.
Hope that helps.

Single phase motors can be used with a single phase VFD. It's not ideal and it is not really common.

3 phase motors can be used with or without VFD. Now, most VFDs hae some intelligence built in, like current protection etc. You can compare it with an amplifier and a sound speaker. it makes no sense to put a 10 watt speaker on a 100 watt amp. In that sense, your friend is right. However, from the motor's perspective, it's all the same. A 3 phase motor is a 3 phase motor no matter how you drive it.