# Control my motor

Dears,

I got this motor from a junkyard, but I don’t know if it is AC or DC.
I would like to control it using Arduino Uno.
If it is a DC motor I know how to make the power circuit.

How can I check if it is DC or AC?
It has 3 input cables and a capacitor in parallel.

Thank you guys!

Looks like a 220vac 3-phase brushless motor. Not sure about the voltage but you can measure the winding resistance and do the math. V = I x R ==> I = V/R Let V = 220Vac then, Motor current per winding (in Amps) I = 220/R The current is an unknown until you figure out the voltage, then it can be calculated using the resistance. Find out the voltage or try different values for the calculation . You did not include a ruler in your photo so that motor could be 3 " or 9 " The cap size suggests it is about 3 to 5 " in size. .

When its got 4 windings, so one thing it can never be is a 3-phase anything!

Its probably a split-phase induction motor, the capacitor derives a second phase from the single-phase mains. The rotor looks to be two squirrel cages back to back, so its probably available in half this stack-length.

When its got 4 windings, so one thing it can never be is a 3-phase anything!

It has 3 input cables and a capacitor in parallel.

Why are there only 3 wires in the attached photo ?

raschemmel:
Looks like a 220vac 3-phase brushless motor. Not sure about the voltage but you can measure the winding resistance and do the math.
V = I x R ==> I = V/R
Let V = 220Vac
then,
Motor current per winding (in Amps) I = 220/R
The current is an unknown until you figure out the voltage, then it can be calculated using the resistance.
Find out the voltage or try different values for the calculation .
You did not include a ruler in your photo so that motor could be 3 " or 9 "
The cap size suggests it is about 3 to 5 " in size. .

the motor is 3’’
The capacitor is a 4uF and 250VAC

MarkT: When its got 4 windings, so one thing it can never be is a 3-phase anything!

Its probably a split-phase induction motor, the capacitor derives a second phase from the single-phase mains. The rotor looks to be two squirrel cages back to back, so its probably available in half this stack-length.

how can I connect it into my circuit? I mean, should I connect only 2 of the 3 cables (phase and neutral)? How to check which one is the right?

The capacitor is a 4uF and 250VAC

I may be wrong about it being a 3-phase motor but clearly I was right about the operating voltage being 220vac.

No. Don't do anything yet. You still don't know what you have or what to do with it. List the wire colors and the resistance from one color to the next. Draw a schematic on paper and post a photo of it showing where the cap was connected.

raschemmel:

The capacitor is a 4uF and 250VAC

I may be wrong about it being a 3-phase motor but clearly I was right about the operating voltage being 220vac.

No. Don’t do anything yet. You still don’t know what you have or what to do with it.
List the wire colors and the resistance from one color to the next.
Draw a schematic on paper and post a photo of it showing where the cap was connected.

There is a capacitor inside the motor connected to the black wire, I dont know its values

The values from the resistances are:

YELLOW / BLACK – 91 ohms
YELLOW / GRAY - 182 ohms
GRAY / BLACK - 91 ohms

Thank you!!

There is a capacitor inside the motor connected to the black wire, I dont know its values

Does it look like the 4uF cap you mentioned previously ?

220vac x SQRT(2) = 311 Vpk AC. I = V/R = 311/182=1.7 A (pk) Irms = Vrms/R = 220Vac/182 ohms = 1.2 A (yellow to gray)

Irms = Vrms/R = 220Vac/91 ohms=2.4 A (yellow /black, or grey/black)

To be honest with you I don't know enough about ac motors to tell you how to connect it. If I had to figure it out I would probably get a variac and set it a some low voltage and try different combinations but I would necessarily recommend that approach for you. Maybe someone else (like Mark) can help with the connection wiring. Do you have access to 220Vac where you are ?

The "capacitor inside the motor" is a thermal fuse to cut all power if it overheats.

Black is one terminal - whether live or neutral is intended I don't know, the fuse would suggest live, but black as a colour doesn't!

Either grey or yellow is the other terminal and the other winding gets its phase-shifted current via the big capacitor. If the windings are identical then it shouldn't matter which of grey or yellow you power. If they are different it will matter and offhand I don't know how to determine this.

Ideally about the same amp-turns will be present on each of the two phases.

Are you absolutely sure its 240V AC? Just because the capacitor is rated that high doesn't mean the windings are, it might be 110Vac - without a ratings plate its rather risky guess work.

And are you sure its 50/60Hz and not some other frequency? (OK, bit unlikely)

You absolutely must add an earth connection to the frame of the motor, given the dodgy source, and check the isolation of the wiring from the frame, preferably with a megger.

Are you absolutely sure its 240V AC?

I don't know where you got 240V from.

I said this:

Looks like a 220vac ....etc....

To which the OP replied this:

The capacitor is a 4uF and 250VAC

250V-220V=30V

30V/220V = > 13.6% margin at 220V 30V/208V => 14.4% margin

As an engineer you know it is standard procedure to overspec components by some specified percentage as a safety margin. The question is , Was 250V chosen because it is more than 10% above the operating voltage or was it chosen because it was close to 15% above the operating voltage. I think 240V is too close to 250V 10/240=> 4% (250V is only 4% above 240V) . It is unlikely 240V is the operating voltage based simply on the value of the cap. It does not mean it is not the operating voltage, just unlikely.

If the operating voltage is 220V, then 250V is a safe rating for the cap. If the operating voltage is 208V, then 250V is about 15% above that and more enough for a 208V circuit.

If you can find something to reduce the mains voltage (like power resistors) it would reduce the current until you know the correct wiring.

Dears,

I've discovered how to turn it on properly!! Keep the black on neutral and yellow or gray on phase (live). Each wire is a different direction!!