Capacitor Selection: Single-Phase Motor without Nameplate - Unknown Power & Value

Hello, I am asking the moderator immediately to move the topic to another section, if I did not write here.

I have a single-phase motor of unknown power without a nameplate with a capacitor that works all the time but I do not know its value. And here is my question how to choose it ??

7A current flows in the working winding (idling), and what current should flow in the auxiliary winding?
After connecting a 25 uF capacitor, 2A flows in the auxiliary winding.

Hello.

sztygar wrote:

Hello, I am asking the moderator immediately to move the topic to another section, if I did not write here.

I have a single-phase motor of unknown power without a nameplate with a capacitor that works all the time but I do not know its value. And here is my question how to choose it ??

Or maybe you know what was driving this engine? Does the engine have a centrifugal switch?
Possibly how many wires come out of the stator (do not count the capacitor wires)

technics6 wrote:

There is probably no centrifugal switch, since current flows through the capacitor during idle operation.

Hello. Logically speaking, you are right, especially since the author wrote;

Quote:

I have a single-phase motor of unknown power without a nameplate with a capacitor that works all the time but I do not know its value.

But he also wrote;

Quote:

After connecting a 25 uF capacitor, 2A flows in the auxiliary winding.

It could also measure auxiliary phase current with old capacitor.
But we do not know the condition of the old capacitor (and we will not telepathically say whether, for example, a centrifugal is short-circuited. Hence the question.

Hello, friend, could you send a photo of this engine.

I started the topic on the initiative of my dad, he has been rewinding the engines for 25 years, so I think there is no point in adding these photos ...

Hello
From what I read from your post, you ask about the work capacitor.
Its value depends on the engine power. For example, a BESEL motor of 1.1 kW runs with a 25 uF capacitor.
Let my father measure the length and diameter of the stator sheet package and I will try to determine the motor power and choose a capacitor from the series of types.

sztygar wrote:

I started the topic on the initiative of my dad, he has been rewinding the engines for 25 years, so I think there is no point in adding these photos ...

? does it make sense to ask?

HELLO.
I have such a problem. I have a rope electric hoist. There is no capacitor next to it. And it should be. Single-phase motor with left-right rotation. The power is estimated at around 400-700W. 3 wires come out of the motor. N power supply is permanently connected to one of them. The winding resistances are: 1-2 = 20 ohms, 2-3 = 20 ohms, 1-3 = 40 ohms. And it is to 2, that is to the "middle" of the winding, N power is connected. How to choose a capacitor ??? And maybe someone knows how to properly connect it to change the rotation left - right ?? Maybe someone will draw a handwritten diagram ?? Because I do not know if I connect correctly. Please help.

Seweras wrote:

HELLO.
I have such a problem. I have a rope electric hoist. There is no capacitor next to it. And it should be. Single-phase motor with left-right rotation. The power is estimated at about 400 - 700W. 3 wires come out of the motor. The winding resistances are: 1-2 = 20 ohms, 2-3 = 20 ohms, 1-3 = 40 ohms. How to choose a capacitor ??? And maybe someone knows how to properly connect it to change the rotation left - right ?? Maybe someone will draw a handwritten diagram ?? Because I do not know if I connect correctly. Please help.

Do you have any qualifications to repair electrical devices?

I have powers. Qualification certificate E

Added after 7 [minutes]:

I see. The winding with the capacitor is permanently on. There is no centrifugal switch.

I have merged the posts, please use the "Modify" button to edit the post. [Luke]

Hello.
I already know for sure that the motor is 580W. So what does a capacitor need ?? I think with 20 uF. That's possible? The windings are 2x20 ohms.

Hello
To change the direction of rotation in a single-phase squirrel-cage motor, you need to reverse the direction of current flow in the auxiliary winding. Unfortunately, you must have four wires on the motor terminal plate for this purpose. You only have three. Possible removal of the fourth wire, rather, have it done by an authorized engine rewinding company. They will do it professionally - that is, safely.

Hello !
In the case of a motor where both windings have the same resistance and only three wires are led out, it is possible to change the direction of rotation.
1-2 = 20ohm
2-3 = 20ohm
The capacitor must be connected to 1 and 3
Wire N (as described by the founder of the second thread of this post Seweras) to 2
Contrast the second power cable to terminal 1 or 3 and thus select the correct direction of rotation.
Greetings. Stefan

sp3ots
And that's what I meant. Specific answer.
Yes, I thought that you need to connect this way, but I did not impose my course of thought. And now I am sure that the motor will work both ways correctly.
Thanks for the answer.
What about the capacitor ?? What should I choose a 580W motor for this?
I think 20uF might be enough. What do you say??

Hello !
I do not know how the manufacturer selects a capacitor for a given motor!
But by peasant reason, knowing that both windings are identical, I think that:
when idling, the same voltage should appear in both windings?
Perhaps you need to choose the capacitor so that U - 1-2 is comparable, similar to U - 2 - 3, but this is just my guess.
Greetings. Stefan
ps. a few days ago I got a 370W 220V 1470rpm Besel motor and there is a 12uF / 500V work capacitor, the resistance of the working and auxiliary windings are different, so this motor cannot be taken as an example.

As soon as I have a war, I will check the voltages and currents consumed by the motor on both windings using a 20 uF capacitor. Because that's what I have. I think that since the windings are identical, the currents and voltages should be different when idling.

As for the drive ...
Motors, or rather windings of single-phase motors, it is known in advance that the shift angle between the main and (auxiliary, starting) is 90 degrees.
In short, so as not to confuse your minds:
1. Symmetrical two-phase windings (where there is only and only starting with a centrifugal or "overcurrent" switch); they play the role of the starting winding (it is turned on during the start-up)
2. asymmetric two-phase winding, where there is a capacitor in p. Not only is it involved in the start-up process, but you might want to amplify the moment.
Coming back to the point.
When choosing a condenser and its parameters ... its capacity, or rather the voltage, is less important.
If the condenser capacity is too small, the motor will only have a low torque.
On the other hand, if you put the capacitor on too low voltage (e.g. 230-250V), you will overheat the auxiliary windings during longer operation.

I suggest a capacitor with the parameters:
approx. 10 uF / 400V

second, if I'm not mistaken. According to of the energy law, 1-f asynchronous motors that can be connected to the public grid must not exceed 1.5kW, therefore they are not produced for higher powers.

Added after 23 [minutes]:

Yes, I did not specify that the capacitor between 14-20uF should meet the expectations, it costs about PLN 20.
However, when it comes to changing the direction of rotation, it is enough to change the direction of the current flow in one of the windings.