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  1. #1
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    Single phase, two cap motor



    Not quite fridge, but someone might know.

    ABAC B2800B air compressor, with Single phase Tipo M80-2M 2.2kw motor.

    The electric motor has a winding to earth, so its being replaced.

    But when having a look at the wiring, it looks as though it has two run capacitors? I thought Id seen something similar before, but online searches dont seem to bring up much on how its connected to the windings.

    Four wires come from the motor,
    One black, connected to Live.
    One white, to a 35uf capacitor which is looped to another 40uf capacitor.
    First red, connected to the other side of the 40uf cap.
    Second red, connected to Neutral.




    A link to another forum (not to promote it) where someone else is talking about the same model of air comp, where they have posted a number of pictures of the wiring and disassembled motor.
    https://www.mig-welding.co.uk/forum/...ressor.132146/

    It looks as though there is no centrifugal switch, or anything else to disconnect one of the caps.

    Just wondering how the circuit works?

    Cheers
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  2. #2
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    Re: Single phase, two cap motor

    I wonder if the 40uf red wire has a ptc in the circuit in the motor to disconnect the 40uf once the motor has started?
    That would make the black wire the live, the red the neutral, the white/yellow the start winding and the other red a switched neutral to disconnect the start cap with the ptc.

    I'd get the ohm meter out and see what resistances there are between all the wires to each other and then draw it out and see if it makes sense.
    Mostly found in Oxfordshire, UK :)

  3. #3
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    Re: Single phase, two cap motor

    Hi monkey spanners,

    Did some searching on the 40uf cap, and it sort of looks like it has a built in timed switch?

    https://www.cem-elettromeccanica.com...ase-motor.html

    First time Ive come across one of those, so not sure exactly how their doing it. Not been able to find any technical info on the cap.

    Hope to have some time on Monday to take some meter readings. Seems funny to run the red wire off the 40uf cap back into the motor.

    Cheers
    Interested to hear about opportunities to learn - linkedin.com/in/s34nf

  4. #4
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    Re: Single phase, two cap motor

    I didn't know that was a thing! Will keep an eye out in future for that type of capacitor.

    Sounds a bit like the Supco hard start kits, basically a start cap with a ptc to disconnect it once the compressor has started.
    Mostly found in Oxfordshire, UK :)

  5. #5
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    Re: Single phase, two cap motor

    Had a look at the cap fitted to the air comp I was looking at.

    Its capacitor is slightly different, a 40uf 262/CR404U. Some of the label has rubbed away, but it has the insertion time as "Autotarabile".
    Measuring the resistance both ways just gave the usual charging as on a normal cap, quickly going from 0 to OL.
    Wired it to live and neutral on its own, and it ramped its current up to 3A and sat there. Didnt leave it powered up to long, maybe 3-4 seconds.

    Measured the resistance between the motors leads.

    B - W = 3.4 Ohms
    B - R going to 40uf cap = 1.1 Ohms
    B - R going to neutral = 1.1 Ohms
    R - R = 0.0 Ohms
    R going to 40uf cap - W = 4.5 Ohms
    R going to neutral - W = 4.5 Ohms

    Kinda looks like its just a CSCR motor with a funny start cap.

    Cheers
    Interested to hear about opportunities to learn - linkedin.com/in/s34nf

  6. #6
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    Re: Single phase, two cap motor

    Just in case anyone wants to know, and maybe save someone some of the hassle.

    The new motor came with the ususal start and run cap, and a RECS-220P electronic centrifugal switch.
    A little electronics box with four coloured wires, that the manufacturer says you need to program by running the motor unloaded.

    They give a method to reset the switch settings if needed.

    http://www.rns-tech.com/UserView/Com...5101144226.pdf

    English starts at page 16.

    After programming the switch with the motor unloaded, and then putting the drive belt back on, it did start fine with no pressure in the air receiver. But on restarting at 6 Bar the motor stalled.
    Had to reset the switch and program it under load for it to work properly.

    Cheers
    Last edited by seanf; 14-03-2024 at 10:15 PM.
    Interested to hear about opportunities to learn - linkedin.com/in/s34nf

  7. #7
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    Re: Single phase, two cap motor

    In case anyones interested.

    Opened the old motor, and it looks like the start winding got hot.
    The two red wires that go into the motor do just join together at the winding connection.

    Opened the old start capacitor. Think its a Comar, 262/CR404U, Autotarabile.
    In the top sits the 40uf cap with the two white wires running through the centre of it, and underneath that there is a circuit board with a Finder 4061 mechanical relay.




    Resistor R1 looks to have gotten hot, couldnt get a resistance reading from it.
    Diode D2 didnt have any info on it. Could it be a Zener? Checked it up to 30Vdc and did nothing. Checked it in series with a resistor on 230Vdc and it seemed to sit at about 125V.

    Cheers
    Interested to hear about opportunities to learn - linkedin.com/in/s34nf

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