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First of all, I'm a total novice.

My parents have an old electric curtain pulley system from probably the 70's. It's run by a universal motor connected to a 3-position switch. The switch positions are OFF - LEFT - RIGHT. 3 wires run from the switch to the motor (common black, plus a blue and a brown from the switch positions).

By inspecting the wiring, it looks like it just runs the universal motor forwards or reverse by engaging only one of the two stator coils (the blue wire runs to one stator coil and the brown wire runs to the other one). Both stator coils share the same black wire (I'm assuming it's the live wire - it runs through an old capacitor/filter thing first and in series with the rotor).

I want to toss the awful, ancient, noisy spark-frenzy fire hazard of a motor and replace it with a quiet DC motor. The old motor is rated 200/90W whatever that means. I would like to keep the switch though, so my question is: How do I control the direction of a DC motor using AC wires - one live wire and two neutrals?

Many thanks in advance :-)

edit: It's actually only 2 wires coming from the switch to the motor. The common live wire is just from the wall.

Here's the current schematic:

schematic

simulate this circuit – Schematic created using CircuitLab

Here's an attempt at a solution. It's probably pretty naive. And if someone could tell me if a relay can be controlled with an AC signal or not, that would be great.

schematic

simulate this circuit

Somebody said relays couldn't be wired in series with the transformer, so here's another attempt using two relays: Please tell me if it would work.

edited: cleaned it up a little

schematic

simulate this circuit

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  • \$\begingroup\$ Are you looking to keep just the switch and the wires to the motor, or also the mains connection into the switch? \$\endgroup\$
    – jonathanjo
    Sep 25 at 13:41
  • \$\begingroup\$ I haven't really considered that as an option actually. I suppose there would be no harm in opening up the switch panel and make changes there too. \$\endgroup\$
    – Bruce Wang
    Sep 25 at 13:46
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    \$\begingroup\$ You can use the schematic editor to shown the current circuit and what you think might work. A current wiring diagram would also help. \$\endgroup\$
    – RussellH
    Sep 25 at 13:57
  • \$\begingroup\$ Cool you guys have a schematic editor embedded :D I just drew the current system. It's really simple. I hope it makes sense. I really don't know much about circuits and motors, so I can't even guess to a solution. \$\endgroup\$
    – Bruce Wang
    Sep 25 at 14:20
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    \$\begingroup\$ I would suggest getting somebody with experiences with the mains to either tutor or help you. There are many ways of becoming crispy and this has many paths. \$\endgroup\$
    – Gil
    Sep 25 at 18:12

1 Answer 1

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The safest way to proceed would be to avoid all connection to the AC mains, except for a DC power supply with about 200 VA capacity (12VDC 16A or 24 VDC 8A). As long as the PSU is properly current limited and fused, you will eliminate most risk of electric shock and fire. Then find a suitable DC motor, which could be a 12V automotive window motor, and build a circuit like this:

schematic

simulate this circuit – Schematic created using CircuitLab

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