Of DC plugs and SPST toggle switches

Discussion in 'General Electronics Chat' started by ricodued, Jul 30, 2007.

  1. ricodued

    Thread Starter New Member

    Jul 30, 2007
    2
    0
    Here's the thing: I've implanted the guts of a massage chair into the passenger seat of my Subaru Forester. The massage parts themselves are powered by a DC plug which plugs into an AC/DC transformer which I'm eliminating so I can wire it directly into the car's power source which goes on with the ignition. I've got a power source, but I can't for the life of me figure out which of the two wires in the cord should be the one to receive the power, and which one should be I assume is the ground (if it helps at all, one is black with the white lettering detailing voltage etc., and one has white rectangular patches I'd say).

    Basically it goes like this:

    Power source -> switch (more on that below) -> massage power cord.

    And then I'm assuming one of the two wires from the cord is grounded and that's it.

    As for the switch, I've got one of these which will control the power flow to the massage parts. However unlike the other switches I've wired, this one has three connectors (Ground, Acc, and Power). I haven't a clue which one I'm wiring to what! :X

    Thanks for any and all help, as always :)

    -Eric

    PS: If you can't tell I'm quite new to this kind of stuff. Apologies :p
     
  2. techroomt

    Senior Member

    May 19, 2004
    198
    1
    first, i'm curious. are there any legal issues with installing a massage system in your vehicle?!?

    -are your massage components rated for 12 vdc?

    - based on your info, the wire with the rectangles are likely large "negative" signs representing the negative or ground wire. leaving the voltage marked wire as the power supply wire.

    - switch markings confused me until i read more - it is a spst. the 3rd (ground) terminal is for the lighting feature, leaving "acc" and "power" for the switch contacts. these are the contacts you connect to to "interrupt" the power going to your load, as you previously noted.

    as far as switch wiring, it looks as though the power should be connected to the "power" terminal, and the massage components to the "acc" terminal. try one way, if the light is on all the time reverse "acc" and "power" wires on switch. maybe someone here has certain experience with this switch.
     
  3. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    1) Look at the AC/DC converter for the massager, and note what the ouput voltage and current are as indicated on the device.

    2) Provided the output voltage of the converter is close to 12VDC, then you can use the massager directly from the car battery or ignition switch. Otherwise, you may be beyond your electronics knowledge to do anything useful.

    3) You will need to plug the converter into the wall outlet, and using a DMM (Digital Multi Meter, or voltmeter), note the polarity of the output voltage (it would be nice to confirm the output voltage as well), as follows:

    Most meters come with red and black leads, the black is usually plugged into the (-) and Red into the (+) holes of the meter. So, if you place the black lead on your black wire, and the red lead on the white wire, you will see the voltage reading as either "+" or "-".

    3a) If the voltage reading is "+", then make a note of which wire the the BLACK lead is on, this is the negative wire, mark it with a piece of tape or something.

    3b) But if the voltage reading is "-", then make a note of which wire the the RED lead is on, this is the negative wire, mark it with a piece of tape or something.

    4) Connect the negative side of the car battery (GND) directly to the massager wire that is the same color as the one you marked as negative in step #3 above.

    5) Wire the positive side of the car battery/ignition to the (+) contact on the switch (you may want to add an in-line fuse holder from Radio Shack, insert a fuse based on 2x the output current of the converter).

    6) You then wire the (ACC) side of the switch to the POSITIVE wire of the massager (same color wire as converter POSITIVE output, the one you didn't tape/mark).
     
  4. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    If you don't have a meter, you can use a simple LED and resistor to determine the polarity.

    Solder a 1K resistor to the Cathode (-, C) of an LED (the other side is the Anode +, A). Place this between the two wires on the converter output, if it doesn't light swap the wires. When the LED lights, the negative wire is the one connected to the resistor.

    ..||..............................||
    ..|| ---+LED---/\/\/\/--- ||
    ..||..............................||
    wire....A.....C.....1K.......wire (if LED is on, this is negative wire)
     
  5. ricodued

    Thread Starter New Member

    Jul 30, 2007
    2
    0
    Ah, thank you so much to all. Now the switch makes loads of sense, and I'm off to go wire this baby up :)

    Oh, and it was rated for 12VDC. I made sure before even starting this :p It should be all good to go.
     
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