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Thread: 12v rocker works; 12v rocker with ground...does not

  1. #11
    Maximum Bitrate kegobeer's Avatar
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    I am assuming that the 12v from your switch goes to the ign wire on your intelligent automotive power supply. I'm also assuming that you've wired your automotive power supply correctly, connecting the 12v input to your distribution block and connecting the ground to your chassis ground.
    1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.

  2. #12
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    Thanks for that confirmation soundman.

    I'm a bit more awake now, but it still perplexes me.
    How can a LED prevent power on?
    And if the load current was too high for the switch, it wouldn't power up without the LED.
    AHA - there we have it - the 20mA LED is enough to overload the 10A switch and hence.... (No - I won't say "now way", but that is essentially ridiculous; a switch instantaneously failing with an additional 0.2% (over)load.. no way!)

    And yes, Archy tried the other switches. So we have ruled out the switches (unless it's a weird batch fault!) and the connection topology, and connections.

    I'm gonna love the solution to this one - especially if it's another one of my Do'hs! that is so obvious. (See if I re-quote my last reply's first line - damned woosy oldfart!)

  3. #13
    MySQL Error soundman98's Avatar
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    ^ it shouldn't overload the switch, as he is only using it to trigger the power supply(the ACC wire input), not cut the main feed.

    i haven't taken one apart, though many of these devices are built the same-- they are almost too simple to mess with outside devices-- it is only a small 1/8w resistor in series with a small led. there is not enough room inside for a pcb to allow for voltage regulation or any complex operations....

    i found a pic:



    it looks like it is connected correctly, and is connected exactly the same as my switches(note-- he did say that he connected the gold pin to ground)

  4. #14
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    Quote Originally Posted by OldSpark View Post
    The PC works with no GND connected - as if the 20mA LED is somehow effecting the connection. (Restating the obvious.)

    Check output with a reasonable load - maybe a light bulb (brake bulb ~21W => ~2A, headlight 60W = 5A etc; a dash globe ~3W = 250mA may be a bit low to detect a high switch impedance - not that a GND via a LED sould impact that). A multimeter alone won't detect the ability to suppply high current (it only draws uA).


    The "always connected to PC" LED (20mA) grounds the PC +12V, but that has no effect - ie, it is +12V when the LED s on (unless a faulty (high-impedance) switch), and it's not keeping the PC on when OFF - that is sometines an issue when LEDs etc are connected in OTHER sitations, but not in this case.



    A solution may be to have the switch energise a relay that powers the PC. Though I'd still want to know ytf the 10A reated switch itself doesn't work, I'd normally wire it that way because I'd use a direct feed via a fuse from the battery (as done by most - it's the cleanest power supply) AND I dislike running more than a few Amps through a switch - even 16A rated switches. (I can expand on that if required.)
    In this case I'd just check that the relay coil gets 12V and not something like 8V which can be close to its drop-out voltage.
    Your obvious statement is definitely true. Somehow it seems as if the LED is making a difference...and/or the ground.

    Not to show my lack of electrical knowledge, but how would I use the switch to power a light bulb? Obviously the bulb would touch/be wired to the center prong(where the PC would be). What would I use to power it? Will the 12v from a fused accessory line be enough to power it?

    How would I add a relay to this setup? I'm not sure if I am committed to that much of a task, but it is worth asking. As of right now, the switch works albeit minus the LED lol.
    Over a year later I guess it's true...a carPC is NEVER complete

    2002 Mustang CarPC

  5. #15
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    Quote Originally Posted by kegobeer View Post
    I am assuming that the 12v from your switch goes to the ign wire on your intelligent automotive power supply. I'm also assuming that you've wired your automotive power supply correctly, connecting the 12v input to your distribution block and connecting the ground to your chassis ground.
    Correct. I have an OPUS 360 power supply(Probably overkill, but whatever lol). I had that previous 12v rocker(MINUS LED/GROUND) that worked fine for over a year, so I can only assume it was wired correctly in the same fashion that you list.

    Quote Originally Posted by OldSpark View Post
    Thanks for that confirmation soundman.

    I'm a bit more awake now, but it still perplexes me.
    How can a LED prevent power on?
    And if the load current was too high for the switch, it wouldn't power up without the LED.
    AHA - there we have it - the 20mA LED is enough to overload the 10A switch and hence.... (No - I won't say "now way", but that is essentially ridiculous; a switch instantaneously failing with an additional 0.2% (over)load.. no way!)

    And yes, Archy tried the other switches. So we have ruled out the switches (unless it's a weird batch fault!) and the connection topology, and connections.

    I'm gonna love the solution to this one - especially if it's another one of my Do'hs! that is so obvious. (See if I re-quote my last reply's first line - damned woosy oldfart!)
    If you think of anything to try...please let me know lol.



    Quote Originally Posted by soundman98 View Post
    ^ it shouldn't overload the switch, as he is only using it to trigger the power supply(the ACC wire input), not cut the main feed.

    i haven't taken one apart, though many of these devices are built the same-- they are almost too simple to mess with outside devices-- it is only a small 1/8w resistor in series with a small led. there is not enough room inside for a pcb to allow for voltage regulation or any complex operations....

    i found a pic:



    it looks like it is connected correctly, and is connected exactly the same as my switches(note-- he did say that he connected the gold pin to ground)
    Yes, that is pretty much what my switch looks like. The left prong is the fused accessory line, the center goes to the OPUS 360...so this is more of a signal wire vs power feed.



    On a side note, I tested ohms with the multi-meter. According to the fancy machine, the switch is hooked up correctly.


    I really appreciate you guys taking so much time to help with this. You all have far more knowledge than I, and I truly appreciate it.
    Over a year later I guess it's true...a carPC is NEVER complete

    2002 Mustang CarPC

  6. #16
    Maximum Bitrate kegobeer's Avatar
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    At the Opus, disconnect the 12v ign line, turn your multimeter to VDC, connect the positive to the 12v line and the negative to your chassis ground. Turn on the switch and tell us what voltage reading you get.
    1999 Mercury Grand Marquis GS with: ASRock E350M1 w/4GB RAM, 80GB Intel SSD, Opus DCX3.120, Visteon HD Radio + HDR-USB, PL-18N wifi, OBDLink Scan Tool, BTA6210 BT, BU-353, Win 7 Ultimate, CF 4.0, Alpine MRP-F240 + MRP-T220, RF Punch 1572s, Kicker 8" Comp.

  7. #17
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    It might be a while until I get around to that. I would have to take apart the dash wish is quite the affair. Once I run the 2 usb extensions to the carPC ill give this a shot and see what I get.

    However, couldn't I do this at the other end of the opus wire(where my rocker switch panel is)? If so, I can do that in the morning
    Over a year later I guess it's true...a carPC is NEVER complete

    2002 Mustang CarPC

  8. #18
    MySQL Error soundman98's Avatar
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    ^ ok, try that same test at the back of the switch. just testing at the far left terminal, and the center terminal and ground(put the positive volt meter lead on each, and leave the negative volt meter lead on a vehicle ground--don't use the switches ground wire for this).

    you should get the same number off both terminals.

  9. #19
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    Quote Originally Posted by Archy88 View Post
    Not to show my lack of electrical knowledge, but how would I use the switch to power a light bulb?
    Yes - exactly as you wrote. Instead of powering the grounded PC, you power the grounded bulb/light/load.

    Can power from fused circuit, though for testing, just from battery to switch +, switch-A to light(+), and light(-) and switch-LED's GND to GND (battery -ve).

    Fuse "should be" included, but if light/load is under switch rating, and cable handles the load, and wiring is correct and insulated, then "no risk". [Wear gloves else prepare do drop the switch quickly if it gets hot due to a faulty switch (but it isn't faulty in THAT way). And should really always use glasses (protective) for any test or new switch-on - besides, you'd look cooler in sunnies.]


    Sorry for delay, but my weekend isn't yet over...

  10. #20
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    Quote Originally Posted by soundman98 View Post
    ^ ok, try that same test at the back of the switch. just testing at the far left terminal, and the center terminal and ground(put the positive volt meter lead on each, and leave the negative volt meter lead on a vehicle ground--don't use the switches ground wire for this).

    you should get the same number off both terminals.
    The 12v(far left terminal) reads 10.75v. The center terminal(when switched on, LED DOWN) reads 10.75v.
    The strange thing is...(This could be perfectly normal lol) the ground terminal reads 9.3v?! Is a ground supposed to do that?

    I performed another test, I got the PC running without connecting the ground(so, just left terminal and center). Once the PC was on, I connected the ground and the PC actually shut down as if the car was powered off.


    OldSpark, I'll give that a shot once I find a light bulb for the rating lol.
    Over a year later I guess it's true...a carPC is NEVER complete

    2002 Mustang CarPC

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