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  • DC-DC USB Info

    Instead of searching for the ignition wire, is it ok to use the cigarette lighter power as the start switch for the power supply?

  • #2
    You can get the ignition wire from the harness where your radio used to go. It's most likely a red wire.
    I think IGN wire is used only to trigger DCDC-USB to start drawing power from the battery, so there's no heavy draw on IGN itself. I couldn't tell you for sure, however.
    If DCDC-USB indeed does not draw that much power from IGN and uses it for triggers only, then I don't see why you couldn't use a cigarette lighter power, as long as your car powers it down. Some cars keep the cigarette plugs on even when the car is off, so I'd verify your car doesn't do that first.
    ------------------------------------------------------------
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    • #3
      I would think that the dcdc simply receives signal instead of draws it. Can anyone else chime in? And would I be good with 16G over 15ft.

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      • #4
        In theory it should only draw microamps off the ignition line for sensing ignition input. You should be fine with 22-24gauge wire, but definitely double check the manual, or email mini-box to be sure.
        "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
        RevFE
        My Shop

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        • #5
          I assume you mean some sensing line to turn on the dc-dc USB power supply as opposed to providing its actual power (eg, 500mA to ~1.7A per USB port depending on design & load(s).


          Note that the cig socket is probably on with ACC hence will switch off during cranking.
          IGN will be on during cranking.

          If both ACC and cranking (IGN) is desired, then 2 diodes to join both circuits. 1N4004 etc diodes are fine for the sensing circuit or a max of 1 Amp.

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          • #6
            I don't think the power being lost through cranking will be a problem because there seems to be a threshold of power loss before shutdown...seems like 5 seconds plus it seems to be adjustable(I'll have to read the manual a little more). However, this diode thing seems like a good backup. Any specific thread with a detailed example?

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            • #7
              The power being lost through cranking?

              If you mean that the dc-dc converter loses its POWER feed (because it's powered by an ACC circuit that is cut during cranking), I doubt it will hold up for long. That would require a battery else copious capacitors.
              It certainly won't last long if the USB loads are drawing reasonable power.


              However, if you mean the sensing input loses power, then that might certainly be adjustable, ie, shutdown after 1, 5, 10, 30 seconds etc after losing the sensing signal (usually IGN, but could be ACC). Just set that to exceed your maximum cranking time.


              Diodes can be used to "OR" inputs.
              EG, if you wanted it to be on while ACC is on but do not want the break when cranking, you could OR the ACC and IGN +12V's thru diodes - a diode (1N4004 etc for up to 1A current) in each line (Acc & IGN) with the line-end of the diodes joined together to the dc-dc converter sensing input. It is the on when ACC or IGN are +12V.

              The same can be done for the power feed, but then each diode must be capable of handling the full current that the converter needs.
              But that's why devices have a sensing or remote input to turn on - ie, to avoid users having to add higher current diodes to the power feeds. Otherwise a relay is used with the "signal" feeds thru diodes to the relay coil (#86), hence no need for high current diodes, and no major power loss. (Diodes typically have a voltage drop of ~0.7V. At 10A, that's .7V x 10A = 7W wasted as heat. But a relay coil might only be 250mA, hence under 200mW (0.2W) of heat due to the diodes.)

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              • #8
                You can use the cigarette supply for the IGN in on the DCDC-USB as it draws its load from the 12v+ cable from the battery. You have to make sure the timing jumper is set to one with an OFF-DELAY but unless you dont set a jumper setting for timing then you will have an OFF-DELAY of at least 5secs which should be enough for you to get your key from 0 through IGN to start the car. Unless you have a car that automatically turns on its accessories, like cigarette lighter, etc when you unlock the car. Then you may need a setting with an OFF-DELAY of 1min+ but it is an extremely configurable PSU if you read the documentation for it, i can link you to it if you need it?

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                • #9
                  After a lot of back and forth with minibox, I now know that the remote line for this thing maximum power is 7V(5V recommended) and 100mA. This is utterly foolish to me to design this thing like that without documenting it. Granted they say to use the ignition wire, but you'd think they'd realize that most might grab another wire somewhere, and may not be inclined or able to cut up every wire to test them. Especially think about testing this thing in the house, what did they think would be supplying the remote line with power? Is it even reasonable to assume that every ignition wire maxes out at 100mA? Anyway, can someone point me to some type of resister or something that will guarantee my power wont pass 5V 100mA? I'd prefer to just keep my current wiring setup and just throw something on the line when I get the new one.

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                  • #10
                    No IGN line would max out at 100mA. They'd be 12V at several Amps.


                    R=V/I.

                    eg, for at least a 9V drop at max 100mA, the resistor would exceed 9/.1 = 90 => 100 Ohms. (1 Watt rating: P = VV/R or IIR)


                    But it is obviously not intended for a +12v remote.

                    Did you get the minimum required voltage & current for a turn on? (hence a bigger Ohmage, smaller Wattage resistor.)

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                    • #11
                      I believe the min is 4V, but I can't find the min current. This is the specs of the switch used: http://www.fairchildsemi.com/ds/NC/NC7SZ384.pdf

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                      • #12
                        Well.... that's a switch - there is no minimum current for A-B (pins 1 thru 2), it only has a max allowance of 100mA with a 0.5V - 7V range.
                        Its On resistance is ~5 Ohms and assume a leakage current of 10uA.


                        The Enable (OE; pin 4) must be low (below ~0.5V) for AB to conduct.


                        It's what's beyond that switch (A-B; pins 1 & 2) that determines what is required - unless the "Enable" (OE-bar) is the "remote on" etc.

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                        • #13
                          OK, forgive me, but I don't understand any of that except no min current and max voltage. So then the switch pretty much only operates off the voltage? What I'll do is find out what exactly my cigarette lighter is putting out by the end of the week and be back with the info. Thanks.

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                          • #14
                            I'd say that if that switch was wired to the cig socket, it's now cactus (12V versus 7V max).

                            It's intended as a "remote" or whatever from a 5V device - eg, USB supply or PC, not a +12V cig socket.


                            But you'd need the circuit diagram etc.

                            Or follow its instructions.

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                            • #15
                              It seems they misunderstood what I was asking. They thought I was asking about the voltage for the circuit itself, instead of the remote line. The remote line can take up to 30V. Anyway, it seems that I got a defective unit. The odd thing is that the defective unit works just fine in the house on the bench test power, but once in the car it doesn't work. Then the new unit won't work on the test bench, but works just fine in the car. To make it worse, the new unit won't activate my desktop switch...which works fine if I manually short it...but it will activate the car computer switch. Talk about gremlins!

                              Anyway, next issue; I have the led jumpers hooked up to an led. My concern is that this may drain the battery if I don't drive for two days, which happens often enough to be a concern. What can I do to make the led pulse instead of staying on constantly in order to save some power? Pulse maybe once every 10sec or so. Would that help?

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