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  • DSATX AUX relay

    Hi!
    I want to operate several devices as soon as my DSATX turns on. DSATX has an AUX connection, which according to the manual (and searching on the forums) connects to ground when activated. That's OK so far.

    Problem is that according to the developer of DSATX and this(Document) , the AUX can stand current up to 100mA (I read somewhere else that it's actually 60mA, though not 100% sure). I can understand that this poses a limitation on the type of relay i can use. Usually relays with this low coil amps (high resistance?) are able to deliver only a few Amperes, but in my case I'll need much more.

    I've visited a local electronics shop and found a small (size wise) SPDT relay (those small blue ones) and i measured it's resistance across the coil which is around 400ohm. Assuming 12V across the coil, this will give current of 30mA. Is my math correct?

    So I'm planning to use that relay and then chain it's NO pin to the coil of a second "bigger" (Bosch type) relay. This will allow me to drive much more current.

    Does my syllogism sound right?Is there any problem chaining 2 relays, a small one and a bigger one, to achieve my goal? Assume that both relays will be fused, and a diode will be used accross each relay's coil.

    Thanks!

  • #2
    You could always use a transistor to drive the larger relay instead of a smaller relay. Pick any schematic here. I never realized there were so many.
    http://images.google.com/images?q=tr...N&hl=en&tab=wi

    The AUX output can easily drive 2 amplifier remote lines at 100mA though, and a Bosch requires 120-150 (just shy of working), but are you sure a relay like that isn't overkill?

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    • #3
      Thanks for the reply!
      If I could do it with just 1 relay, that would be perfect.Spending another 150mA just to switch on the Bosch relay is a waste. I intend to use the AUX of the DSATX to turn on 3 amplifiers (Cannot find through specs exactly how many amps they need on their remote line), and power 3-5 fans. Each fan needs 0.3 amperes, so at maximum I'll need 1.5 Amps for the fans. Now, for the amplifiers, I wouldn't expect them to need more than 1.5 Amps in total (As I said, I'm missing this information, so I'll try to be as much on the safe side as I can).

      So, I need to switch 3 Amperes. My "small" relay, is bought at a local electronics shop. People their are not very informative and they just pointed me some "12V" relays they had. The relay has the following information printed on it.

      GIANT JQC-3F(T73)
      DC12V 28VDC
      10A 125VAC

      It looks similar to this

      Coil resistance as I measured, is 400Ω , so coil amperage at 12VDC is 30mA. This information is NOT printed anywhere

      I guess that "DC12V" refers to the voltage that needs to be applied across the coil? Then, propably 28VDC and 125VAC are the maximum voltages that relay's contacts(not the coil) can handle. and 10A, is propably the maximum amperage the relay can handle at both 28VDC and 125VAC? Is that correct? And if that's correct, shall i expect it to have a capacity of 23Amperes at 12VDC ? (Sorry if i made a mistake, lots of assumptions, but i guess P=U*I, so power is 28 * 10 = 280W. Then, dividing 280 by 12 Volts, gives me approximately 23A)

      Can anyone help?

      Comment


      • #4
        A wire can handle a certain number of amps at any of its supported voltages.

        So let's say I have a wire. It can handle a current of 20 amps. If I pump 1 volt @ 20 amps through it, that's its max... only 20 watts. If I pump 100 volts @ 20 amps through it, that's also its max... 200 watts.

        The relay can handle 10 amps for current. It can handle that current at anything up to 28 volts DC or 125 volts AC.
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        • #5
          Then, if they can handle 10A, they render my bosch relays useless!!! Need to find a clever way to mount them, since they're meant to be mount on pcb boards... . Propably use hot glue on terminals to avoid any accidental short also.

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          • #6
            Originally posted by qpwoeiruty999 View Post
            Then, if they can handle 10A, they render my bosch relays useless!!! Need to find a clever way to mount them, since they're meant to be mount on pcb boards... . Propably use hot glue on terminals to avoid any accidental short also.
            Couple things you can do. To wire them, just solder the wires on the necessary terminals. Hot glue is a life saver. Not so much for shorting, but so you don't rip the cable out accidentally.

            Now to mount, I do several things with these... one is I wrap the whole thing in electrical tape a ton of times and then just zip tie the wire to something. This is somewhat messy but works. Especially if it's in a concealed location. If you're looking for cleanliness, get a small project enclosure and stick the relay inside it. Then just mount the enclosure. That's as clean as you can get it.
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            • #7
              Amplifier remote wires require a maximum of 50mA, and are usually much lower. So you're total current is going to be lower than 1.7A

              That should work fine.

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              • #8
                Really really thank you both!
                50mA is most likely OK, but I prefer to be safe than sorry. Yes, hot glue is perfetct. For mounting, I'll propably make a small enclosure out of thin(1-2mm) acrylic (hot gun is perfect for bending it), paint it and mount it.

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