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How to wire in a Hobbs meter correctly.

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  • #31
    How to wire in a Hobbs meter correctly.

    I apologise for not mentioning the buzzer that they are using as a pull-up current source. I also incorrectly said that the MOSFET was energised when the generator was running when in fact it is the other way around.

    I have edited my post above to correct these mistakes. Of course the buzzer could be replaced with a lamp or simply a resistor if no warning is required.

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    • #32
      How to wire in a Hobbs meter correctly.

      You lot have lost the plot.
      How about a switch, engine running flip the swicth, stop the engine flip the switch again :lol:

      Kev :tongue:

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      • #33
        How to wire in a Hobbs meter correctly.

        Thought I'd just round this off with how I eventually solved my issue very cheeply. (Only just come back across this thread looking for something else.)

        Conrad's idea got me thinking except as I discovered, using a DPST switch for one of the mags doesn't work because it actually switches the meter off when the engine is running because the switch is open for on for the mags. So...

        1. Buy a DPST switch and replace one of the mag switches with it. Wire one side into the mag as usual. (Open/up for on, closed/down for off).
        2. Buy an automotive relay, one where the contacts open when power is applied. (Often you can buy ones with 5 poles so they will work open or closed.)
        3. Wire the relay +ve (control side) into one pole of the second circuit of the DPST mag switch then the other pole connect to the master switch switched side.
        4. Wire the relay +ve input side (load side) into the switched side of the master switch.
        4. Wire the relay +ve output (Load side) to the Hobbs +ve.
        5. Wire the Hobbs -ve to earth.
        6. Wire the relay -ve (control side) to earth.

        Hey presto!

        When you operate the master the relay control circuit is energised which opens the load (Hobbs) circuit which means the hobbs does not run. When you are ready for start you throw the mag switches which cuts the power to the relay (control) which closes energising the load circuit and the hobbs starts. The added benefit is the relay is not energised whilst running and so doesn't add to the load on the battery. It only draws a load whilst the engine is stopped and the master is on which is usually for a short period only.

        Cheers

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        • #34
          How to wire in a Hobbs meter correctly.

          Jack,
          I suggested a DPDT switch. In which case you could have used a Normally closed side to operate one magneto, and a normally open side to supply power to the hour meter. If the hour meter terminal was connected in series with the master switch you would need both the master & mag switch on to energise the hour meter.

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          • #35
            How to wire in a Hobbs meter correctly.

            Hmmmm.

            DPDT would actually have 3 positions wouldn't they Conrad? Wouldn't the centre position have them both off (which would actually be on for the mag). I didn't think of that but the DPST method makes the throw the same as the other one which is unobtrusive.

            Suppost it goes to show there are more than one ways to skin a cat! You inspired me whatever your suggestion. :smilewinkgrin:

            Cheers

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            • #36
              How to wire in a Hobbs meter correctly.

              You're all going about this wrong. What you need is a microswitch attached to a prop blade, with equal weights applied to the same position on the other blades to keep everything in balance (obviously). Then you attach a small weight to the trigger of the microswitch so that as the prop spins, the centrifugal force operates the switch. Then, a simple commutator type arrangement at the prop hub will allow you to operate the Hobbs meter. The beauty of this system is the simplicity with which one can alter the weight on the microswitch to operate it at different revs!

              Genius. Pure genius.

              Carry on.

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              • #37
                How to wire in a Hobbs meter correctly.

                How about this?

                http://shop.airworlduk.com/powergeni...id=63160226708

                John

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                • #38
                  How to wire in a Hobbs meter correctly.

                  :lol:

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                  • #39
                    How to wire in a Hobbs meter correctly.

                    Rick, you're not taking this seriously are you. Now that's just being silly isn't it :yeah:

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                    • #40
                      How to wire in a Hobbs meter correctly.

                      Hmmm, how about a small wind turbine (fan driving a generator) mounted aft of the propeller. When the propeller is turning, the airflow spins the turbine that then generates power that runs the Hobbs meter.

                      Downside is that after an engine failure in flight you'll still get charged for engine hours .... :-(

                      Mike

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                      • #41
                        How to wire in a Hobbs meter correctly.

                        That's ridiculous Mike! Imagine that you parked in a windy spot for a couple of days... You'd be due a 50 hour service and a new wing spar by the time you got back to it!

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                        • #42
                          How to wire in a Hobbs meter correctly.

                          Ah yes, I forgot to mention the automatic airbrake on the turbine that only releases when the oil temp. gets up to 50'C ... [IMG]/forums/emoticons/smile.gif[/IMG]

                          It's a piece of thread tied to one blade of the fan, fastended to the crankcase at the other end with sealing wax. Only a tiny blob needed before each flight, and when the wax melts the thread winds up around the turbine shaft and hence is neatly stored during flight.

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                          • #43
                            How to wire in a Hobbs meter correctly.

                            I haven't read all of this thread, so forgive me if this has been mentioned before, but surely the simplest way is to wire the hobbs meter straight to the regulator? That way it would only get power when the engine is running. No, thats too simple, i must be missing something!

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                            • #44
                              How to wire in a Hobbs meter correctly.

                              I think that the problem with that would be that wiring to the output side of the regulator is like wiring direct to the battery, unless you use diodes... the cable works both ways otherwise!
                              Simplest solution is definately the microswitch on the prop arrangement, with an DPDT switch on the mags coming in a close second. Mike's suggestion is just idiotic, as most of the engine wear will occur before the oil temp reaches 50°C, yet his Hobbs meter won't even have started yet. There's a word for that Mike: Fraud! :rofl:

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                              • #45
                                How to wire in a Hobbs meter correctly.

                                If you connect two wires from the generator (yellow wires) into a bridge rectifier and a 12volt regulator (78 series) the output goes to the hobbs meter. Therefore, when the engine is running approx 24-18volts ac from the generator, rectified to 12volts dc, and on to the hobbs meter. Only 3items, all from maplins and cost less then £2.50. simple….

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