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Recently received my airworthiness for my STOL CH 750 and yesterday was my first flight.  Very exciting hearing the 912iS come to life and it ran flawlessly.  Unfortunately about an hour into the flight I experienced a low battery alarm and landed to investigate.  I found the battery down to just over 9-volts.  The Rotax wiring schematic shows the alternator circuit (pin-3) going to the main buss.  In my system, the contactor is a four-stud unit with diodes and thus will only allow current to flow from the battery side to buss side.  A retired electrical engineer I know said I should move the pin-3 to the battery side of the contactor, which should resolve the issue but only if the system has a regulator, which the 912iS does.

I've not test run the engine and monitored voltage yet but wanted to ask the forum members if this solution seems reasonable.  My main battery has an overcharge circuit built into it to prevent overcharging.

Thanks!

Tim

  • Re: Battery Not Charging

    by » 12 months ago


    Ran some taxi tests after making the change and battery voltage stayed steady.  Saw a slight variance up and down between 13.3 and 13.5 volts during the 45-minute test.  I performed normal warmup, tested generator switchover, runup and high-speed taxi tests.

    Tim


  • Re: Battery Not Charging

    by » 12 months ago


    So I spoke too soon.  Been a few chilly days here and finally got some sun to go run some taxi tests.  Battery was at 12.9 volts and after an hour of taxi tests, voltage had dropped to 12.6 and into the yellow warning area on my ECU.  Battery is an Earth-X ETX900, which apparently is the Rotax preferred model.  Anyway, battery accepts a charge from the charger but slowly drains when performing engine runs.  This tells me I'm not getting a charge from pin-3.

    Here is what I'm thinking:  Disconnect pin-3 from the buss and connect a volt meter to it, start engine and and look for voltage across the circuit.  Was also going to try and measure current.  Was thinking about using an ammeter clamped around pin-3 wire to measure amps but wasn't sure if leaving it connected to the buss would mess up the test.  Anyway, I'm super uneasy about working around a spinning prop but don't know what else I can do to trace this issue down.  Any other ideas?

     

    Thanks.

    Tim

     


  • Re: Battery Not Charging

    by » 12 months ago


    Stupid question: did you perform the discontinuity check? See IM 24-00-00, page 8

    After engine start, increasing rpm to about 2600rpm you should observe the charging current to jump up to about 15-18amps

    32079_2_AA941B17-C739-481C-8A2C-E2C686A5AF91.jpeg (You do not have access to download this file.)

    Karl (Charly) Kistler
    HB-YPL(RV12iS) / HB-YNB (Helicopter CH7)
    karl@kistleronline.ch
    www.kistleronline.ch
    www.chaletferienfurna.ch


  • Re: Battery Not Charging

    by » 12 months ago


    Not a stupid question at all and yes, I did the generator check.  As it turns out, and after spending numerous hours verifying my wiring, the issue was staring me right in the face - I didn't ground Regulator-B.  I had grounded the regulator harness to the ground pins but never ran a 12G wire from the ground pins to the ground block on the airframe.  Real bonehead move on my part but at least it wasn't a major issue.  Seeing 14.2 volts now and all is good.

     

    Thanks!

     

    Tim


  • Re: Battery Not Charging

    by » 4 months ago


    "Battery is an Earth-X ETX900, which apparently is the Rotax preferred model. "..

    Actually, the Aerolithium 680Li-18Ah is the preferred model.


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