Mailing List flyrotary@lancaironline.net Message #65555
From: Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: My EMI journey continues.
Date: Sun, 26 Jan 2020 07:32:27 +0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Hi Finn

RF is black magic. I was once trained as a radio tech in a previous life many years ago. My understanding is even if a circuit is inside a metal box
or a radio tech room inside a faraday cage that will shield it against radiant RF energy, BUT not from conductors carrying that RF directly inside the
shielded box and into the circuit.
All those wires into/out of the EC’s - Power, CAS, Coils, Injectorts, temp, control head, rs232 etc etc are all antennas that can bring RF nasties inside.
Tracy has lowpass filters on the power in and decoupling caps everywhere but it can, and does get in.
The 100nF cap on the MAP output looks like a low impedence to 120Mhz RF that apparently was messing with the MAP to Processor ADC function.

The Dynon ADAHRS has unwanted antennas as well.
Special Note: The dynon data bus is balanced twisted pairs just like our ethernet data in our homes and offices and is very effective
in rejecting RF even though its not shielded. Basically any signal picked up on the pair of wires is canceled out at the ballanced amplifier at the destination circuit.
The other place you might be familiar with balanced feeds is in stage microphone and instrument audio cabling.

The long power feed to the ARAHRS (behind and above the baggage compartment) are susceptible to picking up the RF and feeding it into the circuit.

We people with plastic aircraft and antennas on the inside are more vulnerable to EMI compared with metal cans with radio antenna outside the can.

These days there are ferrites built into so many of our computer and audio cables as we have so much RF nearby from our WiFi, Microwaves, Remotes …..

I found a couple of ferrites quickly attenuated the RF into the dynon ADAHRS, but I had less luck using ferrites on the EC2 to block the RF getting in.

Cheers

Steve Izett

> On 25 Jan 2020, at 11:20 pm, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:
>
> "So the processor A stumble on radio TX is solved by the 100nF cap decoupling the MAP output."
>
> But why???
>
> Those MAP sensors are inside the metal box on the EC circuit board. How would EMI possibly get in there?
>
> Finn
>
> On 1/25/2020 7:05 AM, Stephen Izett stephen.izett@gmail.com wrote:
>> Hi people.
>>
>> An update on the EMI issue with the Glasair
>>
>> I woke up to the engine cut problem over 5000rpm. Obvious when I think about it now.
>>  Its happens at staging.
>> When the secondaries switch on it dies, because there is no power to the secondary injectors.
>> I have some connectors in circuit so I could add Tracy’s injector failure switching.
>> The 14v feed to the secondary injectors had gone open.
>> Touching the connector made the symptom go away with full rpm/load available.
>>
>> So the processor A stumble on radio TX is solved by the 100nF cap decoupling the MAP output.
>> And the engine cut was another problem all together. I will remove the faulty utilux connector.
>>
>> Cheers
>>
>> Steve Izett
>>
>>
>>
>>> On 21 Jan 2020, at 12:44 pm, Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
>>>
>>> Hi Guys
>>>
>>> I got a few hours on the Glasair this morning.
>>>
>>> Last week after soldering 100nF caps across pin 1&2 of EC2, I couldn’t start the engine on either controller.???!!!
>>>
>>> I checked the EC2 today and found the Earth Stud on the case was a little loose, so I tightened it up.
>>>
>>> Engine then started fine and ran on both controllers. One small step for man…..
>>> On Radio tx, NO stumble on either controller! Another small step for man….
>>>
>>> BUT on running up the engine ONE great big step backwards…..
>>>
>>> Slowly increasing the RPM yields a very consistent engine cutout at just over 5000 rpm on both controllers.
>>> At say 3000 and stabbing the throttle yields the same result.
>>> If I pull the throttle quickly when it cuts out, it sometimes would recover. Otherwise it stalled completely.
>>>
>>> I can help but feel the caps are the culprit.
>>> Didn't have time to pull the EC2 and test.
>>> I would like to remove 100nF and retest.
>>> Then I’m tempted to replace with 10nF and retest.
>>>
>>> OR I could just remove the caps and put some Ferrites on the leads going into the EC2.
>>>
>>> The RF getting into the ADHARS has, it appears been attenuated significantly by 2 ferrites on the cables entering the unit and the subsequent reduction in VS indicated on radio tx.
>>>
>>> Till next time…..
>>>
>>> Steve Izett
>>>
>>>
>>>
>>>
>>>
>>> --
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>>
>> --
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>>
>
>
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