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Interference on Turbine RPM line - 9/30/2012 1:47 PM   
i3dm


 

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From: ReutIsrael, ISRAEL
Status: offline 		Hello guys,

im helping a friend setup a turbine (nevermind the brand) that has seperate wiring for RPM, thermocouple, starter, plug etc..

These wires are routed mostly together because of lack of room in the fuselage.
Anyway, it seems that sometimes the starter kicking in would create an intereference on the RPM line in the form of an RPM "jump" for s short time, but the problem is that when this happens while starting, the ECU pre maturely stop starter action causing a failed start.

Since routing the wires further apart is difficult in this airframe, im looking for more creative solutions.

Perhaps a Ferrite ring on the RPM wire could help ?
any other ideas ?

thanks in advance.


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RE: Interference on Turbine RPM line - 9/30/2012 2:13 PM   
aquaskiman



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Status: offline 		Twist the rpm cable and try it, twisting helps a lot.

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RE: Interference on Turbine RPM line - 9/30/2012 2:16 PM   
i3dm


 

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Status: offline 		do you seperate the 3 cords (+,-,S) or just twist as it is ?

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RE: Interference on Turbine RPM line - 9/30/2012 2:22 PM   
Xairflyer



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Status: offline 		Problem normally coming from Glow plug wires, and twisting these is important on earlier gasper ECUs, the interference is not coming from the rpm wires, it is picking them up, so dont think twisting the RPM wire will help. You could also have a faulty rpm sensor or a bad connection/dry joint.

Another problem area is bad grounding of the glow plug wire if it is a turbine that uses a separate ground wire.

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RE: Interference on Turbine RPM line - 9/30/2012 2:28 PM   
i3dm


 

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Status: offline 		I dont think there is a bad ground, the ground wire is good.
none of the wires are twisted as of yet. i will try twisting some.

Also, anyone tried a ferrite ring on the RPM wire ?

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RE: Interference on Turbine RPM line - 9/30/2012 3:21 PM   
i3dm


 

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Status: offline 		So changing the RPM wire extension to twisted was an easy task, and also added a Ferrite bead (cant hurt). but twisting plug and starter wires is going to require a major tear down so im hoping to get around it.

any other ideas guys ?

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RE: Interference on Turbine RPM line - 9/30/2012 3:26 PM   
SMBJets


 

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Status: offline 		 Is the receiver power running on 5v or 6v? The earlier FADECs had this issue when running on a 4 cell NiMH or Nicd pack. Change to 5cell and the problem disappeared.
Another option is to try a 47nf capacitor across the supply to the RPM sensor, I made up a simple lead using a modified extension lead which worked well when using 4 cell batteries.
Usually you need to twist the wires with the power running through them causing the interference, this breaks up the magnetic field around the wires causing the interference. I dont believe a ferrite ring around the rpm cable would help as it is picking up interference not giving it out.


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RE: Interference on Turbine RPM line - 9/30/2012 3:32 PM   
i3dm


 

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Status: offline 		we're running a Li-fe 6.6V Rx pack.

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RE: Interference on Turbine RPM line - 9/30/2012 3:42 PM   
SMBJets


 

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Status: offline 		 Best bet may be to try a capacitor across the wires, get a small servo extension lead and solder an electrolytic capacitor across the power wires (brown/orange). Just checked the size it should be 470 micro farad.
Also, have you checked there are suppression capacitors fitted to the starter? There should be 2-3, with one between each supply wire And the motor case, and also possibly one between the 2 wires.


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RE: Interference on Turbine RPM line - 9/30/2012 3:49 PM   
SMBJets


 

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Status: offline 		Just found an old thread with some more details of the capacitor for rpm sensor:

http://www.rcuniverse.com/forum/m_4416065/anchors_4421596/mpage_1/key_/anchor/tm.htm#4421596

Best of luck with it.


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RE: Interference on Turbine RPM line - 9/30/2012 4:02 PM   
PaulD



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quote:

ORIGINAL: SMBJets

 Best bet may be to try a capacitor across the wires, get a small servo extension lead and solder an electrolytic capacitor across the power wires (brown/orange). Just checked the size it should be 470 micro farad.
Also, have you checked there are suppression capacitors fitted to the starter? There should be 2-3, with one between each supply wire And the motor case, and also possibly one between the 2 wires.



You could modify a y harness to do this as there should be a servo plug on the rpm sensor. Also note that the starter and glow plug leads are only used at start-up and not while in the air. You could also try some braid over the sensor wire and ground it to the glow plug lead at the turbine.

PaulD



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RE: Interference on Turbine RPM line - 9/30/2012 4:15 PM   
invertmast


 

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Status: offline 		Is it 5 wire or 3 wire sensor?

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RE: Interference on Turbine RPM line - 9/30/2012 4:46 PM   
Xairflyer



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Status: offline 		Where is your ground wire attached to the engine?

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RE: Interference on Turbine RPM line - 9/30/2012 5:01 PM   
i3dm


 

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Status: offline 		1. its a 3 wire sensor.
2. the ground is a washer under the glow plug with a wire soldered / crimped to it.
3. i will try the capacitor trick - its very easy to do ! i found a 680uF capacitor at home to test, should be close enough to the mentioned 470uF.


Cool ideas guys.. keep the info coming

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RE: Interference on Turbine RPM line - 9/30/2012 7:31 PM   
Flywagner


 

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Status: offline 		make sure you are using only gold plated connectors and a stable 6v supply and your problem should go away

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RE: Interference on Turbine RPM line - 9/30/2012 11:27 PM   
i3dm


 

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quote:

ORIGINAL: Flywagner

make sure you are using only gold plated connectors and a stable 6v supply and your problem should go away


im using a very stable (A123 pack) power source. problem occured with it.


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RE: Interference on Turbine RPM line - 10/14/2012 10:51 AM   
i3dm


 

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Status: offline 		capacitor did the trick perfectly. thank you guys.

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