Voltage Fluctuations

Aeronca Sedan Airplanes
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Voltage Fluctuations

Post by Guest » Tue Nov 16, 2004 09:59

Voltage Fluctuations
From: Bob McDevitt
email: mcdevitt@sympatico.ca
Date: 29 Oct 2004
Time: 18:11:39

I've got a real puzzeler for you experts out there! On my Sedan, when I transmit on my radio I have noticed that the voltage as measured at the bus goes up!!

During cruise, the reading is 13.8 volts. When I push the transmit button it goes up to 14.3. Also my oil temp guage reads high, goes from 180 to 200 degrees.

I initially thought I might have a corroded connection, but that should indicate lower voltage right??

Thanks in advance. Bob

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Post by Guest » Tue Nov 16, 2004 09:59

Re: Voltage Fluctuations
From: ifust
email: ifust@snowcrest.net
Date: 02 Nov 2004
Time: 01:25:40

Sounds like it could be an electrical grounding problem. Are you sure that your common connections (antenna, radio,etc.) are firmly connected together and to the battery negative and all of these are firmly grounded to the aircraft frame?

Guest

Post by Guest » Tue Nov 16, 2004 10:00

Re: Voltage Fluctuations
From: champdriver
email: mfrazier@southwind.net
Date: 01 Nov 2004
Time: 08:00:52

Bob, What you are experiencing is a text book case of EMI/RFI.

Electo-Magnetic Interference, Radio Frequency Interference. In the Engineering and Manufacturing of Avionics and Electrical Harnesses for Aircraft we try to take certain measures to reduce the effects of these phenominons.

You should make certain that you have a very good electrical bond to the airframe on your Antennas. I suspect that you may not even have a jumper to the Fuselage, Like someone mentioned earlier there are tiny little coils in the meter movements, and when a strong enough field is induced into the meter movement, you have a spike.

You can use your Hand Held to see if the noise is being induced into the meter by simply keying the mike in a close proximity to the meter in question. Or you might have a case of conductive interference, where the EMI from the tranmitter itself is in the wiring, causing the meter to flucuate...

On occasions we have been know to add some capacitance to meter movements to suppress these anomolies...

Good luck, Champdriver

Guest

Post by Guest » Tue Nov 16, 2004 10:00

Re: Voltage Fluctuations
From:
email:
Date: 04 Nov 2004
Time: 18:29:43

Champ Driver, what do you mean "good bonding at the antenna to the airframe" I thought the only ground you wanted was thru the shield on the coax cable. Bob

Guest

Post by Guest » Tue Nov 16, 2004 10:01

Re: Voltage Fluctuations
From: Ron Babos
email:
Date: 29 Oct 2004
Time: 20:29:35

Two questions. Is the oil temp electrical, and close to the radio?

What happens to the voltage readings reading when you trasmit with the engine not running?

Guest

Post by Guest » Tue Nov 16, 2004 10:01

Re: Voltage Fluctuations
From: Bob McDevitt
email: mcdevitt@sympatico.ca
Date: 29 Oct 2004
Time: 23:17:40

Yes the oil guage is electric, it is on the far left side of the panel, the radio is in the middle.

Same result wether the plane is running or not. It seems to affect all electrical instruments. Bob

Guest

Post by Guest » Tue Nov 16, 2004 10:01

Re: Voltage Fluctuations
From: Ron Babos
email:
Date: 30 Oct 2004
Time: 09:12:01

With the engine stopped, kinda rules out the voltage regulator kicking in a few volts.

This is not really my specialty, but I would tend to go with (RF) interferance from the radio. Could be a bad antenna lead etc. Gauges have windings in them which may be picking up the unshielded transmission altering the readings.

This would be a good time for all the radio experts out there to jump in, as to the possibility of this happening. Ron

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