dc0341 Posted October 17 Report Posted October 17 Hello, I had an A&P install a fuel pressure gauge that came off a 80s model M20J on my 83 M20J. The reason being was that the stock fuel pressure gauge was removed when the panel was redone and a EDM 830 was installed. Attached is a photo of the back of the gauge. The power wire is coming from the USB breaker to (IGN) side. The center nut has a wire from the transducer and a ground wire, that is grounded to the screw on the airframe. The nut on the left side of photo is the other wire from transducer. Every time I turn on the master, the breaker on the USB pops. I tried several different grounds and it still pops every time the master is turned on. Is the wiring correct? The gauge is installed on the plastic area next to flap switch, so the housing for the gauge is not mounted to metal. Thank you,
skykrawler Posted October 17 Report Posted October 17 What is a USB breaker? A panel mounted USB charger? Did it ever work correctly? The way these analog gauges typically work is the power goes through the gauge to the transducer which provides variable resistance to ground. This then changes the voltage level the gauge sees. So disconnect the transducer. If a circuit breaker pops you have a short from power to ground somewhere else - possibly within that gauge. 1
dc0341 Posted October 17 Author Report Posted October 17 I have a panel mounted USB charger that has a 5 AMP circuit breaker. The USB worked correctly. A&P installed a fuel pressure gauge, since I didn't have one, I have the EDM 830 but wanted a pressure gauge also. I'll try to disconnect the wire from the transducer to see if it still pops. Thank you,
Slick Nick Posted October 17 Report Posted October 17 Why isn't the A&P diagnosing this for you? You paid him to install the gauge, it was done improperly. He should be making it right. 1
Yetti Posted October 17 Report Posted October 17 There is no voltage between the transducer to gauge. That is all variable resistance ground. did the breaker just start popping? ie has it ever worked properly? If so then something has changed. The wires to look at are between the CB and the USB charger and the gauge. Also check the CB panel. Wire can be loose there and things can fall into CBs. Your back will thank you for using the phone to do the inspection.
Yetti Posted October 17 Report Posted October 17 Also what kind of USB was installed. A 5 AMP breaker for some of the USB might be a bit low rated. Also is your plane 24volts or 12volts. 1
dc0341 Posted October 17 Author Report Posted October 17 5 hours ago, Yetti said: Also what kind of USB was installed. A 5 AMP breaker for some of the USB might be a bit low rated. Also is your plane 24volts or 12volts. The USB has always worked. The breaker only pops when I connect the wire to the fuel pressure gauge and turn on master. If I remove the wire from the gauge, it doesn't pop and USB works fine. It's a 12v system.
hammdo Posted October 17 Report Posted October 17 How many amps does the fp gauge draw? How many amps does the usb draw? Add those up (max draw) and see if the breaker is the right size for the load… or add a breaker and circuit for the fp gauge.. just a thought -Don 1
PT20J Posted October 17 Report Posted October 17 Do you know that the gauge is good? Maybe it's shorted. Did the installer test it?
dc0341 Posted Saturday at 07:09 PM Author Report Posted Saturday at 07:09 PM 21 hours ago, PT20J said: Do you know that the gauge is good? Maybe it's shorted. Did the installer test it? The gauge was working prior to install.
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