Electrical Question

I have an issue that I don't know if it is a safety problem or not. When I key the mike on my 430 Garmin I see my amp gauge go to 10 amps. At the same time my manifold pressure gauge drops considerably and my compass turns 20 degrees. I am going to take it to an avionics shop soon but was just wondering if anyone had any ideas? Its been that way since I bought it

Sounds like you could have RF leakage into your system. Could be as simple as a loose/dirty connection, a bad antenna cable, a loose/bad ground or a bad antenna. The avionics shop should not have a problem fixing it.

A few notes to start

Without knowing what EFIS etc, I would start by looking for any electrical lines near the compass Any electrical current within a few feet of a compass will cause it to shift. This is compounded if you use the body of aircraft as an electrical ground return path.

The EFIS sensors (MP) could be anything from bad grounds to RF interference.

The current draw when transmitting does not seem out of line but then again, I do not own that radio.

Do ALL of your grounds go to a forest of tabs, or are you using the airframe as a ground, looks like a grounding issue?

Coax

KISS
Start with loose coax connections at the radio. A loose connection will leak RF.

wirejock said:

KISS
Start with loose coax connections at the radio. A loose connection will leak RF.

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Not a radio expert here, but when I installed my antennas, there was mention to make sure the base was clean for grounding contact, does the radio receive its RF ground path through the airframe, to outer jacket of coax and then into radio? or is the radio ground good for all this?

Where does your current jump from? I believe the manual for my SL30 radio spec'ed 7.5 amps typical current draw when transmitting. If you were already drawing a few amps when it pegs 10, that seems in line. I wouldn't worry much about the compass, but it does seem like your generating something on the electrical buss that you shouldn't I would be looking at wiring before sending in the radio. Best to check the power and antenna connections first, as they are more likely than a defective radio. The fact that your MAP gauge (assuming it is electrical) changes, would imply something is getting on the power or ground buss that shouldn't. However, poorly designed devices can be intolerant of errant RF. A loose connection seems most probable. FYI, loose connections tend to increase current draw as well.

Larry

Ground

bret said:

Not a radio expert here, but when I installed my antennas, there was mention to make sure the base was clean for grounding contact, does the radio receive its RF ground path through the airframe, to outer jacket of coax and then into radio? or is the radio ground good for all this?

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No. Radio ground is through the ground circuit. Usually the same guage as power. But, antennas need a good ground plane at least 1/4 wave if not more to effectively radiate. Bad ground or center conductor will cause RF to leak or reflect back towards the transmitter. SWR is the ratio of power out to reflected. Bad SWR will increase the amp draw on transmit. A leak can make other electronics wonky (technical term).