Electrical Problem

Just installed new (to me) garmin radio and transponder in my -18. They work great. However, whenever I transmit, my EI bar-graph engine analyzer, which is also powered by the avionics bus, reboots. I’m guessing that the radio is drawing either current or voltage below some critical value, causing the analyzer to momentarily shut off. However, I don’t seem to get abnormal indications from the ammeter or voltage indicator when the problem occurs. The alternator is an interav 12V 50A model. Anyone else seen this kind of issue? Ideas? Thanks in advance.


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Bluebear said:

Just installed new (to me) garmin radio and transponder in my -18. They work great. However, whenever I transmit, my EI bar-graph engine analyzer, which is also powered by the avionics bus, reboots. I’m guessing that the radio is drawing either current or voltage below some critical value, causing the analyzer to momentarily shut off. However, I don’t seem to get abnormal indications from the ammeter or voltage indicator when the problem occurs. The alternator is an interav 12V 50A model. Anyone else seen this kind of issue? Ideas? Thanks in advance.


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Yes, mine has always done that also.

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Your Com coax cable is routed to close to the back of your gauge or it's bundled with the gauge wiring. Separate from ALL wiring and tape or tie it all by it's self.

Web

Why would you power an engine monitor on the avionics bus?

FWIW I have a Garmin G5 electronic horizon in my C180.
I have it wired to the avionics circuit, so it is off when I start the engine,
then powers up (along with the radios) when I turn on the avionics master.
If I had an engine monitor, I'd probably power it the same way.
IMHO if there's a low-voltage or similar issue with my airplane's electrical system,
it probably wouldn't matter which circuit the device is on.
All the milk comes out of the same cow.

Bluebear said:

Just installed new (to me) garmin radio and transponder in my -18. They work great. However, whenever I transmit, my EI bar-graph engine analyzer, which is also powered by the avionics bus, reboots. I’m guessing that the radio is drawing either current or voltage below some critical value, causing the analyzer to momentarily shut off. However, I don’t seem to get abnormal indications from the ammeter or voltage indicator when the problem occurs. The alternator is an interav 12V 50A model. Anyone else seen this kind of issue? Ideas? Thanks in advance.


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How are your grounds wired? I would jumper a ground to your EI from the battery and see if the problem persists.

Tim

stewartb said:

Why would you power an engine monitor on the avionics bus?

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Because the EI says to in the STC installation instructions (i.e. mandatory to power the UBG-16 from the radio bus). Also, EI pilot's manual says to never start the aircraft with the unit powered on.

Electronics International recommends wiring their engine analyzers on the master bus. They told me it would be okay. So far, so good. Garmin also recommends wiring the G5 to the master bus.

hotrod180 said:

FWIW I have a Garmin G5 electronic horizon in my C180.
I have it wired to the avionics circuit, so it is off when I start the engine,
then powers up (along with the radios) when I turn on the avionics master.
If I had an engine monitor, I'd probably power it the same way.
IMHO if there's a low-voltage or similar issue with my airplane's electrical system,
it probably wouldn't matter which circuit the device is on.
All the milk comes out of the same cow.

Click to expand...

The UBG seems a bit of an aberration. The other E.I. instruments show instructions to connect power to the main bus. This is the way I always connect engine instruments as they need to be on line to monitor said engine. Even if I need to shed power, engine instruments would seem to some of the last items I'd shut down.

As for me connecting UBG's to the main harness all these years . . . I just feel awful

Web

Eddie Foy said:

…. Garmin also recommends wiring the G5 to the master bus.

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FI just read through the first 40 or so pages of the 152 page G5 user's manual--
didn't see anything in there about connecting G5 power direct to the master circuit.
Just showed both the power-in pins connected to 14v or 28v power.

Bluebear, let us know what fixes the problem. Pass the knowledge on to others so that they can avoid similar situations.

Web

From the installation manual. A Garmin engineer told me that the main bus was OK.



4.3.2 Power Distribution
The circuit protection device for the G5 and GAD 29/29B must be a push-pull manually resettable circuit breaker or identically rated circuit protection device approved by the aircraft type certificate. See Section 3.2.1 for required circuit breaker part numbers. The G5 must be connected to the battery bus to supply power . (Note: some aircraft manufacturers may label the battery bus as “essential bus” or “main bus”).

hotrod180 said:

F

WIW I have the pre-STC'd version of the G5 in my airplane.​

I just read through the first 40 or so pages of the 152 page G5 user's manual--
didn't see anything in there about connecting G5 power direct to the master circuit.
Just showed both the power-in pins connected to 14v or 28v power.

Click to expand...

Eddie Foy said:

From the installation manual. A Garmin engineer told me that the main bus was OK.



4.3.2 Power Distribution
The circuit protection device for the G5 and GAD 29/29B must be a push-pull manually resettable circuit breaker or identically rated circuit protection device approved by the aircraft type certificate. See Section 3.2.1 for required circuit breaker part numbers. The G5 must be connected to the battery bus to supply power . (Note: some aircraft manufacturers may label the battery bus as “essential bus” or “main bus”).

Click to expand...

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Bluebear said:

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I will certainly share the ultimate solution. I’m out of town at moment. Many thanks to those who have suggested possible fixes.


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Eddie Foy said:

From the installation manual. A Garmin engineer told me that the main bus was OK.
4.3.2 Power Distribution
The circuit protection device for the G5 and GAD 29/29B must be a push-pull manually resettable circuit breaker or identically rated circuit protection device approved by the aircraft type certificate. See Section 3.2.1 for required circuit breaker part numbers. The G5 must be connected to the battery bus to supply power . (Note: some aircraft manufacturers may label the battery bus as “essential bus” or “main bus”).

Click to expand...

That must be out of the manual for the STC'd G5 --
The user's manual for the pre-STC version doesn't even have four sections, just two::
Section 1: installation manual, and Section 2: pilot's guide.

But like I said, the milk all comes out of the same cow--
at least on small aircraft like most of ours.
The "avionics buss" on mine is separated from the "essential buss" / "main buss" by a wire and a switch--
A joggle in the power on the main buss is also gonna result in a joggle on the av buss.
I do have the G5 circuit on it's own circuit breaker, as are the com, txp, and GPS.

The point of an avionics bus is not to have a separate source of power, it's to conveniently control the power to the equipment connected to the avionics bus. I.e. turn off avionics power on start up, with one switch or relay.

All electrical power comes from the same source on all aircraft; a generator/battery system. Even multi engine aircraft. The power generation system is regulated to act as a single source. And aircraft with primary, secondary, and emergency busses have the ability to turn off or select individual engine driven generators and individual battery packs. But ultimately even the batteries are charged by that generation system.

Web

I am absolutely no expert on this stuff, but I had always heard that the purpose of the avionics bus was to allow all the radios (the only sensitive electronics "back in the day") to be turned off with a single switch to avoid "power surges" on startup. But after reading most of Bob Nuckoll's "AeroElectric Connection" book and website, he seems convinced that a switched avionics bus is an ancient artifact, made obsolete by today's electronics which can handle most anything the aircraft's electrical system can throw at it. And that "expert opinion" appears to be vindicated by the installation instructions for pretty much every recent piece of electronic gear I've checked out for my Bearhawk Patrol build... With the caveat that I'm looking mostly at experimental stuff...

Given that as background, and knowing the the EI UGB-16 is a bit "long in the tooth" compared to their MVP and CGR series products, I would suspect that the UGB series may not have the same level of internal protection as the later stuff. Thus EI's recommendation to wire it to the avionics bus. The Garmin G5 on the other hand is a thoroughly modern design, and as such can be (and is recommended to be) installed directly to the main bus.

Personally, I would not want essential engine information switched off with the avionics, nor would I want to delay seeing oil pressure, etc. until I got to the "Avionics bus - ON" item in the checklist sequence... I want to see an oil pressure rise immediately after startup. If the UGB-16 actually is required to be switched off for engine start via the avionics bus, that would definitely lead me to at the very least add a backup "direct-reading" oil pressure gauge, or possibly even better, select a different engine monitor for my airplane.

Instruments aren't avionics.

Web

Isn't "avionics" a contraction of aviation electronics?
So IMHO it covers more than radios.

Gauges are gauges. Other than the UBG, you'd be hard pressed to find an electronic instrument that calls for being connected to anything but main bus power. This is because engine instruments are intended to be online and operational whether the engine is off, running, or being started. Radios/nav are secondary to engine operation.

As most radios, navs, transponders, etc, call for being connected to an avionics bus or at least be shut off during start up, my guess is that the power supplies in the engine instruments are filtered and conditioned to reduce the voltage spikes that occur during start up. If the 'avionics' units are powered down during start up, then they don't need the extra circuitry installed.

Web

Thank you to all for the great thoughts and ideas! It turns out that a simple loose ground was the cause of the problem. Nothing more complicated than tightening a nut on the ground bus. Back to normal ops.


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