How to tell if a GPU is working?

[toto]

I bought one of these …

https://www.aircraftspruce.com/catalog/elpages/portPowerCharger24ces.php

… to keep from using battery while updating avionics databases.

Following the manufacturer’s instructions, everything *seems* to work fine. But the “Batt” display on my G3X shows a “-1” while I’m doing the database updates. I assume that that’s because it sees no output from the alternator and I’m drawing power — and it doesn’t know about the external power receptacle. So a 1-amp draw with radios running seems about right.

But is there any way to know for sure that the panel is running on GPU power? I do hear the “click” that tells me the relay inside the external receptacle has closed when the GPU is powered on, and the GPU itself shows a healthy status. 

Am I overlooking something obvious?

[EricJ]

There may be a voltage difference shown on the G3X between the batterie(s) and the GPU.   e.g., the batteries may show 26V and the GPU may show 28V or something.    You can try yours and see the difference.   Don't switch while it's live, boot everything separately and see if there's a difference.    If your GPU is decent and puts out 28V (or at least significantly better than the batteries), it may may be easy to tell that way.

 

[Fly Boomer]

1 hour ago, toto said:

But is there any way to know for sure that the panel is running on GPU power?

The Spruce web says it puts out 24 volts.  If true and your battery is good, your electrical system may see the GPU as a load.  The GPU should put out about the same as your voltage regulator -- a little over 28 volts depending on temperature.

[Schllc]

Your full panel running will draw more than 1amp. 
also,  it sure if the j has two batteries but on the gx models the gpu only works when on battery 1

[PT20J]

1 hour ago, toto said:

I bought one of these …

https://www.aircraftspruce.com/catalog/elpages/portPowerCharger24ces.php

… to keep from using battery while updating avionics databases.

Following the manufacturer’s instructions, everything *seems* to work fine. But the “Batt” display on my G3X shows a “-1” while I’m doing the database updates. I assume that that’s because it sees no output from the alternator and I’m drawing power — and it doesn’t know about the external power receptacle. So a 1-amp draw with radios running seems about right.

But is there any way to know for sure that the panel is running on GPU power? I do hear the “click” that tells me the relay inside the external receptacle has closed when the GPU is powered on, and the GPU itself shows a healthy status. 

Am I overlooking something obvious?

You are correct. The ammeter only shows that current is being supplied by the wire that runs to the battery. It cannot differentiate between current supplied by the charger and current supplied by the battery. 

Eric is also correct. The voltage shown on the G3X will be higher when running on the charger than on the battery. The 24V listed for the charger is a nominal value. The actual voltage will depend on the charger mode of operation. 

I get about -4A with just the master on which powers the G3X. 

[Vance Harral]

Having a GPU is handy for lots of things, but database updates shouldn't be one of them.  Running a ship on battery power for the few minutes it takes to update databases doesn't consume a meaningful amount of energy from a healthy battery, and isn't worth the trouble of the hookup.

To put some numbers on it, a healthy Concorde RG24-11M is going to have at least 10 amp hours of energy stored in while sitting in the hangar.  Using Skip's number of 4 amps draw and assuming 6 minutes to update your databases (should be plenty of time), that only requires 0.4 amp-hours, or about 4% of the nominal energy stored in the battery.

Different panels and different batteries will have slightly different numbers, but you're generally talking single-digit percentages of nominal storage capacity.  If that makes a difference in being able to start the engine, you have an unhealthy battery.

[Pinecone]

47 minutes ago, Vance Harral said:

Using Skip's number of 4 amps draw and assuming 6 minutes to update your databases (should be plenty of time), that only requires 0.4 amp-hours, or about 4% of the nominal energy stored in the battery.

It takes about 15 minutes to update my G3X.  And either I have to do two cards or use the same card twice to do the second G3X.  So 30 minutes total.  So more like 2 AH.  

But still a small amount of battery capacity

 

[toto]

1 hour ago, Vance Harral said:

Having a GPU is handy for lots of things, but database updates shouldn't be one of them.  Running a ship on battery power for the few minutes it takes to update databases doesn't consume a meaningful amount of energy from a healthy battery, and isn't worth the trouble of the hookup.

I’ve burned through a lot of Concorde batteries - the shop gives them an average of 2 years or so before they say it has failed the capacity test, and it costs me a thousand dollars for a new one. So anything I can do to prevent early battery death is a good thing. It takes me about two minutes to hook up the GPU and twenty to do the db updates - which might not be a big deal in the scheme of things, but I’m hoping it will help. 

[toto]

2 hours ago, PT20J said:

I get about -4A with just the master on which powers the G3X. 

Interesting - I wonder why mine was showing -1. I didn’t watch it for a long time, as I could only see it after the db updates were done, so maybe it bounced around. 

[201Mooniac]

1 hour ago, toto said:

I’ve burned through a lot of Concorde batteries - the shop gives them an average of 2 years or so before they say it has failed the capacity test, and it costs me a thousand dollars for a new one. So anything I can do to prevent early battery death is a good thing.

While I agree that anything to keep the battery healthy is a good thing, I would wonder why you are only getting 2 years from a Concorde battery.  My last one went 8 years before it reached the limit on the capacity test and my current one is 7 year old and it passed the capacity test in January.  I had issues with short life on the Gill batteries I used to use but the last few Concordes have all lasted me many years.

[toto]

4 minutes ago, 201Mooniac said:

While I agree that anything to keep the battery healthy is a good thing, I would wonder why you are only getting 2 years from a Concorde battery.  My last one went 8 years before it reached the limit on the capacity test and my current one is 7 year old and it passed the capacity test in January.  I had issues with short life on the Gill batteries I used to use but the last few Concordes have all lasted me many years.

No idea. I posted a thread about this a while back. My worst experience was just one year on a new Concorde battery before it failed the capacity test, and I had two that failed after two years. That’s flying more or less once a week year round. 

My shop said they have had bad luck with Concorde batteries and have stopped recommending them. I’ve been happy with the battery performance, just not happy replacing them every 1-2 years. 

[201Mooniac]

6 minutes ago, toto said:

No idea. I posted a thread about this a while back. My worst experience was just one year on a new Concorde battery before it failed the capacity test, and I had two that failed after two years. That’s flying more or less once a week year round. 

My shop said they have had bad luck with Concorde batteries and have stopped recommending them. I’ve been happy with the battery performance, just not happy replacing them every 1-2 years. 

Wow, definitely not been my experience, all have been at least 5+ years and the last two have been 7+.  I do fly twice a week on average and keep a battery minder running but I wouldn't recommend one either with your track record.  Just grasping here but have you verified your charging system is working correctly?

[toto]

16 minutes ago, 201Mooniac said:

Wow, definitely not been my experience, all have been at least 5+ years and the last two have been 7+.  I do fly twice a week on average and keep a battery minder running but I wouldn't recommend one either with your track record.  Just grasping here but have you verified your charging system is working correctly?

I haven’t done anything to verify the charging system, but I have had zero problems with the batter(ies). Always a very strong crank on start. The capacity thing is only ever a report from the shop at annual, not a battery performance issue that I have noticed. 

[MikeOH]

12 minutes ago, toto said:

I haven’t done anything to verify the charging system, but I have had zero problems with the batter(ies). Always a very strong crank on start. The capacity thing is only ever a report from the shop at annual, not a battery performance issue that I have noticed. 

This just seems weird...I, too, use Concordes and the first one made it seven years, and the second one is now six years old. I do my own capacity checks.  Not to be disparaging, but are you certain the shop is performing the test properly per the Concorde instructions?  You've been through way too many batteries for me to believe it's the Concorde battery that is the problem.

[Vance Harral]

Another report of great life from Concorde batteries from me: 7-8 years on the first two, third one is running strong at 3 years.  But - and this is critical - battery life can be very climate dependent.  @toto doesn't list his location, but if he's in a particularly hot and/or humid location (including ramp vs. hangar), he'll get different results from those of us living in cooler, drier climates.

As for database update times, I stand corrected - I had no idea G3X updates could take 20-30 minutes.  A quick search suggests nearly all the time is due to chart data, but this doesn't seem to reflect very well on Garmin, given that EFBs can download the same content much faster.  As the saying goes, "it is what it is".

I also had no idea 24V Concorde batteries cost about a thousand dollars (even direct from Aircraft Spruce).  The OP has my sympathies.  Our 12V RG35-AXC was $435 in 2022, and I thought that was painful at the time.  Same battery is now up to $512 at Spruce. 

[Pinecone]

13 minutes ago, Vance Harral said:

As for database update times, I stand corrected - I had no idea G3X updates could take 20-30 minutes.  A quick search suggests nearly all the time is due to chart data, but this doesn't seem to reflect very well on Garmin, given that EFBs can download the same content much faster.  As the saying goes, "it is what it is".

It is the approach plates that take a while to update.  And the G3X does not have HSDB (high speed data bus) so it cannot crossfill from a GTN in a reasonable time.

It would be nice if they included HSDB in the updated/replacement for the G3X.  BUT, it needs to fit the same panel cutout and space of the current one for easy update.

[Rick Junkin]

9 hours ago, toto said:

I haven’t done anything to verify the charging system, but I have had zero problems with the batter(ies). Always a very strong crank on start. The capacity thing is only ever a report from the shop at annual, not a battery performance issue that I have noticed. 

@toto Just a thought, and I’m not disparaging your shop in any way. Have you had a capacity test done at a different shop, or done a “poor man’s test” yourself? Often a second opinion reveals new and useful data.

EDIT: This article from Mike Busch provides some good information about battery care and feeding. He describes how to perform a rough battery capacity test using only the equipment installed on your airplane. It works. I try to do this test and a test flight to perform GAMI sweeps and airborne induction and mag checks before each annual inspection to identify any issues before the inspection starts.

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2011-07_battery-tlc.pdf

[PT20J]

What’s the bus voltage during operation? If it is too high - especially if the temperature is high - it will cause outgassing and shorten the battery life

[toto]

15 hours ago, Vance Harral said:

if he's in a particularly hot and/or humid location (including ramp vs. hangar)

I’m in Kansas City, always hangared 

[Z W]

I have the 12v version of that Schauer charger and leave the plane plugged into it all the time in the hangar. Works great for database updates and I like to start every flight knowing I have a topped off battery.

[DonMuncy]

That is good. but you need to disconnect it occasionally to make sure it holds a charge. It is tough to take a trhee day trip and when you come back to the plane, find the battery is dead.

[Andy95W]

10 hours ago, toto said:

I’m in Kansas City, always hangared 

I’ll second what everyone else has said- only getting 2 years out of a Concorde battery is not normal.

It has to come down to only a few possible causes:

- over or under charging (Concorde provides a table showing proper charging voltage)

- a parasitic drain while the master switch is off

- the test that the shop is doing is flawed somehow

Good luck, keep us posted!

[Marc_B]

FWIW, I have a Concorde battery installed in 2019 and still going strong.  But there IS a process if you have a failed capacity check on a battery that you can do a conditioning charge and retest.  I wonder if your shop just decided that a single fail = new battery every time?

Here is the link for the Concorde RG CMM that describes capacity test (page 19) and conditioning (page 20-21): 

https://batterymanagement.concordebattery.com/BatteryDocs/5-0171.pdf

Here is a good video describing the capacity testing and Concorde recommendations:

PS.  This is definitely a video that you NEED to watch in at least 1.5x speed!!!   SOOOOOOOOOOOOOO SLLLLLLLOOOOOOWWWWWW.

[Fly Boomer]

6 hours ago, Marc_B said:

SOOOOOOOOOOOOOO SLLLLLLLOOOOOOWWWWWW

Couldn't do it at any speed.