Powering avionics on the ground

[NotarPilot]

What equipment are you guys with glass panels using to ground power the avionics to fiddle faddle with your equipment while the engine isn’t running? Would something like a battery charge from Harbor Freight work?

[EricJ]

Some chargers don't support a continuous load well, or only handle a limited load.     I made my own 25A GPU (I'm an EE), but if I were to do it again I'd just get one of these (all the work is done and it has a lot of the right features).   There's a 24V version as well:

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

[NotarPilot]

1 hour ago, EricJ said:

Some chargers don't support a continuous load well, or only handle a limited load.     I made my own 25A GPU (I'm an EE), but if I were to do it again I'd just get one of these (all the work is done and it has a lot of the right features).   There's a 24V version as well:

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

I like it but I don't have the plug receptacle for that. I was thinking of something that clipped on the battery. 

[ArtVandelay]

I use a harbor freight 6A charger, by turning off unnecessary loads you should easily be under 6A.
I don’t leave it connected overnight.

[NotarPilot]

1 hour ago, ArtVandelay said:

I use a harbor freight 6A charger, by turning off unnecessary loads you should easily be under 6A.
I don’t leave it connected overnight.

How long have you been using that? Any issues with it?

[ArtVandelay]

How long have you been using that? Any issues with it?

Years. No issues, I use the ground port so I have to power the relay using a battery because the charger has to sense the battery, then attach the charger.

I tried this first, it failed quickly:



The HF charger is an old style (big and heavy), don’t get the modern types above…less power and don’t have protection against drawing power at the same time I guess.

[PT20J]

I found that the Battery Minder supplies almost enough current. The battery will slowly discharge, but not significantly over 2 - 3 hours, and the Battery Minder will bring it back up to full charge when you are done. 

[EricJ]

9 hours ago, NotarPilot said:

I like it but I don't have the plug receptacle for that. I was thinking of something that clipped on the battery. 

It has an intermediate connector so you can adapt it to pretty much anything.

[NotarPilot]

9 hours ago, PT20J said:

I found that the Battery Minder supplies almost enough current. The battery will slowly discharge, but not significantly over 2 - 3 hours, and the Battery Minder will bring it back up to full charge when you are done. 

I actually have a battery minder but I figured it wouldn’t supply enough juice and having the avionics on while connected might strain or damage the battery minder. I have no knowledge or evidence of that, it was merely a concern of mine.

 

[Fly Boomer]

9 hours ago, PT20J said:

I found that the Battery Minder supplies almost enough current. The battery will slowly discharge, but not significantly over 2 - 3 hours, and the Battery Minder will bring it back up to full charge when you are done. 

I keep a BatteryMINDer on all the time (two series-wired 12V batteries in a Rocket).  Do you think I could stand 2-3 gear swings without significant discharge on the batteries?

[PT20J]

23 minutes ago, Fly Boomer said:

I keep a BatteryMINDer on all the time (two series-wired 12V batteries in a Rocket).  Do you think I could stand 2-3 gear swings without significant discharge on the batteries?

Sure, I did that during my last annual in my hangar. 

[PT20J]

49 minutes ago, NotarPilot said:

I actually have a battery minder but I figured it wouldn’t supply enough juice and having the avionics on while connected might strain or damage the battery minder. I have no knowledge or evidence of that, it was merely a concern of mine.

 

They are pretty well protected to make them idiot proof. Shorting them or reversing the connections won’t hurt them. When they get to the max load, they just current limit. 

[carusoam]

There are a few threads around here to cover exactly this situation….

1) A few MSers acquire a specific power supply to do this often…. Kind of expensive…

2) Most just use the BatteryMinder knowing there is a limit to how much time /hours they want to spend in the hangar simulating…

3) Few use the GPU plug as the safety relay makes it a challenge to use…

4) Most have found a way to directly wire the BatteryMinder to an exterior plug…

5) Having a full fledged power supply would be great to have….

6) If you are concerned about a power supply to operate flaps and landing gear…. Keep in mind battery capacity is rated in amp-hours… not amp-seconds….    The BatteryMinder will be great for this as well…

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[Fly Boomer]

12 hours ago, carusoam said:

Few use the GPU plug as the safety relay makes it a challenge to use…

Why?  Can you elaborate this point?

[carusoam]

6 hours ago, Fly Boomer said:

Why?  Can you elaborate this point?

The relay that closes when you have the right polarity….

Requires near full voltage to operate….

The smart chargers sense proper voltage before delivering any current themselves….

So there you are… with everything plugged in and ready to go…. But get stymied by the safety relay….

Now, you set up a wire to power the relay from your batteries….

 

The safety relay, MAY not be rated for continuous operation… so check on that detail as well…. Its main purpose is to allow a jump-start….safely.  Which only takes a few minutes….

 

By the time you are done… you have opened the access panel to get to the batteries…

It is easy enough to then connect the power supply directly to the battery terminals….  

 

The BatteryMinder makes this chore easy by bringing a wire from the batteries to the outside, simple plug in…

 

Having the safety relay is important… you never know who is going to connect it to a power cart….

Huge expenses follow connecting batteries backwards, or using the wrong voltage….

 

PP thoughts only, not a mechanic…

Best regards,

-a-

[RobertGary1]

I’m had a ground power switch installed when I did my panel upgrade. It powers one radio and the gps only. So I can run off the battery with min load.
Also works as an emergency backup if the master solenoid fails closed.

[Aerodon]

Be careful with this, I have a friend that has fried two batteries by spending too much time on his auxiliary 30A power supply connected to the plane.  It's basically an unregulated charger over charging the batteries.

Aerodon

[NotarPilot]

2 hours ago, Aerodon said:

Be careful with this, I have a friend that has fried two batteries by spending too much time on his auxiliary 30A power supply connected to the plane.  It's basically an unregulated charger over charging the batteries.

Aerodon

I had an avionics shop connect one of these chargers to my battery while doing a firmware update to my Avidyne IFDs and remember seeing the volt meter climb to something like 15 or 16 volts before I finally disconnected it, accidentally arced the clip on the battery box and blew the top off the battery. I was not a happy camper that the guy left the charger hooked up for so long, unmonitored and allowed the voltage to get that high where I finally intervened. 

[Fly Boomer]

3 hours ago, Aerodon said:

Be careful with this, I have a friend that has fried two batteries by spending too much time on his auxiliary 30A power supply connected to the plane.  It's basically an unregulated charger over charging the batteries.

I thought that when you plug in the GPU, it disconnects the battery?  Isn't that why you can't charge via the GPU connector without some electrical monkey business to fool the solenoid?

[ArtVandelay]

I thought that when you plug in the GPU, it disconnects the battery?  Isn't that why you can't charge via the GPU connector without some electrical monkey business to fool the solenoid?

No, you need to close the auxiliary solenoid, smart chargers require sensing the battery, so need to close solenoid first with an external battery, then attach the charger.

[EricJ]

2 hours ago, NotarPilot said:

I had an avionics shop connect one of these chargers to my battery while doing a firmware update to my Avidyne IFDs and remember seeing the volt meter climb to something like 15 or 16 volts before I finally disconnected it, accidentally arced the clip on the battery box and blew the top off the battery. I was not a happy camper that the guy left the charger hooked up for so long, unmonitored and allowed the voltage to get that high where I finally intervened. 

This won't happen with any sort of decent GPU.   A GPU will function the same as a constant-voltage charger, which is also what the regulator and alternator do while you're flying.    If you're comfortable flying for several hours behind an alternator and voltage regulator, a GPU should be no different.

If a unit got your battery up to 15-16 Volts, its regulator was faulty.   

I have my GPU set to 13.7V, which is enough to power everything without draining the battery, but is less than the system voltage regulator is set to, so it should not over-charge anything and won't present any higher voltage to anything in the system than seen during normal operation.   I suspect most are set around there or to 14V, which is not unusual for system voltage during operation.

 

[EricJ]

4 hours ago, Aerodon said:

Be careful with this, I have a friend that has fried two batteries by spending too much time on his auxiliary 30A power supply connected to the plane.  It's basically an unregulated charger over charging the batteries.

Aerodon

It's faulty or a piece of junk if it is unregulated.   Don't hook anything like that to a system that expects a regulator.   Any decent GPU will be regulated.

[Brent]

On 5/31/2022 at 7:02 AM, PT20J said:

I found that the Battery Minder supplies almost enough current. The battery will slowly discharge, but not significantly over 2 - 3 hours, and the Battery Minder will bring it back up to full charge when you are done. 

Plus one on the Battery Minder. That has worked fine of me, though I haven't run anything for hours on the ground - maybe 30-60 minutes of messing around with stuff.  

[flyboy0681]

12 hours ago, Brent said:

Plus one on the Battery Minder. That has worked fine of me, though I haven't run anything for hours on the ground - maybe 30-60 minutes of messing around with stuff.  

Just wondering, if the BatteryMinder is plugged in but the master switch is left on by accident with the avionics switch off, will the Minder keep the battery nearly or fully charged or would I come back two days later to a dead battery?

[Brent]

1 hour ago, flyboy0681 said:

Just wondering, if the BatteryMinder is plugged in but the master switch is left on by accident with the avionics switch off, will the Minder keep the battery nearly or fully charged or would I come back two days later to a dead battery?

Depends on what's connected to the Master and what's switched on. I believe a Battery Minder trickle charger delivers around 1.2 to 1.3 amps. Avionics wise, my setup has a G3X and one GI-275 (as well as autopilot controller, lighting, pitot heat, etc.) on the Master and the rest of the avionics on an Avionics Master.

According to the Garmin installation manual, the G3X display (alone) draws 1.1 amps (14 volt, half that for 28 volt) and the GI 275 typically draws 0.7 amp. So if I have those powered on, leaving the Master on will out run the Battery Minder. I'm no EE, but I assume the time that takes would be related to the excess of draw above the Battery Minder and the capacity left in the battery. So I guess we better turn the Master off....