Powering avionics on the ground

[47U]

2 hours 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?

I’d think it would maintain the battery ok, as long as any high-amp items aren’t turned on, like pitot heat or the avionics master, perhaps.

When I update my nav data, I pull CBs for gear position, T&B, low vac, FP-5, etc.  It raises the volts by a few tenths on the ‘Fisher-Price’ voltmeter I have plugged into my cigar lighter.  The voltmeter isn’t that accurate and is probably reads a few tenths less that battery voltage, but it stays at 12.5-12.7 for the 20-30 minutes it takes to update nav data.  I don’t think I’m hurting anything doing it this way.    

[flyboy0681]

1 hour ago, Brent said:

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....     

The two items that I'm aware of that would still be running are the turn coordinator and the HSI gyro in the back.

[PT20J]

BatteryMinder spec is 8A for the 12V model and 4A for the 24V model. With the master and avionics master on in the hanger and the BatteryMinder connected to the battery, my G3X, GFC 500, GTN 650Xi, PMA 450B, GNC 255A, GTX 345 panel shows about a 2A discharge.

[Brent]

15 hours ago, PT20J said:

BatteryMinder spec is 8A for the 12V model and 4A for the 24V model. With the master and avionics master on in the hanger and the BatteryMinder connected to the battery, my G3X, GFC 500, GTN 650Xi, PMA 450B, GNC 255A, GTX 345 panel shows about a 2A discharge.

Thanks for clarifying. That reminds me, what discharge to you get while flying? Is it neutral? I thought I had my shunt setting right after the avionics upgrade (at a shop that is now out of business), but I don't think so now. I show negative 1-2A on the G3X EIS while flying. 

[PT20J]

20 minutes ago, Brent said:

Thanks for clarifying. That reminds me, what discharge to you get while flying? Is it neutral? I thought I had my shunt setting right after the avionics upgrade (at a shop that is now out of business), but I don't think so now. I show negative 1-2A on the G3X EIS while flying. 

It should be slightly positive depending on the charge the battery is taking. It sounds like the sense wires on the shunt may be reversed. 

[William A]

On 5/30/2022 at 11:29 PM, 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

my 1984 m20J looks like it has 2 male prongs (aux port on the left side of the tail section). this link looks like it has a 3 prong for cessna. im not seeing any other options on this website. am i missing something?

[ArtVandelay]

my 1984 m20J looks like it has 2 male prongs (aux port on the left side of the tail section). this link looks like it has a 3 prong for cessna. im not seeing any other options on this website. am i missing something?

My 78J has the 3 prong version.

[EricJ]

5 hours ago, William A said:

my 1984 m20J looks like it has 2 male prongs (aux port on the left side of the tail section). this link looks like it has a 3 prong for cessna. im not seeing any other options on this website. am i missing something?

Look more closely, it is probably 3 prong.   The 3rd prong is short so that it engages last after the two power conductors are already connected.   The shorter prong powers the relay that switches to external power.

[EarthboundMisfit]

We use a StartPac mini on our airplane - https://www.aircraftspruce.com/pages/el/chargersbattery_portable/startpacpowersup.php

[kortopates]

This used computer rack 28V 20amp power supply I got off ebay plus plug and cables from spruce set me back at most $200. Very easy to put together and it’s voltage regulator is adjustable to exactly what my plane’s system puts out.


Sent from my iPhone using Tapatalk

[ZuluZulu]

I tend the battery with a BatteryMinder but run avionics off of this (which you can find used on here, or BT, etc. if you're patient):

https://www.aircraftspruce.com/catalog/elpages/portPowerCharger24ces.php?clickkey=6344

It has a loud (for its size) cooling fan but otherwise works fine.

[rbp]

On even days, I do the database updates on the #1 battery and start the plane on the #2, and vice versa

[Brent]

On 6/4/2022 at 10:07 AM, PT20J said:

It should be slightly positive depending on the charge the battery is taking. It sounds like the sense wires on the shunt may be reversed. 

Finally got back to messing around with this. (Would have pursued it sooner, but my avionics installer went out of business, so I've just been living with it.) I think I got the right ratio in the G3X set-up, but as you suggested, I think the ammeter wires are reversed. Does this (chart below) look like the ammeter wires are reversed on the shunt? 

If so, I gather from other posts that the CB panel has to come out to get access to the shunt. 

[PT20J]

28 minutes ago, Brent said:

Finally got back to messing around with this. (Would have pursued it sooner, but my avionics installer went out of business, so I've just been living with it.) I think I got the right ratio in the G3X set-up, but as you suggested, I think the ammeter wires are reversed. Does this (chart below) look like the ammeter wires are reversed on the shunt? 

If so, I gather from other posts that the CB panel has to come out to get access to the shunt. 

Looks that way to me. On my M20J, there is a shelf behind the circuit breakers accessible from the top with the glare shield removed and the shunt is on that shelf. It's cramped, but possible to get to it without removing the whole circuit breaker panel (which is really a nasty job).

Skip

[carusoam]

Wait a sec…

Sure, the two wires may be reversed…

But where is the reversal?

It may be easy to swap the wires at the G3X…

 

Just something to consider…

Essentially, the ammeter is measuring the voltage drop across the highly calibrated shunt, and displaying the voltage drop converted as current flowing…

Swap the wires… at either end… you get a negative value… swap them again, you get a positive value…

 

If the original wires connected to the shunt are still in place… somebody probably accidentally swapped the wires closer to the instrument…

Expect that these wires also have a fuse on each one…. To keep the high volume of electricity from escaping when a short occurs…

 

PP thoughts only, not an electronics guru…

Best regards,

-a-