Ground Power Idea - Comments?

Guest Discussion
1

Why not a successful union of a 3-prong plug (Sporty’s, Aircraft Spruce, others) and a 24-volt DC output charger? With the charger set to “manual” it will provide output up to its rated direct-current amps; some I see are 10 amps, others 20 amps. Isn’t “direct-current” at 24-volts all-the-same, whether from batteries or charger? Unlike AC which might have a compromised/changed sine-wave, I would think that “DC is DC”. I understand that 10 (or even 20) amps is not engine starting power, but to learn and program the Garmins and power up the ARNAV, wouldn’t 10 amps of DC ground power give me powered-up avionics in the hanger without battery discharge? Also, does the ground power port charge the battery or just supply DC power to the bus?

Your comments appreciated - don’t want to endanger all those $$$ in the panel.

Randy

(saw a 10 amp 24 volt DC charger today at WalMart for $64)

2

Randy,

sorry, your 24 Volt WalMart charger won’t work. The Cirrus SR2x have a relay sensing the incoming voltage and require at least 27 Volts, better 28. By this, Cirrus wants to prevent from unintentional discharging of the battery. The third wire in the Sporty’s or Spruce cable (good choice)is the voltage sensor wire. I bought a 28 Volt stabilized 5 amps DC source (you might find it at Radio Shack or other electronic shops). Ask for one which creates a “smooth” DC, with not too much sinus noise; if you tell them that you want to run a radio or TV in your RV on it, they’ll know what you need. 5 amps are okay for playing with the Garmins as long as you make sure that the electrical vacuum pump and the ARNAV circuit breakers are off.

Have fun!

Timm Preusser N747TG

Why not a successful union of a 3-prong plug (Sporty’s, Aircraft Spruce, others) and a 24-volt DC output charger? With the charger set to “manual” it will provide output up to its rated direct-current amps; some I see are 10 amps, others 20 amps. Isn’t “direct-current” at 24-volts all-the-same, whether from batteries or charger? Unlike AC which might have a compromised/changed sine-wave, I would think that “DC is DC”. I understand that 10 (or even 20) amps is not engine starting power, but to learn and program the Garmins and power up the ARNAV, wouldn’t 10 amps of DC ground power give me powered-up avionics in the hanger without battery discharge? Also, does the ground power port charge the battery or just supply DC power to the bus?

Your comments appreciated - don’t want to endanger all those $$$ in the panel.

Randy

(saw a 10 amp 24 volt DC charger today at WalMart for $64)

3

Why not a successful union of a 3-prong plug (Sporty’s, Aircraft Spruce, others) and a 24-volt DC output charger? With the charger set to “manual” it will provide output up to its rated direct-current amps; some I see are 10 amps, others 20 amps. Isn’t “direct-current” at 24-volts all-the-same, whether from batteries or charger? Unlike AC which might have a compromised/changed sine-wave, I would think that “DC is DC”. I understand that 10 (or even 20) amps is not engine starting power, but to learn and program the Garmins and power up the ARNAV, wouldn’t 10 amps of DC ground power give me powered-up avionics in the hanger without battery discharge? Also, does the ground power port charge the battery or just supply DC power to the bus?

Your comments appreciated - don’t want to endanger all those $$$ in the panel.

Randy

(saw a 10 amp 24 volt DC charger today at WalMart for $64)

Our local ag operator bought a used electric golf cart (24 volt) that he uses for towing his planes as well as boosting. Plenty of battery too.

4

Thanks Timm!

But why do others on this site speak of 2 X 12volt batteries in series (making 24volts) as a good power source via that same plug?

How does our Cirrus “know” whether or not there is a 24volt double battery or a 24volt charger at the end of the plug?

Based on what you know, sounds like 2 X 12volt batteries (or even 1 X 24volt aviation battery) would NOT work when plugged in because of the voltage regulator.

And yes, I’ll definately try Radio Shack for a 28volt power supply. Do you know of other sources?

Randy

5

Randy,

sorry, your 24 Volt WalMart charger won’t work. The Cirrus SR2x have a relay sensing the incoming voltage and require at least 27 Volts, better 28. By this, Cirrus wants to prevent from unintentional discharging of the battery.

Timm…

From what I can see in the wiring diagram, the relay that switches in the Ground Power Connector is a standard 24 volt (not 27/28) relay. In any case, ANY charger that hopes to charge a 24 volt battery has to be able to provide some “head voltage” - they typically do provide 27 to 28 volts with no load. What is true, though, is that many of them provide pretty dirty DC - very noisy and unregulated.

Mike.

6

Randy,

I don’t know because I did not try with 2 x 12 Volt batteries. Mike gave a good comment by indicating that normally any charger would lead the 24 Volts a little (he is right), but in my case I had bought a constant voltage source of exactly 24 Volts, very smooth, and that gave me the problem. There is also a very old thread in this forum(1 yr. or more)where the same problem was mentioned, I’ll try to find it for you.

No, since I’m living in Germany, I don’t know a better source than Radio Shack in the US, but there probably are more suppliers, for sure.

Timm Preusser

Thanks Timm!

But why do others on this site speak of 2 X 12volt batteries in series (making 24volts) as a good power source via that same plug?

How does our Cirrus “know” whether or not there is a 24volt double battery or a 24volt charger at the end of the plug?

Based on what you know, sounds like 2 X 12volt batteries (or even 1 X 24volt aviation battery) would NOT work when plugged in because of the voltage regulator.

And yes, I’ll definately try Radio Shack for a 28volt power supply. Do you know of other sources?

Randy

7

Mike,

I tried it out with a regulated 24V stabilized source and got no charge (no, the battery was not fully loaded, and also there was no “click” of the relay to be heard), so I anticipated that the relay needs a little more juice; with my new 28 Volts regulated and adjustable charger, I increased Voltage from 22 to 26 until I heard the relay cklicking. But the most important point, we agree, is that you need “clean” DC which usually does not come from a 24 Volt truck battery charger.

Timm Preusser

Timm…

From what I can see in the wiring diagram, the relay that switches in the Ground Power Connector is a standard 24 volt (not 27/28) relay. In any case, ANY charger that hopes to charge a 24 volt battery has to be able to provide some “head voltage” - they typically do provide 27 to 28 volts with no load. What is true, though, is that many of them provide pretty dirty DC - very noisy and unregulated.

Mike.

8

Mike, Randy,

maybe I ran into the same problem Mike had when I first tried the stabilized regulated 24 volt source…see below…

I like to sit in the 'plane with the battery Switch ON and play with the avionics - it’s a great way to learn - more real than the PC sims, and less stressed/hurried than in actual flight (especially IMC).

"I bought the Schauer Four Seasons Fully Automatic 24 Volt 20 Ampere battery Charger through Aircraft Spruce & Specialty Company . It cost about $200 (there’s a 10 Amp version, certainly ample, for $124). It’s in the Electrical Section of my printed catalog, on page 350. I also bought a Lexan plug - AN2551 - from the same source. This is the plug that fits into the external 24 volt source on the side of the airplane cowling.

I connected the charger to the airplane, switched the battery Switch to ON… and nothing happened.

The problem is that both devices (the charger and the airplane) are too smart. The airplane has an “External Power” relay that won’t connect the outside power source until it sees voltage is present; and the charger won’t provide power until it senses at least SOME battery voltage. In effect, both devices stand there saying “After you” - “No, After YOU”… etc.

An obvious solution is to use the charger the way it was intended - i.e. hook it up to a 24 volt battery (or 2x12 volt batteries in series), and connect those batteries in turn to the airplane. This arrangement has some advantages - for example, you could connect the battery to the airplane without the charger, provided it is charged; this would be very useful where there is no AC available.

However, I didn’t want the extra hardware (battery), so I modified the charger to add a pushbutton “trigger” to feed just enough voltage to the sense circuitry to convince it that it’s OK to start charging.

Now, after hooking the charger to the airplane, I switch the battery Switch to ON, and press my Trigger pushbutton, and off it goes.

The actual modification is very simple. If you’re interested, send an email, and I’ll fill you in on the details.

Mike.

Timm…

From what I can see in the wiring diagram, the relay that switches in the Ground Power Connector is a standard 24 volt (not 27/28) relay. In any case, ANY charger that hopes to charge a 24 volt battery has to be able to provide some “head voltage” - they typically do provide 27 to 28 volts with no load. What is true, though, is that many of them provide pretty dirty DC - very noisy and unregulated.

Mike.