Running Airconditioning on the ground 690C

[kent4142]

Hi All,

If I wanted to run the aircraft air conditioner on the ground, and I have access to 110 volt power in the hangar.  What is the easiest way to cool the cabin prior to flight?

Thanks,

Kent

[Adam Frisch]

Don't think you can unless you have a Schiff CCM.

[donv]

You need a 24V DC source to power the airplane. So some sort of GPU or battery cart. I use my Lektro tug.

The problem is those air conditioners have a pretty high amperage draw, and the cheap GPUs only do about 25 amps. So I think you'll have to spend some money on a quality GPU.

[Bruce Byerly]

Yes all of the above. I have a like new Hobart GPU 600 for which I’d take $10,000. It’s a real GPU.

[schrambow]

I just purchased one of these from sporty's:
https://www.sportys.com/pilotshop/70-amp-aircraft-ground-power-unit-gpu-with-batteryminder.html

It works pretty well, you have to make sure you have a 20 amp breaker in your 120 box.  I just got it a few days ago, and the GPU function works well for turning on all avionics and many other item without wearing down your batteries.  I did just turn on the cabin bus with just the AC going and it was pulling about 25- 30 amps by itself, i think if you went crazy and turned on everything, one might overload the unit.  This unit will do 70 amps and then will flash warning of an overload.  I haven't tried to push this unit yet to see if it will kick out or shut down once it gets to 70. But for 1400 bucks, and the amp read out screen, i thought it wasn't too bad for just preflighting (database updating) and checking things out without worrying about battery drainage(lights, heat items-not necessarily all at once though, common sense does dictate a bit here, etc..)
There also is a kit we are installing in a few days, which is suppose to be a battery minder feature on this unit which is suppose to keep the batteries charged up when the machine is sitting, but it is using a different separate connector directly wired to the batteries i am assuming.  I am still a bit fuzzy on this, but once my local guy installs this battery minder kit, I will report back here to what we found and the results also.

[donv]

I don't know how much my AC draws (Keith Freon system), but I would guess it's at least 70 amps.

[Bruce Byerly]

It would be nice if that unit worked for AC. It might. Which would be great.

The trouble is that there is no way to know on a stock Commander if you are overcharging the batteries or undercharging them unless there has been a modification to give battery voltage.

Basically, a Commander will either start or it won’t. It’s a great system until you try to run aux power for an extended period.

I’m no electrical engineer, but have been served well by either running AC on a start capable GPU or avoiding AC operations on external power.

Complicating the above is the fact that some will run without the battery in the loop.

[donv]

I always turn the battery off when using external power for an extended period. Are you saying I shouldn't be doing that?

My airplane even has a placard on the GPU door which says something about "Do Not Attempt to Charge Batteries using GPU."

[donv]

I just looked at my PDF of the 980 AFM, and under "Ground Power Unit" in the "Handling, Service and Maintenance" section, it says the following:

CAUTION

To prevent damage to the batteries, DO NOT turn the battery switch to BATTERY position if the GPU is used for a prolonged period of time. Do not charge the batteries through the external power receptacle.

Unfortunately, I don't have easy access to my airplane. But I think the supplement for the Keith Freon system tells you how many amps it draws.

[kent4142]

Thanks Everyone.  I have a lot of learning to do, and I appreciate the input.

Bruce you type those numbers like $10,000 so nonchalantly.  I am one of those bozos who spent all he had buying the airplane.  Now I can't afford all the frosting for the cake.   : - 0      : - )

Don't get me wrong I am having more fun flying my 840 all over North America than I have ever had in my life!!!!  I love my Commander!!!!!!!!!!!!!!!!!!

Right now my work around is what I call, a "roly poly" air conditioner, that has a big exhaust tube and wheels.  It fits just inside the door with just enough room to enter and exit.  (I am losing a little weight, and that helps.).  For extended periods.  20 or 30 minutes I will drape a drop cloth over the door opening.  It works pretty good, and I have a considerably oversized extension cord 12-2 guage.

TTFN   (Ta Ta for Now)

Just as a reminder - I am based near Orlando, FL. Temperatures last week were near 100, with humidity over 90%.  I needed to take a family - Mom, Dad, and two children under 3 years old to Michigan.  It was brutal by 10:00 am, and the AC in the door worked good.  It just looked kinda "Rube Goldberg".

[donv]

Kent, a few thoughts:

1) I've used an air conditioner setup like you describe. It actually works pretty well. The issue I had with it is that when the passengers show up and you have to turn that thing off and put all the pieces away and wheel into the hanger, etc etc the airplane has heated up again by the time you start.

2) Does the local FBO, or whoever supplies you with fuel, not have a GPU that you could use? Even if they charged you a small fee (which they shouldn't, if you are buying fuel), it might be worth it. Especially if it comes with a line guy who can pull the plug after you have the door shut and engines running.

3) Does your tug have a GPU option?

4) When all else fails, I just tell the people that it's going to be hot for a few minutes, get the engines started promptly, and turn on the air conditioning. With the Keith freon system, it's very effective and the airplane starts to cool right away. I remember hot days in the 1000 with just the Sundstrand and 7 or 8 people, and that was miserable. Today with a few people and the Keith freon system, it's really quite reasonable.

[Bruce Byerly]

Kent - ha! -  that number is for a real GPU that will start it all day long in addition to running the ac.  Those 1000 amp units are expensive.  I have seen a 110v GPU converter that was supposed to work for starts but haven’t verified that.  If the sportys box works, then  that’s the answer.

You can get cabin bus GPU power on the late models without the battery but seems not all of the earlier planes and AC installs will run without the battery.  So then the question becomes how long can you run it on the ground safely? I don’t know the answer but try to avoid it. Maybe the book defines what “extended” means but I don’t remember. Is it 5 minutes? 15?

The other thing I’ve seen on enviro planes is the big AC breaker in the back popping when the AC is cycled on/off  before and after a start. I’ve seen that a few times and you’re out of business on the AC until you can crawl back there.

Not to overthink it, but while we are on the subject, the G600’s are all powered all the time with the battery. I was always under the impression that the voltage swings were hard on the radios. Are we past that with today’s solid state equipment? What about a quick turn where you just shut one down, do you turn the radios off?   

[donv]

Not to overthink it, but while we are on the subject, the G600’s are all powered all the time with the battery. I was always under the impression that the voltage swings were hard on the radios. Are we past that with today’s solid state equipment? What about a quick turn where you just shut one down, do you turn the radios off?   

We are past that, at least with Garmin equipment. Ever since I was doing air ambulance in Commanders 10 years ago, start first engine, let amps come down to 150 or so (I use 125), turn radios on, let amps come down to 100, start second engine.

I've been doing that with Garmin radios on my airplane for the last 7 years with absolutely no issues.

I believe the Garmin equipment is specifically designed to handle those sort of voltage spikes.

Don't try that with your old King Gold Crown stuff, though!

[Adam Frisch]

Steve has an avionics bus power that just powers up the radio so you can get the ATIS or call GND before start or you put master on. Do you guys really need to power up radio after first engine start?

[donv]

Yes, the old "Ground Clearance" switch.

In my airplane, the only radio you could power up is either the GTN750 or GTN650. The reality is that those Garmin units only use a fraction of the power of the old radios, and so even running both of them isn't a big issue. I turn on my #2 avionics bus and get the ATIS and clearance most of the time before I close the door.

As for the time, yes, the startup time is fairly substantial. I would say it takes about the same time as an engine start, so if it can be happening concurrently, that's a win in terms of getting the noisy airplane off the ramp that much more quickly.

However, you should do what you are comfortable doing. I'm used to a fairly quick operational cadence, so that's what I do. You might be used to something different, and you should stick with that.

Steve has an avionics bus power that just powers up the radio so you can get the ATIS or call GND before start or you put master on. Do you guys really need to power up radio after first engine start?