A slightly differnt A/C system

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pbreed
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Re: A slightly differnt A/C system

Postby pbreed » Tue Aug 29, 2017 10:40 am

GPU is home built from a 24V 100A 220V Server supply and a pair of deep discharge 12V batteries...
The voltage is well regulated at 28V.

At one point I drained enough refrigerant that it ran for an hour on the ground providing marginal cooling, but with the vibration of flight popped the breaker
in 10 min.
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bohica2xo
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Re: A slightly differnt A/C system

Postby bohica2xo » Tue Aug 29, 2017 12:00 pm

I generally approach OEM stuff from the view that it worked ok at one time, and that something has changed.

However, it is time to ask - did this thing EVER work well? Do other owners have the same issues?

Back in the early '80's there were lots of little vendors like the one that built that motor in So Cal. Some were great, some were scary - all called "...xxx... Engineering" A few we used to call "Al's Surplus Electronics & Bed Spring Works" - a generic denigration of so called engineering firms my peers had worked for... briefly.

If it worked well once, the answer is there someplace. But if it was always crap...
pbreed
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Re: A slightly differnt A/C system

Postby pbreed » Tue Aug 29, 2017 2:55 pm

There are people that say the electric A/C works fine.

There are also people that have similar issues....

This is complicated by the fact there are two different electric A/C systems.

When the motor test comes back with results I'll make a decision....

There is a 9K STC to switch from Electric to engine driven compressor, alas 75% of the people
that have done this say there are too many connections in the engine driven system and its
always leaks. The engine driven system is a R134A system so not holding a chagre is not as big a deal as
134a is readily available.

Since the A/C is placarded Day VFR only, I'm looking into what it would take to get a 337/approval to replace the
old brushed motor with a BLDC motor system that would automatically limit current.

The compressor draws 45A and the Condenser Blower 12A. I think both would benefit from modern BLDC conversion....
I got a quote from a company that makes modern A/C system for aircraft of $45K to STC and install one of their systems....
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bohica2xo
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Re: A slightly differnt A/C system

Postby bohica2xo » Tue Aug 29, 2017 4:52 pm

Some of the BLDC stuff I have looked at was pretty sketchy. What sort of motor are you looking at?

That motor is placarded at 52 amps & 1.5 Horsepower. If you were expecting 45 amps you will never see that with full output.

If I was going to jump through the 337 hoops for a new motor I would probably move up to a 2hp unit with a known track record like this:

http://www.globalindustrial.com/p/motors/ac-motors-2-phase/dc-motors/motor-zls56cz-tefc-1800rpm-c4d18fk6a

Use a standard iron pulley in the right diameter. Far better than the tiny pulley on the motor now. Lower motor speed, more belt wrap. Less belt wear & slip.

Unless you can find an identical aircraft that has had a motor replacement under a 337, and go for "Approval by Examination of Data Only" by duplicating the modification...
pbreed
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Re: A slightly differnt A/C system

Postby pbreed » Wed Aug 30, 2017 6:00 am

The motor you quote is 42lbs.
The motor I'm trying to replace is <15lbs....

I have not found one of similar weight that was not brush-less...

The other possibility I'm looking at is replacing the whole assembly with a
a "hot" box out of a G8 Airvan airconditioner system. not PMAed, but on the TC for a certified aircraft.
It would fit in exactly the same location and has a modern sealed brush less compressor...
Its also probably about 10lbs lighter than what is there.

i have preliminary understanding with the FSDO on this, and have prepared a data package for 337/review.
Just not sure I want to spend $10K to make a one off odd ball system.

If I can make the existing system work that would be ideal.
So in a few days I should know if the existing motor is up to spec or has issues...
pbreed
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Re: A slightly differnt A/C system

Postby pbreed » Wed Aug 30, 2017 6:02 am

yes the motor is placarded at 52A.
The aircraft maintenance manual says it should be running at a max of 45 A
(Implies running at less than full load as a conservative design should)
Mine is more like 60A
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bohica2xo
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Re: A slightly differnt A/C system

Postby bohica2xo » Wed Aug 30, 2017 9:33 am

You could install one of these units:

https://www.seanhylandmotorsport.com/SHM-Electric-Air-Conditioning-Compressor-6613

But I doubt the FAA would make it easy...

A 15lb 1.5 horsepower motor will always have issues with lifespan.

So what BLDC stuff are you considering?
pbreed
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Re: A slightly differnt A/C system

Postby pbreed » Wed Aug 30, 2017 1:21 pm

That compressor looks identical to the compressor in the GA8 Airvan hot box I mentioned earlier.

That would be the technically correct solution to this whole problem.

As for BLDC I'm workign with a gentleman that does custom BLDC for Military UAV systems. ecerts and all of that, jsut not FAA aproved. Finding a controller with any EMI data is harder. The motor is the easy part.
ice-n-tropics
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Re: A slightly differnt A/C system

Postby ice-n-tropics » Mon Sep 04, 2017 7:49 am

One concern is excessive oil quantity would increase running torque and reduce refrigerant mass flow.
I was involved in copter application of scroll compressor where weight and el motor torque limits immediately rule out the 2 banger. Personally, I'd reduce weight 60% and increase isentropic efficiency from 50% to over 90% be installing a scroll and installing the shaker device to my boat anchor (Increased cooling vs. HP)
A serpentine belt verses a single vee belt is worth 2 to 3%.
hotrodac
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bohica2xo
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Re: A slightly differnt A/C system

Postby bohica2xo » Mon Sep 04, 2017 10:42 am

Ice, this is one application a scroll would be good for. Constant speed drive.

Is there a scroll small enough to actually work at 1kw of shaft input? Because that efficiency only happens if it spins fast enough.

I dealt with AstroFlight stuff in a UAV. The 100khz square wave motor control noise found it's way in to both the uplink receiver & the downlink transmitter. The solution was separate batteries for power & radios - not an option in this case. A 50 amp choke will weigh a lot.

B.

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