Air Conditioner from GPU

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VickersPilot
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Re: Air Conditioner from GPU

Post by VickersPilot »

CFIDave, perfect. It appears now established that the base GPU can run the the AC for short periods on the batteries and longer periods if plugged in. Therefore, we can say 28vdc is not required to run the AC.

Thanks all for the feedback.
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Re: Air Conditioner from GPU

Post by CFIDave »

I just checked the user manual from the Best Tugs website -- apparently they've changed the built-in GPU, plus they also confusingly show an External charger. So if you bought a new B8 tug, the GPU probably doesn't look like the one I have shown above.

The latest B8 user manual specs table shows a maximum continuous current draw from the GPU of 56 amps @ 28V.

This might be adequate for powering Diamond's RACC unit. Years ago I flew a DA42 TDI that drew only 55 amps total from both engine alternators (there was no 3rd AUX power alternator installed with that plane's retrofitted non-Diamond air conditioning), when running the plane's G1000 and air conditioning on the ground on a very hot humid day in Houston.

Diamond's factory-installed RACC unit is not very powerful, so my guess is that it probably doesn't draw more than about 50 amps. The RACC compressor is a US-made Masterflux unit with model number SIERRA03-0982Y3. If you look at the spec sheet for this unit, it shows a maximum draw (at 55 deg C!) of only 37 amps (see page 6 of .pdf):
https://www.masterflux.com/userimages/S ... _SHEET.pdf
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ultraturtle
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Re: Air Conditioner from GPU

Post by ultraturtle »

Davestation wrote: Mon Jan 04, 2021 12:56 am ...50A is not quite enough to run the AC on top of the avionics iirc, which is what many portable GPUs are...
RACC Air Conditioning is completely separate from the aircraft's electrical system. It can run with both the Master and Avionics switches in the off position. It has its own master switch which sends power to only the AC system, drawing power only from either the dedicated alternator on the left engine, or external power.
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Re: Air Conditioner from GPU

Post by CFIDave »

ultraturtle wrote: Mon Jan 04, 2021 11:44 pm
Davestation wrote: Mon Jan 04, 2021 12:56 am ...50A is not quite enough to run the AC on top of the avionics iirc, which is what many portable GPUs are...
RACC Air Conditioning is completely separate from the aircraft's electrical system. It can run with both the Master and Avionics switches in the off position. It has its own master switch which sends power to only the AC system, drawing power only from either the dedicated alternator on the left engine, or external power.
When 24-28VDC is applied to the DA62's external power port, it provides power to both the RACC air conditioning and to the G1000 which boots up automatically, regardless of whether the red Electric Master is ON or OFF. Unless you pull G1000 circuit breakers, the Best Tug needs to have enough current to supply both the G1000 and RACC. (The DA40NG doesn't work this way -- you have to turn the key to ON before the G1000 will run off of external GPU power.)
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