Air Conditioner from GPU

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VickersPilot
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Air Conditioner from GPU

Post by VickersPilot »

The RACC supplement states the GPU supply to run the AC must be 28v @ 100amps.

Previously, CFIDave mentioned the AC worked off the Best Tug B8 (I'm in the process of ordering one...) and wanted to know:

1) Is the Best Tug basic 24V GPU psu (720 cca at 24V/35ah) sufficient to power the AC or does one need the 28V boost function?
2) What is the realistic power draw for the AC once the start is initiated? Is there soft-start circuitry in the DA62 to flatten the demand spike?

Thank you !
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Re: Air Conditioner from GPU

Post by CFIDave »

FWIW, my Best Tug B8 contains four 12V 35ah batteries inside, so with the batteries wired in series/parallel, the GPU is good for 24V 70ah. It has no problem powering my DA62's RACC unit on the ground.
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Re: Air Conditioner from GPU

Post by Davestation »

CFIDave wrote: Wed Dec 30, 2020 7:10 pm FWIW, my Best Tug B8 contains four 12V 35ah batteries inside, so with the batteries wired in series/parallel, the GPU is good for 24V 70ah. It has no problem powering my DA62's RACC unit on the ground.
70Ah is the capacity, those would probably supply a thousand amps but not for long.

50A is not quite enough to run the AC on top of the avionics iirc, which is what many portable GPUs are. Battery minder makes an odd 75A or so GPU that would likely work but I have not tried it.
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Re: Air Conditioner from GPU

Post by CFIDave »

Davestation wrote: Mon Jan 04, 2021 12:56 am
CFIDave wrote: Wed Dec 30, 2020 7:10 pm FWIW, my Best Tug B8 contains four 12V 35ah batteries inside, so with the batteries wired in series/parallel, the GPU is good for 24V 70ah. It has no problem powering my DA62's RACC unit on the ground.
70Ah is the capacity, those would probably supply a thousand amps but not for long.
Yes, but I can also plug in the Best Tug's power cord into a 120V AC outlet in the hangar while the tug is powering the DA62 RACC unit with 24-28VDC. So while the batteries are powering the DA62 G1000 and air conditioning, they're also being re-charged by the Best Tug's built-in charger. I've run the plane's air conditioning on the ground that way with no ill effects.
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Re: Air Conditioner from GPU

Post by Davestation »

So the real question is what’s the tug’s GPU’s specs
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Re: Air Conditioner from GPU

Post by VickersPilot »

CFIDave,

The standard output of the B8 is 24vdc unless you purchase the additional boost function to raise it to 28vdc. Are you using this feature or straight 24vdc out?

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Re: Air Conditioner from GPU

Post by Chris »

Davestation wrote: Mon Jan 04, 2021 4:44 am So the real question is what’s the tug’s GPU’s specs
Here's a link to the marketing page showing 75 amps max draw.
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Re: Air Conditioner from GPU

Post by Davestation »

Chris wrote: Mon Jan 04, 2021 6:22 am
Davestation wrote: Mon Jan 04, 2021 4:44 am So the real question is what’s the tug’s GPU’s specs
Here's a link to the marketing page showing 75 amps max draw.
Curious what they mean by that exactly. From their manual:
GPU: The Ground Power Unit is used to power your avionics and other lower power demand systems in your aircraft from the standard 110 Vac wall connection. You have 28.5 Vdc at 25/50 Amps. Note: Do not use the GPU to power air condi- tioning or pitot tubes. Warning: bat- tery damage is possible—the GPU should not be used to charge either the tugs or the aircraft’s batteries!
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Re: Air Conditioner from GPU

Post by VickersPilot »

There seem to be three GPU variants:

1 - straight 24vdc from batteries
2 - 24vdc from batteries topped up to 28vdc by mains power (boost function, little silver button with 30 min boost timer)
3 - Straight 28vdc from mains power

I stand to be corrected but AC limitations may relate to the GPU type.
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Re: Air Conditioner from GPU

Post by CFIDave »

VickersPilot wrote: Mon Jan 04, 2021 5:40 am CFIDave,

The standard output of the B8 is 24vdc unless you purchase the additional boost function to raise it to 28vdc. Are you using this feature or straight 24vdc out?
I got my completely "tricked out" Best Tug (it even has blue underglow) 2.5 years ago by winning an EAA Oshkosh fund-raising auction (it was donated to EAA by Best Tugs). So I don't know anything about a "boost function." It has a built-in GPU running off the internal tug batteries that supplies 12 or 24VDC, depending on how the red cable end is plugged in to the tug.
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