DA40 24volt outlet

[DiamondMike70]

The DA40's that I rent have a 24volt outlet on the right side of the instrument panel that is labeled 'ground use only'.

Does anyone know the reason for this limitation for ground use only?

Any problems with using the outlet in flight?

I wanted to be able to keep my IPad fully charged on long flights.

Thanks.

[N143NG]

I don’t know why the limitation, but I always keep an extra battery to keep my I phone and iPad charged.

[Colin]

Many of the "spare battery" units are assembled cheaply and are sensitive to altitude. Fire. Explosion. I am uncomfortable with it.

I tried three times to use that power port on my DA40. I wish I had just had it removed and had the USB power port from MidContinent installed instead. That's what I did in the DA42 and it's fantastic.

[Steve]

I'm not sure of the reason for the "Ground Only" limitation. I do know that the outlet is fused, rather than on a circuit breaker-protected circuit, and that the fuse is in the engine compartment.

[Rich]

I've used this adapter quite a bit over the years with no problems - Garmin 695, 795, Zaon XRX, a tablet PC, and on occasion, providing power to my Stratus II.

[CFIDave]

An issue that may have led to the "ground use only" placard:

Many pilots insert cheap automotive 12V-28V DC to 5V DC USB outlet converters into their aircraft's "cigarette lighter" outlets. While these may work OK most of the time, they have been known to create audio static over aircraft radios and intercom.

A friend of mine just spent $35K upgrading the panel of his Piper Arrow, only to find unacceptable static/noise in his headsets, so he flew the plane back to his avionics installer for diagnosis of the problem. The owner was embarrassed to find that the noise was being generated by his cheap USB adapter.

Separately, you should also be aware that many of the cheaper USB adapters don't supply enough current at 5V to keep an iPad charged. If you use one of these adapters, you might want to purchase from an aviation-related supplier like Sportys or Aircraft Spruce where these devices are expected to work well with iPads.

[Steve]

Possibly, but my 2001 Star has the same placard. USB cigarette lighter converters didn't exist back then (or at least were uncommon), plus the outlet in my panel is a different type, which requires a special plug.

[CFIDave]

Possibly, but my 2001 Star has the same placard. USB cigarette lighter converters didn't exist back then (or at least were uncommon), plus the outlet in my panel is a different type, which requires a special plug.

I think the issue is that ANY type of electronics plugged into the "cigarette lighter" power outlet could potentially generate electrical interference or inject electrical noise into the aircraft's electrical system. Electrical noise could potentially flow back through the various 28V busses to affect radios or other avionics systems (as in the USB adapter example I cited earlier).

[Steve]

Possibly. There are a lot of aircraft that have these type of outlets. I'm not aware of any that have a similar prohibition against in-flight use.

[Rich]

I think Dave's point is correct. Allowing any-old-unpredictable-thing to be attached to your electrical system when every single other device on the power bus is certified could be considered a compromise to the integrity of the electrical system. Whether other manufacturers choose not to consider this a potential problem is irrelevant. Most of the GA aircraft in the sky today are either experimental or are leveraging type certificates originating in the 1960's or earlier. An era where radios and electrical systems of the era were crap anyway

And we have found from experience that there are in fact devices that cause electrical noise problems when plugged into this port.