Recommended CB size for ADSB-470/472

[cbretana]

Hkw big of a CB should I use for tbis? Could I use the same (3 Amp) one the SV-XPNDR-261 Transponder calls for?

 

[swatson999]

Power Specifications Approximate current consumption at 12 volts DC Approximate current consumption at 24 volts DC
SV-ADSB-470 0.2 amps 0.1 amps
SV-ADSB-472 0.1 amps 0.05 amps
Table 90 – SV-XPNDR-261/262 Power Consumption

 

[John Bright]

SV-XPNDR-261 and SV-ADSB-472 are on the same protective device per Dynon dwg 103488-000 “Skyview HDX Wiring Diagram - Single Engine”

For the current rev, which is G, ref sheet 4 - Transponder Wiring and sheet 5 - SV-ADSB-472.

Find this document at dynonavionics.com, choose Dynon (not Dynon Certified), Support, Documentation, Skyview System, Installation Guides, SkyView HDX Wiring Diagram

A 3A CB is shown.

Getting off-topic:

• I'm a fuse guy and 5A is the smallest I use to reduce spare parts inventory.
• AFAIK 22 awg is conventionally protected with a 5 A fuse or CB and 20 awg with a 7-1/2 A fuse or CB, This is conservative. 22 awg fuses (melts) at 42 A and 20 awg at 59 A.
• Voltage drop over a long run should also be considered, usually not a factor but sometimes it is, include both feeder and ground return in your calculation.
• Wires in a bundle and high altitude reduce current capacity but don’t over-analyze our small simple aircraft. To repeat, the wire current ratings we are given are conservative to begin with.
• Why not choose smaller than 22 awg for devices that draw less than 5 A… because smaller than 20 awg becomes mechanically fragile and weight savings on our small simple aircraft is negligible. Smaller wires may be justifiable in bundles and cables or where space is limited like to reduce the size of the hole in the control stick so as to not reduce its strength too much; for instance the Tosten CS-8 grip uses 22 awg cable and I imagine its wires have /18 insulation. Purchased harnesses will typically use 22 awg or even smaller. M27500 cables use M22759/18 wires that have thinner insulation versus M22759/16 hookup wire.

 

[cbretana]

Yes, that's the bit I couldn't find... And it makes sense, ADS-B In is not a critical issue, so protecting it, (with a separate CB), in the case of losing the Transponder is not worth the cost of the extra CB.

And 3Amps seems more than reasonable. CB sizes are not specified to protect the component attached to them, they are there to protect the wiring... And if Dynon says 3 Amp is enough ...

 

[swatson999]

The only concern I'd have with putting them both on the same CB is that if the ADS-B faulted and tripped the breaker, you'd lose your transponder as well. ADS-B is not necessary for safety of flight, but a transponder is a pretty important piece of equipment. You might not *need* either one to get you safely on the ground, but I'd sure like to have my XPDR operating in an emergency for the sake of ATC assistance.

Thus, despite what the stock wiring diagram shows, I'd put the ADS-B on a separate 1A fuse or CB.

 

[swatson999]

And 3Amps seems more than reasonable. CB sizes are not specified to protect the component attached to them, they are there to protect the wiring... And if Dynon says 3 Amp is enough ...

It's not that 3A is "enough"...the question is if it's *too much* for the wire size. That is, if the box faulted and started pulling more than the rated 0.1A, and went all the way to 3A for some reason like an internal short, would that 3A be too much for the wire size and cause it burn/melt/etc.?

 

[Carl_Froehlich]

It's not that 3A is "enough"...the question is if it's *too much* for the wire size. That is, if the box faulted and started pulling more than the rated 0.1A, and went all the way to 3A for some reason like an internal short, would that 3A be too much for the wire size and cause it burn/melt/etc.?

I suggest for any avionic power leads you stick to #20 wire. #20 wire will handle a short long enough to trip a 5 amp breaker. Also #20 is not as fragile as smaller gauge wires.

Carl

 

[GKC Aviation]

22AWG wire will carry max 7 amps.
So a very short duration in excess of 3 amps will not harm the wire

 

[swatson999]

22AWG wire will carry max 7 amps.
So a very short duration in excess of 3 amps will not harm the wire

Depending on length, of course.

 

[Rhino]

True, but going from 1 foot to 10 feet is only an increase of .14 amps, so the difference is negligible. I'd still stick with 20 AWG though.

 

[Raymo]

If cost is the issue, install an inline fuse. Sharing a breaker is not a good idea.