I was just flying with a friend who had a 1 amp breaker, installed by
the glider factory, protecting a fancy LXNav flight computer. Manual
said current draw was 700 ma. Unfortunately the breaker was popping
frequently at the end of long flights.

Manual for the LXNav recommended a 3 amp breaker. It probably draws
more current at low voltage, I assured him a 3 amp breaker would be a
fine choice.

No sense trying to use the tiniest fuse or breaker you can, just use
something appropriate to protect the wiring. Breakers are great for
airline pilots who like to have lots of buttons to push.




On 7/15/19 1:48 PM, wrote:
I always try to size the fuse to match the expected draw of the device I'm protecting. No idea what an RT-551 radio draws but a Becker 3201 draws a max of 1.4 amps when transmitting (according to their literature, anyway). So, if you protect it with a 2 amp rated fuse then Ohms law tells us that you'd only lose 0.11 volts across the fuse (E=IR or 0.109v = 1.4 A * 0.078 ohms). Negligible. I guess I don't really understand all of the concern over losing 1 tenth of 1 volt across the fuse.

Robert


On Sunday, July 14, 2019 at 1:40:14 PM UTC-5, John DeRosa OHM Ω http://aviation.derosaweb.net wrote:
On Saturday, July 13, 2019 at 11:24:31 AM UTC-5, soaringjac wrote:
Anyone know what fuse rating i would need for an old Edo-Aire RT-551 radio. Its marked inop now but i still want to replace the fuse in the panel for it

Between you, me, and the fence post, I prefer breakers rather than fuses. Breakers are easier to reset while in flight than replacing fuses.

Remember to use a minimum of 3A fuses/breakers or risk loosing precious volts. See page 86 of this presentation http://aviation.derosaweb.net/presentations/#wiring.

John OHM