scottfromiowa Posted October 10, 2010 Report Share Posted October 10, 2010 Glad everything worked out O.K. Can't blame you for your decision. I am a VFR pilot and only occasionally fly at night. That said I commonly run strobes, both coms, portable GPS and HID landing light as well as GEM, Transponder, boost pump...The HID light just doesn't draw much amperage. No issues even with an older (two 1/2 year old battery) out of Class C Cedar Rapids... How old is your battery? Do you have an HID landing light or sealed beam/quartz. The difference in draw is amazing between the two. Quote Link to comment Share on other sites More sharing options...
scottfromiowa Posted October 10, 2010 Report Share Posted October 10, 2010 I have an Ei voltage indicator so I know EXACTLY what the amperage draw is from each piece of electrical in the aircraft. The old Sealed Beam landing light was an inefficent HOG. Quote Link to comment Share on other sites More sharing options...
Kwixdraw Posted October 10, 2010 Report Share Posted October 10, 2010 Quote: danb35 Not so. According to Klixon, at 25 deg C, the minimum current for the breaker to trip is 115% of its rated capacity; maximum is 150%. At 71 deg C (160 deg F), the breaker can trip at as low as 90% of rated capacity, but I don't expect any of us fly our planes in 160-degree ambient temps. I expect other manufacturers may have different performance characteristics, but I can't see any sense at all in a 50-amp-rated breaker that trips (and is designed to trip) at 40 amps. Quote Link to comment Share on other sites More sharing options...
danb35 Posted October 10, 2010 Report Share Posted October 10, 2010 I don't believe it's correct that the FAA expects a breaker to trip at 80% of its rating, though I'd be interested in seeing an FAA publication to the contrary. I do understand, though, that they expect that continuous loads on a circuit should not exceed 80% of the circuit's capacity (i.e., continuous loads on a 20-amp circuit should not exceed 16 amps)--might that be what you're thinking of? If your understanding is correct, then the Klixon 7274 breakers (which are ubiquitous in aircraft) are grossly off from the FAA's specs, or their published technical data is lying. Quote Link to comment Share on other sites More sharing options...
takair Posted October 10, 2010 Report Share Posted October 10, 2010 FAA guidlines are that the total load should not exceed 80% of the charging capacity, under continuous load. Circuit breaker size is to protect the wiring. A 70amp breaker should trip at it's rated capacity, within the tolerance established by the manufacturer. AC43-13 has details of both. Basically, for a 70amp alternator, your continuous loads should not exceed 56amps. A breaker that is on the lesser end of tolerance might trip at 63 amps based on the spec quoted above, but that would need to be a continuous 63 amps or more. Loads not concidered continuous might be flaps and gear. This 80% rating allows for some margin for these additional short term loads. Quote Link to comment Share on other sites More sharing options...
Gone Posted October 10, 2010 Report Share Posted October 10, 2010 Quote: scottfromiowa ... How old is your battery? Do you have an HID landing light or sealed beam/quartz. The difference in draw is amazing between the two. Quote Link to comment Share on other sites More sharing options...
craigsteffen Posted November 25, 2010 Report Share Posted November 25, 2010 RE edgargravel: Taxiing on the ground in Montreal for over 40 minutes at relatively low rpms. JPI was reading as low as 11.2 at one point. No problem. Been there before. I realize that this is water under the bridge now, but just adding to the discussion for the sake of future thread readers: If your electrical bus is at 11.2V, then your battery is pretty seriously discharging. 40 minutes of that and your battery was probably mostly dead. Any time the voltage is below 12V the battery is discharging, which is Ok for a couple of minutes but very bad for a long time when you're going to be taking off. Quote Link to comment Share on other sites More sharing options...
Jerry 5TJ Posted November 29, 2010 Report Share Posted November 29, 2010 More food for the run-on topic... In the middle of annual inspection, I found the generator bracket was loose. I took the generator out to get at it. Man, it is heavy. But, I found an FAA cert. shop who will rework it for a modest fee. Mind you, it has been working for a long time, the logs are mum on just how long, but while I have it out might as well get it checked, new bearings and new brushes stuck in, I figure. I did the alternator upgrade on my previous Mooney. It did indeed start charging at a much lower RPM. BUT, to add more info to this thread -- on THIS Mooney I replaced the Delco mechanical "regulator" with a Zeftronics unit, and THAT also improved the charging performance. I'd say a generator with the Zeftronics controller is a good half-way step -- it starts charging the battery at about 1400 RPM. The Delco + generator duo would not come on line (and start charging the battery) much below 1800 RPM. The alternator was better yet, it would start charging that battery at 1200 RPM. I also note that the generator is rated to 50A, which is more than I need. The more I upgrade the plane, the less current it pulls. The old landing light sucked 20 amperes, the new LED lamp is a third of that. The old (tube type!) radios pulled 10 amps, the solid-state King and Garmin units about a third of that total. Only the pitot heat current drain is the same as when the bird left Kerrville 45 years ago. So, who needs 70A? (me, in a Meridian, but that's another story) Quote Link to comment Share on other sites More sharing options...
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