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#11
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#12
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Someone should make a panel display with LED's for all three, and a small digital meter that will cycle between them. ************************************************** *************** Well, that would be a nice gadget, but I do take exception with the need for an amp meter in flight... All the amp meter tells me is which is higher in voltage, and therefore pushing the current at that instant, the battery or the charger - it does not tell me what the state of the charge is... The battery can be at 11.8 volts and the alternator on it's last living diode at 12.0 volts, and you will not show a big discharge on the amp meter, but you are in for deep doo doo, very soon... Give me a good volt meter any day... Luckily, aircraft share the 12 volts with autos, and any auto store will have an expanded scale DC voltmeter that you can plug into the cigarette lighter... Have one of those in the plane and you can quickly verify that the alternator is doing the job or not... None of this waiting for the amp meter to go into discharge to tell you are in trouble - which is way too late - the volt meter will warn you of impending problems long before the battery goes toes up... I have used the voltage reading in the GPS295 as my generator testor for years now... Unfortunately, Garmin did not include that feature on the 296 on my yoke, and now on run up I have to lean over and look at the copilot yoke to check the gennies... There I am, leaning way over to the right, one hand down on the floor flipping generator switches, one eye on the tach, one eye on the GPS295, and if my passenger is young and female, my head between her boobs... Life is tough I gotta tell ya... cheers ... denny |
#13
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"Denny" writes:
Someone should make a panel display with LED's for all three, and a small digital meter that will cycle between them. ************************************************* **************** Well, that would be a nice gadget, but I do take exception with the need for an amp meter in flight But it WILL tell you that both {*}ators are working; not just one. Or than one is doing 90% of the work, and the other 10%, etc. (You can force the issue, to be sure. On the ramp; load the system -- all lamps, electric heat props, whatever. Run up #1 and see what happens. Throttle back and repeat w/#2. You don't need matched regulators to see that both sides charge -- but in flight, I'd rather have.. alternator on it's last living diode at 12.0 volts, and you will not show a big discharge on the amp meter, but you are in for deep doo doo, very soon... Give me a good volt meter any day... On a twin; I'd want two single-ended ammeters, one on each {*}ator. Not the zero center kind that tells you NET gain/loss the battery. Then a good voltmeter on the bus/battery. As for bad diodes; I trust my ears. But ammeters will tell you. Luckily, aircraft share the 12 volts with autos, and any auto store will have an expanded scale DC voltmeter that you can plug into the cigarette lighter... Have one of those in the plane and you can quickly verify that the alternator is doing the job or not... None of With this proviso... that kind of crap [engineering term of art] is notoriously uncalibrated. http://www.its.bldrdoc.gov/fs-1037/dir-001/_0125.htm But so what? You just want REPEATABILITY. Borrow a DVM and calibrate it with your car, if nothing else. Mark the face at oh say 14v, 12v and maybe 15. Then gather experience as you fly. Note, BTW, that even a cheapo DVM typically offers good accuracy; all the magic is the chipset and oscillator. Buy one. this waiting for the amp meter to go into discharge to tell you are in trouble - which is way too late - the volt meter will warn you of impending problems long before the battery goes toes up... Maybe....BUT one side could be all but dead and the other coping just fine...until... -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#14
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As for bad diodes; I trust my ears....
What do you mean by this? That you hear something distinctive when a diode goes out? Do you hear it directly, or is it through your headset or audio system? What does it sound like? -- Thanks! John Clonts Temple, Texas N7NZ |
#15
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"John Clonts" writes:
As for bad diodes; I trust my ears.... What do you mean by this? That you hear something distinctive when a diode goes out? Do you hear it directly, or is it through your headset or audio system? What does it sound like? With all six diodes intact, the rectified DC from the 3-phase AC waveform is reasonably low-ripple. Lose a diode and that takes a chunk out. On a car, you can hear the whineeeeeee change pitch in the radio, esp. AM, as you go through the gears. See http://www.allaboutcircuits.com/vol_3/chpt_3/4.html and look at the "3-phase full wave bridge rectifier" and the waveform below. Now, take away the blue and see what it looks like.... But as a pilot, you are far smarter than Fred Freeway. You can usually tell a bad diode without listening, just by the ammeter readings. Not directly, but rather from knowing your aircraft. Make some tests: run landing lights before approach, and at X rpm, you see Y amps. Make a note. And so forth...If one day, it makes about 30% less current than it normally does, in similar circumstances [i.e. climb-out from your home field, at X rpm, for n minutes..]; be suspicious.... One confort: You'd think that losing one diode would increase the strain on the other 2 and THEY'd soon fail as well. But I've seen 'whiners' that lasted for months. I guess the diodes are usually NOT the weakest link; the ones that fail are not from overheating but other causes [bad bonds, vibration, etc.] -- A host is a host from coast to & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 |
#16
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Just a final comment to repeat my recommendation that every airplane
owner have a copy of Robert Nuckolls book THE AERO ELECTRIC CONNECTION ($33 and worth ten times that in what it will save you in mechanics fees by identifying problems before they are problems) http://www.aeroelectric.com/Catalog/AECcatalog.html and scroll down... It is aimed at the homebuilders, but tons of information any airplane owner can use... Denny 73 de k8do |
#17
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Have had a 1960 PA23-250 for almost 10 years now, love it. Two years ago switched from the generators to the InterAv alternator kit. Feel it was the right decision and am pleased with the results. Reasons for switch: 1) Generators do NOT put out any charging current below a certain RPM, in our case it took 1700 RPM to get any appreciable output, they were calling us the AzJet because we were blowing over the 172s behind us in order to keep the battery up. 2) My partner called me several times to come jump start the plane, he would forget to turn off all unneeded lights and radios while taxiing back and the battery would run down. 3) Went through the trouble about 5 years ago to get the generators overhauled, new regulators and balancing relay, still had balance and charging problems. After the conversion: 1) alternators put out good current at idle, radios operate just fine with engines idling. 2) End of dead battery problems, no more dead battery when opening up the plane. 3) I can taxi around without blowing the 172s all over the place. 4) So far (find some wood) have not had a balancing or charging problem. 5) Generator whine (feedback through intercom) is gone, radio sound is noticeably cleaner. Notes to pay attention to: 1) make sure the black ring (the diode holder) on the back of the alternator does not contact anything, has plenty of clearance around it, else it grounds out through the diode holder and will burn out the alternator. 2) Use the old regulator mount on the aft side of the firewall to mount the new regulator assembly to, stays cooler and cleaner, much neater wiring installation. 3) Absolutely replace the output wires with a #4 guage wire up to the fuselage juction block. 4) Use a #4 guage wire to fabricate the ground bonding wire, make absolutely sure the bonding straps on each side of the engine case to the engine mounts are clean and in good condition. 5) Add an additional ground wire from the regulator to the alternator (solved a balance problem). 6) weigh and track all parts coming off and going on, including wires pulled and installed for form 337 weight and balance changes. (Hint: weigh the wire spool before and after you run it, in order to get accurate weight of what was installed.) I am an A&P in the D.C area, my I.A. and Balto FSDO were watching over my shoulders, the more meticulous I was, the happier FSDO got, and signed off the 337 on the spot. Good Luck -- AztecN867DC Powered by www.flight.org |
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