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Likely the brushes finally wore down to a nub, tilted in the holder and you heard the "ping" as the wires snapped off them as the parts got carried through the spinning rotor.
This is the most common failure on high mileage Hitachi and Denso alternators at least that I've worked on for several decades. In fact, about the only type of failure I've ever seen on them and I used to run an auto repair shop for mainly Japanese brands eons ago. The Hitachi in our shop car had 360,000 km on it when the same thing happened to it. Let's call that around 6000 hours. |
A Data Point
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Skylor |
Apples to oranges comparison
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The description of your replacement alternators failure sounds very much like a shorted stator. Most electronic devices that have a manufacturing defect will fail within the first 6 weeks of service. Most retail Electronics have a failure rate of about 6% during that first 6 weeks. Charlie |
[quote=rv6ejguy;1383599]A few points. If your engine is in proper tune, you shouldn't have to turn it over for more than 5 seconds. This takes very little out of the battery and therefore won't result in very high charge current from the alternator to replenish it in the first minutes.
If you're concerned with too much charge current, keep the engine at idle for a minute or so. A 60 amp alternator will be lucky to produce 30-35 amps at slow idle. My experience differs quite a bit from this. The current generation of alternators (PP and B&C) that I have tested will put out full rated amps at low idle on our airplanes, except the stnadby alternators on the vacuum pad. Even with a very quick start the lithium battery will take a full load for a few seconds, so it is not uncommon to see 60 amps for 10-30 seconds after a startup. I tell new owners of lithium batteries to not be concerned, as it is normal operation. If you've sat there for a while with the power on prior to engine start while you o perform a checklist or receive a clearance, the high amp load will last much longer, perhaps a minute or 2. Usually by the time the runup is completed, the charging output is back to normal, around 20 amps or whatever your wsteady state load happens to be. Vic |
[quote=vic syracuse;1384045]
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Average drive ratio is about 3.9 to 1. Using an alternator test graph I have on my 70 amp ND alternator, it generates 51 amps at 2500 rotor rpm (641 engine rpm). Starter draws around 150 amps for 5 seconds which is 12.5 amp/ minutes. That would mean the alternator would top up the battery in about 15 seconds with no other load on. Nothing is going to get very hot in 15 seconds. You could slow this rate down by throwing on extra load before turning the alternator on. My estimate of of 30-35 amps was based on my installation which has a much smaller pulley ratio than the average Lycoming installation. My bad there. This again speaks to the advantage of larger alternator pulleys, both to reduce bearing and brush wear, and charging rates at idle for more sensitive Lithium batteries. Dropping the rotor speed to 1500 rpm at idle would drop my alternator output to around 23 amps. |
Good information above on alternators and Earth-X batteries. Every airplane has unique electrical systems. I decided to test and log my amp draw at the time of engine start-up. The following is my Hartzell (PP) Alternator, Earth-X battery and Garmin G3X system results:
Airplane RV14-A- ALT Test: Actual AMP Draw for Hartzell/PP (AL12-C60) Alternator - Serial # date code ?S?= 2018 Hartzell date code ?R?= 2017 and later are improved manufacturing process. (According to Hartzell) Battery: Earth-X; ETX-900 (15.6 ah) 13.2 volts; CCA AMPs 400 (4.9 Lbs) Test Date: Nov 4 2019 Airplane Status: hangered for 48 hours (cold) Ambient air temp when started: 70 F Engine Start Procedures Used: ON: TCW ? IBBS-12v-6ah Backup Battery ?(G3X Checklist reviewed, ATIS) ON: G3X Touch GDU 460 screens and GEA 24, GSU 25 ? (120 seconds IBBS) Master- ON for 30 seconds, Strobes- ON; Fuel pump- ON Started Lycoming IO-390 ? Hartzell (PlanePower) 60 amp Alternator amp draw results displayed on G3X: 48 amps ? first 7 seconds, then Alt draw drops to 23 amps for 10 seconds, then 13 amps for 15 seconds. Avionics and AP Masters ? ON ? (Garmin IFR GTN 625, Dual VHF?s, GTX 45R, GMA 245, others). Engine RPMs =1000 - Hartzell/PP (AL12-C60) Alternator Amp Draw - 9 amp load after 2 min. 9 amp load includes recharging: TCW ? IBBS-12v-6ah Backup Battery Add: 5 amps for the Garmin Pitot heat if needed; 3 amps for the Fuel Pump and 2 amps for the LED Land lights. Normal in-flight alternator amp draw is 9-10 amps. (No fuel pump, pitot, defroster or landing lights) Full Amp draw with every switch in the airplane- ON = 22 Amps in-flight at 2300 RPMs. My alternator and Earth-X 900 seem to be a good match for the Garmin G3x IFR panel given the 10-20 amp normal draw. Every airplane is different, I would be interested to see results of other similar electrical systems. |
low voltage regulator to lower charging amps
Is there a simple/cheap external regulator that's 2-stage?
Initially have a lower voltage so that the charging amps (and alternator output) is lower. I suppose you could have 2 (switchable) external regulators. lower voltage could then be a hot spare. |
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