Master Left ON - Question about Charging

[rolivi]

The operator I rent from when I need extra seats has a strict replacement policy when this happens. I discovered it once because the Hobbs was off by 23 hours and then no juice during preflight checks.

Not sure if trickle charging it and then flying it would be acceptable. As Walt mentioned taking off and using the alternator to charge it doesn't sound right.

Minimum... full charge and test before flying with it. Better to replace it. That's what? Half a tank of 100LL. You are worth it

[erich weaver]

Originally Posted by Sam Buchanan

Yep, I ran the engine to charge a flat battery and saw the poor little 30 amp alternator putting out 49 amps in an attempt to refill the dead battery. The alternator was dead within the hour....

Charge the battery before starting the engine.

Not an expert, but I am skeptical of this. I seem to recall from my Aeroelectric Connection education that alternators are incapable of putting out much more amperage than they are rated for (unlike voltage, where a faulty alternator can result in runaway voltage).

Any others with more knowledge than me care to comment?

erich

[rzbill]

Originally Posted by erich weaver

Not an expert, but I am skeptical of this. I seem to recall from my Aeroelectric Connection education that alternators are incapable of putting out much more amperage than they are rated for (unlike voltage, where a faulty alternator can result in runaway voltage).

Any others with more knowledge than me care to comment?

erich

In systems with external regulator, the regulator is part of the above equation, meaning that if the regulator will put out more field voltage than the alternator is "designed" for, the alternator will at least temporarily put out higher amps than rated. Since there is a mix and match arrangement for these two components in HB craft, I could see this happening easily.

For internally regulated alternators, it could be that the field voltage is limited in some way by design to ensure only rated output but that is simple speculation on my part.

[Sam Buchanan]

Originally Posted by Sam Buchanan

Yep, I ran the engine to charge a flat battery and saw the poor little 30 amp alternator putting out 49 amps in an attempt to refill the dead battery. The alternator was dead within the hour....

Charge the battery before starting the engine.

Originally Posted by erich weaver

Not an expert, but I am skeptical of this. I seem to recall from my Aeroelectric Connection education that alternators are incapable of putting out much more amperage than they are rated for (unlike voltage, where a faulty alternator can result in runaway voltage).

Any others with more knowledge than me care to comment?

erich

The engine monitor was displaying 49 amps. It came back down to a lower level in a short period of time but I suspect the very heavy initial load is what killed the externally regulated alternator.

[BobTurner]

Odyssee claims their batteries are capable of recovery from deep discharge, But, the charging current must be carefully regulated - not likely from an aircraft alternator.

[dynonsupport]

Originally Posted by erich weaver

Not an expert, but I am skeptical of this. I seem to recall from my Aeroelectric Connection education that alternators are incapable of putting out much more amperage than they are rated for (unlike voltage, where a faulty alternator can result in runaway voltage).

An alternator is rated for X amps at it's rated voltage. When you battery is dead, it is at a lower voltage and thus the alternator will put out more current. This is just basic ohm's law, where the voltage differential is higher and thus the current is higher. You do eventually run into magnetic saturation, but that will depend on a variety of factors so it's not unexpected that you could do 1.5X rated current into basically the dead short of a discharged battery.

This doesn't mean that the windings, diodes, etc are happy with this additional current though.

Years ago a Diamond DA42 crashed when both engines failed on takeoff. The batteries had been discharged, it was jumpstarted, and then flown. When the pilot retracted the gear, this was enough electrical draw to overpower the alternators, and the engines stopped because they needed electrical power to run (Thielert Diesels). So if you do ever jumpstart or hand prop a plane, make sure the flight you are about to take requires *no* electrical power to do safely or you may be in for a surprise when your overstressed electrical system goes on vacation.

--Ian @ Dynon

[Canadian_JOY]

Originally Posted by BobTurner

Odyssee claims their batteries are capable of recovery from deep discharge, But, the charging current must be carefully regulated - not likely from an aircraft alternator.

Having discovered the battery in my wife's Miata was flat, I thought I'd recharge it. We've got an intermittent low-current load that will draw down the battery during winter months when the car isn't being driven. The battery is a PC680. It has responded very well to a 10 amp recharge current from a not-so-smart charger. After two weeks of sitting, the battery had retained its charge and is cranking the engine with ease.

No, I don't plan on testing this again - I AM planning on installing a battery cutoff circuit in the ground wire to ensure we don't discharge the battery again next winter.

[KatieB]

In our experience with many individual Odyssey batteries in many different airplanes, they're pretty hit-and-miss when it comes to recovering from a master left on. Sometimes they do, sometimes they don't. If it happens, we usually try charging them overnight and see if they come back to life.

That said, if the engine depended on battery power, I would replace the battery immediately. Not worth taking the chance! (I wouldn't fly in an airplane that required battery & alternator power to run even with a new battery, but that's just me...)

[Greg Baron]

Most certified aircraft have small-even D cell packs- to provide a current to excite the alternator. Should our amateur craft have something similar?

[chrishalfman]

....since it was brought up, here's Odyssey's take on a deeply discharged battery:

http://www.odysseybattery.com/docume...gedODYSSEY.pdf

I completely killed mine at Oshkosh last year (master on). Took it to the emergency repair station, put it on a charger for a couple hours, got it to hold voltage under a load, got the plane to start, and increased voltage all the way back to Omaha. Luckily it has never missed a beat since. Does worry me a bit about the alternator. I'll see what happens.

YMMV

BTW-I ran around like a mad-man when the battery was on the charger looking for a replacement. Spruce had several PC680's on hand at their booth. In the event you need one during Air Venture. :-)