What may cause this type of electrical failure

[rapidshot]

Below is the brief summary of the failure , aircraft type LSA, EV97

Startup: as usual, no evidence of weak battery, actually it was new, 50 hours of use, voltmeter between 12.7 and 13.8 depending on the rpm, charging is normal,

1 hour flight: no traces of any failure, no rough engine, no loss of comm transmission power, all gauges are good

Landing roll: as the throttle went into idle, garmin 430 began blinking and shutdown itself , screens running on backup batteries, gps system failed, transponder failed, voltmeter turned into red and displayed zero value,

Restart attempt. Everything was dead, battery was empty

[this is my username]

If it's not the battery then try the voltage regulator - they have been known to fail.

Before you start swapping bits over, connect a meter up to the aux power socket (cig lighter) or similar, get the engine started and see if you have about 13.8v with the engine running at various rpm settings.

[darkroomsource]

You mention charging at startup, then flew for an hour, did you happen to look to see if it was indicating charging during the flight?

It seems to me that the engine was not charging the battery sufficiently during the flight, so you were draining the battery the entire flight (or much of it).
When the RPMs were reduced for landing, you stopped getting enough power from the charging system, and hence the electrical equipment all started to quit.

I would suggest the regulator between the charger and the battery, as it may not be allowing enough power through to the battery.

In other words, the charger may be outputting enough, but the battery isn't receiving it.

[rapidshot]

At this point a question comes to my mind,

If the battery is not charged, say 1 hour, what is draining the battery to empty it to zero voltage , if i am not wrong the system is directly fed by the engine,

If the question is found to be very simple please forgive my ignorance,

Can a mulfunctioning regulator corrupt the chemical structure of the battery and empty it in a sudden, is this possible as well?

[Lightning Mate]

It's also worth bearing in mind that most modern aircraft are fitted with an AC generator and feed the DC bus through a TRU.

A fault in the latter can cause many problems, but, being solid-state, they are usually reliable.

[this is my username]

At this point a question comes to my mind,

If the battery is not
charged, say 1 hour, what is draining the battery to empty it to zero voltage ,
if i am not wrong the system is directly fed by the engine,

If the
question is found to be very simple please forgive my ignorance,

Can a
mulfunctioning regulator corrupt the chemical structure of the battery and empty
it in a sudden, is this possible as well?


If the regulator has failed / is failing then the battery wouldn't necessarily be fully charged at the start of the flight.

You are the running your starter motor, lights/strobes , GPS, transponder, radio, aux fuel pump etc etc.

I have had exactly the sysmproms you describe from a failed voltage regulator.

Before you swap the regulator it is worth checking that the connector on the regulator hasn't melted and the spade connectors on the regulator are clean. If you have the regulator with the connector on the bottom and the fins facing towards you, then in my experience it is the second pin/spade from the left which can poverheat / arc / melt the connector.

[ShyTorque]

Bear in mind that when the engine is running the normal electrical load is served by the generator. Any extra ergs charge the battery.

If you lost all power with the engine running then it's probably not primarily a battery fault.

[Fieldhawk]

Unless I have missed something, I have not yet seen reference to an ammeter. A centre-zero ammeter installed in the battery line (but not including starter motor loads) will give you a true picture of battery charging / discharging. As has already been said, if the sum of the running loads exceeds the generator output (amps), then the battery will take the load. Some hint to this appears in the reference to the 12.7V, this represents only 2.12V per cell - hardly enough to produce a charge. The other thing to install is a bus bar low volts warning, a light that will come on when the bus bar voltage is 13.75V or less. Start by measuring your loads (one at a time), sum them, and look at the generator output (in amps).Good luck!

[phiggsbroadband]

Hi, If your plane has an alternator, there is a common misconception that the regulator controls the main flow of alternator current....
What it actually controls is the supply of current to the field windings of the alternator, about 0 to 2 amps max. The alternator output is wired directly to the Battery and can supply in the order of 60 Amps.
Looks as if the alternator is not producing any current, or you switched it off from the master switch, or a loose connection did the same thing.

[Zulu Alpha]

My bet is that the alternator or regulator failed, or partially failed. Maybe just as you took off ie after your initial checks. Flying around with a load of avionics etc on drained the battery.

I had exactly the same thing happen. I now check the battery voltage after start and make sure it goes up when I switch the alternator on. In my case it was the regulator that failed.

Recharge the battery

Measure the battery voltage when recharged.
Run the engine and switch everything on and see what the voltage has dropped to.
Switch on the alternator and check that the battery voltage goes back up a bit.
You may need to rev the engine for this. If it doesn't go up then the alternator/regulator isn't working.

[cockney steve]

"12 volt" Battery (Lead-acid) SHOULD have 14.2 volts.

13.8 would suggest that load is greater than DELIVERED output.

As has correctly been stated, the regulator on an Alternator system, controls the "field" (as in magnetic) current.

An Alty is , effectively an inside-out dynamo without automatic rectification...the clue's in the name - ALTER nating current the STATOR (fixed carcass) carries the generating windings, the ROTOR has 2 slip-rings and a smallish winding....the sliprings (cylindrical, or end-face( centre-spot surrounded by a ring)) carry the field-current from the regulator, which , in turn is often arranged to deliver this via the "ignition warning light"....
the stator is normally wound to produce 3-phase (in essence, 3 separate generating coils around the same rotating magnet)

This is usually rectified by a diode-bridge and connected straight to the battery.....current CANNOT back-flow as the diodes are "one way valves"
Conveniently, the starter usually has a lead straight from the battery to the pre-engage solenoid and this makes a close-handy junction to fix the alty output to.

I f a phase goes down, (diode or winding U/S) the others will put out ~10 volts....usually enough to sustain non-voltage-sensitive-loads, but as revs drop, so does output!

If a warning -light is fitted, this will glow DIMLY until the battery depletes to the same voltage as the output.

I, personally , don't see the point of electro-mechanical regulators

A previous post has pointed out the terminals can corrode and this , together with undersizing , can cause burning, high resistance and all sorts of problems.


DO NOT RELY ON THE ALTY TO RECHARGE A FLAT BATTERY -IT WON'T

When charging commences, the battery-plates take a surface-charge which soon hits the requisite 14.2V.... charging slows/stops....this is to ensure that overcharging does NOT electrolyse the water-content into Oxygen and Hydrogen....unfortunately, to deep-charge a battery, you need to keep "pushing in" a higher voltage to get a current ~10% of the total battery capacity.....when it's fully charged, it will "gas" freely, though some bubbles will be produced during normal charging and can be heard rising if you tilt the charging battery and level it again.

In summary....look for 14.2V at the alternator output terminal
if it has a separate Reg. check the terminals and wiring.....DON'T FORGET some designs have the warning-lamp in series with the Field....blown bulb = no charge (well, a big one from the engineer!)

OCCASIONALLY a "full-field" fault can occur and then the output runs away,boils the battery dry save some neat Sulphuric at the bottom...so check the levels, acid will spray everywhere and stink if this happens.

sometimes ,you can get away with refilling with distilled/de-ionised water and rebalancing the acid concentration, but usually, it's curtains for the battery.



PHEW! :8 here endeth the lesson!

[smarthawke]

The Rotax 912 only has a 20 amp alternator as standard - integral installation. An external belt driven 45 amp item is available.

I use to fly a Tecnam P2002-JF and after an hour in the circuit in 'poor' viz with nav lights, strobes, landing light (all non LED), GNS430, transponder and electric fuel pump on, we had the same situation with the 430 blinking off line when taxying in. The next day the battery (effectively a motorcycle battery) was flat, obviously drained whilst supporting the load.

Working things out afterwards, a standard non-LED landing lamp will draw 10 amps all on its own. By the time you add all the rest of the kit it is easy to see that the standard alternator cannot cope with what would be a normal load on Lycoming powered (65A alternator) machines. Have a look at a load sensing ammeter in a PA28 and see what load the alternator is putting out.

On the RV-12, we carefully calculated what the max load would be (a bit like Apollo 13....) before deciding on the final fit.

The other problem that can be encountered with the Rotax is looking after the voltage regulator. With the lighting kit on the RV-12, Van's supply a cooling shroud and blast tube for the regulator. Without this it will fail after a lengthy period of high load. The regulator did fail on the Tecnam after around 200 hours - it did not have a cooling shroud.

[Zulu Alpha]

FYI

The battery voltage (with no load) gives you a good idea about the state of charge. As long as you haven't recently charged or discharged it you should get these voltages at 25 degC:

12.8v is 100%
12.2v is 50%
11.8v is 20%

[Lightning Mate]

Battery condition is more accurately checked "on load".

[Agaricus bisporus]

A loose battery connection can do that.

The clue is that all was well while the alternator was running at speed but as soon as revs went to idle the flat battery couldn't take the load. For some reason the Alt is producing enough power to run the systems but either there isn't enough surplus to charge the battery or it isn't getting through to the bat. Alternators usually work or don't work so it probably isn't the Alt.

Have you checked the belt?

[smarthawke]

There is no belt on the Rotax 912 unless it has the optional external alternator which is unlikely on the EuroStar. The standard alternator is integral.