Hi,

I came across the following question in the PPL sample examination question on the CASA website:

"During flight, a centre-zero ammeter shows an abnormally high positive reading for an extended period of time. The correct interpretation of this is that -"

My understanding is that if the ammeter is reading positive, the battery is charging, and negative if the battery is discharging. What is it most likely to mean when ammeter is reading a high positive reading for an extended period? My thoughts were that it's a battery problem(i.e. it won't charge) but, I found an answer to the question on some website that said "Voltage Regulator damage -> too much current into the battery", could it not be either?

Thanks

Hi there,
Yes, it could be either!

It could be the battery if it is weak or dying. In this case, the Voltage regulator will limit the rate of charge to the battery to its preset maximum so it can do its job of protecting the rest of the electrical system from overcharging. Therefore, the indication should'nt be abnormally high as described in the question. It would probably occulate around quarter to mid scale with the strobe flashing or other electrical equipment working with a recharge in between.

If it is an abnormal high and steady or high and continually climbing to full scale, it will most likely be a failure of the Voltage regulator. That fast spinning Alternator at cruise power setting will be pumping that electricity into the system like there's no tomorrow. Left unchecked it could boil the battery and possibly spill acid and cause overheating of electrical wiring, damaging the electrical system (think retractable undercarriage ) or even cause a fire.

This is why we have either separate battery and alternator switches (like on the older types) or a split switch so we can isolate the alternator if need be.
Also, it's good airmanship to include the Ammeter with the rest of your engine oil/fuel checks while flying. It only takes a glance.

Hope this helps.

Cheers and Merry Xmas!

Mister W.

Thanks Mister W, that definitely helps. It was the "abnormally high" bit that was getting me, but the voltage regulations makes sense after some explanation.

Have a good Christmas.