The International Cessna^® 170 Association

Here's a discovery I made earlier this year:

One year old battery seems to have no capacity. Charging it up until the battery charger amps drop off to "zero" (indicating the battery is either fully charged or will not accept any further charge).

Then placing a heavy electrical load onto the ship's electrical system (such as in turning on all the landing/taxi lights to adjust their aim at night), causes the entire airplane electrical system to die.

Hmmmmn... Check the battery again.... indicates 12 volts. Turn on the taxi lights.... all is OK, they turn on. Add the landing lights....everything dies. Everything.

Scratch head.

Jump the charger onto the battery AND simultaneously turn on the lights.... same behavior. The taxi lights do fine...but adding landing lights kills the entire electrical system.

Scratch head and check all connections. Now battery won't come online at all.

Check logbooks and discover battery is almost 18 months old. Curse battery that doesn't last as long as previous one did. Order new battery.

Install new, fully charged battery. Turn on taxi lights. Good. Turn on landing lights. Everything dies.

Scratch head. Decide to trace electrical system from battery all the way to ground connections on downstream side of land lamps.

Discover ordinary, common hardware "star" washers beneath nuts used to hold ring-terminals to ammeter gauge behind panel look slightly "powdery" like dissimilar metals. Clean terminals, replace with new plain brass washers.

Try all the lights again.

Everything works as designed.

I had not considered that everything electrical runs thru that ammeter connection except the starter! It's my belief that the common hardware was supplied as original equipment with the ammeter gauge when it was installed about twelve years ago.

(Sure glad this failure didn't happen on a night flight or IFR. Check yours.)

Nice write up, George! Thanks!

I've nearly gave up on my "Fluttering Amp Meter" I mentioned awhile back in the forum, but I now have a new lead to follow....Thanks for the info George....

Also, be advised that even tight connections at the wiring harness can still give poor indications and poor connectivity....INSIDE THE GAUGE! The long "studs" (threaded studs) which exit the rear of the gauge have a nut on them which hold them snug to the case, usually thru a paper gasket. Those studs actually connect inside the case to the "shunt" which carries the real current to the main buss.

Unless those studs are very snug to the case....there can be a poor connection at the shunt, even tho' the wiring harness is tight at the studs. I discovered this when I totally removed a "defective" ammeter once. When the nuts were tightened on the studs, the ammeter behaved perfectly ever-afterwards.