wanttaja@ssc-vax.UUCP (Ronald J Wanttaja) (11/20/84)
An interesting occurence: A week ago, I went out to fly my 1965 '150, and the battery was dead. I had flown it two weeks earlier, starting it with no difficulties. I jump-started it, and noticed a good rate of charge on the ammeter (why do we call it "ammeter" when it is an "amp-meter"?). Therefore, I assumed the problem was in the battery. I pulled it out, took it home, and put the charger on it. It charged up normally, and held the charge for the rest of the week, sitting on my workbench. I shrugged off the problem, assuming I had left the master on the previous time I had flown it... although I was sure the switch was OFF the day I found the battery dead. Yesterday, I installed the battery, and everything worked fine. I flew a couple touch-and-goes, then landed and shut it down to wait for my wife to pick me up. I sat in the cockpit, as it was raining a bit, and read the logs to determine how old that battery was. As I was reading, I listened to the gyros winding down. Suddenly, it hit me- the noise was now INCREASING in pitch. I looked, and the fuel guages were coming up, just like the power was on. The master switch was pushed in (off position). I pulled it out (to on) and pushed it back in again, and the guages dropped, and the gyros wound down again. I reset the clock to 12:00, and nothing else occured before I left. I went back today at noon, and the battery was dead... again. The clock had stopped at 4:00, so it took either four hours or sixteen hours to run down. I'm suspecting the master solenoid, but a "Fail on" from the off condition seems a little far-fetched. Does anyone have any ideas? Could the master switch itself be bad? Is there some other route that could apply power (My owner's manual doesn't have a wiring diagram)? Does it need an exorcism? Where's Bill Murray when you need him? Ron Wanttaja (ssc-vax!wanttaja)
oscar@oakhill.UUCP (Oscar Strohacker) (11/29/84)
YES, RELAYS DO FAIL
or
CLEAR PROP BEFORE TURNING ON MASTER SWITCH
The original comment was that the power sometimes stays on with the master
off, and the battery discharges.
I had a 79 Cessna Aerobat 152 in which two relays ("contactors") failed in
a 4 year period after it was new. Both failed in the on state. One was a
starter relay and one the master relay. The parts are similar if not identical.
The first time was during an annual inspection. I wasn't there to see it,
but apparently the master relay failed inactivating the master switch,
and the A & P created a short while working on the starter. In the time
it took him to disconnect the battery, it and starter were destroyed.
It cost us > $800 for a new starter, battery, two relays, labor, etc.
The second time, about a year later, I was sitting in the cockpit with the
window open, saying goodbye to my brother standing next to the door.
I flipped on the master to check the fuel guage, and the prop started
cranking just a couple of feet from him! This time it was a shorted
starter relay.
I sawed open one of the stuck relays with a band saw, and the copper
contacts were sort of pitted and fused as if they had welded themselves
together by sparking when closing. I inquired about getting the kind
of relays that Cessna uses on its twins, and they were over $200 apiece.
Cheap transpo, huh?
oakhill!oscar
Oscar Strohacker (Commercial-Inst/ASMEL)
Motorola MPU Design
Austin, Texas