Mystery Battery draw

[seebruce]

I've had a dead battery the last two times I went to fly my plane. I checked everything and the only thing that I could find drawing any power was the electric clock which I don't think would draw the battery down so quickly.The first time the plane sat for about a week and a half, The second time for about tree days. The first time it happened I checked the fluid and recharged it. The second time I started it with the external power cable and flew it for about an hour. The amp meter showed good charging and by the end of the flight it showed little charging as I would expect with a fully charged battery. I then checked the battery with a load meter and it held up fine and showed full charge. I then disconnected the battery from the plane and checked it three days later and it was still fully charged so I don't believe the battery is the problem.

Anyone have any thoughts on what could be causing this.

[hansel]

Baggage door light on? --the bane of many Mooney owners. Not sure if you have an auto-shut off (or maybe you've had it removed all together).

[seebruce]

First thing I checked.

[Rustler]

Have you checked the overhead-light switch to make sure it isn't on? It is very difficult to see if the interior lights are on in the daylight. I had a passenger accidentally turn mine on, and, of course, the battery went south.

[Piloto]

Disconnect the + battery and connect in-line between the battery and the aicraft cable terminal a digital voltmeter capable of reading current (amps). Set the voltmeter to amps and master off. Anything above 0.2 amps will discharge the battery totally in one week. At the master relay on the battery side there is one wire with a fuse used to feed the clock and overhead lights. If you have a current reading higher than .050 amps disconnect this wire. If the current still high check for corrosion on the master relay. Corrosion on the master relay will cause current leaks thus battery discharge. On the M20J the master relay is next to the battery box.

José

  

[seebruce]

Thanks Jose, I try that tomarrow.

[Jeff_S]

Bruce, have you had any success with this? I am also having a mystery battery draw that just seems to sap the battery faster than one would otherwise expect.  Today I went out after only about 10 days off and as soon as I turned on the Master I got the low-battery alarm which I think is coming from the JPI.  And the starter cranked very poorly, although it did ultimately start the engine.

This all started not long after I got the plane, when after a two week lay-off the battery was totally dead. It was a three year old battery so it was reasonable to suspect that it had just lost its mojo. But now I'm seeing similar behavior (although not totally dead) with the new one. Also, when we put the new one in I started getting a weird pulsing ammeter which subsequently disappeared all on its own after the A/P futzed around just checking all the connections.

It clearly seems like there's a bad ground issue somewhere, but we've cleaned off the Master switch and don't know where else to look (maybe the master relay next to the battery?). The prior owner had a Battery Minder attached, and even though I'm just on a ramp I've left those connections hooked up. Could that be causing some type of draw even though it's just the cables that go out to the baggage area and aren't attached to anything?

[scottfromiowa]

Anybody switch to the maintenance free sealed battery?  I did and 1.5 years later am glad I made the switch.

[Ned Gravel]

Scott:

 

I switched to the Concorde sealed two years ago.  That battery and the Skytec NL starter combination is awesome.  Haven't had any difficulty since.  Cranks great - even when the battery is really cold (although I have warmed up the oil with an electric heater).

 

[scottfromiowa]

I have same battery and SkyTech.  They are a winner.  I will never go back to a non-maintenance free aircraft battery.

[seebruce]

Jeff, I checked my battery as Jose suggested and found no indication of any power draw other than a few milli amps from the clock. At this point I thinking the battery is going bad. It's a regular Gill and only 2 years old.

[Piloto]

Quote: seebruce

Jeff, I checked my battery as Jose suggested and found no indication of any power draw other than a few milli amps from the clock. At this point I thinking the battery is going bad. It's a regular Gill and only 2 years old.

[seebruce]

Mystery solved. I noticed that when I tested my annunciator lights the start power light light didn't come on. I assumed that this light should come on when I used the external power plug when jumping a dead battery so I hooked up the external power cables to a battery charger to see if the light came on. When I turned the charger on I heard the solenoid kick in. The light didn't come on. When I disconnected the power cable I didn't hear the solenoid kick out. I thought it strange so I reconnected the power cable. This time I didn't hear the solenoid kick in. So I disconnected it again and still no click. I then went to disconnect the battery cable to check for a currant draw and noticed that when the battery cable lost contact with the terminal the solenoid clicked. It turns out the auxiliary  start solenoid is not dropping out after being energized hence draining the battery.

Anyone have any idea how the solenoid can stay energized after the power plug is disconnected?

[Piloto]

Quote: seebruce

Mystery solved. I noticed that when I tested my annunciator lights the start power light light didn't come on. I assumed that this light should come on when I used the external power plug when jumping a dead battery so I hooked up the external power cables to a battery charger to see if the light came on. When I turned the charger on I heard the solenoid kick in. The light didn't come on. When I disconnected the power cable I didn't hear the solenoid kick out. I thought it strange so I reconnected the power cable. This time I didn't hear the solenoid kick in. So I disconnected it again and still no click. I then went to disconnect the battery cable to check for a currant draw and noticed that when the battery cable lost contact with the terminal the solenoid clicked. It turns out the auxiliary  start solenoid is not dropping out after being energized hence draining the battery.

Anyone have any idea how the solenoid can stay energized after the power plug is disconnected?

[seebruce]

I did disconnect the power plug from the plane. Are you saying that the solenoid will energize when the power cable is plugged in with out any power to the cable?

[Piloto]

Quote: seebruce

I did disconnect the power plug from the plane. Are you saying that the solenoid will energize when the power cable is plugged in with out any power to the cable?