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Mystery slow battery drain.

Corvus

By Corvus
in Vintage Mooneys (pre-J models)

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Corvus Enthusiast

Corvus

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A few weeks ago, I had a "low battery" out of the blue. I gave the go ahead to replace the battery as I am not one to mess around with a battery in marginal health, even it the battery is not the direct cause. That seemed to take care of the issue. The plane went into annual and was test flown about a week ago by the previous owner after the annual. Everything went fine and it was returned to service.

I went to fly it yesterday and once again the low battery showed up again.

It's a bit of a challenge to figure out common factors as the plane is flown by several different people.

Anyone have any experience with a slow drain?

Aircraft is a 1974 M20F

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Marauder Grand Master

Marauder

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A few weeks ago, I had a "low battery" out of the blue. I gave the go ahead to replace the battery as I am not one to mess around with a battery in marginal health, even it the battery is not the direct cause. That seemed to take care of the issue. The plane went into annual and was test flown about a week ago by the previous owner after the annual. Everything went fine and it was returned to service. I went to fly it yesterday and once again the low battery showed up again. It's a bit of a challenge to figure out common factors as the plane is flown by several different people. Anyone have any experience with a slow drain? Aircraft is a 1974 M20F
When you say low battery, what do you mean? Slow cranking to start? If so, sounds like either something is left on and is slowly draining it or you are not charging it fully while flying. You can have a load test done on the alternator to make sure it is producing. Was anything added electrically to the system recently?
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rbridges Grand Master

rbridges

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When you say low battery, what do you mean? Slow cranking to start? If so, sounds like either something is left on and is slowly draining it or you are not charging it fully while flying. You can have a load test done on the alternator to make sure it is producing. Was anything added electrically to the system recently?

Alternator came to mind, also.

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Corvus Enthusiast

Corvus

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Low as in it has enough power to do preflight checks, but once the starter is engaged, there isn't sufficient power to engage the starter. I mention it being low as opposed to dead because I am in agreement, it wasn't charged on the previous flight, or something is slowly draining it. I haven't checked the interior lights, but are they always hot?

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Marauder Grand Master

Marauder

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Low as in it has enough power to do preflight checks, but once the starter is engaged, there isn't sufficient power to engage the starter. I mention it being low as opposed to dead because I am in agreement, it wasn't charged on the previous flight, or something is slowly draining it. I haven't checked the interior lights, but are they always hot?

 

Well the good news (not counting you paid for a new battery) is that you should have eliminated one of the variables -- the battery. Doing a load test on the alternator would be my next step. You didn't mention any diagnostic you may have available and what they are reporting (ammeter gauge, buss voltage). I would expect to see a steady negative (and it may be very little negativ indication on the ammeter and if you can see buss voltage, a slow decrease in flight.

 

Unless something was added to the plane and it is drawing excessive power while the plane is sitting, then the most logical thing to look at is why your battery is not being charged in flight. It could be a slipping belt, bad alternator or other issue within the charging circuitry.

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DonMuncy Grand Master

DonMuncy

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did not know that.  learn something new every day.

If you have any interest in avoiding the problem of running down the battery with the interior lights, see the thread I started on July 5, 2013 titled cabin and luggage area lights in the general Mooney forum.

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tony Mentor

tony

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You could have a bad ground.  On my F the negative lead is grounded to the avionics shelf.  After sorting it out, I determined that the shelf was painted during manufacture and there as not proper faying surface for the shelf to make adequate contact with the airframe.  So over the last 45 years I guess the resistance slowly increased making starting difficult at times.  Cleaned up the ground  and now everything works like its suppose to.  That's should be pretty easy to check with a volt meter and another person helping you.

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DrBill Mentor

DrBill

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I just assisted a Cherokee driver in solving his battery issue earlier this week.  The battery(Gill sealed)  was 1 year old, so we put it on charge overnight and really did not suspect it as bad.  We disconnected the battery negative lead and measured absolutely no drain on the battery with the master off.  We reconnected the battery and measured the voltage at 12.9. The next morning we checked the voltage and it had dropped to 12.3.  That told me the battery was toast. The engine barely started and the voltage dropped to under 10 during cranking and the voltage jumped up to 13.9 after the engine started and while charging. That told me the alternator was charging properly. The owner ordered a new .Concorde sealed battery and installed it yesterday. After 24 hours, the battery voltage remains over 13 with the master off. The owner was suspicious of the battery but he was using a Battery Minder when not flying (aircraft model) and he found that at times, the plane was hard to crank.

Good Luck, hope this helps.

BILL

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Corvus Enthusiast

Corvus

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Thanks for the input, charging system is functioning and aircraft cranks strong after a few days of sitting. So the big stuff seems to be in order. Plane has logged another 10 or so hrs since I posted this without further incident, so knock on wood, maybe the door wasn't completely latched and it went unnoticed.

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sreid Community Regular

sreid

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Thanks for the input, charging system is functioning and aircraft cranks strong after a few days of sitting. So the big stuff seems to be in order. Plane has logged another 10 or so hrs since I posted this without further incident, so knock on wood, maybe the door wasn't completely latched and it went unnoticed.

 

What door?

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Bob_Belville Grand Master

Bob_Belville

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I have found that if I turn the landing light on 10 miles out, after I land the EDM will start flashing low voltage, an it won't start agin. It's worse at night. I want a LED landing light so bad.

I replaced my 2 100W conventional landing lights a couple of weeks ago, thanks DrBill!, with 2Whelan PAR-46 LEDs, one a spot, the other a wide flood for taxi, @ about $315 total from NeedLights.com through Amazon. 3 amp total draw, thousands of hours life, plus really bright! Ain't that sweet? 

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  • 3 weeks later...
rbuck Collaborator

rbuck

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I've got the same problem, a slow drain. I have a Gill battery, 1 year old, that I'm going to replace after reading this thread. (I'll proceed with your other recommendations if that doesn't work.) If I buy a Concorde, though, which battery do you all get? 

I currently use a Gill G-35S.

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