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TOPIC: electrical drain

electrical drain 3 months 1 week ago #642

  • cgill
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Hello All,

Sorry I did not report this sooner- but the problem I had with my battery constantly draining, even to the point my radios would fail in flight, was the two contact points on the alternator--- a mechanic found it in 10 minutes.. The two wires on the alternator were so close that as soon as the engine was warm, they would arc, basically telling the alternator there was enough charge, so even though the alternator worked fine, it was getting the signal to stop charging (??). That is how I understand it- anyway, the problem was fixed by installing boots on each terminal on the alternator... Problem has been gone for months;)
Chris
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electrical drain 1 year 2 months ago #522

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Thank You Steve, I will investigate further B) I am very concerned since this problem happened last year, seemed to go away on its own, then returned again this month. This is my 4th battery in 6 years, and the voltage regulator and solenoids have been replaced this year. I am very curious about the in-line sensor that sets off the overvoltage light. I will keep you updated.
Thanks again,
Chris
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electrical drain 1 year 2 months ago #518

  • STEVE ELLS
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Hi, This is the response I wrote to another C-150 owner with what appears to be the same problem. It first appeared in the Cessna Q & A column in late 2015.
Hello,
I have a c-150L, while the master switch is off, there is still a drain on my battery. (no clock, nothing I can see running). My mechanic says the master solenoid or starter solenoid may be leaking voltage, or even the master switch. Has anybody run into this problem?
Thanks,
Chris

Hi Chris;
I’m guessing that this drain is great enough to leave you fuming when you go out to the airport after a week only to find that the prop won’t turn when you try to start the engine. There can be a number of reasons this battery is depleted.
I doubt that the battery or starter solenoid (they’re called contactors in aviation) is the source of the power drain. Contactors are remotely-controlled switches—when you activate the master switch on the panel it completes a circuit that makes power flow through a coil of fine wire inside the battery contactor can; current flow through these windings creates magnetism that pulls a brass bar down so it connects the two large wires attached to the contactor. This creates a large capacity path connecting the battery to the aircraft bus and to the starter contactor (and ammeter). The starter contactor works the same way. These contactors look alike but they’re not. The battery contactor is a continuous duty contactor; the starter contactor an intermittent duty contactor.
Battery and starter contactors fail in two ways. Either the small copper wires inside the can burn and separate, thereby opening the electrical circuit consisting of the coil windings inside the can. This lessens or eliminates the magnetic force needed to close the power path connection between the battery and the bus. The contactor won’t close so the airplane can’t be “powered up.” A simple continuity check using the ohms setting on a multimeter will show if the fine copper wires are open.
Another contactor fault is a stuck starter contactor. This occurs when the brass bar and one or both of the large contacts inside the contactor weld together. When this happens the contactor won’t open when the key is released from the start position and the end result can be very expensive since the starter, the alternator and the battery are severely stressed if the problem isn’t realized and the battery contactor opened quickly to stop the runaway battery drain. This fault is so serious that Texas Skyways (www.txskyways.com) has obtained a supplemental type certificate (STC) to install a stuck starter warning light. It’s called a Starter Indicator Light System.

There’s a very easy test to determine whether current is draining from the battery when the master is off. Remove the big wire from the negative (-) battery post and put an ammeter between the end of the wire and the negative battery post. Since no current will flow unless there’s a complete circuit all current flowing out of the battery will have to return through the negative (ground) side of the battery. This test can also be done on the positive wire and battery post.
If you discover current flow I would next look for a fuse holder near the battery. This fuse is installed on most single engine Cessnas. It is there to provide the battery power needed to wind the electric clock and draws a small current even when the master switch was off and the battery contactor was open. It’s not uncommon for an avionics shop or mechanic to re-purpose this circuit to provide power to the “keep alive” needs of modern avionics. Any “unswitched” current draw is also known as parasitic draw. This small current drain doesn’t cause problems if the airplane is flown often. If current flow is shown on your negative ground-ammeter test the next step is to determine which circuit is drawing power.
The first step in determining which circuit is drawing power is to remove one fuse or pull one circuit breaker at a time until there’s no longer any current draw.
Once you located which circuit is draining your battery some disassembly is usually required to determine which component is causing the problem.
If you don’t find a current draw in the test described above, I would next look at your battery.
Battery health tests are looking for two things. Is the battery getting fully charged by the airplane charging system and is the battery still healthy.
The FAR related to battery health is 23.1353 (h) (1). It says that a battery
“must be capable of providing electrical power to those loads that are essential to continued safe flight and landing for:
(i) At least 30 minutes for airplanes that are certificated with a maximum altitude of 25,000 feet or less; and
(ii) At least 60 minutes for airplanes that are certificated with a maximum altitude over 25,000 feet.
(2) The time period includes the time to recognize the loss of generated power and to take appropriate load shedding action.”


If your battery has removable caps on top it’s a flooded lead-acid battery. Remove a cap and look down to see that the electrolyte fluid completely covers the plates. If it doesn’t the battery capacity is compromised. If it does check to see that the battery is fully charged after an hour long flight. No load (open circuit) voltage for a fully charged battery is 12.9 volts or above. No load voltage for a battery charged 50 percent is 12.3 volts. Check the no load (open circuit) voltage; if it’s below 12.9 charge the battery; if the battery won’t charge above 12.5 volts it is unairworthy since it can’t meet the capacity requirements of the regulation. Aviation-specific battery chargers/maintainers such as the ones sold by www.batteryminders.com are advertised as being able to reduce sulfation and restore battery function. The normal life span for a flooded cell aero battery varies but without a regular maintenance program a three to four year life span is normal. If you’re battery charging tests good it may still have little capacity to supply current. You or your mechanic can test for capacity by using the poor man’s load bank (see drawing) and following directions at www.concordebattery.com.
If the battery tests good the problem may be a faulty charging system.
If the battery isn’t fully charged after flying for an hour check to see that the charging system is healthy. The output of a 12 volt alternator or generator should be between 13.8 and 14.2 volts. If your charging system uses an alternator and you hear a high-pitched whine in your headsets that varies directly with the engine rpm that indicates that one of the diodes in the rectifier bridge of the alternator has failed. If that’s the case you’ll never get a full battery charge. You’ll have to either replace the alternator or install a new rectifier bridge. If your system uses a generator I recommend replacing the original vibrating points regulator with a solid state voltage regulator from Zeftronics (www.zeftronics.com). These regulators are very well built and dependable.
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electrical drain 1 year 2 months ago #517

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Hello All,
I have a recurring electrical problem on my 1971 c-150 L. My battery keeps dying (sometimes in a few days, sometimes 2 weeks). We have replaced the battery, voltage regulator, solenoid. With the master switch off, I still get 3.8 volts between battery and ground. My mechanic is perplexed, as am I. Does anyone have any ideas? Thank you in advance, Chris
* Update- 7/3- I left it alone for over a week now- then it started right up, but my red over voltage light comes on ( the alternator seems to be charging fine, needle is deflecting to right). I shut it off and restarted several times, same results.
Is it possible something is draining the battery (shorting) while the master switch is on? Any ideas are appreciated, Chris
Last Edit: 1 year 2 months ago by cgill.
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