Slow Battery Drain

[jpharrell]

In the short time that my RV-7A has been flying I have observed a slow drain on the PC680 battery between flights. For example, when I returned from my flight last a week ago, the battery voltage was reading 12.8V with both Dynon EFIS's running. When I powered up the Master on Saturday morning and both EFIS booted, the voltage was down to 12.1V. (Actual voltage right at the battery is about 0.6V higher than the numbers above when EFIS's are not powered up and the current from the battery is zero.) I thought it was just a bad battery at first so I switched it out with a new one but the same problem persists.

I have looked for a parastic leak on the battery but nothing is connected to it except on the switched side of the master contactor. If the master switch is off the battery should be isolated from all loads. So Saturday I used a handheld voltmeter to measure the voltage from the switched side of the master contactor to ground with everything shut off. It reads 0.07 volts. Small, but I expected zero with the master switch off. Is it possible that my master contactor is leaking a small amount of current through when powered off and that is causing the slow drain? I have the standard Vans master contactor.

[AltonD]

I had a USB adapter plugged into the cigarette lighter port. I have decided it is a small drain on the battery. I removed it last week and did not see the voltage drop I have previously seen over a week's time.

[Bill Boyd]

Take a battery cable off and put your digital DVM in series to read mA. It will reveal a drain if any exists.

[Mike S]

Do you have a clock by any chance?

Also, some avionics have a "keep alive" circuit that is wired to the hot side of the master relay.

Do you have a diode installed on the master relay---------and is it correctly installed?

[jpharrell]

I have a DC power port but it is wired to the switched side of the master contactor so it should not see any power when the master switch is off.

I don't have a clock and nothing is wired to the hot side of the contactor except the battery + terminal and the diode. The diode is installed the way Vertical Power shows it between the hot terminal and the terminal that gets grounded when the master switch is closed so that shouldn't bleed off current unless the master switch is faulty or there is some short on the order of 200 ohms between that wire and ground.

I will try taking the battery ground off the firewall and measure current with the ammeter in line but it sure seems like the contactor is allowing some current to leak through to the switched side when open. Has anyone else ever seen this occur before?

[Richard Connell]

If you have an external voltage regulator for your alternator, is it connected to the battery side of the contactor or the main buss?
It will have a very small drain even when all switched off. So needs to be on the main buss, not battery buss.
Cheers

[Bob Redman]

G'day John,

I had the same symptoms several years ago. Eventually, after multiple charges, the battery would regain the volts, but not enough amps to swing the prop. Finally detected that the master contractor was leaking milliamps. I replaced the master contactor & no problems since. Still using the same battery.

[jpharrell]

Thanks for that reply Bob. It sounds like the same thing I am seeing. I wonder if anybody else has had this problem or if it is a really rare thing.

[PerfTech]

Originally Posted by jpharrell

In the short time that my RV-7A has been flying I have observed a slow drain on the PC680 battery between flights. For example, when I returned from my flight last a week ago, the battery voltage was reading 12.8V with both Dynon EFIS's running. When I powered up the Master on Saturday morning and both EFIS booted, the voltage was down to 12.1V. (Actual voltage right at the battery is about 0.6V higher than the numbers above when EFIS's are not powered up and the current from the battery is zero.) I thought it was just a bad battery at first so I switched it out with a new one but the same problem persists.

I have looked for a parastic leak on the battery but nothing is connected to it except on the switched side of the master contactor. If the master switch is off the battery should be isolated from all loads. So Saturday I used a handheld voltmeter to measure the voltage from the switched side of the master contactor to ground with everything shut off. It reads 0.07 volts. Small, but I expected zero with the master switch off. Is it possible that my master contactor is leaking a small amount of current through when powered off and that is causing the slow drain? I have the standard Vans master contactor.

....Interesting that I see this thread as I just had this identical issue. After chasing this and trying several things I was sure were the cause, I finely discovered it was a current leak in the energizer coil of the master solenoid. I replaced this solenoid and problem solved. Thanks, Allan...

[jpharrell]

Allan,

Was it the standard Vans master solenoid that failed and did you replace it with another of the same type?