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-   -   Parasitic battery drain (http://www.vansairforce.com/community/showthread.php?t=171569)

219PB 05-16-2019 09:05 AM

Parasitic battery drain
 
Here is an interesting question for the group. My wiring is now complete and have configured everything that I can until the aircraft is moved to the airport. While completing some other fiberglass parts, my electrical system sat for a couple of weeks. One day to break the monotony, I turned on the panel to bask in my work. Nothing happened. My main battery was dead.

Now I know that you do not know the specifics of my system, but basically I have a two buss system. A main and an essential. Each has an EarthX battery on it.

My first thought was a bad EarthX battery. It took a charge and I left it on the bench for two weeks recording the voltage each day. Over two weeks the voltage dropped from 13.8 to 13.3. Did not see any issue with that.

My next step was to swap batteries. My essential buss battery which was still at 13.3v was moved to the main buss. The old main buss battery was moved to the essential buss. Two weeks went by and the battery installed on the main buss was dead.

Ok, the problem was definitely with the main buss. After recharging the battery, I disconnected the main battery cable and installed my Fluke between the battery cable and the positive battery terminal of the EarthX to measure amperage. The Fluke was reading 27 mA. A discussion with the engineer at EarthX revealed that their battery would last about 14 days with this load. That matches what I am experiencing.

Next step was to disconnect each lead in my system until the culprit was found. One by one I disconnected the leads to the VPX, starter contactors, EFII Bus Manager, seat heater relay, etc with no change to the 27 mA current flow. When I disconnected the main B lead at the alternator, the current went to 0. Just for grins, I reconnected it, verified that the 27 mA current returned, and spun the alternator. Spinning the alternator had not effect but I had to rule it out. Disconnected the alternator and the current went to zero.

The alternator and external voltage regulator were sent to B&C for evaluation and so far they cannot find any fault with it. They have my wiring diagrams and are working with me to find a solution. I am reaching out to the group to help me look at this from a different perspective and other ideas.

Any help?

Mike S 05-16-2019 09:45 AM

Quote:

Originally Posted by 219PB (Post 1346835)
When I disconnected the main B lead at the alternator, the current went to 0.

Where is the other end of the wire hooked up to? For the purpose of this question, forget about the breaker for the moment.

219PB 05-16-2019 10:53 AM

It goes to a 60 amp ANL fuse and then the battery.

Mike S 05-16-2019 11:13 AM

Quote:

Originally Posted by 219PB (Post 1346857)
It goes to a 60 amp ANL fuse and then the battery.

I suspect if you moved the lead from the battery to the load side of the main/master contactor you would solve the problem.

Carl Froehlich 05-16-2019 11:14 AM

Quote:

Originally Posted by 219PB (Post 1346857)
It goes to a 60 amp ANL fuse and then the battery.

The alternator output should go to the load side of your master relay(s), not hard wired to the battery.

Carl

219PB 05-16-2019 12:11 PM

I have the Bus Manager installed so the main contactor is inside this box. Their wiring schematic has the main battery lead and the alternator output going to the same terminal.

https://www.flyefii.com/media/Bus_Ma...structions.pdf See drawing 4 towards the end of the pdf.

Spoke with B&C and they did not have a problem with this setup.

airguy 05-16-2019 12:37 PM

You're likely seeing an early-stage failure of one of the diode in the rectifier pack on the alternator.

In any case, the advice to put the B-lead on the cold side of the master is good and will solve the problem.

Carl Froehlich 05-16-2019 01:15 PM

Quote:

Originally Posted by 219PB (Post 1346881)
I have the Bus Manager installed so the main contactor is inside this box. Their wiring schematic has the main battery lead and the alternator output going to the same terminal.

https://www.flyefii.com/media/Bus_Ma...structions.pdf See drawing 4 towards the end of the pdf.

Spoke with B&C and they did not have a problem with this setup.

Yep - you wired it just like they said - and found an inherent problem in the design. I suspect as this is a new problem the alternator has an issue so that would be the next step.

Carl

Richard Connell 05-16-2019 02:30 PM

Where do you have your regulator voltage sense wire connected?
I had the exact same symptoms as you. Took me a while to figure it out, but I had the voltage sense wired to the battery buss rather than the main bus. It drew about 25mA and was always hot.

219PB 05-16-2019 03:54 PM

Quote:

Originally Posted by Richard Connell (Post 1346915)
Where do you have your regulator voltage sense wire connected?
I had the exact same symptoms as you. Took me a while to figure it out, but I had the voltage sense wired to the battery buss rather than the main bus. It drew about 25mA and was always hot.

Thanks, I will go and check that right now!


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