General electrical problem

[pjazz]

Hi all, just bought a new (used) trimaran. Question for you please:

My house battery ( only one, 12V AGM) gets completely drained overnight even if all breakers on panel are off. Only exception is when main power switch is also off, i.e. if it is left in «*on*» position, but all panel breakers are off, the battery goes dead!

I checked basic connections:
Outboard 10HP electric start with alternator, solar panel charge controller to battery, and that seems all good.

I suppose the problem is in the breaker panel?

Any ideas how or where I should look for the power drain culprit?

Thx, Pierre J

[sailorboy1]

I would look for something that doesn't get powered from the DC panel with a breaker, like a bilge pump with a stuck float running all night.

[er9]

Maybe start by looking for wires that are attached directly to the battery + terminal? iv'e also seen wires stacked on the back of the 1 and 2 studs of a 1-2-B selector switch. I think any of these would/could be a direct drain on the battery and that bypass the panel breakers.

[barnakiel]

Something that is wired ex panel.


Or the panel.


b.

[Stu Jackson]

One battery? Could it be dead?

[Shrew]

Originally Posted by pjazz

Only exception is when main power switch is also off, i.e. if it is left in «*on*» position, but all panel breakers are off, the battery goes dead!

To clarify this is the Battery Switch? Not the Main Breaker (Frequently a 30 amp double-breaker) on the panel?

Anything connected directly to the battery terminals wouldn't be isolated by the battery switch. I would look at whatever is wired directly to the positive side of the battery switch.

It might help to start at the positive battery terminal and follow the flow from there to the battery switch to the panel.

[CassidyNZ]

If the “main” switch stops the drain, the leak must be downstream from the switch. Check what cables/wires are connected to the downstream terminal on the main switch.

If necessary, undo the terminal and a spark will result from the wire that has the leak. Follow the wire to its logical conclusion.

[dmdelorme]

could be short that is not enough to trip a breaker does not sound safe. use an amp meter to see how big a load it is.

[loneshark64]

Originally Posted by CassidyNZ

If the “main” switch stops the drain, the leak must be downstream from the switch. Check what cables/wires are connected to the downstream terminal on the main switch.

If necessary, undo the terminal and a spark will result from the wire that has the leak. Follow the wire to its logical conclusion.

Agree. I would go one step farther. Buy a multimeter, they don't cost much and are useful. I use a multimeter to check what is draining.

I am NOT an electrician so will likely get corrected on this but what I do is is first charge the battery all they way. Then disconnect the negative lead on the battery. Connect the red from the multimeter to the negative battery wire and the black from the mm to the negative battery post (this way it is connected in series, and less risky than connecting on the positive side). Set the mm on like 20 amps and it should show 0. If it doesn’t you have a parasitic drain. Then start disconnecting stuff, and turning stuff on, and check what’s drawing the most amps. Logically it is probably the bilge pump or something else attached directly to the battery post like a charge meter but it could be a something else or a previous owner wiring experiment. Multi meter can help you narrow it down.

[CassidyNZ]

Originally Posted by loneshark64

Agree. I would go one step farther. Buy a multimeter, they don't cost much and are useful. I use a multimeter to check what is draining.

I am NOT an electrician so will likely get corrected on this but what I do is is first charge the battery all they way. Then disconnect the negative lead on the battery. Connect the red from the multimeter to the negative battery wire and the black from the mm to the negative battery post (this way it is connected in series, and less risky than connecting on the positive side). Set the mm on like 20 amps and it should show 0. If it doesn’t you have a parasitic drain. Then start disconnecting stuff, and turning stuff on, and check what’s drawing the most amps. Logically it is probably the bilge pump or something else attached directly to the battery post like a charge meter but it could be a something else or a previous owner wiring experiment. Multi meter can help you narrow it down.

Be aware that most multimeters used by non-professionals have a limit if 10A when testing as described above. More than that and you may see some smoke

[Bycrick]

The 10 amp limit is very common for in-line current measurement. But I’ve never seen a meter "smoke" from too many amps. There’s (almost) always an internal fast-blow fuse in the meter. Of course, you might have to take the meter apart and unsolder the fuse to replace it, if you can find a replacement that fits.

When you get to the point that you know enough electronics to know when, where and how to measure current, you’d be better off buying a clamp-type ammeter. You don’t need great accuracy, so they’re relatively cheap($50-75).

[knot smart]

Good morning.. first thing I would check is the battery itself. It might not be able to hold a charge. Pull the battery, bring it to pep boys and have it load tested.