Battery Discharges if not disconnected

thomsonr · Aug 4, 2010

I bought a 1989 17' bowrider with 3.7 Merc 180hp i/o this spring to get started in boating. If I leave the battery connected it will discharge and I cannot start the boat. How can I trace down what's discharging the battery, I want to install an auto bilge which would only further drain the battery.

Thanks!

EddiePetty · Aug 4, 2010

Re: Battery Discharges if not disconnected

....with one terminal of the battery disconnected, insert a multimeter set on the 0-15 vdc range between the disconnected terminal and the battery post. If a current drain is present the meter will show the voltage. Begin removing fuses, one at the time, from your panel (don't forget the in-line fuses) until the meter drops to 0 vdc. This will isolate the defective CIRCUIT. From there it will be a hand-over-hand until you find the culprit.

Edit: Begin the isolations by removing the output lead from your stator or after market alternator (potential regulator short)

Anchor Management 1 · Aug 4, 2010

Re: Battery Discharges if not disconnected

Remove neg. battery cable,install a circuit tester between the neg. batt. and the neg. wire you just removed.If the light is on there is a draw,Start pulling the fuses 1 at a thime till the light goes off. If you have a memory wire on the amfm radio it will light the light.

Sorry eddie your post was not there when I started typing

EddiePetty · Aug 4, 2010

Re: Battery Discharges if not disconnected

I FINALLY OUT-TYPED SOMEONE!!!!!!

Good point on the memory circuits!!

thomsonr · Aug 4, 2010

Re: Battery Discharges if not disconnected

I was under the dash today looking at removing a depth finder that's not working (lcd dim). All I saw was one fuse for the depth finder. Is there generally a box like you'd find in car? If so didn't see it.

Oh and there is a cassette player I've never used, no am-fm radio.

I'll borrow a multiplexer tomorrow or buy one at Canadian Tire and check for drain.

thomsonr · Aug 4, 2010

Re: Battery Discharges if not disconnected

Ignore this post- mistake

BoatNoobie · Aug 4, 2010

Re: Battery Discharges if not disconnected

some fishfinder with external GPS unit needs a switch to power off the GPS, even though the unit itself is turned off.

Silvertip · Aug 5, 2010

Re: Battery Discharges if not disconnected

Since this is an I/O powered boat, you might find the problem to be a bad diode in the alternator. Do the voltmeter test indicated above and then disconnect the charging lead at the alternator. If the meter now shows no current flow you have a bad alternator.

EddiePetty · Aug 5, 2010

Re: Battery Discharges if not disconnected

thomsonr said:
I was under the dash today looking ...... All I saw was one fuse....... Is there generally a box like you'd find in car?

....unlike cars, boat manufactures like to hide fuse panels in various places!!!
A few pictures of your Maru would help the folks here point you in a general direction to find your fuse panel. Many hulls have fuse inserts adjacent to each circuit switch on the instrument panel, some have circuit breakers.

It would be helpful if we knew if your 470 has the original stator/water-cooled regulator or the after market alternator setup.

Edit: I, like Silvertip, would initally suspect the alternator/regulator. Isolate that first.

Chris1956 · Aug 5, 2010

Re: Battery Discharges if not disconnected

BTW - If you put the multimeter in series with the pos battery cable and the pos battery battery post, you are measuring current in amps. Make sure you set the multimeter to the highest amperage setting it has(usually 10A), and even then you risk blowing out the meter. Some multimeters have fuses inside them in case you connect them to higher amperage than they can handle.

MerCruisers usually have a main electrical plug connection. Disconnect that and try the amperage test. If the drain stops, the problem is likely in the boat wiring. If it persists, remove one wire at a time from the starter solenoid until the drain stops. The alternator is a prime suspect and was pointed out.

bruceb58 · Aug 5, 2010

Re: Battery Discharges if not disconnected

Instead of measuring voltage, I would measure current as the previous poster said. You can easily be fooled by a very high resistance circuit that would cause you to measure 12V but is not your problem.

thomsonr · Aug 9, 2010

Re: Battery Discharges if not disconnected

EddiePetty said:
....unlike cars, boat manufactures like to hide fuse panels in various places!!!
A few pictures of your Maru would help the folks here point you in a general direction to find your fuse panel. Many hulls have fuse inserts adjacent to each circuit switch on the instrument panel, some have circuit breakers.

It would be helpful if we knew if your 470 has the original stator/water-cooled regulator or the after market alternator setup.

Edit: I, like Silvertip, would initally suspect the alternator/regulator. Isolate that first.

I am pretty sure it is a regulator, when the mechanic at the marina first looked at it I remember he couldn't find the alternator.

I don't have a good pic of the full boat but see attachments.

Haven't gotten around to getting the multimeter yet.

Battery Discharges if not disconnected

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