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Author Topic:   Low voltage drain
Linesidesonthefly posted 07-02-2007 04:21 AM ET (US)   Profile for Linesidesonthefly   Send Email to Linesidesonthefly  
Boat is a '73 Katama powered by a 1987 70h.p. 3cyl. Johnson

Isolated the sources of the potential problem by systematically removing accessories one at a time.

Purchased a new Optima Battery this past Friday. Saturday a.m. the thing is drained. Same thing on Sunday. Its now fully charged sitting on my deck.

I have narrowed it down to the ignition switch at the helm or the motors own charging system.

Looked for frayed or burnt wires at the motor and found none. The lone fuse in the charging system relay is good.

The ignition key is in the off position. Could that switch be faulty and cause a dead battery overnight?

Do I need a new power pack or rectifier?

Any help is highly appreciated.

Chuck Tribolet posted 07-02-2007 06:09 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I'd start by getting a factory service manual.

You really don't want to debug this by discharging the battery
every night. It will take a long time to find the problem
and is really bad for the battery.

If it discharges overnight you have pretty decent current
flow (5 amps or more). You'll see sparks when you disconnect
the battery. That's one rather crude test to tell you if
the problem is still there. A less crude test is to use
an ampmeter.

You can test the switch by simply disconnecting it and seeing
of the discharge current is still there, but I suspect it's
not the switch (I doubt the engine pulls 5A with the ignition
on and and engine not running).

Disconnect the battery when you aren't working on the problem
so you don't run it down.


jimh posted 07-02-2007 09:33 AM ET (US)     Profile for jimh  Send Email to jimh     
If the motor appears to be the source of the parasitic current drain, you probably have a diode in your alternator system which has excessive leakage current.
Linesidesonthefly posted 07-02-2007 06:32 PM ET (US)     Profile for Linesidesonthefly  Send Email to Linesidesonthefly     
Am I on track with the Rectifier and how costly is that item?
Lastly is replacing this something a backyard mechanic like myself can accomplish?
jimh posted 07-02-2007 09:52 PM ET (US)     Profile for jimh  Send Email to jimh     
Disconnect the rectifier to see if it was the source of the parasitic current drain.

A rectifier for a 70-HP OMC motor is probably under $50. It is easily installed.

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