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Author Topic:   Battery Drain Mystery
lurkynot posted 04-19-2008 09:13 AM ET (US)   Profile for lurkynot   Send Email to lurkynot  
My 2001 18 Dauntless with a 135 Optimax has been exhibiting some peculiar electrical problems since the end of last season and now at spring startup has me wondering.

The last time I used the boat back in November I was coming across the lake near wide open in moderate chop when the auto bilge lamp lit while under way. All seemed normal except that it stayed on for about 15 minutes all the way to the ramp. I listened to what I thought was the bilge pump dieing while putting the boat on the trailer and verifying that the bilge switch was in the off position.

I disconnected the battery and ended up winterizing the boat figuring I would deal with a new pump this season.

I made the mistake of just cutting the power leads without checking the pump while it was in the boat and just for kicks wanted to hear what a sick bilge pump sounded like so I connected it to a battery I leave on the boat for the winter. Much to my suprise it sounded normal. Reinstalled it verified that indeed it worked and thought that was the end of that.

Went out to dinner believing my spring startup had gone smooth and all was well. Wrong, as I was covering the boat after dinner I noticed the gauges were lit as though the motor would be running except there was no key in the ignition and it was indeed in the off position.

Any thoughts on where I should start? Thanks,Tony

One strange note I made while I had the pump cut out of the circuit was that there was no power at the leads from the boat side while the bilge switch was in the off position. I have noticed that in the past the bilge would go into the auto mode when there was enough water in the bilge signaling the pump to do its job.

Is this normal - should'nt there be power no matter what in the event the bilge float system detects water and activates itself?

Also now that I think of it the old battery I leave in the boat over the winter to lift the motor if need be had adequate power in it to lift and drop the motor when I picked up the boat for the spring start up routine of mine although it was in its usual weak condition.

Just seems odd the battery was not zapped of its power from a trickle drain after sitting for 4 -5 months.

Is there a way to measure if there is a small load on the battery with the boat and all switches in the off position?

Chuck Tribolet posted 04-20-2008 10:02 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
You can measure small currents with most DVMs (Digital Volt

I'm guessing your 15 minutes of bilge pump running was a
stuck float switch.

The instrument lights on should be sufficient to completely
kill the battery over a few months. And they would be more
than a really small load -- probably enough to make a small
spark when you disconnect the battery lead. Are they wired
to the ignition switch? or the running lights?

I think what you need to chase this down are:

A buddy who knows a bit about electicity.
A nice day
And a six pack.


jimh posted 04-20-2008 11:09 AM ET (US)     Profile for jimh  Send Email to jimh     
It is hard to deduce exactly how the bilge pump circuit was wired in your boat, although it is typical that a bilge pump is connected to the battery via its own circuit that by-passes much of the rest of the boat's 12-volt distribution. This is often done to keep the bilge pump operating in an automatic fashion when the boat in unattended.

On my own boat I do have the a sump pump located in the deepest part of the boat which is wired directly to the battery via its own fused lead. There is a switch which controls the operation of the pump, and it can be left in an automatic mode, as well as completely cut off.

I mention this because you may have something similar on your boat and perhaps don't realize it. If you are the original owner, you can probably get an accurate wiring diagram from the boat builder, but if you got the boat second hand, there is no telling what modifications might have been made to the electrical system by a previous owner.

There is a breed of bilge pump which contains an integral controller which will cycle itself on at a preset interval, and, by measuring how much current is needed to spin the motor, deduce if there is water being pumped. While those automatic pumps sound like a great innovation, I prefer the old fashioned kind where the pump is only a pump, and the decision of whether or not to be running is left to either a human or an old fashioned float switch.

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