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Author Topic:   Battery Charge Low
bdubbs posted 06-22-2007 02:58 PM ET (US)   Profile for bdubbs   Send Email to bdubbs  
[I] [please spell the personal pronoun "I" with a capital letter] need some help with the diagnosis of a failure somewhere in my electrical system. [H]ere [please begin each sentence with a capital letter] are the facts:

boat: 1984 Montauk with 1984 70-HP [Y]amaha
problem: battery with no charge.
initial cause: left dash lights on for three days.
fix 1: pull-start outboard, run for 1.5 hours.
result: did not charge.

Could the battery be toast and not accepting a charge?

During the 1.5 hours of running, [I] also ran my fishfinder and GPS. Why not fish while recharging? Maybe there wasn't enough [current] left to charge?

Battery connections are bad?

Battery cable shot?

Alternator bad?

The only reason this [problem] appeared is because the dash lights were left on for three days. [I] guess [I]'ll be spending a better part of the weekend trying to figure out my [problem], but any insight would be appreciated.

Bella con23 posted 06-22-2007 04:00 PM ET (US)     Profile for Bella con23  Send Email to Bella con23     
I don't think that I would look much further then the battery itself. I believe the charging circuit require a small amount of current in to produce a larger current out. It's called and exciter field in the alternator.

If the battery is older then a couple of years, and or has been discharged completely before this, then replace the battery and work from that point.

I think you will find the new battery will solve your problems. After installing the battery, check the voltage with the engine off and again with the engine running.

bdubbs posted 06-22-2007 04:23 PM ET (US)     Profile for bdubbs  Send Email to bdubbs     
[I] tend to agree with your reasoning that a new batt[ery] would solve this [problem], but now [I]'m curious about the other [problems]. [W]hat is the best [easiest] way to test an alternator? [W]hat should [I] expect from my alternator? [S]hould [I] be concerned about the battery cable in the bilge?
Bella con23 posted 06-22-2007 06:30 PM ET (US)     Profile for Bella con23  Send Email to Bella con23     
There is a great article pertaining marine electrical systems in the reference section of this site -

The quick and easy of it is, you should have somewhere around 12 to 12.5 volts engine off and 14 to 15.5 volts with the engine running at an elevated idle.

There are many variables as JimH has pointed out such as outboard age, manufactures, RPM, etc.

Chuck Tribolet posted 06-22-2007 09:33 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Fishfinder and GPS use almost no current (tenth of an amp
or so)

But a lot of early outboard alternators are pretty wimpy.
I'd put the battery on a 110V charger for a while and see
what happens. How long is a while? Typical battery is about
60 Amp Hours. If you have a six amp charger it will be
at least 10 hours. Watch the ampmeter on the charger.

Was it just the dash lights? Usually they are wired with
something else (running lights or motor).h


acseatsri posted 06-23-2007 11:48 AM ET (US)     Profile for acseatsri  Send Email to acseatsri     
One of the reasons I repowered was because my 150 Evinrude didn't put out enough juice to keep up with my electronics at normal cruise and idle (max of 9 amps). It was a great excuse for getting an engine that burns 1/2 the fuel I used to burn. :)
jimh posted 06-25-2007 10:35 PM ET (US)     Profile for jimh  Send Email to jimh     
In any battery operated system, when there is a problem, the first component to check is the battery. Connect the battery to an external charger. Charge it until its terminal voltage rises to over 12.9-volts. Load test the battery with an external load. Once you have verified that the battery is in proper condition, examine other components in the charging system. Of course proper connections are needed. Electrical current does not flow through oxidized and corroded connections. This is fundamental to electrical circuit operation. You can easily check the alternator output by measuring the voltage at the battery terminals. When the alternator is working properly it should raise the terminal voltage at the battery to about 14 to 14.5 volts when the engine is running at fast idle or higher speed.
jimh posted 06-26-2007 08:39 AM ET (US)     Profile for jimh  Send Email to jimh     
On most lead-acid flooded cell cranking batteries, if the battery is several years old and you completely discharge it, your chances of recharging the battery to full capacity and having a reliable battery are not very good. Go to some discount retailer and get a new 12-volt marine cranking battery for $35. It is a rather modest investment compared to the overall cost of operating a boat for the season.

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