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Alternator or Second Battery?


Keith_Menard
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I'd start with a new battery and test the alternator. There is no way in the world that a stock alternator should not be able to keep up with 2 heated seats and a little bitty pump. A standard alternator has no trouble keeping up with a ghetto blasting stereo, 4 ballast pumps and charging 2 batteries.
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@"Keith Menard" : have the alternator tested for output, as noted it should not have a problem with those added components. How old is the battery, it may be on its last legs. What are you using as indicator of the problem?
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Also check the voltage at the output of the alternator.

 

Any idea what kind of alternator is on your boat? Is it single wire or externally regulated by either a regulator or the ECM?

 

But I'd definitely start with the battery - at a minimum bring it in and have it tested if you don't want to just replace it. Not knowing the history of the battery I would probably just spend the $80-$120 and start fresh.

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@"Keith Menard" Sounds like the alternator has output but not much if only 12 v, at a low idle it may not produce any charge so the change is showing alternator is putting out some charge. Is that off the boat gauge or a good voltmeter, I would not really trust the boat gauge, I would check with a known good meter.
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Going off the voltmeter is just an idea. Due to weak/old/corroded connections and I’m betting way too small of wire running from engine to dash causing significant voltage drop. I would check voltage at alternator and battery with engine off, then idle, then 2500 or so RPM’s. When I did my PP I ran it’s own power supply the whole way knowing the PP likes good voltage and Correct Craft didn’t do the best wiring jobs.
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If it isn't charging at idle it could be a single wire internally regulated alternator. You would need to find the alternator model and specs to see what RPM it needs to see to get full output. One solution if that is the problem is changing to a smaller alternator pulley to get it spinning faster at idle.
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There is the problem solving way or the parts throwing solution.

 

If you use a voltmeter you want to look for differences between voltage at different points.

 

If the gauge says 14.4

And the alternator + to block says 14.6

But across the terminals on the battery roads 12.8 you have bad connections somewhere. So you have to move around from power points to ground points and look for where it changes.

 

Alternator to block.

Starter positive to block.

Starter to battery terminal.

 

Eventually you are going to find the drop.

 

Internal regulated one wire alternators will not charge your battery if its low so long as they keep the power at their B+ post high enough. Remote sensing alternators wired back to the battery will keep going up till voltage at battery is 14.8.

 

Since usually in a boat we read our power at the starter always suspect the.battery cables of being bad early in the process.

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I do not understand the science behind it but I ran an independent 10AWG ground from my PP master module to the main grounding location on the rear of the engine block (instead of grounding to the RPM gauge as it was originally, and most, are set up) and it solved all voltage drop issues on my 99 SN. Maybe some of the electricians above can chime in on if they think that would help you?
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@Gar early ski boats had little to no need for more power.

Analog gauges, no stereos, a few running lights and a coil. 40 amps was more than enough juice.

 

Using a volt meter will tell you if this is alternator, wiring, or output issues. Another component that is available would be a smaller alternator belt pulley. This increases the rpm of the alternator at all engine speeds and is very useful if you use power at idle. Check specs on your alternator max rpm.

 

@OSUwaterskier the science is that electricity is flow. As you ask for more and more flow the voltage will drop if the wire isn't both large enough or in good condition. PP is a power hog as evidenced by the large hot resistor on the power servo. When you start looking at the common ground in your dash you see that there are a bunch of eyelet terminals and crimps all smashed up in there, if any is loose or corroded there goes your flow. In response PP can't perform. It really should have it's own dedicated power and ground if possible.

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Another problem is 12v is the most useless retarded voltage. It doesn’t take much to impede it. You couple that with the average backyard hack who isn’t afraid of 12v and is unaware of how electricity works and you have a real mess on your hands that otherwise could be simple.

 

Think of electricity just like the water coming from your hose bib on your house. Put 25’ of hose on it and turn on at full volume and you have good water coming out the hose. Now reduce that volume to 12% of its original value. Meh, you have a trickle but it’s still there. Now take that 25’ hose and add another 100’ to it. At 12% flow you probably won’t have ANY water at the end of the 125’. Or take that original 25’ hose, turn it on at 12% and put a kink in it. It’ll definitely stop the flow where as at 100% it’ll knock that kink straight. Think of that kink as corrosion or poor connection.

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