High Amp Alternator More Output at Low RPM’s?

[skiguy]

My existing alternator outputs roughly 12.2v at idle (600 rpm). I had the alternator checked at a local shop and they said it was good. With accessories on its often pulling voltage even lower and over the course of an afternoon my batteries get discharged just enough to cause issues with my stereo (amps have significant draw apparently). Luckily, Nothing that disrupts the functionality of the critical systems in the boat.

Was in my friend’s Nautique and he’s at 13v at idle so something is up.

My question. Would a new high amp (95) alternator generate more voltage at lower rpm’s?



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[chpthril]

My first question would be, we did you measure that 12.2? Technically, thats lower then battery voltage, so that 12.2V is not coming from the alternator. Whats the output above idle, like 1200?

Next question, did the shop test the alternator as is on the boat, or did you take it off and take the alternator only, to the shop? The alternator is one component that can go bad. Checking it independent of the boat, leaves dozens of other points of failure, left behind.

How much are you idling that you begin to see an issue?

What engine does the boat have? I thought it would already have a 95A alt on it.

[Bamer]

The alternator should be putting out about 14.4V at the alternator output when the batteries are being charged. Chp is right....where was 12.2V measured at?


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[skiguy]

I measured the 22.2v of output at the alternator post. I pulled the alternator off and took it to the shop. They weren’t phased by the the low output.. It puts out 13+ volts when I raise the rpm’s over 1200. They said to just increase idle speed [emoji12]. If my batteries aren’t fully charged before going out the alternator just can’t add enough charge to the batteries as there are lots of alternating cycles with the boat surfing, picking up riders, filling ballast etc. Over time, I start to see weirdness with my stereo. Volume controls stop working on the head unit and the remote.

I replaced the alternator a couple years ago with a similar model off some marine supply place I found on the internet. I don’t remember exactly what the amp rating is on this one but I don’t think it’s 95.

I half suspect the alternator just isn’t right. But before I buy another I was hoping for some input from the experts.

Appreciate the help!


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[Bamer]

What is you electrical loads look like? Do you have 2 batteries, House bat and crank batt? Do you have a crazy stereo? Anything else consuming electricity?


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[skiguy]

What is you electrical loads look like? Do you have 2 batteries, House bat and crank batt? Do you have a crazy stereo? Anything else consuming electricity?


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Yep. 2 batteries Joined with an ACR. Single perko switch I don’t distinguish between house and crank battery. Just use the selector switch to choose the battery of the day. Stereo has two amps. Nothing crazy. Only other accessory would be perfect pass and depth finder.


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[chpthril]

I suspect there is a ground supply problem. However, I would find out what amp alternator would have been on there originally, and see what amp is on there now. Unless you got jipped with this alternator, the amperage is typically stamped into the casting and thats what the guts should reflect.