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Old 17-02-2018, 18:36   #1
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Fluctuation in RPM

Hi Guys,

I have a Perkins 4108 Marine Diesel and it drives a Analog RPM gauge which I noticed was fluctuating a lot in RPM.

As part of some upgrades I have added a Actisense unit to allow things like RPM to be displayed on the chart plotter.

However the fluctuating is still present (and I have since had the Taco gauge tested so I know the gauge is ok). Its going up and down a few hundred RPM.

Presumably the fluctuating is somehow coming from the alternator?

I have two alternators (Balmar 90-100) and another one right at the bottom of the engine called Valeo and its bloody hard to see). The Taco wire comes off the Valeo.

Any ideas what might cause this?

I have tightened the Valeo belt as it looked a bit loose but the pulsing/fluctuating is still present.

Cheers

AG

(Here is a video of what I mean : )
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Old 17-02-2018, 19:27   #2
rbk
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Location: Whitehorse, YT
Boat: Tayana 37
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Re: Fluctuation in RPM

Mine does similar when the batteries are fully charged and the field current causes the jumping as it energizes and deenergizes trying to float the bank. Had a switch installed to deenergize the alt as it can damage the tach, maybe similar?
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Old 17-02-2018, 22:52   #3
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Re: Fluctuation in RPM

Quote:
Originally Posted by rbk View Post
Mine does similar when the batteries are fully charged and the field current causes the jumping as it energizes and deenergizes trying to float the bank. Had a switch installed to deenergize the alt as it can damage the tach, maybe similar?
Yeah that sounds exactly the same as this : Bouncing Tach Needle

If I used the Balmar alternator we have on board for house stuff which I think runs through the regulator there is a feature to stop this.

Would have to get a electrician in to fix it in the Valeo.

Thanks for the tip.

AG
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