Electrical issues

[drolds72]

Boating with a friend this weekend. 2000 Mercruiser bravo 1, with a 350 mag. He had replaced the alternator after spotting the pulley wobble. At 2600 rpm, the voltmeter begins to flick to the low side, and engine stumbles. At 3000 rpm, the voltmeter begins to really spike and the engine will cutout if rpms aren’t reduced. The first time it happened, it also tripped the breaker that feeds the ignition switch. I am thinking it would be pretty coincidental that he just replaced the alternator, but more wondering what exactly is going on. Rectifier no good? Bad battery (that spins motor no problem when starting)? Fried ignition component ? Under 2600 rpms there seems to be output from alternator and motor runs as it should.

 

[NHGuy]

Pull that alternator and take it back.
Something is way wrong.
That is a new defect alternator.

 

[wellcraft-classic210]

Pretty likely a Defective voltage regulator that is an internal part of the alternator --

FYI
Running at higher voltages than intended ( as in -- over 15 volts ) can increase current to unsafe levels and can destroy components and is also a fire hazard. // The risk increases as the voltage increases.

 

[drolds72]

That is the weird thing, volt meter never indicated high voltage- the spikes were voltage drops on the gauge

 

[wahlejim]

Are the grounds and connections cleaned to shiny metal? Voltage drops can indicate a bad connection.

 

[drolds72]

Are the grounds and connections cleaned to shiny metal? Voltage drops can indicate a bad connection.

Everything that I could see while we were on the water looked very clean. I know that doesn't mean it really is, but everything seemed to be clean, tight and greased

 

[drolds72]

Follow up. Buddy had pulled alternator and battery to bench test, both passed. He noticed, however, that upon reinstallation of the battery with perko switch off, he had power to the dash switches and lights. Removed cables from back of switch and bolted together. Boat ran fine all the way up to full throttle. No stumbling or flickering in the voltmeter. Anybody ever had one of those switches go bad?

 

[wellcraft-classic210]

Any switch can go bad --

Design-- Its typically 2 pieces of metal / thinly plated with a corrosion resistant finish / being held together under some sort of spring force.

Possible reasons
In the case of a battery switch if its turned on / off while under a load that can cause arcing and degrade the surfaces that make electrical contact. Corrosion form exposure to moisture or salt and or wear can degrade the surfaces as well. Once that starts degrading can be worsened if any heat is generated by current passing through a small contact area.