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Motorboatin SOB
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Discussion Starter #1
Working on our boat.

2 new diesel batt's this season

While idling its charging 13.2/3 volts and every 5-10 seconds the voltage spikes from there to around 14.5. Sometimes it does it bad enough where the ECM (MegaSquirt) misses and kills the motor just for a split second.

Im seeing all the spikes on the dashboard of the laptop watching through tunerstudio (the megasquirt tuning software) that I have a volt gauge on. When it does it real bad and causes it to miss, the volt gauge goes red where its seeing around 16 volts.

Checked all connections, batt cables, etc and its all tight and clean.

We put a new alt on and same deal.
 

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Q(t)=ṁCpΔT
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28,142 Posts
Sounds like the voltage regulator is going out or you have some resistance between your system bus and the battery.

Also, go to Radioshack and get one of those AM/FM/Stereo radio filters that has enough wattage to support all of you sensitive electronics. It will smooth these types of events out. attach the megasquirt and DAS if you have one to this.
 

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Motorboatin SOB
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Discussion Starter #3
We called the company we got the new alt from b/c the one that was on the boat already was theres, told them the problem and their tech guy said voltage regulator like you did. So we got another one from them, except I think this may be a 1 wire deal, but like I said, its doing the exact same thing.

They are getting called tmw for sure to see if they can help as well.

Thanks for the response, ill look into that filter
 

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Q(t)=ṁCpΔT
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where is the charge wire from the alternator attaching to the electrical system?
 

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Motorboatin SOB
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Discussion Starter #5
I cant remember off the top of my head, the boat is at dads house...ill have to check.
 

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My first thought would be agree VR, but otherwise check connections. With boats, especially, I'd think this is a problem.........Separate ground buss, and lots of shock and vibration, depending on the boat. And, there's always the "wiggle test"
 

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At the alternator output stud, check for AC voltage. There should not be over .1V (one-tenth volt) AC. If you have a recording oscilloscope see if the spike is associated with an AC transient. It could be a loose connection on a rectifier diode or a bad diode, however I would expect that to soon simply fail completely and then not be intermittent, the AC would be continuous.
 

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Motorboatin SOB
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Discussion Starter #8
All the connections are tight and clean.

Theres 2 batteries and one ground goes to the block, and the other battery goes to the front of the engine on the procharger mounting bracket.

We can run it on the hose to check for the AC voltage yeti.
 

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Q(t)=ṁCpΔT
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Copper on aluminum with water is not a good grounding technique.
 

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Motorboatin SOB
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Discussion Starter #10
Power wire goes from the alt to the starter solenoid.
 

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SASQUATCH RACE TEAM
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it sounds like the vr is losing reference but i have seen diodes that were shorted and caused a over excitation problem on a genset. if one of you diodes were intermittently shorting closed it would decrease the amount of power required to reach its desired voltage setpoint. if the diode were to open it would make the voltage go low because of the increase in power required to reach its voltage setpoint.
 

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Motorboatin SOB
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Discussion Starter #12
At the alternator output stud, check for AC voltage. There should not be over .1V (one-tenth volt) AC. If you have a recording oscilloscope see if the spike is associated with an AC transient. It could be a loose connection on a rectifier diode or a bad diode, however I would expect that to soon simply fail completely and then not be intermittent, the AC would be continuous.
I ran it earlier on the hose, and I got a steady reading of 30.9 AC volts going from the stud on the back and grounding the other lead to the alt case...
 

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I ran it earlier on the hose, and I got a steady reading of 30.9 AC volts going from the stud on the back and grounding the other lead to the alt case...
The alternator is kaput. Replace the alternator or the rectifier diodes in that alternator. There is a popped diode so the AC is passing through to the DC system. This ain’t good because it can damage any of the other electronics in the boat, though most should be protected with diodes of their own to prevent damage from such an alternator diode failure.

If there is a battery cutoff switch that can disconnect the alternator from the batteries and it is opened when the engine is running, that can cause this. That switch should never be opened when the engine is running.

I have seen diodes pop when a slip with a wrench inadvertently grounds the B+ output terminal on the alternator.
 

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The alternator is kaput. Replace the alternator or the rectifier diodes in that alternator. There is a popped diode so the AC is passing through to the DC system. This ain’t good because it can damage any of the other electronics in the boat, though most should be protected with diodes of their own to prevent damage from such an alternator diode failure.

If there is a battery cutoff switch that can disconnect the alternator from the batteries and it is opened when the engine is running, that can cause this. That switch should never be opened when the engine is running.

I have seen diodes pop when a slip with a wrench inadvertently grounds the B+ output terminal on the alternator.
This would be my thought too. Or do you have an isolator in the system as well, i.e. a hose battery and a start battery? Typical of boats. Some times it is just a switch that goes battery 1, battery 2, or both batteries.
 

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do you have an isolator in the system .
I almost mentioned this. He's talking about the 3 terminal isolators, which are really just two huge diodes "back to back." They should be outlawed. Here's why......

Let's say you have something "simple" like a small motorhome, two batteries and one of these isolators.

Let's say the "main" diode opens which does happen.

What does this do?

This removes the alternator from the main battery. IF THE ALTERNATOR has a separate sensing line (not a one-wire) the sense will now be "low" on the main, non-charging battery, and so the regulator ramps the charge up to max.

Meanwhile, the output of the alternatoris till hooked to the second battery, and it's boilin' like mad because the alternator is essentially "full fielded"
 

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Motorboatin SOB
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Discussion Starter #16
Thank you for the replys, still working on this.

Yes there is a Battery cutoff switch, it has batt 1, batt 2, off, and All.

Boat does have 2 batteries and we always put the switch on All when starting and running.

Dad tried separating the power and ground wires for the megasquirt ECM and the msd box...didn't change anything.

I also moved that ground from the front of the motor to the factory stud on the bellhousing, no help.

It just seems weird that this new alt we put on is doing the same thing as the one we thought was bad.

Thank you guys again for the help, I appreciate it
 
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