Alternator reading 17 volts

[Boat]

That pos wire running to the batts look a little small to you all?

[joe_db]

Here are a couple photos from my Balmar install thread:


Your alternator really looks like it is about the same thing, but wired way wrong. For one thing, while the field is grounded, if it is isolated ground like it may well be if it is like mine, the alternator itself is not grounded!
With everything OFF measure the ohms from the alternator case - you may have to scrape paint off, to the ground terminal, which should be the connection next to the "250 volt" box, which contains something
(also note the wire gauge on mine)

[joe_db]

If the alternator is grounded, you might try removing the jumper from + to the field and replacing it with a small lightbulb as a test.
Here is a relevant thread for that:

https://www.moyermarineforum.com/forums/showthread.php?t=11313&highlight=light+bulb+regulator

[stevebonifield]

Alternator

Thanks Joe and everyone for their guidance. First, I just purchased this boat. The couple I purchased it from have been cruising for over a year in the gulf of mexico, east coast of florida and in the bahamas. I met them in Ft. Pierce on their return from the Bahamas. This has been wired this since 2021. Does not mean it correct just letting you know. I am in Indiana and the boat is in my slip in Florida. I changed out the lead acid battery before i returned to indiana. The old battery was tested and still had 266 cca potential from its original 425. I was out for 4 days sailing and motoring occassionally until the last day where I motored for 4+hours straight into the wind when the engine died. The battery did not have enough juice to start. Upon arriving to my slip I jumped it and it started and ran from quite awhile without an issue. When I tried to start without any assistance it would not start. That is when I changed the battery and had the old one tested. I know my way around engines but am not even a novice mechanic. I will tell you that the output from the alternator never wavered from high 16 to 17+ volts. When I tested at the amp guage (engine running) it tested at 5 volts which I couldnt understand but it was hard to reach to test. I have attached a picture of the Victron monitor after i replaced starting lead acid battery. The amp guage never moved when engine was running even at higher rpm's

[stevebonifield]

Alternator

Forgot to mention the controller is set to charge the Lead Acid battery to 12.5 then charges the lithium.

[joe_db]

The mystery gets deeper and deeper. The DC-DC charger should NOT be set that way for one thing. 12.6 volts is WAY too low for it to start charging, that is about the resting voltage of a charged and resting lead-acid battery. It should be set somewhere around 13.5 or so, depending on how your regulator is set. You do not want it charging when the engine is off.
Speaking of regulators, you do not appear to have one! My random guess would be that the regulator died on the previous owners and this is a kluge to get the boat sold, but I do not know for sure.
Please trace the (too thin) red wire from the alternator and see where it goes.
It will help a lot if you can do the tests from a couple of posts up and you'll need to be at around 1500 RPM for good numbers.

[stevebonifield]

Alternator

It my understanding that when the lead acid is charged to 12.6 volts then it allows the charge to go to the lithium battery. It doesnt Start charging at 12.6 volts it charges up to 12.6 volts then switches to the other battery.

[hanleyclifford]

Couple of things. Your alternator clearly has a regulator appended, whether it is being defeated thru improper wiring is another question. Mixing battery types is bad news on a boat - especially if one of them is lithium. The atomic 4 can easily be started by a deep cycle flooded battery which is cheap and easy to maintain, and can be used in conjunction with additional house deep cycles, all separately switched. Battery controllers/isolators and other gadgets are an invitation to trouble. In view of your recent acquisition of the boat (and therefore lack of knowledge and understanding of what the PO was thinking), I recommend that you wipe the whole charging system and start over. Moyer Marine has some excellent wiring diagrams available to study, and if you want to design a system yourself this forum stands ready to help in any way we can.

[stevebonifield]

Alternator

Ok Thank you. It seems I can immediately separate any connection between the batteries by removing the controller. The Lead Acid only starts the engine and runs the bilge pump. All else is run by the Lithium which is charged by a solar panel. Does that make sense? Is it a foregone conclusion that I need to replace the alternator since it is reading 17 volts or is that a normal reading without a regulator? The PO said it has a built in regulator btw

[joe_db]

It my understanding that when the lead acid is charged to 12.6 volts then it allows the charge to go to the lithium battery. It doesnt Start charging at 12.6 volts it charges up to 12.6 volts then switches to the other battery.

That is not how those work. That is an 18 amp DC-DC charger. When the source battery gets over a set voltage, it starts charging the destination battery at the desired voltage for that battery type at up to 18 amps. It will keep providing current until the source battery voltage goes below a certain point. It is not really any different than a battery charger that plugs into an outlet except that it runs on DC.
12.6 volts is FAR too low a setpoint for it to charge. The start battery will not get any charge at all at that voltage. 13.8 is about as low as you can go and still get a decent charge into that battery chemistry. If I had your setup I would set the start-charge voltage at about 13.5, that will allow the start battery to get a decent charge before sharing with the lithium battery.

[joe_db]

Ok Thank you. It seems I can immediately separate any connection between the batteries by removing the controller. The Lead Acid only starts the engine and runs the bilge pump. All else is run by the Lithium which is charged by a solar panel. Does that make sense? Is it a foregone conclusion that I need to replace the alternator since it is reading 17 volts or is that a normal reading without a regulator? The PO said it has a built in regulator btw

It is not a forgone conclusion at all yet, we are not even sure it HAS a regulator.
17 volts or more is certainly possible when full-fielded like it seems to be in your case.
Are you on the boat now?

[hanleyclifford]

Ok Thank you. It seems I can immediately separate any connection between the batteries by removing the controller. The Lead Acid only starts the engine and runs the bilge pump. All else is run by the Lithium which is charged by a solar panel. Does that make sense? Is it a foregone conclusion that I need to replace the alternator since it is reading 17 volts or is that a normal reading without a regulator? The PO said it has a built in regulator btw

An alternator might max out at 17 volts if unregulated. Your alternator does have a regulator but it might be wired wrong or simply defective. The regulator performs it's duty by supplying amperage to the field terminal on the alternator based on what it (the regulator) is sensing. If your alternator is putting out 17 volts it is not defective; however, if one or more diode pair are not delivering the output could be limited. An alternator shop can quickly answer those questions. The shop could also remove or defeat the regulator and leave the field connection to be serviced by an external regulator, which is what I recommend. Regarding the lithium battery charged separately by a solar panel and responsible for all house functions I can only say YIKES. - I hope the solar panel is unimpeachably regulated. Frankly, your system seems to be unnecessarily complicated.

[joe_db]

FYI - here is what the wiring SHOULD look like:

[hanleyclifford]

FYI - here is what the wiring SHOULD look like:

That would appear to explain the shut down. The alternator went wild, fried the coil, and the engine shut down. Now for the low voltage at the starting battery.....?

[stevebonifield]

Alternator

Joe, can you re-read your last post? You wrote 13.8 is about the lowest you would set my controller then you said I should set it at 13.5. Did you mean 12.8?