Alternator not providing output

[OfficeMonkey]

Original Motorola Alternator, Prestolite/Leece Neville Regulator.

On the up side, I successfully replaced the raw water pump before taking a week-long trip, our longest ever!

On the down side, our engine started being problematic on the last night (motor became rough; RPMs swung wildly and engine sounded starved at idle throttle, but could run fine at 1500+ RPM), and our trip home was only possible because I kept a solar panel connected to the battery so we continued to have power for the electric fuel pump.

I had a bluetooth voltage monitor connected across one of the battery terminals in the cabin (either a Ranger 29 feature or added by a prior owner) to check cranking voltage (which appears to be a problem, dropping to below 8V cranking), which was how I first noticed the problem, born out by the alternator voltage gauge. Previously, the alternator voltage gauge showed ~13V reasonably consistently. Yesterday, the alternator gauge showed 12V almost the entire day, regardless of tachometer reading, throttle, or variations thereof. I was able to get a 5-ish second period of charging (12.4V measured across battery under load) ONCE by throttling all the way back to idle then back up.

I HAD done a bad thing on the previous -- I had left a solar panel connected directly to one of the batteries, which would have both had the two batteries with uneven levels of charge and may have communicated false "charge" levels to the regulator. In short, I MAY have broken the alternator. Maybe?

Honestly, I'm not even 100% sure where to start -- tachometer reading being present would seem to suggest that the mechanical linkage/pulleys/belts are all fine.

[joe_db]

Original Motorola Alternator, Prestolite/Leece Neville Regulator.

On the up side, I successfully replaced the raw water pump before taking a week-long trip, our longest ever!

On the down side, our engine started being problematic on the last night (motor became rough; RPMs swung wildly and engine sounded starved at idle throttle, but could run fine at 1500+ RPM), and our trip home was only possible because I kept a solar panel connected to the battery so we continued to have power for the electric fuel pump.

I had a bluetooth voltage monitor connected across one of the battery terminals in the cabin (either a Ranger 29 feature or added by a prior owner) to check cranking voltage (which appears to be a problem, dropping to below 8V cranking), which was how I first noticed the problem, born out by the alternator voltage gauge. Previously, the alternator voltage gauge showed ~13V reasonably consistently. Yesterday, the alternator gauge showed 12V almost the entire day, regardless of tachometer reading, throttle, or variations thereof. I was able to get a 5-ish second period of charging (12.4V measured across battery under load) ONCE by throttling all the way back to idle then back up.

I HAD done a bad thing on the previous -- I had left a solar panel connected directly to one of the batteries, which would have both had the two batteries with uneven levels of charge and may have communicated false "charge" levels to the regulator. In short, I MAY have broken the alternator. Maybe?

Honestly, I'm not even 100% sure where to start -- tachometer reading being present would seem to suggest that the mechanical linkage/pulleys/belts are all fine.

Your solar panel has nothing to do with the issue, so rest easy on that score.

[Al Schober]

Start from ground zero. Disconnect the batteries, let them sit overnight, then check their voltages. If you've got a low one, see if it will take a charge from a known good charger.
Once you know your batteries are good, you can start connecting other stuff - one at a time.
12.4 V is NOT a charging voltage. The stock Motorola will put out 13.5 V, while a good regulator will start at over 14 V and then taper down from there. Sounds like your alternator/regulator are not doing their thing.

[ndutton]

The stock Motorola will put out 13.5 V, while a good regulator will start at over 14 V and then taper down from there.

Oh-oh, taper down to what? More detail please.

[Al Schober]

A 3 stage regulator will begin with a current limited phase where the voltage will be what is needed to provide a certain current. This voltage will increase with time until it reaches a limit. In the second phase, the voltage is held steady and the current will gradually decrease. When the current decreases to a certain level, the regulator goes into phase 3 where the voltage is maintained at a lower lever to maintain battery charge.

[joe_db]

Oh-oh, taper down to what? More detail please.

I think mine is set to 13.6 volts float and 14.2 for charging. I can change it if I want to.

[Al Schober]

As I recall, my charge was a bit higher, the float a bit lower. But the modern regulators will let you change these parameters to suit the owner - I like that!
Cohort at work had an old Toyota - regulator died so he put a switch on the dashboard. ON for charge, OFF for no charge. Not sure how he decided when to throw the switch.

[ndutton]

Ah yes, the 'popular' smart regulator. Other than a brand name, do we have any indication that's what O-Monkey is dealing with? Do we know if he has exotic battery chemistry that depends on multi-stage charging?

[OfficeMonkey]

My boring old lead-acid batteries (they came "free" with the boat) are connected to a very stock regulator. The Prestolite is as boring as it comes -- and I had been planning to replace it with something lithium-ion-aware in the next several months.

I've already been able to confirm that my batteries charge and hold a charge when charged via either solar power or an AC-powered charger via shore power; I think that leaves the alternator as the next step. I'll setup a multimeter closer to the alternator itself and see what I can measure.

[ndutton]

Don't sell yourself short. You and I have the same boring systems (traditional lead-acid batteries and fixed point charging) and mine performs well, batteries last 10 years or better, don't cost as much as dinner for eight including wine and dessert and don't need a fancy charging system. All that variable voltage business does not apply to us.

I agree with you that the alternator and/or its regulator is suspect. If you choose to remain boring (I'd like to think you're in good company), there is a wide variety of alternator products that will serve you well for a comparatively reasonable cost (compared to the dinner mentioned above) including Moyer Marine. If you decide on replacement (I'm confident you will), be sure to get an alternator that is marine grade, ignition proof (SAE J1171 standard) and has an output of somewhere close to 14~14.2 volts to keep your batteries and ignition system happy.

[joe_db]

Before we go regulator shopping, it would be wise to determine that is the issue. You can remove the regulator to access the field coil wire. With the field disconnected and the engine running there will be no output. If you connect the field to 12 volts it will drive the alternator to full output. Just do this VERY briefly, you might see 15 volts or more.
If this works, get a new regulator. If it doesn't, likely you blew some diodes in the alternator.

[joe_db]

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

Here is an idea - replicate my light-bulb regulator if you want to for a test.

Warning - all these ideas make unshielded sparks, make sure there are no gas fumes present.

[OfficeMonkey]

Joe_db, that is the most beautiful light bulb fixture I've ever seen.

AND it's within my skill set!