Alternator Overcharging

[mplangley]

So I have a problem I have been attempting to chase down.

With the engine running I read the volts at my starter battery at an initial 16 volts and that climbs to 18+ volts before I shut the engine down.

My Alternator is a 24Volt Prestolite Leece-Neville One Wire Alternator. All of my batteries are new. I took my alternator to a shop and the guy tested it and said it was good. He did curiously ask me "Is this a 24 Volt alternator". I assume he say it was putting out more than 12 volts.

I actually have two questions

1.) Shouldnt the regulator shut down the charge at roughly 14 volts regardless of the fact its a 24 volt alternator?

Perhaps another way of asking this is absent any other devices am I wrong to use a 24Volt Alt on a 12 volt battery system? I actually did this by accident because my old alternator went and they replaced it with the 24volt Alt. I did not notice the difference.

2.) On a one wire Alternator how does the regulator know when to limit the output? I never understood how this works as opposed to alternators with a "sensing" wire.

thanks

P.S - Another part of the mystery is that my side A and B banks charge at different voltage. I assume there is a wiring problem here an perhaps Side B is really not getting any charge at all. The alt puts out only a single charge so I assume that whatever is causing the low/different charge is not related to an alternator problem. But perhaps this mystery explains the other?

 

[Bacchus]

I'm not familiar w 24V systems so no comment there.
By any chance is there a diode isolator that separates batty Banks A & B? If so and Depending on how its wired it could drop V by about 1V +/-
There are many better options these days to satisfy the isolator function. It would help the understanding a lot if you can trace the charging system wiring and diagram what you have.

 

[twistedtree]

A 24V alternator in a 12V battery systems? I'd start right there. No, that's not good and is likely the cause of your high charge voltage. That needs to be fixed immediately.


Then I'd proceed from there. The first step in addressing the difference between banks is to figure out how they are interconnected. Hard wired together? Connected via a voltage sensing relay (VSR)? Connected via a combiner diode (what Bacchus asked)? A combiner diode is the least desirable, so if that's what you have, I'd suggest switching to a VSR. I think DC to DC charging is the best, but I would probably only do it on a complete refit, or if the cost is close to a VSR, and high current charge isn't required.

 

[DavidM]

Get a marine electrician to look at your electrical system. With all due respect, if you have to ask the question you just asked, you do not understand enough about marine electrical systems to process the answers.


David

 

[High Wire]

You took a 12v alternator to a shop and they gave you a 24v replacement on purpose? Take it back! You will kill your batteries at a minimum. Hopefully you don’t have expensive AGM batteries.

 

[mplangley]

@DaveM - No disrespect but I would guess by your answer that your not in the teaching profession.

 

[Lepke]

Without a regulator, voltage increases with rpm. Most alternators are 3 phase AC and the diodes convert it into DC. The regulator sets the charge rate. So if it's overcharging, some part in the regulator isn't operating correctly. I've made 32v & 48v alternators out of 12v alternators by modifying the regulator.

 

[C lectric]

If you truly have a 24vdc alternator then change it IMMEDIATELY to the 12v unit you need. At least get the regulator changed.

You will damage your batteries AND electronics with the too high voltage.

1} NO, with a 24V alternator it has a 24 v regulator so it is trying to drive your entire system up to 24v specs which for recharge purposes will in reality approach 27v or 28v.

The regulator could care less about the rest of your system and the 12V needs.


As for the rest of the suggestions get the alternator taken care of FIRST or suffer some potentially expensive damage.

THen and only then assess if anything else is needed.

 

[DavidM]

No I am not a teaching professional, but I did just send you a PM with an offer to help by phone.

David

 

[C lectric]

I see D.M. has offered to help off forum.


I will also suggest that you look up and get a copy of:
Nigel Calder's book Mechanical and Electrical Manual. It is now in the 4th edition but even a used , older earlier edition would help fill you in a lot.



Forgot about 2} THe regulator senses from inside the alternator. If there are other devices such as diode isolators between the alternator and the batteries and the rest of your system it has no idea. THat can lead to improperly, undercharged batteries and some other problems sometimes. There are of course ways around that but you need to understand the implications.

 

[mplangley]

Thanks for your help all

I think my original problem is that until today in fact I had no idea that my previous alternator was 12Volts. I replaced it a few years ago and I guess at the time I trusted the alternator shop to match up my old alt correctly with a new one. I was not paying attention. Adding to my lack of awareness is the fact that during these two years even though my helm voltmeter was registering high (14 volts ish) it never went into the red zone. Even taking the voltage at the battery terminals indicated the same.

So with everything apparently working (accept for some weird electrical problems) and with so many other issues to contend with I never dug into the boats electric and went on my merry way.

But now recently one battery started to fail and my voltmeter started to peg at the extreme end of the red zone and my manual readings corresponded to this. I replaced the battery and am still getting the same.

I dug out some old digital photos today of the old alternator and low and behold it was in fact a 12 volt. I don't know if I can use a DC-DC converter to step down my existing ALT down so for now I think I'll just pick up a 12Volt and hope there are no other issues.

This is a new mystery for me though. Why was my 24 Volt alternator until previously only charging my batteries at 14+ volts and why did it change? I've gone two years after-all without any apparent issues. Or at least not major ones. At least I have had no battery explosions or electronic failures.

Anyway thats the story. I'd love to hear speculation as to the above question. I'll install the 12Volt and report back.

Thanks - C lectric - I actually bought the Calder book and read it frequently. its a great help however I think it is missing a section that warns dingbats like me to make sure to not accidentally swap out a 12 Volt alternator for a 24 volt. In troubleshooting this I was always assuming the Alt was not the problem but was looking for failure elsewhere.

D.M - thanks. I think if I might I'll take you up on your offer.

 

[DavidM]

So first let me apologize for my snobbish post above and offer the following:

Yes I suspect that your current alternator is a 24V one, but I have another theory so I would confirm it as follows:

Disconnect the output terminal (the heavy red one) on the alternator and connect it to two 12V light bulbs wired in series. Wire the other side to a nearby ground. This will give it a simple 24V load independent of the batteries. Then start the engine and measure the voltage at the alternator terminal with a multimeter. Since 12 V alternators are usually regulated to about 13.5 volts I would expect a 24 V one to be regulated at 27 V or so. If it is in that range then it is a 24V alternator.

But another theory is that it is a 12 V alternator and the internal regulator has failed and letting it put out whatever voltage it can. In that case the voltage will be commensurate with the load: light load high voltage, heavy load, low voltage. Since a light bulb is a light load it will probably show a fairly high voltage, maybe as much as 20 V. With a heavier load and it will be difficult to find and hook up such a load, it will be lower, even below 12 V.

The bottom line is: unless you measure 13-14 volts across a pair of 12V light bulbs, the alternator or regulator is bad and needs to be replaced. There are lots of variations to the Leece Neville alternators and if you need the high output get one that uses an external regulator and hook it up to a Balmar regulator.

If you do measure 13-14 volts, there is much more going on and I go back to my original suggestion.

David

 

[BruceK]

...I actually bought the Calder book and read it frequently. its a great help however I think it is missing a section that warns dingbats like me to make sure to not accidentally swap out a 12 Volt alternator for a 24 volt....

It would be a multi volume new edition if warnings like that were added. I hope the new 12v alternator solves your problems.

 

[High Wire]

Never mind

 

[C lectric]

You are having some interesting problems.
Get that alternator checked. If it really is a 24v unit then get the appropriate 12 v unit.

I never considered that you might have a failing 12v unit. You could have. Regulators do fail and one of the signs is a too high voltage. Actually similar to what you reported.

It was your mention of 24v that got me onto that. But is is possible that you have a faulty regulator in your 12 V alternator and my CAUTION stands.

Either way get that unit checked and corrected. Either a new regualtor for your 12V alt. or the 24v alt simply replaced or reregulated.

If indeed your alter. is in fact a failing 12v unit then maybe the shop missed it because the alternator needs to heat up somewhat for a goofy regulator to show up. Heat can take a while to build and can cause many problems to not show up for a while. Your shop likely ran it for a minute or two, maybe not long enough to show the problem up.

A warning also for any others. Too high a voltage from a failing regulator can destroy equipment and batteries. One warning is a climbing voltage above what you normally see. A 12V alt. will in fact, as the batteries come up to full charge, approach 14 or 14.5 V depending upon the regulator. IT may take many hours to do so if the batteries are well discharged AND depending upon the bank capacity, the loads on line and the alternator output.

THis is true of internal reg. and external regs. But much beyond that look out.

For a 24V system expect to see approx. 28 to 29v but the same cautions apply, just different voltages.

Another note is that alternator regulators regulate the voltage output of the alternator. They do not regulate current directly except by the voltage and the loads applied up to their current capacity. If the voltage rises to high then the alternator AND the equipment can be damaged by the overvoltage and the resultant over current.

An unregulated or failing regulator alternator could potentially produce up to about 50V. So if you see voltages over about 14 or very close beware of a failing alternator regulator.

 

[jleonard]

That sort of happened to me once with a new Balmar. I noticed my temp gage going crazy. It looked like the engine was overheating but it wasn't. I checked things then noticed the SOC gage was showing 17 volts. I continued to cruise a little longer to get to an overnight location and it went up to 18+ volts.
Luckily I had a spare alternator and all was back to 14+ volts.
Sent the Balmar back and they rebuilt it under warrantee.
Nothing else blew out. I was lucky.

 

[mplangley]

So I swapped out the 24V alternator for a 12V and guess what? Three years worth of odd electrical problems seem to have vanished. I can't believe it. The whole things makes me feel sick. On the bright side I have a much better understanding of my electric systems and replaced a few bad connections along the way. Its amazing how hard troubleshooting is when rules out the most likely cause from the beginning. To be fair to me though my 24v Alt did not seem to be way overcharging things so thats a bit of a mystery. I can't believe I got away with it (sort of) for three years.

Thanks all for your help.

 

[High Wire]

Thanks for closing the loop.
Btw, I hope you have checked your battery electrolytes levels. High voltage gasses off the water and runs them dry in a hurry.

 

[twistedtree]

Learning, one breakdown at a time.

Glad you got it sorted.

 

[Ski in NC]

Gad that poor alternator was working its ever living butt off trying to raise voltage!! Credit to it that it did not smoke!!

Glad you got it sorted.

 

[C lectric]

Glad you got it sorted out and that you appear to have gotten away with it.

Keep a close eye on things for the next while.