Electrical conundrum...

[weinie]

A friend at my marina has a Catalina 310 and his voltmeter is pegged at over 16V when the engine is running or the AC charger is on. However it reads about 12V when the engine and charger is off but the key is turned.

I'm not sure if its coincidental or not, but we had just finished moving the alternator to tighten a squeaking engine belt when we noticed this issue.

Unfortunately, we did not have time to test everything with a multitester but other than a bad voltmeter, I'm not sure what else could give such a wacky reading! Any ideas?

 

[SamNelson]

should not be a problem.

The ratio you describe (16 volts charging and 12 volts standby) is not real bad. If you figure the voltmeter is a little out of calibration, I would accept those readings as a good system.

Typically a 12 volt system sees around 15 to 16 volts on full charge.

Are you measuring these voltages at the battery terminals?
Sam

 

[Maine Sail]

If you are seeing 16v with both the battery charger and the alternator it is more likely a volt meter out of adjustment than two bad charging sources.. Check the voltage with an accurate digital volt meter. With a stock alt you should see 14.2V to 14.6V and with the charger similar depending upon the settings.

 

[Don S/V ILLusion]

If you really have over 16V, you are cooking your batteries. electrical problems like this are impossible to diagnose over the internet. It could be a bad battery cell, bad connection, fault in the voltmeter or any number of other things. The only suggestion I can make is stop doing that or you will be replacing your batteries soon.

 

[Ross]

Get 8 or 10 new 1.5 volt cells and put them in series one at a time and check the meter.. You can always use a dozen "AA" cells.

 

[Maine Sail]

Get 8 or 10 new 1.5 volt cells and put them in series one at a time and check the meter.. You can always use a dozen "AA" cells.

For the price of the AA batteries you can buy a cheap DVM at Wal*Mart and know the voltage to within a few hundredths.. The Analog volt meters installed on boats are often anything but accurate, especially after a few years in the marine environment. Yet to see more than a couple agree with my Fluke. Some are off by over 2.5 volts or more.

 

[Chris Patterson]

The Fluke don't lie man, it's my most valuable piece of diagnostics. Those analog meters look cool on the panel, but most are junk. Especially when you want to know that critical measure between 11.8, and 14.2 volts.
I have a very nice 87 that I use most often, but I have a 73 that I've had for over 20 years, maybe 25, that works like the day I bought it. I have the good rubber case on both of them, but that old 73 has been drug through the mud and the blood. Keeps on tickin..
I've gotta admit, I did hard wire in a cheap DVM on another boat I've got. A glance at it, tells me what I need to know. Accurately.

 

[kenn]

Right on, Chris.I love the Fluke meters - I bought model 77 meters when I was doing service some... 20+ years ago. But for my home use, I have had pretty good luck with mid-priced 'clones'. My oldest digital meter is a Radio Shack 'clone' of the Fluke 70 series, complete with auto-ranging, that responsive analog bar, and even the rubber "slipper" . I was able to compare it with better meters and the voltage accuracy is pretty good. Also had good result with Canadian Tire's top ($60) meters, which go on sale for ~ $20 at least once a year...

Warning - really cheap DVMs ( < $20 ) can sometimes be out by up to a half volt on the 20v scale; it all depends how much attention was paid when they were aligned at the factory. Compare with a known good meter before trusting it 100%.

 

[weinie]

Thanks for the help guys!

It wasn't till later in the day that my friend told me that the AC battery charger was also causing the voltmeter to spike to past 16V, so my original thought was that I shorted something behind the alternator when I moved it! And then I was mystified that a short or a fried diode could cause and increase in voltage rather than decrease. It also seemed coincidental that the voltage spike and the loose fan belt occurred almost simultaneously on relatively new and well maintained boat.

I didn't have my multimeter with me, but obviously the first thing to check is the gauge.


On my own boat, I have a "similar" problem with my tach where it sometimes bounces higher than normal for no apparent reason as if the alternator is putting out more juice to the tach sender wire than normal. I'm thinking I may replace the tach in the near future.

 

[AXEL]

It sounds to me like it's the alternator voltage regulator (diodes). You said you read 12 volts with nothing on, that's the battery by itself. When you start the engine it's over charging. I had this happen to me last year when my boat was struck by lightening. After the strike I fired up the engine and the volt meter was pegged at 16 volts. BoatUS told me not to run the engine and have it towed for survey. The alternator had to be sent out for repair. Came back fine, problem went away.

 

[Charlie Jones s/v Tehani]

It sounds to me like it's the alternator voltage regulator (diodes). You said you read 12 volts with nothing on, that's the battery by itself. When you start the engine it's over charging.

How so? Since it also happens with the AC charger, how can it possibly be the alternator alone?
Sounds more like a bum meter to me.

 

[weinie]

I didn't see it happen with the AC battery charger itself. My friend only told me about it later that evening when he plugged in.

That not withstanding, is it possible that an alternator or regulator could "fry" without the engine even running? It did have battery power to it, but I didn't think I jumped out any terminals with my tools while I was tightening the belt. I did ask my friend if he had switched the batteries or turned them off while the engine was running and he said he did not.

My other theory is that somehow the alternator fried up first and kinda locked up and perhaps created a lot resistance to spinning with the belt, causing the belt to squeak.

I know I'm guessing here without actually testing the voltages at the battery with a tester, but it's not my boat, so I am not going to fiddle around with it when he is not there.

 

[Bill Roosa]

You folks who are poo pooing analog volt meters are being kinda harsh IMHO. With just a little practice you can read to the tenth of a volt. As for inaccurate, they do have a calibration feature.

 

[weinie]

UPDATE:

I met my friend at the marina who confessed to me that he let the marina's mechanic take a look the problem. Sure enough, the alternator was toast. I'm still wondering, though, how it simultaneously caused the belt to squeak while putting out a huge output in voltage.


New alternator installed already and the boat is good to go. I will try to get more info if I see the mechanic next week.

 

[Bill Roosa]

High output implies high power draw through the belt so I'm thinking that is why it squeaked.
A bad alternator does not explain the high voltage when using the charger though.

 

[weinie]

A bad alternator does not explain the high voltage when using the charger though.

I know, but as I said, I wasn't there to actually see that part.