Voltage Issues

[Rost]

Last night I noticed my voltage meter was pretty much maxed out at 18 as I was heading back to the dock. It should read around 13 volts. Correct me if I am wrong, but this typically means the voltage regulator is bad, however, I noticed that when I shut the motor down and turn the key off, the peg on the gauge only falls back to about the 10 volt mark.

Also, when your voltage regulator goes out, usually your tachometer goes out as well and my tach still works. Is it possible that it could be my gauge?

I have no clue with this stuff! Any ideas?

[Eric Wettschreck]

Dude, if your stuff is totally shut down, and you're getting a reading on your voltmeter, you have a bad guage, or a short.

Best way to tell for sure is to disconnect your battery. If you're still reading 10 volts it's either magic or a bad gage. My bet would be gauge. Flick it with your finger a couple times and see if it drops to nothing.

[Macgyver55]

The first thing I'd do is check the voltage across the battery with a volt meter while its running and verify if the gauge is accurate or not. When you get the result, you'll know if the problem is the gauge or the regulator.

[Rost]

Thanks Fellas! This after noon, I am taking it over to a guy that will test the actual voltage coming through. But before I do that, I will try disconnecting the battery as Boiler mentioned. Geeze, I sat there for hours last night looking at this thing and never once thought to disconnect the battery Good Call man! Thanks Again!

[BobT]

When I bought my preowned boat I noticed the gauge indicated the charge was up around 16v when running and about 14v with the engine shut down. It goes to 0 with power off. I checked with my voltmeter and the gauge is off by a couple volts. I have not found any means to manually calibrate the gauge so I'm stuck with it as is unless I replace it. Since I know how much it is off, I can calibrate it in my head.

Bob

[marine_man]

Rost -

Let us know what you find out... I would do like others have said and check the voltage at the battery - it could be a voltage regulator - which is a different component than the rectifier which is what your tach reads off of. That said though, usually a bad voltage regulator will take out the rectifier too... good thing you caught it if it ends up being the regulator.

Good luck!

marine_man

[Rost]

I started it on the muffs during my lunch break and I brought up the the voltage feature on my GPS overlay. According to my gps, at idle I was getting about 12.5 volts. I then accelerated up to 2000 rpms and my gps read 13.3. During this experiment, my voltage gauge peg was maxed out at 18 volts.

I would think my gps would give a true reading correct? If so, that pretty much means the voltometer is shot...not the regulator?

Again, thanks for everyone's imput on this!

[JohnMickish]

In this case I would trust the meter in the GPS over the gauge.

[marine_man]

Sure sounds like a volt gauge issue to me...

I would be inclined to keep an eye on it the next couple of times... but it is very likely the voltage gauge - and your GPS should almost always be right.

marine_man

[Whoaru99]

Quote:

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I started it on the muffs during my lunch break and I brought up the the voltage feature on my GPS overlay. According to my gps, at idle I was getting about 12.5 volts. I then accelerated up to 2000 rpms and my gps read 13.3. During this experiment, my voltage gauge peg was maxed out at 18 volts.

I would think my gps would give a true reading correct? If so, that pretty much means the voltometer is shot...not the regulator?

Again, thanks for everyone's imput on this!

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Quote:

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I would think my gps would give a true reading correct?

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Maybe - unless the GPS has a built-in voltage regulator. Connecting a spendy GPS to a potential electrical system fault was a pretty risky move, IMO.

It would be best to check with a multimeter. You can buy a shadetree-mechanic-grade multimeter that works OK for this sort of thing for roughly $20 or less. I have a couple of very good Fluke meters, but got caught with my pants down one time and bought a cheapie to get by. Just for kicks I brought it in to work and checked it against a couple of calibration standards. That cheap meter is more than accurate enough on both volts and resistance scales for general electrical troubleshooting.

[Eric Wettschreck]

Since my boat still is not running, I'd be glad take yours for the weekend. Given that amount of time I should be able to figure out the problem for you.

[Rost]

Quote:

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Quote:

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I started it on the muffs during my lunch break and I brought up the the voltage feature on my GPS overlay. According to my gps, at idle I was getting about 12.5 volts. I then accelerated up to 2000 rpms and my gps read 13.3. During this experiment, my voltage gauge peg was maxed out at 18 volts.

I would think my gps would give a true reading correct? If so, that pretty much means the voltometer is shot...not the regulator?

Again, thanks for everyone's imput on this!

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Quote:

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I would think my gps would give a true reading correct?

---

Maybe - unless the GPS has a built-in voltage regulator. Connecting a spendy GPS to a potential electrical system fault was a pretty risky move, IMO.

It would be best to check with a multimeter. You can buy a shadetree-mechanic-grade multimeter that works OK for this sort of thing for roughly $20 or less. I have a couple of very good Fluke meters, but got caught with my pants down one time and bought a cheapie to get by. Just for kicks I brought it in to work and checked it against a couple of calibration standards. That cheap meter is more than accurate enough on both volts and resistance scales for general electrical troubleshooting.

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Again, I really don't know much about this stuff...but isn't this why we have a fuse between the battery and the unit?

[Scott K]

The fuse will protect the wires from a melt down, or a fire, it limits the draw the protected item can draw, (amperage) it does not limit the voltage to it!

[Giant_Jackpot]

What kind of GPS do you have? I know on both my 5500c and 3500c the voltage will read differently with the backlight on and backlight off. Check it out and you will see what I mean. I would not use the reading on the GPS to diagnose the problem you are seeing. The best way is as others have described and get a volt meter connected across the battery. What people do not realize is that there is a voltage drop associated with the wires that connect the battery to the gauge (or meter). The longer the wire, the more voltage drop you will have which means less accuracy.

[Whoaru99]

Generally, for voltmeters, the length of wire is a non-issue for the accuracy of the reading.

This is because a voltmeter is a high resistance device. High resistance = low current draw. It is the current draw that causes voltage drop. Thus, with the miniscule current draw of the voltmeter, there is virtually no voltage drop so the accuracy of the voltmeter isn't affected in any significant way by the length or gauge of the wires feeding it.

[Giant_Jackpot]

99,

You are correct. I should have kept Ohm’s law out of the discussion. My point was to eliminate the unknowns like gauge accuracy; bad connections etc. and check the voltage at the battery with a good voltmeter to see what the deal is.

[Whoaru99]

Agreed.