What does my Voltage Gauge tell me?

[ranger58sb]

The remaining mystery is how are the batteries on that bank fully charged after a 10 hour run?

Are you running the genset underway? For AC or whatever? With charger on?

We replaced an alternator just prior to our run to Florida last year. Got about halfway down the Chesapeake, no chargee. ???? Turned out to likely be a faulty installation, but the upshot was we ran all the way to JAX with no working alternator on that engine. Genset (for inside heat) and charger underway solved that.

I do have one question here. If it shows the voltage coming out of the alternator, why does it show 12 volts when I turn the ignition key to run BEFORE the engines start? Alternator isn't outputting at that point. Does that show the battery level, and somehow it switches over to the alternator output? Because again, the batteries themselves show 12.8 even when that gauge shows less than 11.

Yes, it sorta-kinda shows battery before you start and then it begins to show alternator voltage.

Your air pre-heaters start sucking down the battery voltage when you turn the key on, too, so that's maybe another factor at play. The pre-heaters cycle on and off, so it wouldn't surprise me if you were to see initial voltage (engines not yet running) -- say 12.6 at the helm -- falling to 12.2V then bouncing back up to 12.6V.

Can't explain why you're only seeing 12.0V at the helm when you've got 12.8V at the batteries. But then again, I can't remember what the Faria presentation was or how accurate I thought it might be... since I switched everything to digital gauges.

-Chris

 

[C lectric]

There is a cheaters way to test that voltmeter. Make some LONG leads for both the negative and positive side of the guage. Use some #16 or 14 wire. DOesn't need to be pretty, just good connections.

All this should be done with No loads, No charge source except the alternators.

Run the engine and test the voltage as the guage is wired, both at the batteries AND the guage. Then shut down the engine and disconnect the existing leads at the guage. Just be sure they are dead and tape them separately as they will come live as you do the next test.

Then use the long leads after running directly between the guage and the batteries. What does the guage say then? Confirm the readings with your DMM. Of course if the guage still reads too low than it is likely the guage.

I think I would double check the reading at the original leads as your DMM uses a TINY amount of current to get a reading, far, far less than the guage so it won't cause any appreciable Vdrop. If there is a problem in the guage wiring then the voltage will likely almost mirror the battery voltage. The guage uses much more current so any circuit problems will show only when the guage is connected.

With the LONG leads, if now the guage reads the same or basically the same as the batteries then you know there is a wiring problem. The trick will be too find it. You will then have to find the source of the original V meter signal. It could be right at the panel. Often the meters/guages , all of them are fed from the panel by the ign. sw. run position or there may be a small relay operated by the ign. sw. run position to feed power to the panel and guages. If the whole panel is low then maybe there is a questionable connection there.

 

[Bacchus]

I do have one question here. If it shows the voltage coming out of the alternator, why does it show 12 volts when I turn the ignition key to run BEFORE the engines start? Alternator isn't outputting at that point. Does that show the battery level, and somehow it switches over to the alternator output? Because again, the batteries themselves show 12.8 even when that gauge shows less than 11.

BD

Many alt outputs are wired to the pos starter lug and use the starter cable as the return to the batty. So with eng off you will have the same 12V at alt + as at starter + unless you have an isolator in between.

 

[Darlin]

Wow. Very confusing. One recommendation. Test the battery with one lead disconnected to get an accurate battery reading. Don't trust the battery off switch, stray voltage will find its way to the battery from charger wires.

 

[Robvald]

well you all are making me dizzy. but I'm trying to follow along as I have 1 set of gauges down at the moment and i suspect its related to the alternator wiring.

 

[BDofMSP]

Back at it

Hello folks. Finally returning to this issue. Two weeks ago our new dinghy tubes arrived and that consumed my weekend replacing them. Last weekend we had guests so I couldn't work on it. The good news is a) I'm on the boat and I'm here for over a week, and b) I now have SCHEMATICS of the boats systems. Unfortunately it's the entire owners manual pdf, so massive. I can only post a link to it.
410 Sport Bridge Owners Manual

The schematics are at the very end of the document. Unfortunately there are schematics for a couple other similar models as well, but fortunately they are labeled. The other unfortunate thing is that I don't see the (shore powered) battery charging system anywhere on them.

There have been a ton of great suggestions here and I'm just getting started on them. This morning I've:

• Taken the batteries of the charger and disconnected the starboard bank. Batteries disconnected each show 13.3 or 13.4 volts. But that's right after coming off the charger.
• Reconnected the bank, leaving charger off. Measured output from the alternator directly (fast idle 1000 rpm). 12.7 volts
• At same idle measured the reading at the gauge. 11.9 volts

So clearly the batteries are taking a charge (not sure about holding it, but that's a separate issue - no indication that they are not). It seems pretty clear that the alternator is not outputting it's full potential, however I'm not sure if it was "excited" per previous posts. It also seems clear that there's additional voltage loss between the alternator and the gauge.

Side note - all this is on the starboard. I have not yet replicated the tests on the port side, which seems to be working fine, but I will.

I hate to complicate this further, but it seems pretty relevant so I'll add it. Last weekend, after the boat had sat on the charger for a week, we took off of shore power and prepared to hit the water. Went to start the starboard engine first, and although I got a buzzer I got zero action when I turned the key. Went down and measured the voltage of the bank and it was 13.3, came back up and tried again, still no joy. Hit the parallel switch and everything worked fine.

Since then I've started that starboard engine 6 times out on the water that weekend without requiring the parallel switch. Pops off instantly. This weekend after sitting just like the week before, everything works perfectly fine (starting-wise).

I'm hoping to attempt C Lectrics test next but I don't have enough wire on board to make that run from the fly back to the cockpit and into the salon and down to the ER. And of course now that I'm up at the boat my only nearby option is the ship store so I'll have to make a drive for it.

 

[BDofMSP]

Tested voltage at the ignition switch - 12.8
Between the closed switch positive and the gauge positive - 12.8
At the gauge (after grid heater draw ceased) - 11.3

Wait. By closed I mean off. But I guess that's really open. Sorry.

 

[Newtrawlerowner]

Hello folks. Finally returning to this issue. Two weeks ago our new dinghy tubes arrived and that consumed my weekend replacing them. Last weekend we had guests so I couldn't work on it. The good news is a) I'm on the boat and I'm here for over a week, and b) I now have SCHEMATICS of the boats systems. Unfortunately it's the entire owners manual pdf, so massive. I can only post a link to it.
410 Sport Bridge Owners Manual

The schematics are at the very end of the document. Unfortunately there are schematics for a couple other similar models as well, but fortunately they are labeled. The other unfortunate thing is that I don't see the (shore powered) battery charging system anywhere on them.

There have been a ton of great suggestions here and I'm just getting started on them. This morning I've:

• Taken the batteries of the charger and disconnected the starboard bank. Batteries disconnected each show 13.3 or 13.4 volts. But that's right after coming off the charger.
• Reconnected the bank, leaving charger off. Measured output from the alternator directly (fast idle 1000 rpm). 12.7 volts
• At same idle measured the reading at the gauge. 11.9 volts

So clearly the batteries are taking a charge (not sure about holding it, but that's a separate issue - no indication that they are not). It seems pretty clear that the alternator is not outputting it's full potential, however I'm not sure if it was "excited" per previous posts. It also seems clear that there's additional voltage loss between the alternator and the gauge.

Side note - all this is on the starboard. I have not yet replicated the tests on the port side, which seems to be working fine, but I will.

I hate to complicate this further, but it seems pretty relevant so I'll add it. Last weekend, after the boat had sat on the charger for a week, we took off of shore power and prepared to hit the water. Went to start the starboard engine first, and although I got a buzzer I got zero action when I turned the key. Went down and measured the voltage of the bank and it was 13.3, came back up and tried again, still no joy. Hit the parallel switch and everything worked fine.

Since then I've started that starboard engine 6 times out on the water that weekend without requiring the parallel switch. Pops off instantly. This weekend after sitting just like the week before, everything works perfectly fine (starting-wise).

I'm hoping to attempt C Lectrics test next but I don't have enough wire on board to make that run from the fly back to the cockpit and into the salon and down to the ER. And of course now that I'm up at the boat my only nearby option is the ship store so I'll have to make a drive for it.

Battery Voltage
To correctly test battery voltage you should remove surface charge. On AGM battery, let the battery sit for minimum 12 hours off the charger with no load then test surface voltage. 12.65-12.77 indicate 100% charge, 12.45-12.54 = 75% charge, 12.24-12.29 = 50% charge. If you have a "wet" battery, use a hydrometer to test.
Alternator Output
With the engine off, test the voltage at the batt terminal on the alternator before starting engine. You should see 12.6-12.7 volts (or less depending on battery state of charge). Then start the engine. Voltage should rise to 13.5-14.6 volts at 1500 rpm with no other loads if the alternator is working. Higher than than could indicate a problem with the voltage regulator. Some alternators have external regulators, some are internal. If it's internal, you'll need to rebuild or replace the alternator.

If you have 2 engines, perform this test on both to compare readings.

 

[BDofMSP]

Battery Voltage
To correctly test battery voltage you should remove surface charge. On AGM battery, let the battery sit for minimum 12 hours off the charger with no load then test surface voltage. 12.65-12.77 indicate 100% charge, 12.45-12.54 = 75% charge, 12.24-12.29 = 50% charge. If you have a "wet" battery, use a hydrometer to test.
Alternator Output
With the engine off, test the voltage at the batt terminal on the alternator before starting engine. You should see 12.6-12.7 volts (or less depending on battery state of charge). Then start the engine. Voltage should rise to 13.5-14.6 volts at 1500 rpm with no other loads if the alternator is working. Higher than than could indicate a problem with the voltage regulator. Some alternators have external regulators, some are internal. If it's internal, you'll need to rebuild or replace the alternator.

If you have 2 engines, perform this test on both to compare readings.

Thanks. Regarding the first part, that would be nice to do but I'm living on the boat all week. Leaving no draw on the batteries for 12 + hours isn't possible.

Regarding the alternator test, that's what I did, although it appears I didn't include that step. After reconnecting the batteries, I tested the voltage at the alternator with no charger and engine off (got 13.2), and compared it to with the engine started (got 12.7). I reached the same conclusion - the alternator is not outputting appropriately.

There still is a 1 volt discrepancy with that and the dash gauge however. And there still is the question of how the starboard bank is remaining charged even after 12-14 hours of running (without gen). It's obviously getting charged via the port engine alternator, but I'm not sure how.

 

[BDofMSP]

Hmmm. Just checked the output of the port alternator the same way. Oddly It shows me the same 12.7 volts. But that's at 1000 RPM, like I tested the starboard. So I cranked it up to 1500 RPM per the above recommendation. Basically no change. 12.75.

So measured directly both alternators are showing the same thing as each other. The port shows the same thing on the gauge, and the starboard shows a volt less on the gauge. Over time cruising has shown that the port gauge will remain constant and the starboard dash gauge will trail off over the course of the day. It will move up and down a little but the general consistent trend is down.

But at the end of the cruising day the batteries are fully charged. Odd.

Either way, I have a spare alternator so I'll swap out the starboard and see if anything changes. I'll get the current one rebuilt. If swapping makes a difference I'll get the port rebuilt too.

If not I have a wiring issue somewhere, which I dread the idea of resolving.

BD

 

[BDofMSP]

Okay! Swapped out the starboard alternator today (full disclosure - had the yard do it). Afterwards I saw the same readings ... Until I got it cranked up over 1500. THEN she jumped up to 14.1 both on the meter and the gauge. Victory.

The old one will be rebuilt and the rebuild will replace the port. That will be rebuilt as a spare.

Lots of battery monitoring to come. Long cruises planned Friday and Saturday and hopefully Saturday night on the hook.

BD