Alternator Output Question

[kthoennes]

So my port engine voltmeter is reading 11.-something volts initially when I start the engine. My batteries (two, parallel) on the port side both read 12.6 (individually), they both match (FLA), and they're relatively new, 2021. When the engine is running I get 13.4-13.6 at the batteries, so I assume it's a bad or sticky or stiff gauge. The gauges are original to the boat, 1996 VDO gauges. The alternators are probably original to the boat also, Marine Power, 55 amp, double pulley. After about ten minutes though and the engines are warm, the port volt meter reads just over 13. Starboard engine reads between 13 and 14 right at startup. In other words, as the port engine warms up, the volt meter creeps up. So my question is, alternators don't warm up, do they? In other words, the output is the output, right, they don't gradually creep up after they start, do they?

I have a new Arco 70 amp (20830) on order just for general good maintenance and a slight upgrade in amps, but I'm really hoping the gauge isn't failing because I've done a diligent search and you can't get them anywhere anymore and I really don't want to have to start sawing different sized holes in the helm dash panel and changing sending units.

Thanks.

 

[DavidM]

On the surface, your port alternator sounds like it is bad. But first double check the voltages with a good meter.

David

 

[kthoennes]

Thank you. I'm actually hoping that's what it is, and I'll swap the new alternator in and see how the gauge behaves. The port gauge is a triple in one housing, oil pressure, volts and temp. If the volt gauge is going I suppose I could install just a new separate voltmeter and continue using the VDO gauge for oil and temp and just leave the volt meter dead and disconnected in the VDO gauge, but that violates my sense of good order. Faria makes a triple (GFC610A) but then I assume I'll need all new sending units, different size hole in the dash, etc.

 

[STB]

I don't trust gauges that don't work (.)

Check with a good meter at the alternator before doing anything else.

Trying to correct a bad sensor by intuition is really tough. Approximately as tough as knowing the measurement by intuition.

 

[tiltrider1]

I would test the alternator with a multimeter before I swapped for a new alternator. Boat gauges are notoriously inaccurate and faulty.

 

[twistedtree]

If you are reading 13.4 to 13.6 at the batteries when the engine is running, then the alternator would appear to be good. Measuring at the alternator would confirm this. Sounds like a failing gauge.

 

[Simi 60]

If you are reading 13.4 to 13.6 at the batteries when the engine is running, then the alternator would appear to be good. Measuring at the alternator would confirm this. Sounds like a failing gauge.

Yep.

 

[Barking Sands]

9 times out of 10 when the gauge is reading lower than what is measured at the batts or alternator its due to corrosion on contacts or in plug breaks/terminal strips and especially grounds. It can be a bear to track down. But changing a gauge wont fix it.

I would start by measure votage at the gauge with a meter. if the meter matches the gauge, but both are much lower than the batt or alt reading then its the wiring. I would then take a wire and attach it to a very good ground and then touch it to the ground wire on the gauge and see if voltage rises. If it does clean all grounds, terminals and plugs in between. If that does nothing then you'll have the follow the power wire back and clean all contacts. You can also run a long wire from the alternator to the gauge direct to double check.

 

[FlyWright]

Do you have upper and lower helms to crosscheck the alternator readings? To me, it seems like your port battery voltage may be dropping off more after the start than the stbd battery. Could it have a weak cell?

Have you checked the water level and the specific gravity of each cell?

 

[kthoennes]

Upper helm only, no lower. Battery water levels good but I didn't test sg. That's the thing, the volt meter gradually creeps up after start, from 11.-something to eventually 13, doesn't drop. I'm pretty attentive to the batteries. I'd simply swap the wires from starboard to port volt meters as a test but the helm access panel to the underside of the dash is only big enough for my head or arm but not both, and I'd need to use a jumper wire so it's a challenge to swap wiring in there.

 

[KnotYet]

Easier to check the voltage at the batts with a good hand held meter.
If it correlates to the helm gauges then you know they are correct and can move on.

 

[C lectric]

Which battery set starts the engines?

Which alternator recharges those engine start batteries?

Starting engines draws a lot of current which will knock the battery voltage down.

Then the alternator, once the engine is actually running, will replace the power lost but it may take a few minutes. Alternators do NOT produce full power/amps without actually being spun to about at least half of their rpm range which is more than an engines typical idle RPM. To be a bit clearer that usually is about 1/2 the engines rpm range.

So it may take a few minutes for the battery to get close to gaining back what it lost.

Do the checks as described above but be aware that the alternator cannot instantaneously replace the lost power and especially if the engine rpm are low.

 

[ronobrien]

I will emphasize what others are saying, in that you want to use a GOOD meter for testing. A friend was looking for a problem on his boat with a Home Creepo cheapo meter and couldn't figure out what he was doing wrong, so he called me for a 2nd look. I used my Fluke 87 and found the problem in a couple minutes. We re-tsested with his meter and it didn't see the small resistance problem. His methods were right, his equipment was bad. You're less likely to have that problem with what you are testing, but just something to be aware of.

 

[kthoennes]

Thanks for the responses everyone, sure appreciate your time and help. We'll, I just replaced the original 1996, 55 amp alternator with a new Arco 20830, 70 amp. Might be my imagination but the engine seems to run slightly smoother. But the volt gauge is still coming up to just below 12 when it starts, then about five min later, comes up to halfway between 12 and 13. Starboard engine comes straight up to 14 and stays there, as it did before. Next I'll fabricate a little jumper from the starboard gauge volt wire to the port gauge to see if it's the gauge or wiring somewhere. (I'm using a PT multimeter, automotive, made by a company called Performance Tool, Kent, WA. Not high end certainly - junk?)

 

[twistedtree]

Thanks for the responses everyone, sure appreciate your time and help. We'll, I just replaced the original 1996, 55 amp alternator with a new Arco 20830, 70 amp. Might be my imagination but the engine seems to run slightly smoother. But the volt gauge is still coming up to just below 12 when it starts, then about five min later, comes up to halfway between 12 and 13. Starboard engine comes straight up to 14 and stays there, as it did before. Next I'll fabricate a little jumper from the starboard gauge volt wire to the port gauge to see if it's the gauge or wiring somewhere. (I'm using a PT multimeter, automotive, made by a company called Performance Tool, Kent, WA. Not high end certainly - junk?)

A clamp-on ammeter is a good investment, and would tell you conclusively if the alternators are putting out current. The discussion (I think elsewhere) about engine intake heaters that run on a timer on first start could easily give the illusion that an alternator isn't working because the heater is sucking up all the output.

 

[kthoennes]

Yeah, that does make sense to me (the other discussion I mean) but if that were the case on my boat, seems to me the starboard alt wouldn't read 14v a second after startup. We'll see, I'll continue to chase the problem.

 

[Bmarler]

Sounds like a flaky connection to me. When things warms up the connection tightens a bit and reads closer.
It could be happening within the gauge too, I know my old Stewart warners get pretty warm when they’re operating.

 

[Turtle Blues]

Are you certain your loads are identical side to side?
My system has an isolation block to split charge between house and start batteries on one side that shows higher draw and slightly lower voltage at the helm until the house batt is full. Other side powers the steering pump so it sees a different amp draw when running. Adding a couple of connections and 60 feet of wiring to the meters I hardly ever see exactly the same numbers but at the end of the day the charge levels are good.
I think that the digital display to 10ths of a volt causes more anxiety than the old analog "it's in range" comfort zone.

 

[kthoennes]

That's certainly one of the possibilities -- the two sides are very different. Single FLA starting battery on the starboard side, two FLA batteries in parallel on the port side. Two of the three bilge pumps are wired to the port side, not starboard, and the fridge -- although I switch off the fridge and almost all the house load and of course the battery charger when I'm chasing this problem. If I'm thinking clearly, swapping the two gauge wires with a jumper this weekend should at least tell me whether it's the gauge, or something else. If I connect the port wire to the starboard gauge and it reads 13-14, then I know it's the port gauge.

 

[Barking Sands]

That's certainly one of the possibilities -- the two sides are very different. Single FLA starting battery on the starboard side, two FLA batteries in parallel on the port side. Two of the three bilge pumps are wired to the port side, not starboard, and the fridge -- although I switch off the fridge and almost all the house load and of course the battery charger when I'm chasing this problem. If I'm thinking clearly, swapping the two gauge wires with a jumper this weekend should at least tell me whether it's the gauge, or something else. If I connect the port wire to the starboard gauge and it reads 13-14, then I know it's the port gauge.

Or, once you have access to the back of the gauge use a multimeter to see what voltage is actually at the gauge. I suspect the meter will read what the gauge is reading. Then use a wire to connect the ground on the bad side to the ground on the good side, providing an alternate and additional ground path. See if your readings improve.