Alternator problem or normal?

[Delta4242]

Hi, I have a 2005 Grand Banks Europa trawler with Cat 3126B 450HP diesels.
On startup, both alternator outputs are at 14.0 volts. After departing the marina and raising the rpms to 2400, the voltages decrease to 13.3 with rpm. Returning to the marina, the rpms are brought to 650 for docking. The alternator voltages return to 14.0 where they started from.
Essentially, the voltages are tracking inversely with rpm's!
After plugging in the boat, and switching on the dockside charger, the batteries charge up and switch to float mode in about a half hour, which is normal.
This has been going on for quite some time without any other issues on the boat.
Everything is OEM, 110 amp alternators, #8 AGM Lifeline batteries, etc.
I don't get it. The alternator on my truck puts out 14.7 at startup then decreases to 13.3 after a 1 hour trip and stays there including parking it.
Any help would be appreciated.

 

[Bmarler]

Hi, I have a 2005 Grand Banks Europa trawler with Cat 3126B 450HP diesels.
On startup, both alternator outputs are at 14.0 volts. After departing the marina and raising the rpms to 2400, the voltages decrease to 13.3 with rpm. Returning to the marina, the rpms are brought to 650 for docking. The alternator voltages return to 14.0 where they started from.
Essentially, the voltages are tracking inversely with rpm's!
After plugging in the boat, and switching on the dockside charger, the batteries charge up and switch to float mode in about a half hour, which is normal.
This has been going on for quite some time without any other issues on the boat.
Everything is OEM, 110 amp alternators, #8 AGM Lifeline batteries, etc.
I don't get it. The alternator on my truck puts out 14.7 at startup then decreases to 13.3 after a 1 hour trip and stays there including parking it.
Any help would be appreciated.

if you start the mains and raise the rpm in neutral will the voltage drop right away? is it possible they're at 14 volts for a short time just to replace the power what you used to start the engines? or to replace power used on docking using thrusters?

 

[koliver]

Lots of threads on the subject of regulators. Use the Search function.
Speaking generally, OEM alternators often (usually, always) are designed to replace the amps used to start the engine, in a battery designed for starting.
Boats often (usually, always) have deep cycle FLA batteries for house use, Start technology for Start. For this difference, you need the right regulation, start regulation for your start battery, Three stage: Bulk, acceptance, float, for your house batteries.
You don't offer clues as to what your boat is equipped with. You may be watching a regime that is designed for your boat, or you may be watching something that needs to be altered by the addition of proper regulation.
More information would make a proper analysis possible. by some one here with knowledge of what behaviour you should expect in your exact circumstances.

 

[KnotYet]

Also, clean all the connections to shiny metal and retry the measurements with a
hand held voltmeter. You may be seeing the effect of a poor connection when the
charging system gets warmed up during use.

 

[Delta4242]

To Bmarler, The voltage begins to drop as soon as the rpm's are increased.

To koliver, I agree. But, I've never heard of any boat with two types of regulation. But, I'd like to hear more from possibly other GB owners.

Thanks to you both!
Rich

 

[utclmjmper]

Your alternators and regulators are responding as designed,, suppling the need..Just after starting,, the "need" is to replace starting energy,diesel engines need only a tiny amount of electricity to run after being started, compared to a gas engine that feeds the ignition system while running.. Normal "full charge" of your bank is 12.6,, any above that is to supply other "needs and bring the bank to float.. ( Float is only a temporary surface charge and will dissipate quickly.)>>>Dan

 

[Delta4242]

To KnotYet, Thanks. That's all been done twice. The kicker is why is it on both alternators?
Rich

 

[koliver]

To Bmarler, The voltage begins to drop as soon as the rpm's are increased.

To koliver, I agree. But, I've never heard of any boat with two types of regulation. But, I'd like to hear more from possibly other GB owners.

Thanks to you both!
Rich

With twins on my boat, the port engine feeds the start battery, through a built in regulator on the OEM 50 amp alternator. It even has green paint on the case. The Stb engine feeds the house system through an external 3 stage regulator on the much higher capacity alternator. Unpainted, so a later addition.
I didn't design this system.
So from my perspective, a common system.

 

[CaptTom]

Yeah, that's backwards. The voltage shouldn't decrease when RPMs increase. If it always, consistently does that, it makes no sense. Is there any other load which would come on coincidentally with low RPMs? Have you done multiple tests of different RPMs while tied up at the dock, to eliminate external factors?



The only other thing I can think of is slipping belts. Odd that both of them would be loose at the same time, but it's worth a check.

 

[KnotYet]

To KnotYet, Thanks. That's all been done twice. The kicker is why is it on both alternators?
Rich

It sounds like your charging system is working as intended as utclmjmper says.
Another factor is the age and condition of the batteries. As they age they might
reach the fully charged condition @ 14V sooner due to reduced capacity.

 

[firehoser75]

+1 for what Keith said.
From my experience (and I am not a marine electirician) most stock alternators on boat engines are designed and setup to restore the charge to the start battery after starting the engine and to provide the small amounts of power used to run. Therefore, they run for a very short period of time at a higher output and then quickly drop the level, somewhat like you describe. Maybe the higher "ending" output is due to thruster use??? As designed and installed they usually do a poor job of recharging the house bank. These "standard" alternators are basically automotive/light truck alternators and are internally regulated. They are not "heavy duty" and cannot operate producing high current for long periods of time (they will burn out if asked to do so).
Personally, I did not count on my alternator to do any recharging of my house bank (although it did provide a very small increase in charge), it just recharged my start battery and provide some charge to my bow thruster/ windlass battery, while operating "systems" while underway.

To improve these alternators capability to recharge the house bank (if desired), they will require being "rebuilt" (sound like you did that recently) and changed over to temperature compensated external programmable regulation. Some rewiring is probably also needed to send the charge directly to the house bank, with another way to recharge the start and thruster batteries (like ACR, Echocharger, etc.). If you do this, it will provide a limited improvement. If you want the maximum value from your alternators, install new externally regulated heavy duty alternators as they are designed for this purpose including better alternator cooling.

Just what I have experienced and been told over the years, including from my electrician.

 

[diver dave]

I think you have some amps running thru the voltmeter NEG reference. More charge amps, less V to the meters. Nothing broken, just suboptimum wiring.

 

[High Wire]

Verify the helm gauges with a DVM at the alternator output terminal. The alternator may have the output cut back by a temperature sensor.
Just one more reason a cruiser should have a DC clamp-on ammeter on board.

 

[C lectric]

I think DiverDave has a very good point.

As the engines rev up the alternators should be producing more current. At idle they will produce only a fraction of their capacity. Maybe as little as 10-20%. They simply are not being spun fast enough for full output.. The voltage will be up, the current low. So any Vdrop will be low.

If the wiring or a few connections are not up to the job then
excessive Vdrop will occur and ultimately cause a slower charge rate.

Since most voltmeter readings are taken from the panels the Vmeter will show the lower system voltage. If the V is read at the alternator it may well show the higher voltage.

THe excessive Vdrop will occur because a too small cable or poor connections will produce excessive resistance, thus heat and limit current output. The higher Vdrop will show on the Vmeters as lower voltage. It will also limit the actual higher current to the system even though the alternator at the higher running revs is capable of a higher output.

This can be checked by running the engine and doing some checks. THe boat can be tied to the dock, out of gear.
You are looking for too big differences in voltages between the alternator, the batteries, the dash meter and also at the dash meter sensing terminals.

While the engine is idling with a low load, 15-20A:
-- check the alternator output voltage.
--Then read the Dash meter AND check the Dash meter reading at its terminals with your DMM.
--Check the voltage at the batteries.

Then raise the engine rpm untill you see what you described plus a few revs.
Recheck those readings.
-- The alt. V should remain or be very close.
--Check the dash meter reading, check the dash meter terminal readings,
---check the battery voltage.


If you can a current meter reading between the alternator and the batteries could be usefull. You should however be able to see if excessive Vdrop is occurring.

If the wiring and connections are in good shape and adequate the voltages at the alternator and the dash meter should be virtually the same.

If there is much difference at all then you have a poor cable, either + or - leads, or connections.



A quicker way, maybe, would be simply let it run for a bit at the higher revs and then feel the main connections and wires between the alt. and batteries. If they are warm or hot to the touch you have an answer.

Just be carefull as any jewelry could lead to a serious injury. Take it off.

If you have a thermal camera or app. for your phone that could also be used.

 

[contingensea]

ER heat will adversely affect Alternator output which may explain the decrease in output while underway.
From the info provided I’d say the system is working as designed particularly since batts are back to float charge, on shore power, after only an hour.

 

[Mobcat]

I actually think you over thinking a non existent problem, all sounds fine to me, I would be worried if it was displaying 15volts or 10Volts, all is in range alls good ….., move on to real problems around the boat that actually need attention NOW … if you have any problems????…….maybe you don’t have any issues and that would be good for a boat …..but you could just be trying to create one that’s my thoughts anyway .

 

[SteveK]

Another thought. IMO.
You say the voltage is high at lower rpm then lower at higher rpm then returning to higher voltage with lower rpm after a time when the battery should be topped up.

I would check the fan belt for slippage. Look at the belt for signs of glazing. Higher rpm and belt slips a bit lowering alternator rpm, lowering voltage.
Of course if you have serpentine then ignore.

 

[cafesport]

So that alternator charging profile, if correct, is incorrect for your batteries. It will actually promote sulfation which will cause your alternator to behave the way you have described.

Start by verifying that the readings you are seeing on your panel meter coincide with the readings at your battery terminals. Next verify your alternators. Once you’ve got that sorted out have a good look at lifeline’s charging parameters here https://321166-984045-raikfcquaxqnc...2015/12/6-0101G_Lifeline_Technical_Manual.pdf .

Final step would be to verify your alternator and shore charger parameters agree with what lifeline recommends. If you have a Balmar external regulator, setup can be a bit tricky, but if you search the archives here there is good info on exactly how to do so.

 

[sunchaser]

Delta
On our vessel, the two dash mounted voltmeters read close to the profile you have mentioned. They are both reading the voltage as measured for the start bank only.

Both start and house banks have a BMK which provides "battery health" for each. The BMKs tell the tale with the start bank normally full and the house bank going up and down in concert with house demands.

Our house bank was installed after the original build with no attempt or need seen to modify the original dash meters from their start bank only setup.

As several have suggested you likely have no issue provided your start and house banks are staying topped up. Do you have a non dash monitoring system via a BMS setup to monitor your batteries' health?

 

[Mischief Managed]

First things first, the voltage you see is not just the alternator output, it's a combination of the alternator output AND the battery bank the alternator is connected to.



I bet you have an ACR (automatic charging relay) in you boat's wiring. As RPMs increase and the start battery gets fully charged, the voltage goes high enough on the start battery to trigger the ACR contacts to close. This connects the starting bank/alternators to the house bank, and the house bank, even fully charged, is only 12.6 Volts, so it drags the voltage of the entire system down. If you have house loads while underway, the house batteries may never get to float, so the voltage will just stay under the 14 volts you typically see when the ACR contacts are open. When you throttle back, the alternators can't keep up with the house loads and the ACR opens, to prevent discharging of the start battery, and the voltage will go back up to 14 as the alternators re-charge the start battery. It's perfectly normal and has nothing to do with your alternators, they are likely internally regulated and "dumb".



Assuming I am right about having an ACR, try locking out the ACR and see if the voltage stays up at high RPM. I bet it will.