starter battery charging to 15volts

[john102345]

Hi everyone
Having a few problems with my charging setup.

On a recent trip north from Plymouth to Largs my Bavaria 301 panel started to alarm read 15.0 volts for the starter battery & my Volvo EVC at the helm came up with the battery warning symbol.
The house bank was all fine as we were using quite a lot of nav gear & running lights etc.

I first suspected the Alternator voltage regulator so changed the Alternator for a new Parts4engines one same as before 115amp version
after going out for a run for 20 mins at 2000 revs the 301 panel threw the same battery voltage alarm 15.0 volts

So I tested the starter battery & it is the original Banner battery from the first commissioning 2011 the state of condition read at 61%
So ordered & fitted a new starter battery like for like lead acid 95amp hr 720 cranking amps.

Took her out on Saturday for a run & after running for 20 minutes at 2000 revs she alarmed again at 15 volts on the 301 panel & at the EVC helm panel as soon as took off the revs the alarm would drop off.
I took out my multimeter while the alarm was running & the starter battery read 14.9 - 15 volts so same as the 301 panel ( thought it may be a panel reading slightly out)

So now a bit stumped, can anyone suggest a route forward, please?
bit of a novice with electrical & had the alternator professionally fitted I fitted the new battery.

The boat is a 2011 Bavaria 36 cruiser with a 95amp hr starter battery & 420 amps of AGM house bank 3 x 140 Exide's all 3 were fitted in 2022, did not have any issues before we put just under 100 hours on the engine for the trip. Total engine hours on the clock is as of 06/11/2023 is 599

Just a new note I can confirm before I had the 15v warning my Alternator belt was not tight enough so I had belt dust on the engine & could not adjust the adjustor as it was not there physically I think it was removed at not refitted for some reason (not me) when we fitted the new alternator we fitted a brand new belt & replaced the adjustment body so nice & tight within spec.

Thanks

[Krumelur]

Been there, done that :-)

Diode splitter broken. One diode of it, to be more specific.

This low-cost part acts as a drop-in replacement: https://www.victronenergy.de/battery-isolators-and-combiners/cyrix-battery-combiner-kit

And here's the full thread when I had this issue: https://bavariayacht.org/forum/index.php/topic,3767.msg24336.html

[sunshine]

Might be the yellow sense wire - did you have any problems with it when fitting the new alternator?

[tiger79]

Diode splitter broken. One diode of it, to be more specific.

No, if that was the case, there'd have been no charge to the house bank.

Much more likely is a disconnected sensing wire.

[Krumelur]

Given the poster's input I would not rule out the battery isolator.
"The house bank was all fine as we were using quite a lot of nav gear & running lights etc." does not indicate that the aux battery was being charged, but neither that it was not.
Wouldn't the house bank deliver power just fine for an extended period of time? After all, that's what its job is.
What we don't know is what the voltage of the house bank is when the issue occurs.

[JEN-et-ROSS]

Diode splitter broken. One diode of it, to be more specific.

I would agree with ,Krumelur' and suspect the splitter, if it's an older diode only type....
You'll always lose 0.5v or so at each diode...
But if the 'house' diode side is faulty and losing more, this will confuse the regulator into bumping up the output to compensate...(assuming the sense wire is on the 'house' bank..)
(are the splitter cooling fins hot?)
This means your 'engine' battery is getting the full whack, maybe a volt or more than it needs and setting off your alarm...

(Note... 0.5v splitter drop doesn't sound a lot but bear in mind that a 'flat' battery is only a couple volts less than a fully charged one, so a 0.5v loss is approx. 25% of your charging ability = greatly increased time for a full charge. There are more modern 'zero loss' splitters)..........Bill.

[IslandAlchemy]

I had the same when the diode splitter went on my boat.

[SYJetzt]

The sensor cable has been ruled out as the cause. If the sensor cable is not connected, the generator regulates internally to 14.4V and the warning message from the MDI does not take effect. Rather, the diode splitter is suspect. If the connection between the generator and the service battery is interrupted/defective, the service battery is not charged, the voltage there remains at 12.8V (or less) and the yellow sensor line reports that the voltage to the generator is too low. This then regulates the generator voltage higher and higher up to 15V until the warning message appears on the MDI. This also explains why the warning message only appears after a certain time, namely when the generator has fully charged the starter battery.

[john102345]

Thank you to everyone who replied
We have a few things to check from all of your contributions I have put them forward to my engineer & will report back with an update when I get one.
Thanks again
John

[john102345]

Hi Everyone

Thanks for all of your help with my electrical issues here's an update.

My engineer
Took out all fuses cleaned & refitted them checking for poor connections

stripped off all alternator connections cleaned then & refitted checking for poor connections, cable breaks
checked & metered the output of the new alternator all good readings as they should be

checked & metered the split diode box inputs & both outputs all Ok

run up the engine for over 60 mins alternating the revs from 1000rpm - holding at 2300rpm for 20 mins no over voltage readings on the MDI panel at the helm or on the Bavaria panel.

batteries where fully charged from shore power prior to starting the engine so we did not have to wait for the batteries to come up from lower voltage.

All as should be correct voltage readings throughout.
could not find a fault or smoking gun.

when I am next up at the boat I will take it for a run & see if I can replicate to the issue.
just wondering if we made good some sort of connection by disconnecting everything first then reconnecting.

I will I think replace the split diode charger for a newer version as  suggested by a few here to save on the voltage drop but apart from that a bit perplexed.

Does anyone have any thoughts?

Thanks again
John 

[tiger79]

Most likely a poorly connected sensing wire, as I suggested earlier.  Re-making all the connections will have sorted it.

[Krumelur]

My 2 cents:

* Throw out the diode splitter. It's nothing but an ancient radiator :-) The 50 bucks drop-in replacement using 21st century tech is worth it.
* "My" technician made me pay €400 to tell me that there was no issue and that the diode splitter was ok. That's when I started to learning about the stuff myself (this forum is great), took a digital meter and measured resistance myself. What can I say? The diode splitter was broken.
* The sensor cable is a quick and easy replacement, go for it.

[john102345]

Hi All
Engineer tested all systems cabling & disconnected - reconnected all then checked voltages read all good as discussed before, no issues ran boat up for 1.5 hours at various revs etc batteries where charged fully before starting engine as boat on shore power as I have been running the dehumidifier.
No faults found could not get it to charge to 15.1 volts on the starter battery

I have an original fit Sure Power 1202 multi battery isolator 120 amp version this was extensively tested on the outputs before the engineer left hence we thought we had cracked it.

Now just arrived on boat for a week of sailing & started up the boat charged starter battery to 14.8 then 14.9 then 15.0 & 15.1 then alarmed on the helm volvo tacho just as before.

As you have said change the split diode isolator It must have a intermitant fault
I will order new one now.
Does anyone have any thoughts on the best one to fit Isome mention Sterling or Victron quite like Victron kit so will have a look at that first
Thanks all
John

[tiger79]

As you have said change the split diode isolator It must have a intermitant fault
I will order new one now.
Does anyone have any thoughts on the best one to fit Isome mention Sterling or Victron quite like Victron kit so will have a look at that first

If you're sure it's an intermittent diode fault (rather unlikely), I'd suggest replacing it with a low-loss isolator.  I'd look at a Victron ArgoFet.

[Jess21]

The voltage drop over the power diodes in your diode splitter is most likely to be 1,1 .. 1,2 Volts when a large charging current is feeding your maintenance battery.
The voltage drop over the power diode feeding your starter battery is 0,6 .. 0,7 Volts since (almost) no charge current is flowing to your starter battery.
Since the sense wire is connected to your maintenance battery, the voltage of the starter battery will be 0,5 .. 0,6 Volts higher than the load voltage on the maintenance battery.
Depending on the voltage regulator in your alternator, the sense voltage setting is most likely 14,2.
A load voltage of a starter battery of 14,8 V can be expected for short duration time.
When the maintenanc battery get loaded, the load current decreases and the voltage difference will also decrease until both batteries will have same loading voltage.
It's all quite easy to measure with a voltmeter by measuring the voltage drop over both power diodes of your diode bridge
When the voltage drop appears to be higher than 1,2 Volts, the diode bridge is most likely damaged.
When you end up in situations that your maintenance battery is often depleted, an argofet diode bridge is a good solution since voltage drop over the diodes is limited even by large current flows.

[john102345]

Hi All
I hope you are all well.
Still having issues with my charging set up.
Here,s an update.

Original fault
Current set up suddenly started to charge the starter batter to 15.1 - 15.2 - then 15.3 volts then triggers helm tacho with battery alarm.
The house bank at 420amp was fine charging to 14.5 v no problems

Changed the alternator on advice from my engineer still same
Changed the starter battery for a new one old one as measured 62% state of condition still the same
Checked again with my engineer all connections disconnected cleaned and reconnected fault became intermitant.
Changed out the diode splitter as reccomended on here for a Victron argofet splitter

Now come to the boat after a couple of weeks of it charging to 14.5 volts & holding as it should thought we had cracked the fault.

Just tried it now to go out for a motor and at 100% battery charged on both the house bank and stater battery before starting engine.

Charged to 14.8 then 14.9 all the way up to 15.5 volts which I have not seem before what was odd this time is it was charging both the starter battery & house bank to 15.5 volts,  not seen that before this fault was only on the starter battery side hence here some suggestion that it maybe the original fit diode spliter that was at fault.

To be honest I am lossing the will to live with this last time at the boat I could have drilled a hole in the bottom & gone for a coffee!
Its been going on since August 23 & have not been able to trust the engine to go out.

I really don.t know enough about electrics to move forward can anyone suggest anything that will help something else to check ?
My engineer is very busy and sometimes takes a few weeks to get to the boat to have a look see but when he,s onboard it works normally and tops out at 14.5 volts everytime he,s here I have filmed it on my phone just so he thinks I!m not going bonkers

Thanks
John

[elias]

Most likely a poorly connected sensing wire, as I suggested earlier.  Re-making all the connections will have sorted it.

Back in the past similar problem solved this way .

Try this ,instead the sensing wire connected to the house battery , connect it to the starter battery

[tiger79]

Try this ,instead the sensing wire connected to the house battery , connect it to the starter battery

That's not a good idea; the house batteries will get less charge.

[elias]

Try this ,instead the sensing wire connected to the house battery , connect it to the starter battery

That's not a good idea; the house batteries will get less charge.

You are right but if it works he can go out for a sail with less stress .

[SYJetzt]

this time is it was charging both the starter battery & house bank to 15.5 volts,

Check your alternator regulator.....

[marioxp]

measure the voltage between the sensing wire and the alternator housing (or from where it gets the negative pole) to determine what battery voltage the alternator sees.  And compare it to the battery voltage.  Either the alternator sees a lower battery voltage and therefore charges it with a high voltage, or the regulator on the alternator is faulty.