starter battery

[john102345]

Hi everyone




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.

[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.

[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.

[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.