Battery charging via alternator (complex system) - how is this lot controlled?

[dunedin]

OK, so following on from an intermittent engine start issue, which MIGHT be related to low power in the engine crank battery, I got to wondering .......
(a) so how does the alternator charge flow get controlled and diverted to the various batteries?
(b) could my new Victron MPPT solar controller accidentally confuse the other stuff ?

Particularly interested in the charging "off the grid", as typically away from shore power for a number of weeks.

Apologies for a bit of detail, but don't know what of this is relevant
* Engine battery - 50Ah AGM
* Service batteries - 3 x 130Ah AGM
* Engine alternator - not been able to find any labels/specs, but on Volvo D2-52
* Battery Isolator (splitter?) - MasterVolt Battery Mate 1602 (IG bit not connected)
* Mains charger - MasterVolt Chargemaster 12 / 35 – 3
* Solar controller - Victron 100/15 - fitted near to service batteries and connected ONLY to service bank
All other than solar controller is original builder fitted, circa 2011

We took the view to connect the Victron solar controller only to the service bank for three main reasons - recommended to be fitted as close to battery bank as possible, engine battery a long way apart from service bank, and wanted to avoid complexity risking engine battery problems (ironic, eh).

So per the original questions
(a) what controls how the alternator charge gets to the two battery banks?
(b) could the solar controller increase the voltage seen on the service side and confuse things somehow ?

 

[jdc]

The alternator is self-regulating and produces a presumably reasonable output (should do if a modern one).

To Qu (a): The Mastervolt 1602 is a sort of ideal diode splitter, so it can go after the alternator without dropping Volts across it. So on charge the Alternator is controlling the charge of both battery banks, and they are being charged to the same level.

However I do not understand the comment you made about the 1G bit being not connected: the manual http://images.mastervolt.nl/files/ManualBatteryMate031021.pdf shows one input terminal and two output terminals, and a low-current reference ground. Which of these is not connected? Edit: ok you have the version with the Ignition (not 1G) input! It won't matter as this is designed to supply some power to the alternator if it doesn't have sufficient /built-in field excitation. That's unlikely to be an issue for you.

To Qu (b): It shouldn't matter as the Alternator would in any case produce sufficient Voltage for either battery attached to the ideal diode splitter.

 

[pvb]

So per the original questions
(a) what controls how the alternator charge gets to the two battery banks?
(b) could the solar controller increase the voltage seen on the service side and confuse things somehow ?

The BatteryMate allows the engine and service batteries to be charged together, without allowing the engine battery to discharge into the service bank. In other words, it's a low-loss splitter. If you haven't got the IG connection, the alternator will just output whatever voltage its regulator is set to, probably around 14.0-14.4v, and most of this will reach the batteries, as the BatteryMate is low-loss.

The 2 banks will accept charge according to their needs.

The solar controller will also try to charge the batteries, but it shouldn't confuse things in any way. The batteries will accept charge according to their needs, and I can't see that you have any chance of overcharging your batteries. Nor, indeed, with only 390Ah service bank, are you likely to undercharge your batteries, as the engine (which I imagine is a D2-55, not a D2-52) should have a 115A alternator fitted as standard.

 

[dunedin]

Superb, very helpful thanks

The Volvo contact suggested the standard alternator was a bit smaller - don't have my notes here but from recollection 60 or 70 amps, but will try to get a definitive view

And jdc thanks also - there seem to be a few versions of the BatteryMate, and ours has an extra IG slot on the front, which is not connected up. The manual online suggested for ignition sensing alternator, or something, and optional - so per pvb note probably not an issue on this setup.
Thanks