Alternator sensing anyone?

[fisherman]

I have a split charging system, alt to diode, then to two battery banks. Does the alternator sense via the engine panel red light, which is to the start bank, and if so is it missing the fact that the service batteries need more charge.

 

[TargaLout]

The engine panel red light is normally a charge indication lamp from the regulator part of the alternator and not the battery sense circuit. You can run a sense wire via a 5 Amp fuse (which should be mounted close to the +ve post) of the domestic battery back to the alternator +ve sense. This is what Fairline did on my last boat which had a start and a domestic bank via a split charge diode block. The wire that was connected to the alternator +ve sense is then insultated up and tie-wrapped to stop it shorting out.

 

[halcyon]

Most alternators regulate by the alternators output voltage, ie machine sensed. The blocking diodes then drop 0.6 - 1.2 volt, killing a big chunk of your battery charging capacity.
Two options, fit a charge relay to avoid volt drop, or a smart alternator regulator overcome the volt drop in the blocking diodes.

Brian