Solution for Dual Engines Charging Single House Bank

[Poozer]

I have a catamaran with a single house bank and a start battery for each engine (port and stbd). Each alternator goes to a separate battery isolator that isolates the house and start batteries. The alternators on the Volvo engines are 60 amp Valeos that have a separate voltage regulator mounted on the outside of the case. The schematics from the boat builder have the regulator voltage sense wire from each alternator tied together and brought back to the house batteries so that the alternators will regulate to maintain 14.2v at the house battery bank terminals.

The port alternator does this just fine, but the PO had never gotten the stbd alternator to charge the house bank, (the stbd start battery charges OK). I looked into this and found the external voltage sense wires on the stbd regulator are disconnected, so the alternator is being controlled to output 14.2v at the alternator terminals. Subtract 0.6v drop through the splitter and 0.5v drop between the splitter and the house bank and the best case would be 13.1v at the house battery terminals. This isn't going to do much charging!

I'm planning on reconnecting the sense wires so they are tied together per the schematic to see if that resolves the issue, but as I've thought about this more, it seems unlikely that I will be able to get both alternators perfectly in sync due to voltage differences between the two engines.

So what will happen in this case? I'm assuming one alternator will dominate, and do the bulk of the charging, with the other kicking in when the battery bank voltage is quite low. I don't really see this as a big issue, but am I missing something?

Since my primary charging sources are my solar panels and genset, I don't want to go to the added expense and complexity of adding balmar regulators and centerfielder if I can avoid it.

Regards,
Doug

[djmarchand]

The original system is a pretty good one. Tie the two alternator sense wires to the same battery and they will coexist just fine. The two alternators will approximatiely balance the load.

David

[bill good]

Just check that the starter batteries don't finish up over voltage by doing so.

Bill

[Florida Mike]

I ran a small shrimp boat with an electric winch. Although it was single-engine, single alternate 2 battery banks I put the sense wire to the start battery. The only other power consuming devices on the start battery were engine related such as gauges and the alternator field current. It pull enough to activate the alternator when I use the winch. I personal feel that the start battery is more important than the house battery. I don't know if you can hand crank your engine I couldn't. Just my two cents, Mike.

[donradcliffe]

Originally Posted by bill good

Just check that the starter batteries don't finish up over voltage by doing so.

Bill

No worries, mate. The starter batteries should be just fine.

[Poozer]

Thanks for the advice, I'll make sure the start batteries aren't getting cooked. I have a manual changeover switch on each engine that will connect the house batteries to the starter in case of a failure.