using charging relay in multi-bank/multi alternator configuration

[pasty63]

We currently utilize 5 12v battery banks on board, windlass (1), house (2) and engine (2). The windlass bank is two 6v 2GC batts in series, the house is 4 6v 2GCs in series/parallel and the engine batts are 2 group 31 12v - each in their own bank. The house and engine banks have manual on/off/combine switches. We have twin diesels, each running a 60amp alternator with an internal regulator. All batteries are the lead acid variety. The port alternator services the house banks while the starboard charges the engine banks. The windlass bank is only charged when the battery charger is connected while the boat is docked.

This all works fine as long as we don't need to bring the anchor up on the windlass more than 5 times between docking - or spend more than 3 days on the hook without running extensively. The house batteries are never fully charged by the alternator since the available amperage at cruise speed (2000 engine rpm) is too low to bring 50% of the 490 ah bank back up to full. I would like to remedy these issues by adding a high output alternator and a auto charging relay. The HO alternator would go on the port engine (dedicated to the house bank) and the charge relay would go between the engine bank and the windlass bank. Further, I'd like to replace the 6 volts in series in windlass bank with single group 27 12v, or perhaps two group 27's in parallel. For the alternator, I'm considering a 150 or 200 amp unit using an external SAR (smart regulator).

Have others divided up the banks a way that might work better for me? Are the auto charge relays a good idea between engine and windlass banks?

The batteries have been sitting for 3 years while I repaired/replaced tank and coring issues. I've already recycled the engine batts, and I'll need to replace the other batts as well. I'm considering AGM's for the house and windlass banks as the are located in lockers within the living spaces of the boat.

Thanks for the feedback -.b

[michael pierzga]

Battery charging and smart switches are all a mystery to me. What I can tell you is that the charge cycle of a battery charger outpit is a steep high amp "ramp up" followed by a shallow, low amp.. absorbion cycle. Takes much longer than you think to replace the one hunderd amp hours comsumed with fresh 100 amp hours from your charger . A very helpful instrument is a digital "amp out"..."amps in " counter meter. Not so expensive and worthwhile.

[Landlubber]

patsy63,

My way of charging batteries in your situation is to run the alternator charge direct to the house battery bank first upon starting. Use a VSR to do this. After a while the house batteries will be charged and the relay will then connect the start batteries to top them up.

You can simply connect say a 25mm2 wire from the start bank to the anchor battery via a 50amp thermal resetting cb and diode to keep the anchor battery fully charged. The cb will prevent the winch from pulling too much current through the charge wire if the anchor battery was to be flattened.

[pasty63]

Originally Posted by Landlubber

My way of charging batteries in your situation is to run the alternator charge direct to the house battery bank first upon starting. Use a VSR to do this. After a while the house batteries will be charged and the relay will then connect the start batteries to top them up.

Thanks all for the replies. Landlubber - what you propose is what I might call a "cascading" charge - in that the banks are logically stacked in order of charge need, then the voltage sensing in the system could direct to the next bank as the charge needs are met. I have thought about this a bit and I like it as an alternative. I'll need to scribble on a wet cocktail napkin a bit this evening to see if I can translate it to my configuration.

-.b

[Landlubber]

...yes mate, there will be many ways to do the same job, just remember KISS as you go along, good luck.