T&T: Genset Battery capacity

[Peter Bennett]

My boat also has a Cummins 6BT5.9.  When I bought the boat, the starting
battery was a single Group 27 - it did start the engine, but I always
felt that it almost wouldn't, so added a second Group 27.  The engine
starts promptly now, with no sign of hesitation, so I'd suggest that
a 4D or 8D is overkill for a Cummins 6BT.  If I recall correctly,
Cummins recommends a CCA rating of 900 or 1000 amps (but the engine
manual is on the boat...).

On my previous boat with a single 4 cylinder Lehman, a single Group 27
was adequate.

On my last sailboat, with a Yanmar 2GM13, I also used a single Group
27 with no problems (a Group 24 would probably have been adequate.).
This engine may be comparable to your genset engine.

It seems from my experience and comments on the list, that most boats
have much larger starting batteries than necessary.

Sunday, July 5, 2009, 6:52:32 PM, Steve wrote:

SS> The start battery on my Westerbeke 12.5kw genset is shot. I suspect my
SS> main engine start battery may not be far behind, they're both the same
SS> age. I may down size one or both, with some other changes. What I'm 
SS> considering for the genset is to replace the 4D start battery with a grp
SS> 31 (mfr. spec's 300-400 CCA), and add a manual parallel switch to the 
SS> main engine battery, they sit next to each other. My reasoning is that
SS> under normal circumstances, the grp 31 should be adequate to start the
SS> genset, and if the occasion arises that more cranking is needed, 
SS> switching the manual parallel switch would bring the main 8D starting 
SS> battery in parallel to help. If that isn't enough, a set of jumper 
SS> cables will reach the house bank easily.

SS> The other option I'm considering is to downsize the 8D on the Cummins 
SS> BTD5.9 to a 4D. I really dislike 8D's for their sheer mass, especially
SS> when I need to manhandle them up and out of the engine room!

SS> What say the list?

SS> Steve Sipe
SS> Solo  4303 "Maerin"
SS> Chesapeake Bay


-- 
Peter Bennett, VE7CEI    Vancouver, B.C., Canada
Ennos 31 "Honeycomb"
GPS and NMEA info: http://vancouver-webpages.com/peter 
Vancouver Power Squadron: http://vancouver.powersquadron.ca