There are special battery load balancing boxes commercially available=20 inexpensively. These are a 3-wire device and use a switch-mode=20 converter to transfer charge from the top battery to the bottom battery. I see them used in commercial trucking - many of those vehicles are=20 set up for 24 Vdc rails (battery, alternator, starter, HVAC) with the=20 remainder of the vehicle electrics being at 12 Vdc. The units that I've seen in the past do not appear to interfere with=20 the 2-way radios those trucks use (CB, VHF, UHF). dwayne At 06:14 PM 7/27/2015, Adam Field wrote: >This is a former Canadian vessel, which uses mostly 24VDC electronics as >well as alternator, starter, etc. The 24V lead acid battery bank is 2 x 12= V >batteries in series. > >South of Canada, the standard is 12V so we have a lot of 12V electronics - >radios, GPS, etc. > >Can I borrow the center tap of the batteries to make a 12V bus? This would >create an imbalance during charging I imagine - lowering the charge voltag= e >across the battery connected to ground. > >The batteries in question are 12V AGM, 200AH each. > >The 12V bus would supply up to 25A, but only when the alternator is runnin= g >- otherwise I imagine the charge imbalance would get out of hand. > >Am I better off with a DC to DC converter? >-- >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >View/change your membership options at >http://mailman.mit.edu/mailman/listinfo/piclist --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .