BoatBanter.com - 24 / 48V System

Years ago I was involved in earthmoving equipment - all 24V. I saw repeated
attempts to save money by connecting 12V CB radios, security systems, car
radios to one 12V battery of a 24V system.
The only consistent result was abject failure - either one battery was under
charged, or one battery used so much water it was run dry. The result was
always grief, either battery failure, or flat battery.

My conclusion ( and ultimately edict) was that NO permanent connection was
to be made to the 12V point in a 24 V system. either but 24V ( and more
expensive) equipment, or buy a 24 / 12V converter and switch off the 24V
supply when not in use.

Whilst electronic systems have improved, I don't think there has been much
change in the physics of lead/acid batteries. Mixing 12/ 24 V or 24/ 48 V
has the same issues - if you expect to have reliable service from batteries
connected in series, they must have near as possible identical, and they
must see the same charge and discharge current. I'm sure there will be
examples of reliable systems which don't meet these criteria, but they are
the exception, not the rule.
I know the energy efficiency arguments against voltage converters, but if
there is no current connection to the mid point of batteries connected in
series, at least one is assured of even charge / discharge between the
batteries.

David Flew
"David Clark" wrote in message
...
Hi,

Seeing the dual output alternator posts has just made me wonder if anybody
here might be able to help me. I'm restoring a dutch barge on which the
majority of the systems will be 24v, but, I've been given a Victron 2kVA
uninterruptable power supply which needs extra batteries grafted on at
48V.

Has anybody got any ideas on how best to combine a 24 and 48v systems? I'd
pondered whether it was possible, with 4 12v batteries in series (to give
the 48v, which will be charged by the ups) to take 2 24V taps from them?

Any ideas or advice gratefully rec'd!

Cheers
Dave