[C320-list] Battery Isolation

[catalina at thehares.com]

For what it's worth,  I use the Blue Sea ACR to do this.  It's a very
versatile device and can be used for a number of different purposes on
board.  (like auto-disconnecting the fridge if the house bank voltage drops
too low).

My ACR simply connects the house bank to the starting battery when a
charging source is present at the house bank.  

My alternator Feeds the house bank directly and my shore power charger
feeds both house and starting battery.

What's not an issue:
====================
* Voltage drop/undercharging of the starting battery due to the diode
junction drop isn't significant.  Remember, the starting battery is not a
deep cycle device and under normal circumstances is almost never drawn down
more than a tiny bit.  So it is normally recharged within a few minutes.

* Signal Noise.  Your Alternator, VHF, Autopilot, Radar circuits introduce
far more noise than these relays could ever hope to do.  In short, you
won't hear it in your onboard Stereo if that's the concern.

Now all this assumes that you wire the ACR (or other device) so that a
charge source on the *HOUSE BANK* feeds the starting battery (and not the
other way around).  If you want to charge your house bank from an
alternator feeding your starting battery, then that's a bit different. 
Factors such as how much current can this ACR carry (and for how long), how
much voltage drop happens across the ACR, possible undercharging of the
deep cycle house bank etc. come into play since fully recharging deep cycle
batteries is a longer more complicated process.

All that said, it's extremely simple to wire an ACR to isolate the starting
and house banks, but depending on how your starting battery is wired and
operates may alter some of the minor details.

Cheers!
-Jeff Hare



On Wed, 8 Apr 2009 07:59:02 -0700 (PDT), jelliott at landspring.net wrote:
> I am in the process of modifying my electrical system, and am curious as
> to how others electrically isolate the house bank from the starting
> battery.
> 
> I have two 4D's under the settee paralleled as my house bank, and a
> separate  starting battery located in the port lazarrette.  Both are
> connected to independent channels of a Xantrax Truecharge 20.   The house
> bank is monitored with a Link 10.
> 
> The banks are still not electrically isolated; I assume this is a result
> of a common connection to the alternator?  How do others handled this?  I
> understand there are battery isolators that do this?  Any advice on how
to
> "break" this return circuit (if that's the cause) would be appreciated. 
I
> am not very interested in adding a second switch which I know some have
> done.
> 
> Thanks,
> 
> Julian
> Polaris #340