[Elecraft] Battery back-up system for multiple rigs

[Mel Farrer via Elecraft]

If I read the question correctly, the need is to provide a what if protected system of power delivery.  Well, if the system design can handle the load for a "period" of  time, say 8 hours. The simple and easy solution is to have several of the same battery sources on independent standby and just switch them in as needed.  No complex charging,protection, isolation systems required.  If one fails it will not affect the others.  The independent battery smart chargers at <$50.  Use knife switches and your are a go.  Thats what I have..  KISS. approach.  What say you????   
Mel, K6KBE

      From: "Joe Subich, W4TV" <lists at subich.com>
 To: elecraft at mailman.qth.net; "N2TK, Tony" <tony.kaz at verizon.net> 
 Sent: Thursday, January 22, 2015 12:21 PM
 Subject: Re: [Elecraft] Battery back-up system for multiple rigs
   

Tony,

I'd start by building one of these "powergate" modules for each battery
and connect the Station Equipment terminals in parallel:
<www.nfarl.org/kits/powerGate/Power_Gate_Assembly_Instructions_v2.pdf>

Alternatively, you can use the design approach with appropriately sized
individual Schottkey diodes mounted to heat sinks for each battery or
power supply.  In essence you want the low Vf drop diodes to isolate
the batteries and power supplies from each other in case of a failure
of any one device.

One could build more complex circuits using relays or power FETs to
disconnect the batteries when mains power is available but the diode OR
circuit with the mains power supply set to 14.8V provides full supply
power while "on mains" and suffers minimum  (~0.4V) voltage drop in
battery voltage in "back-up" mode.  If one is anal about having exactly
13.8 V for the rig, one can even add a boost/buck regulator for each
rig (or group of rigs in the case of the VHF boxes).

73,

    ... Joe, W4TV
        Any opinions express here are my own and are not representative
        of Elecraft, any other amateur manufacturer, or organization.


On 2015-01-22 2:47 PM, N2TK, Tony wrote:
> Looking for some advice. Trying to help out a friend who is setting up an
> emergency communications system for the Hams in their condo group.
>
> They have several marine batteries they want to tie in parallel so they can
> run multiple rigs,  K3's plus UHF/VHF for extended periods. They have a
> charger for the batteries. They use the 12V off the batteries to a
> distribution box for the 12V equipment.
>
>
>
> Questions:
>
> -          What is the best way to isolate the equipment from the batteries
> if something happened to the battery (ies).
>
> -          Is there a way to isolate the batteries from each other if
> something happened to one battery so it didn't draw down the other
> batteries?
>
> -          Am I missing anything else that should be done for safety of the
> equipment, batteries and the operators?
>
>
>
> Tnx
>
> N2TK, Tony
>
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