[TenTec] Backup Batteries (was - boost mobile voltage?

[W1GOR]

While following the discussion of boosting mobile voltage and operation with 
deep cycle batteries, I was reminded of a method that is used in battery 
backup systems for commercial two-way radio, and microwave systems.

In these systems, an additional '2.2 volt cell' is inserted in series with 
the main battery supply, increasing the overall supply voltage from 13.2 
volts to 15.4 volts.  The additional 2.2 volts is offset by series-connected 
diodes, called a CEMF cell, providing a voltage drop equal to the additional 
battery cell.   A relay contact, is connected across the diodes, and 
controlled by a voltage sensing circuit (comparator).

During normal operation, a 'float' charger keeps the batteries charged to 
15.4V (13.2V plus the additional 2.2V cell).  The relay contact is kept 
'open' in order for the diodes to drop the voltage back to 13.2 volts, by 
compensating for the additional cell voltage.   When the primary AC power 
fails, the charger drops off-line and the radio system continues to operate 
normally.  Eventually, depending upon the load, the battery voltage drops to 
a level where the relay contact 'closes', bypassing the diodes, thereby 
eliminating the voltage drop, and restoring the operating voltage to a 
nominal level of 13 (plus) volts.  This operation is 'seamless', in that 
there is no interruption of radio service.   Depending upon individual 
system designs, more than one CEMF cell might be inserted, increasing the 
time that the system is able to operate.

Some research into commercial battery backup and charging systems will yield 
more details that may be applicable to field day and emergency operations.

73, Larry - W1GOR, ARRL 40 year Life Member




----- Original Message ----- 
From: "Bob Stephens" <bstephens1 at mindspring.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Tuesday, April 26, 2005 7:30 AM
Subject: Re: [TenTec] boost mobile voltage?


> Please let me clarify this.
>
> The 7 hr gel cell was only a test. I wanted to make one or two contacts to
> see if it would be worthwhile to buy a larger battery. The fully charged,
> almost brand new battery failed the test in the first minute.
>
> The question has changed. I plan to purchase a deep cycle marine battery
> tonight. The 90 amp hour version will be somewhat hard on my weak back,
> although I could carry it around if I'm careful. The question now is :
> would a 65 amp hour deep cycle marine battery power a Corsair for at least
> 5 hours in SSB assuming I'll be listening for at least 50 % or more of the
> time?
>
> 73 -Bob KB1CIW
>
> At 05:09 PM 4/25/2005 -0500, you wrote:
>
>>For something like the Corsair, you really need much more than a 7 Amp Hr.
>>battery!   Get a full size car or Marine battery, fully charged.  The rig
>>wants 12 volts and a bit more for most stable operation, and I think the
>>Corsairs pulled 20 amps on transmit unless you had the power reduced some
>>way.
>>-Stuart
>>K5KVH
>
>
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