Battery Backup or Backup Battery

What size battery do you need to power your radios?

Here is a simple formula :
[Total Receive Amperage Draw + {(Transmit Amperage Draw X Mode Duty Factor) X Percentage of Transmit Time}] X Hours of Operation = Amp Hours

OK, how to "plug in the numbers:

Start by looking in your manuals. To figure you amperage draw, you need to figure all connected equipment. You need to know what each piece of equipment draws on receive, and what it draws on transmit. You also need to use a duty factor for the mode you are operating. Here is a good guide to those factors:

Mode Duty Factor
(CW)
40%
SSB
20%
FM
100%
Digital
100%
AM
100%

To get to the
"Total Receive Amperage Draw" add all the amperage figures for your connected equipment on receive. For instance:

VHF Radio = 3 amps
TNC = 1 amp
Total = 4 amps

Then figure your "Transmit Amperage Draw":

VHF Radio = 7 amps
TNC - 2 amps
Total = 9 amps

Now apply the "Transmit Mode Duty Factor":
9 amp X 100% = 9 amps (duh!)

Now, multiply the
"Transmit Amperage Draw X Percentage of Transmit Time". Say you figure you will be keyed 50% of the time...
9 amps x 50% = 4.5 amps

Add that to the
"Total Receive Amperage Draw" to the "Total Transmit Amperage Draw"...

4.5 amps + 4 amps = 8.5 amps

Multiply that figure by the "Hours of Operation", say 5 hours...

8.5 amps x 5 hours = 42.5 "Amp Hours"

So you need a battery rated at 42.5 amp hours or greater to operate 5 hours without a recharge.

SLA type computer UPS battteries are good choice for the station backup supply. Some power supplies can be used to charge a battery, some cannot. A better solution is a 3 stage charger, with the lowest stage being a "trickle" or "maintenance" charge.

WARNING: All the above data is to be used at your own risk!