How much power is enough?

I have an Ademco 20P with three key pads, several PIRs, several glass breaks and 2 scirens w/ strobe (like a back up since this is a local alarm only). I just orderd the ELK 1.0 amp supplemental power supply w/ relay but still fill underpowered. Figuring the max draw on the key pads, the way I plannned to split things up is: 547 mA on the 20P (rated 600 max), and 850 mA on the alarm output (Bell) ( 2 amp max). The supplemental power supply will run 212 mA (one 6159 key pad plus a few PIRs) and power the back up 750 mA siren with the relay for 963 mA total (1 amp max).

The 20P has a 8 ah battery 547 mA draw without sciren = 14 hrs back up
The ELK has a 4 ah battery 213 ma draw without scrien = 18 hrs back up

Is this enough? For UL approval the 20P should only have 600 mA total including the bell! To do that I would need a 2 amp back up. The higher amp systems are really pricey. Any suggestions on a resonable one?
My power rarely goes out for more than a few hours, but when the power is out for a few days when you are on vacation, thats when you really need it.
Am I going overboard?

Thanks / Chet

 

You should be fine. Those current draws do have a bit of engineering leeway built into them. Try triggering the system into as full blown alarm as you can. With a Vista 20p, if you are drawing too much current, the system will shut itself down (the PTC will trip).