Thanks for coming to the rescue, BT
Here's the updated scoop:
I sold my original 1 yr old DIY unit to a guy in my reef club, as the Mag 18 I am using creates pretty severe voltage spikes that damaged the inverter during testing. He has sinced used it several times over 6 months running with a Mag 7 and it's worked great. I figure it is good to at least a 9, maybe a 12. Someday I'll bring a scope home and see what the hey is going on with the pumps...
Anywho, I started looking around for components to make a new BIGGER and BETTER backup. In addition to a higher capacity inverter, I wanted a 3 stage battery charger. By the time I priced the components out, it was close to a commercial extended run UPS...
After MUCH searching, I picked up a
Tripp lite APS512, and it's the nutz! It has the old technology transformer style inverter, which produces a cleaner waveform and surges to 1200 watts (500 continuous), as well as multiple battery capability. Price varies to over $400, so be careful. I don't recall where I got mine from, but the above link is the cheapest price I ran across today (Batteries not included).
So, if you have a reletively small system, my original backup is very cost effective and reliable. However, for larger pumps and demands, a commercial unit may be better.