After getting sick of my tiny 500VA UPS which can only drive one power head, and worrying that power might go out while I am not home (I do have another deep cycle battery/charger/inverter setup and a generator, which are not much use unless I plug things in manually), I decided to get a beefier UPS. Scared away by new heavy duty UPS's prices, I turned onto craiglist. I thought it was my lucky day when I saw an ad for a "BRAND NEW" APC su3000net UPS for only $250 (Well, I said "only" since the new ones can easily go above $1k). When I got there, it did not look like brand new, but still looked clean. The guy promised me that it was used for less than 60 days. Being a trusting guy, I bought it because I do not want to worry about it anymore. Well, after got back home, I found it did not work at all. Don't wanting to have the bad taste of bringing it back to the guy and dealing with him, I pulled everything apart, and found the batteries are pretty dead (btw, I figured out after coming home that it has to be used for a lot more than 60 days since this model was discontinued quite a while back). Really hating to deal with the sleazy guy who sold me the unit, I decide to gamble on it by assuming only the batteries are bad and turn it into something I will be happy with. Given the four APC small replacement batteris are more than $200 plus shipping, I went to Costco and bought 4 of their largest deep cycle batteries for $320 
, and spent another $25 in home depot for connectors and connecting wires. Then I found the external battery connector from APC cost $90, just for two stupid connectors and a piece of wire :mad2: . Instead of getting ripped, I used my dremal tool on the connector of one of the APC dead battery, and vola, it fits perfectly after some mod. I also pulled the two 100A fuses from the dead batteries and put them on the new batteries. So after $595 and many hours of lost sleep, here is my new UPS that I will be proud of 
. The only remaining thing to do is to build a cover for the setup so nobody in the house risk been electrified.
Btw, each battery is rated for 115AH, so the 4 batteries should give me 4*114*12 = 5520VAH. I will use it to drive three 7W Tunze 6045, one 130w Pan World return pump, and a couple of 10W fans. Assuming the UPS will consume 50W by itself, I should have a run time about 5520/(21+130+20+50) = 25 hours. This way, I even do not need to fire up my generator if the outage is less than 25 hours, which is the case most of the time. If I only use it on the three Tunzes, it should last 5520/(21 + 50) = 78 hours!
It costed a lot more than what I planned for, but at least I can sleep without nightmares about power outage anymore.
, and spent another $25 in home depot for connectors and connecting wires. Then I found the external battery connector from APC cost $90, just for two stupid connectors and a piece of wire :mad2: . Instead of getting ripped, I used my dremal tool on the connector of one of the APC dead battery, and vola, it fits perfectly after some mod. I also pulled the two 100A fuses from the dead batteries and put them on the new batteries. So after $595 and many hours of lost sleep, here is my new UPS that I will be proud of . The only remaining thing to do is to build a cover for the setup so nobody in the house risk been electrified.Btw, each battery is rated for 115AH, so the 4 batteries should give me 4*114*12 = 5520VAH. I will use it to drive three 7W Tunze 6045, one 130w Pan World return pump, and a couple of 10W fans. Assuming the UPS will consume 50W by itself, I should have a run time about 5520/(21+130+20+50) = 25 hours. This way, I even do not need to fire up my generator if the outage is less than 25 hours, which is the case most of the time
. If I only use it on the three Tunzes, it should last 5520/(21 + 50) = 78 hours!It costed a lot more than what I planned for, but at least I can sleep without nightmares about power outage anymore.
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