On Wed, 15 Dec 2004, djgoku wrote:
I have spent $70 on a 400VA 700W apc UPS, I would like to seek out another alternative that maybe better. I wouldn't mine making something that would that would cost a little more then what I paid already that would say better quality and will last longer. How long do UPS batteries last do they need to be changed every couple of years? I would like for all my computers to last 2-3 days if needed... How much are marine batteries and how do you charge them? How you know how much juice it currently has? Do you charge them periodically? And is all this in an enclosure that could pass safety regulations?
All APC UPS batteries will dehydrate their gell cell batteries in about two years. The more expensive APC UPS units will dehydrate their more expensive bigger batteries in the same two years. APC is evil and sets their float voltages too high. Its a great business model.
Marine batteries are about $60 for the 125 Ah sizes at Walmart. Pretty big bang for the buck. That's about 20 times more power than the original UPS battery.
You can attach marine batteries to the UPS, but they will need to be watered every 3 months due to the high float voltage.
If you do decide to use a marine battery, invest in safety. Pay attention to wire size, strain reliefs, and high current connectors. Also, its not a bad idea to have your battery in a sturdy battery box, since not only are they HOT with respect to the mains, they can leak and corrode other things. If your home engineering skillz make it look good and attractive, an inspector might even be pleased and admire it. They just want things to be safe and not blow up.
Your UPS will charge this huge battery in a few days and keeps it charged. The charge on lead acid batteries at rest can be approximated by voltage:
12.0 volts: 0% dead 12.5 volts: 50% 13.0 volts: 100%
If you see more than 13.5 volts on the UPS unit, you can assume its charged and ready for the Great Ice Storm. Lead acid batteries are voltage sources. If a dead lead acid battery sees 14 volts, it will consume infinite current until it is nearly charged, then taper off the current. This is the reason why you don't charge a motorcycle battery with a car alternator. It will get too hot. The UPS only has about an amp to charge with, so its slow and safe. Your UPS is friendly to lead acid batteries, except for the high float voltage.
-=Duane http://dattaway.org