Hello @Job, I'll add to what others have mentioned so far. Pls avoid extra batteries for a system that has not been designed to handle extra time. A few points to consider : a) UPS transformer : Extended time will cause the transformer to heat up, internal flux can melt and shortout the copper windings b) Charging circuit : The built-in circuit is designed for the normal one/two battery operation and will cause the charger circuit to burn out on extra amp charging load. c) Power Mosfets : These drive the two/more windings of the invertor tranformer and drain a large current from the battery. On a small UPS they are rated at around 30amps surge load/ 10amps running load. By increasing the available current using an additional battery, the mosfets will drain more current at load startup surge and blow. The safety circuit on these has an overload mechanism, thus if the load is increased the ups will shut down because it is related to drain current. But the damage to components takes places in micro-seconds which is not enough to protect your equipment from taking a severe hit. A fuse blows in milli-seconds and will break the wire under short circuit conditions i.e the load across the wire exceeds the rating. I'd highly recommend you to go for the correct UPS which allows for your scenario below, else you will be putting your equipment at a severe risk of damage or even start a fire. Pls be careful and consider the outcome should the system fail. But you are welcome to innovate by adding extra cooling fans, change the power mosfets and at minimum double the transformer copper gauge with safety fuses all the way. HTHs. Rgds. On Sun, Apr 18, 2010 at 11:54 PM, Job Muriuki <muriukin@gmail.com> wrote:
How practical is replacing a UPS battery with one with higher capacity in order to get longer battery life using same equipment. Say I want a 1kva ups to last 6hrs or over. WIll it work or will i have to change a circuit?