I'm looking to design a UPS for my PC. I've dealt with switch mode supplies and inverters before, so there's no problem there.
My initial design idea would be the following:
High power SMPS -> Laptop Batteries -> Inverter
My computer currently runs a 1kW PSU, so I'd buy a 1.2kW one to run this UPS. I'd build a basic laptop battery charger to run off the PSU, then power the inverter directly off the PSU. In order to detect the drop in power, I'd probably use a relay from the input power to switch between the battery and the PSU. However, to allow continuous power during switch-over I'd need some serious capacitors.
Anyone spot any flaws in this design?
My initial design idea would be the following:
High power SMPS -> Laptop Batteries -> Inverter
My computer currently runs a 1kW PSU, so I'd buy a 1.2kW one to run this UPS. I'd build a basic laptop battery charger to run off the PSU, then power the inverter directly off the PSU. In order to detect the drop in power, I'd probably use a relay from the input power to switch between the battery and the PSU. However, to allow continuous power during switch-over I'd need some serious capacitors.
Anyone spot any flaws in this design?
I'm not sure what you mean. Are you saying bypass the inverter completely, and just power the PC's PSU directly off the batteries by hooking them to the B+?
So...
UPS PSU -> Batteries -> DC/DC Convertor -> PC PSU's B+
The problem with that design is that I want this to be re-usable for any device, so I can basically put a pair of plug sockets on the top of my UPS and run any devices I like for a short amount of time in the event of power failure. There's no use having a UPS for my PC if my monitor has no power going to it!
So...
UPS PSU -> Batteries -> DC/DC Convertor -> PC PSU's B+
The problem with that design is that I want this to be re-usable for any device, so I can basically put a pair of plug sockets on the top of my UPS and run any devices I like for a short amount of time in the event of power failure. There's no use having a UPS for my PC if my monitor has no power going to it!
First flaw is that you can buy used UPSes for next to nothing. I have a 1250VA SmartUPS that I bought for $20, only had to put two batteries in it (cost me $50) and it works great.
I wouldn't use laptop batteries, I'd use SLA lead acid. Much cheaper, easier to charge, and you don't have to parallel an ungodly number of cells to handle the current requirements of sourcing 1KW from the battery bank. Simply buying a pile of surplus LiOn batteries and connecting them in parallel probably isn't a safe thing to do either.
I'd also power the PC directly off the wall when the power is on. This way you're not losing efficiency in the AC/DC->DC/AC conversion, and the AC/DC can be a much smaller battery charger instead of a big SMPS that has to power the load. When power fails, start up the inverter and switch the PC to it.
I wouldn't use laptop batteries, I'd use SLA lead acid. Much cheaper, easier to charge, and you don't have to parallel an ungodly number of cells to handle the current requirements of sourcing 1KW from the battery bank. Simply buying a pile of surplus LiOn batteries and connecting them in parallel probably isn't a safe thing to do either.
I'd also power the PC directly off the wall when the power is on. This way you're not losing efficiency in the AC/DC->DC/AC conversion, and the AC/DC can be a much smaller battery charger instead of a big SMPS that has to power the load. When power fails, start up the inverter and switch the PC to it.
AC has voltage interruptions every 120Hz, and your equipment deals fine with it 
Most equipment will continue to work with power loss of up to 100ms, and if you detect the loss of a single 120Hz half-cycle, you can perform the switch in <10ms.
Commercial UPSes work this way without any problems.
Most equipment will continue to work with power loss of up to 100ms, and if you detect the loss of a single 120Hz half-cycle, you can perform the switch in <10ms.Commercial UPSes work this way without any problems.
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