I would like to have two laptop power bricks plugged into different battery backups to ensure continuous power. What should be my starting point? (actually for a cool mod I have in mind for a Mac mini "server")
I'm not quite sure what you mean. Do you want a UPS sort of thing or a spare power brick that only works if the first fails?
It depends on the input voltage really but you might find that this would work if your "server" will accept a 12v input. When you say different battery backups do you mean that both supplies are battery backed (so that if one battery fails the other takes over) or a simple UPS that supplies power if the mains fails? Moriquendi
well unless you are planning on having 2 DC boards inside the mac mini it will all go back to 1 at some point, mainly the plug now if your not going to open the mac mini then you can just take the plug from the back of the mac mini and split it in to 2 and have one run to each AC-DC brick then each brick have its own UPS or what ever the more info the better the answer
You cant directly connect the outputs of two power supplies like that, it doesn't work. Although you might have two identical PSUs the actual output voltage will be slightly different, this is particularly true for something like a laptop PSU where it's only an intermediate converter, the laptop doesn't care if it's a bit high or a bit low. However if you connect two PSUs of slightly different voltages together then bad things start happening, you get a very large current flowing from the higher voltage PSU to the lower. It might be possible to connect two PSUs together through diodes but I haven't heard of anyone doing it. Moriquendi
never said it would work just a casual rambling you could possibly use a relay DPST when the main PSU is on, the circuit would be completed with its power source and if/when it dies then the relay would go to its normally closed position allowing the other PSU to step in and do the job just another thought
With a UPS you would already have two battery backups - the laptop battery, and the UPS battery. You want a third redundant power source? If you've by any chance been considering chaining two or more UPSes, do not do that - APC says never to do that.
You can't do that either, a relay takes many milliseconds to switch and the computer will die in that time. Moriquendi
so your computers have always died when the lights flicker? wow my old lappy that the battery no longer works wouldnt the battery would stabilize the power flow just long enough
Not always and there's a couple of reasons why: Firstly most ATX PSUs will accept any voltage down to about 90v so if the voltage doesn't drop that far it's fine. Secondly, a full size ATX PSU contains vastly more smoothing capacitance than a laptop can, if you look at the caps inside a ATX PSU they're much bigger than a laptops capacitors. Finally, when the lights flicker it's normally only for a couple of milliseconds, a relay can take tens to hundreds of milliseconds to switch and they have contact bounce, rather than just switching once you get several switches in rapid succession, not something you want to subject a running computer to. Moriquendi
well first of all he needs to tell us if its going to be an ATX or a laptop brick before we speculate any further
