Any electricians in the house?
20 years in military and 18 years with GTE doing UN-interruptible power supply systems for Telephone exchanges. Commercial power goes to an inverter/rectifier that converts line AC to 54 Volts DC. This charges a HUGE battery bank. When commercial power drops the whole telephone exchange goes on battery in milliseconds. Then the huge 12 cylinder Turbo Cummings Generator fires up (Super size Telephone exchange). When the Gen gets warmed up, it auto switches the system off battery, again in milliseconds and the gen runs the inverter/rectifier to power the switch and charge the batteries.
At no time is commercial/battery/Generator touching each other, 100% isolated.
I have installed and maintained up to 5 racks of batteries like this below. That is 48 Volts (nominal) DC. About 1,500 pounds of Copper Buss bar.
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I spent two and a bit years working for Marks & Spencer in their London (outskirts) Computer Centre back in the mid 1990's. We had 2 x big UPS rotating machines that ran directly from the mains supply into the premises. These machines generated 500 Volts DC and continually charged a bank of 2 Volt batteries split between two cooled rooms. Outside of the UPS room we had 5 x One-Megawatt diesel Cummins powered generators.
The idea was that if we had a sudden power failure, the flywheels on the UPS machines would take at least 10 minutes to drop below the required RPM's needed to generate sufficient voltage to charge the batteries. By the time the voltage had dropped, the batteries would already be supplying the entire building WITHOUT and noticeable difference inside the building to any of the staff. We had alarms to say we had a loss of mains supply, but apart from that, you wouldn't know it.
The generators were designed to start up and be ready to take over the job of the batteries within 2 minutes.....so we had loads of redundancy built in. The reality was, the generators were starting up within seconds of any power failure, and were generating way more than required.
Every week on a Tuesday morning we had our scheduled generator test. Because we had 5 x generators, we took it in turn and rotated so that we only used 2 on every test. We would run them for an hour or so....and the amount generated was way more than what we needed, so we sold the excess back to the National Grid. I think it was quite a hefty payback in those days. We also had 500 gallons of diesel under the carpark in special tanks, as well as another stockpile of diesel in storage, looked after by our contractor Harry. Harry was our fixer....he could organise anything we ever needed. He was like the Harrod's of outsourcers. :D
You might be thinking why all that power back-up....well, back in those days, Marks & Spencer was apparently Number 5 on the UK Terrorist Hit-list, and our computer centre being what it was....lots of precautions were taken - bomb deflector shields on all windows, IR perimeter fencing around the entire building, card access everywhere- even in & out of the roof access doors. I asked one day if that was slow down potential parachutists breaking in.....wrong question apparently. :rolleyes: It was a fun time and a fun place to work all the same.
Many happy memories there.