On Thu, 06 September 2001, Alex Bligh wrote:
a wide frequency tolerance. The only problem you may run into is that some boxes are too clever by half, and autosense input frequency to determine output frequency.
Actually, its not being clever, its being cheap. If you use the input frequency to drive the output frequency, you don't need an extra crystal oscillator. Its cheaper, and results in fewer customer service calls about the clock running fast or slow. It also means, you can't just take a 50/Hz european UPS and plug it into an US plug at 220vac, and expect to still get 50/Hz out of it. When you plug it into the US grid, you'll get 60/Hz out. I spent a day troubleshooting a problem, until someone explained to me what was happening. That's why I now use a bench power supply, which explicitily generates the type of "international" power I want, instead of using a Rube Goldburg setup.
Most UPS's pass line voltage straight through unless it disappears or goes out of range. It's more efficient and results in less wear and tear than running Ac->DC->AC all the time. You can usually tell when they are generating power by the neat buzzing noises they make. So they all have an ocsillator for when they need to generate power, but otherwise what goes in is what comes out (voltage and especially frequency). A 240V/50Hz ups will probably generate the desired 240V/50Hz signal only when in battery only mode (or plugged into a 50Hz line source). Check the specs to be sure. KL Sean Donelan wrote:
Actually, its not being clever, its being cheap. If you use the input frequency to drive the output frequency, you don't need an extra crystal oscillator. Its cheaper, and results in fewer customer service calls about the clock running fast or slow. It also means, you can't just take a 50/Hz european UPS and plug it into an US plug at 220vac, and expect to still get 50/Hz out of it. When you plug it into the US grid, you'll get 60/Hz out.
--On Thursday, 06 September, 2001 10:47 AM -0700 Sean Donelan <sean@donelan.com> wrote:
Actually, its not being clever, its being cheap.
Some do both (or their spec sheets lie). I was about to recommend a unit to Randy, until I downloaded the PDF and thought 'how the hell do you set the frequency'. Further investigation revealed something very like: Input frequency: 47Hz-53Hz, or 57Hz-63Hz Output frequency: 50Hz +/- 0.1%, 60Hz +/- 0.1%, autosensing I guess that has a crystal with two dividers, a PLL, and no obvious way to turn the autosense off. Most units have some reasonably accurate oscillator or it makes regenerating the output hard when there is no input to sync to :-) Some good ones have a PLL to minimize cutover disruption if you take the electronics out of band. -- Alex Bligh Personal Capacity
participants (3)
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Alex Bligh -
Kevin Loch -
Sean Donelan