View Full Version : BUCKING VOLTAGE

11-08-2003, 08:37 AM
My UPS tell me I have it.......what does it mean and is it good or bad.....I know I am always asking questions but some day I may contribute.......

11-08-2003, 09:27 AM
Bucking means that if the mains voltage coming in to UPS drops, then the UPS output will still maintain the correct output voltage to your PC . It's a good thing.
Overall, it means your voltage output to your PC will stay the same if the incoming mains voltage rises or falls (within limits).
As for contributing, you will. If everyone knew everything, then we couldn't post replies, and that would take the enjoyment out of it. So post away :)

11-08-2003, 10:11 AM
>then the UPS output will still maintain the correct output voltage to your PC

not all UPS's will do that. a lot are simply a backup ups ie a non-interactive UPS. check what type of UPS you have, if in doubt post make/model.

11-08-2003, 10:15 AM
Actually, bucking voltage is the opposite of the reply above.

If the voltage momentarily raises above a given level, the UPS will "buck" it and reduce it. (for a cycle or two only).
If it momentarily drops below a set level, it will "Boost" it. (Also for a cycle or two only).

Outside these parameters the UPS will auto-switch to backup battery supply until the mains supply comes back within the acceptable range.

Billy T
11-08-2003, 10:38 AM
Actually, bucking means to apply an opposing voltage to reduce an excessive voltage. I believe the simplified one-word expression originates from the early days of radio where power supply filtering was very poor. It didn't help that the filter inductor for the power supply was also the speaker (electro) magnet, as that made sure that the audio was well modulated at 100 Hz. In this application is was known as "hum bucking".

Consequently hum levels from the loudspeaker was rather high and a small proportion of the hum voltage was fed antiphase through the voice coil of the speaker, thus cancelling out (bucking) the hum. Now that I think of it, the hum-bucking coil may have been a separate winding on the output transformer.

This usually applied to the big speakers in larger cabinets where low frequency output (hum levels) were accentuated by the speaker cone size and relatively efficient cabinet baffle. Smaller speaker/cabinet combinations were too inefficient to put out enough low frequency to worry about.

It is many years since I last serviced a radio of that type so I may be wrong on the finer points of the technique (come in Godfather please) but that is the principle.

So, in a UPS, bucking would be applied to reduce the output voltage if the input exceed the normal mains parameters of 5%. This would only be used in off-line type UPS technology as full time on-line would regulate its own output.


Billy 8-{)
[pre][b]Contrary to popular opinion, (recently expressed on
PF1 too!), old radios did not enjoy good fidelity. They had
negligible high frequency response, very limited low frequency
response (to limit hum even further) and distortion levels were
very high indeed. That "beautiful mellow tone" so often lauded
simply means nothing much above 5 kHz or below 150 Hz.

11-08-2003, 10:52 AM
I stand corrected, and now better informed on the history thanks to BillyT :D

Graham L
11-08-2003, 03:00 PM
It's probably not needed, anyway. :D Modern computer supplies have a pretty wide voltage capability. It's easy enough to incorporate though (I have an idea that UPSs will be like modern inverters, with no "Iron" transformers) and it's a Marketing Feature .

In the days of Real Computers, a UPS was (in the extreme) a big alternator, with a flywheel. There was an electric morot at one end of the shaft, and a diesel engine at the other. A momentary drop was looked after by the flywheel, any more would start the diesel.

Lesser systems had a resonant "constant voltage" transformer. (These were notorious for bad waveform, and BAD power factor) .

The nicest units I ever saw were used on a radar (GL2 :D) installation. The three phase supply had three of these boxes, large oilfilled boxes each conttaining a tapped transformers and motor driven tap switch. The moretor was controlled by mercury switches, tilted by a solenoid voltage sensor.