[BC] Cyberpower brand UPS

[RichardBJohnson at comcast.net]

AC power 101
All utilities in the US that are in any way connected to the grid, are required by regulation to keep magnetic components, including generating equipment, under 2 kG for 2% silicon steel equivalent, guaranteeing that the harmonic distortion is under 1%. However, many rectifier circuits draw current only on the AC voltage peaks, creating lots of distortion. That is why there are now requirements for PF correctors, which are really load correctors, so that harmonic power is not fed back into the power line. Something as simple as a choke-input filter is all that is required to cause the rectifiers to draw current throughout the complete alternating current cycle, reducing distortion. However, as most everybody knows, magnetic components with lots of iron and copper are expensive so an attempt is made to emulate the circuit by using high-frequency switch-mode techniques with tiny cheap components. It sort-of works with the trade-off being unusable AM radio reception.

Standby generators are not subject to regulation and, in the US; emergency generators are not even required to be UL compliant! Emergency generators are things that are not permanently connected, standby generators are, but do not need to be automatic. They both often use field coils that are too small for their rating, wound on magnetics that are running at saturation, five or more kG, and rely on forced air from the engine cooling to prevent them from burning up!

Sizing a generator at a rating higher than the load requires does not help the distortion problem. This is because the rating of the magnetics has the dimension of volt-seconds. The voltage per turn determines the field. The field varies inversely with frequency and directly with voltage. The only way to determine if a generator you intend to purchase has low harmonic content is to measure it. The vendor often does not know and the manufacturer does not put it in the specifications.

Quiet liquid cooled generating sets often have better alternators because they do not move a lot air, used to cool the alternator frame. Loud, industrial, construction-site generators have the smaller alternators, generating the greatest distortion.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Gary Peterson" <kzerocx at rap.midco.net>

Even utility power can be nasty, as far as THD is concerned.  At some radio
studios, on the 6th floor, of a ten story building, I once hooked a HP
distortion analyzer to the secondary of a 6.3 V filament transformer.  When
the primary was plugged into a wall outlet, I measured around 10% THD on the
60 Hz AC.