OT: UPS for FreeBSD
list_freebsd at bluerosetech.com
Mon Dec 1 05:16:26 UTC 2014
On 11/30/2014 1:03 PM, RW wrote:
> On Sun, 30 Nov 2014 11:31:31 -0800 Darren Pilgrim wrote:
>> An unloaded, ideal, single-phase FWR produces Vdc = 0.900Vrms. The
>> factor is 2sqrt(2)/pi, to be precise. A half-wave rectifier produces
>> half that.
> That's the mean voltage, which is of limited relevance.
The mean voltage is the output DC voltage.
>> From where did you get your figures?
> He's referring to a rectifier charging a smoothing capacitor; the
> voltage will rise to sqrt(2)*Vrms.
No, the voltage across the capacitor will rise to 0.900*Vrms. Look at
it this way:
The output of the diodes is a time-varying (AC) signal with a DC offset.
The cap provides a low-impedance path for the AC signal, turning the
voltage cycle into a current cycle that accumulates a charge in the cap.
Once the cap is fully charged, it fully negates the AC component and
you're left with just the DC offset of 0.900*Vrms.
> He's added on an unnecessary factor
> of two - possibly because he's mixing it up with a bridge-rectifier in a
> centre-tap configuration.
A bridge rectifier doesn't use a center-tapped transformer. You
wouldn't see 2*Vpeak in a two-diode rectifier either. The voltage
between the center tap and either diode tap is at most Vpeak.
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