Re: Stupid Electronics question

On Tue, 14 Mar 2006 16:00:28 +0000, pentagrid@xxxxxxxxx wrote:

On Mon, 13 Mar 2006 21:59:09 -0500, Spehro Pefhany
<speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Mon, 13 Mar 2006 20:00:58 -0500, the renowned Spehro Pefhany
<speffSNIP@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Tue, 14 Mar 2006 00:31:26 GMT, the renowned "Jerry Foster"
<jmfoster711NOSPAM@xxxxxxxxxxxxx> wrote:

Surprised no one pointed this out. 110 VAC is rms voltage. The output of a
bridge rectifier/capacitor combination will be about that times the square
root of two, practically somewhere around 150 volts.

You probably need a variac in front of the rectifier if you really want 110
VDC.

Jerry

Act-ually, the first thing Gunner <snip>

Sorry, forget it, the bridge clamps it to two diode drops on top of
the input supply anyway. <dunh>

But there is a potential problem when the input connection is broken
with no capacitor on the input or output of the bridge.


Best regards,
Spehro Pefhany

With the coil fed by a bridge rectifier, when the AC input
is disconnected, the inductive overshoot drives all four diodes
into forward conduction and this safely dissipates the stored
energy in the resistance of the magnet coil. A protective
capacitor is not necessary on the input or output of the bridge.

With no output capacitor the DC output voltage will be the
MEAN value of the input voltage - 0.9 x RMS. less the diode
drops.

With a large output capacitor the output approaches the
PEAK value of the input voltage, again less the diode drops.

Jim

Yup, the diodes will snub the coil on turnoff.

Most DC voltmeters do respond to average value. However, neglecting
diode drops, the RMS value of the rectified DC must be the same as
the RMS value of the AC by definition. The rectified voltage
waveform is the same as the AC wave except that alternate
half-cycles are reversed in polarity. RMS means root mean squared,
and the squaring operation makes polarity irrelevant. Therefore, the
RMS values (neglecting diode drops) are identical.

.

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