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Default capacitor across an AC line

I know that a capacitor does not consume any power if connected across an AC
line except for a small ammount , but lets just say a pure capacitance.

I was playing around with a meter similar to the Killowatt meter and with a
hair dryer the voltage and current multiplied together came to the same as
the displayed watt on the meter within a few percent. Then I hooked up an
amplifier that has a transformer in it and the displayed power was about 80%
of the volts times amps.

I then hooked a 50 uF capacitor across the line, only the capacitor. Just
rough numbers calculate the capacitance reactance as 53 ohms at 60 hz. Sure
enough the meter shows about 2.3 amps just about what a 50 ohm resistor
would show. However the wattage display was about 2 watts which still
seems normal due to a slight leakage and such. I understand the meter
showing this due to the lead or lag of reactance and wattless power.

Finally getting to the question is that if I bring up the AC up slow with a
variac to keep the main surge down would a 1 amp fuse blow at around 50
volts when the current got past 1 amp or could I keep going to the full 120
volts AC ?


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Default capacitor across an AC line

On 27/12/2015 11:55 AM, Ralph Mowery wrote:
I know that a capacitor does not consume any power if connected across an AC
line except for a small ammount , but lets just say a pure capacitance.


**Wrong.


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www.rageaudio.com.au

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Default capacitor across an AC line

Ralph Mowery wrote:


I know that a capacitor does not consume any power if connected across an AC
line except for a small ammount , but lets just say a pure capacitance.

I was playing around with a meter similar to the Killowatt meter and with a
hair dryer the voltage and current multiplied together came to the same as
the displayed watt on the meter within a few percent. Then I hooked up an
amplifier that has a transformer in it and the displayed power was about 80%
of the volts times amps.


** That is rather high, normally is it closer to 65%.

IOW transformer fed PSUs have a PF of 0.65.


I then hooked a 50 uF capacitor across the line, only the capacitor. Just
rough numbers calculate the capacitance reactance as 53 ohms at 60 hz. Sure
enough the meter shows about 2.3 amps just about what a 50 ohm resistor
would show. However the wattage display was about 2 watts which still
seems normal due to a slight leakage and such. I understand the meter
showing this due to the lead or lag of reactance and wattless power.

Finally getting to the question is that if I bring up the AC up slow with a
variac to keep the main surge down would a 1 amp fuse blow at around 50
volts when the current got past 1 amp or could I keep going to the full 120
volts AC ?


** Strange question.

The fuse will blow when its current rating is exceeded by a sufficient ratio - about 50% or so.

That the load is a capacitor ( with current and voltage not in phase) has no effect.


.... Phil
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Default capacitor across an AC line


"Phil Allison" wrote in message
...
Ralph Mowery wrote:

I was playing around with a meter similar to the Killowatt meter and with
a
hair dryer the voltage and current multiplied together came to the same
as
the displayed watt on the meter within a few percent. Then I hooked up
an
amplifier that has a transformer in it and the displayed power was about
80%
of the volts times amps.


** That is rather high, normally is it closer to 65%.

IOW transformer fed PSUs have a PF of 0.65.


I then hooked a 50 uF capacitor across the line, only the capacitor.
Just
rough numbers calculate the capacitance reactance as 53 ohms at 60 hz.
Sure
enough the meter shows about 2.3 amps just about what a 50 ohm resistor
would show. However the wattage display was about 2 watts which still
seems normal due to a slight leakage and such. I understand the meter
showing this due to the lead or lag of reactance and wattless power.

Finally getting to the question is that if I bring up the AC up slow with
a
variac to keep the main surge down would a 1 amp fuse blow at around 50
volts when the current got past 1 amp or could I keep going to the full
120
volts AC ?


** Strange question.

The fuse will blow when its current rating is exceeded by a sufficient
ratio - about 50% or so.

That the load is a capacitor ( with current and voltage not in phase) has
no effect.



I looked over the numbers and the amplifier without drive was about .66 and
when loaded heavy was .75.

I though the fuse would blow when the amp meter was showing enough current
for it to blow with just a capacitor across the line. As we all know a fuse
does not blow at the exect time the current is slightly exceeded.

I had never looked into the effect of inductive and capacitive loads on an
AC line. Just knew there was a power factor due to the lead and lag of
current and voltage. My main item of interist is at Radio Frequency and
only look at the AC power was to make sure it was enough to power the
equipment. I just hapen to see some numbers come up on the meter I had
gotten a few weeks ago and got courious as if it was a cheep meter from
China and giving false readings or if they were reasonable close. I do have
a good multimeter to check the actual voltage and a clamp on meter for the
current. For most work if it is from 5 ot 10 percent from those it is
close enough for me. With the first calculated and displayed values were way
off I started to see why. Such as the meter showed 100 watts and the volt
amp multiplying was showing 150 watts and under load it was 1200 on the
meter and 1500 calculated with the V and I . Checking with a hair dryer for
a mostly resistive load the V and I calculated the same as the meter.



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