AC Line current detector problems

[zyxxix]

Hi

Playing around with the Bowden AC current detector:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif

but I have had no success with my modification of using a low
resistance (0.02 ohms) sense resistor in place of the coil. As this
resistor is in line with the live feed, it should have a small voltage
drop across it in line with Bill's inductive pickup - but is this the
wrong thing to do?
With no AC current, there is about 1.9V from pin 7 which seems to be in
line with his notes on "no-signal". With an AC load sufficient to give
about 8mV across the resistor, pin 5 still reads 0 volts. Do I have a
bad circuit, or just a bad idea?

 

[Homer J Simpson]

Hi

Playing around with the Bowden AC current detector:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif

but I have had no success with my modification of using a low
resistance (0.02 ohms) sense resistor in place of the coil. As this
resistor is in line with the live feed, it should have a small voltage
drop across it in line with Bill's inductive pickup - but is this the
wrong thing to do?
With no AC current, there is about 1.9V from pin 7 which seems to be in
line with his notes on "no-signal". With an AC load sufficient to give
about 8mV across the resistor, pin 5 still reads 0 volts. Do I have a
bad circuit, or just a bad idea?

Is the power supply adequately isolated from the line? Are you getting 4 or
more millivolts?

 

[John O'Flaherty]

Hi

Playing around with the Bowden AC current detector:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif

but I have had no success with my modification of using a low
resistance (0.02 ohms) sense resistor in place of the coil. As this
resistor is in line with the live feed, it should have a small voltage
drop across it in line with Bill's inductive pickup - but is this the
wrong thing to do?
With no AC current, there is about 1.9V from pin 7 which seems to be in
line with his notes on "no-signal". With an AC load sufficient to give
about 8mV across the resistor, pin 5 still reads 0 volts. Do I have a
bad circuit, or just a bad idea?

It seems as if it should work with the values you describe. Maybe you
have a bad part or connection. I'm assuming the whole thing is battery
operated or otherwise floating wrt the line; if it's not then it's a
very bad idea.

 

[Chris]

Hi

Playing around with the Bowden AC current detector:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif

but I have had no success with my modification of using a low
resistance (0.02 ohms) sense resistor in place of the coil. As this
resistor is in line with the live feed, it should have a small voltage
drop across it in line with Bill's inductive pickup - but is this the
wrong thing to do?
With no AC current, there is about 1.9V from pin 7 which seems to be in
line with his notes on "no-signal". With an AC load sufficient to give
about 8mV across the resistor, pin 5 still reads 0 volts. Do I have a
bad circuit, or just a bad idea?

Hi, zy29. Mr. Bowden's circuit has the definite advantage of being
isolated from line voltage. This is pretty close to essential for
hobbyists -- it keeps newbies from dancing the 60 hertz. ;-)

Given that, your 0.02 ohm resistor would probably work OK in stead of
the U-bolt transformer. But troubleshooting why it isn't working could
be hazardous.

If you want to do this (and I'd really recommend against it), try to
get an isolated AC voltage source with a couple of divider resistors
(make the sense resistor 1 ohm or less), and apply the 8mVAC or so to
the inputs of the circuit where the U-bolt current transformer is. Get
it working before you apply line voltage.

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(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Once it works with this circuit (which should apply between 4.8mVAC and
60mVAC to your circuit input) you could consider putting it with your
0.02 ohm resistor and the line voltage.

Stay safe
Chris

 

[Ban]

Hi

Playing around with the Bowden AC current detector:

http://ourworld.compuserve.com/homepages/Bill_Bowden/page8.htm#aclatch.gif

but I have had no success with my modification of using a low
resistance (0.02 ohms) sense resistor in place of the coil. As this
resistor is in line with the live feed, it should have a small voltage
drop across it in line with Bill's inductive pickup - but is this the
wrong thing to do?
With no AC current, there is about 1.9V from pin 7 which seems to be
in line with his notes on "no-signal". With an AC load sufficient to
give about 8mV across the resistor, pin 5 still reads 0 volts. Do I
have a bad circuit, or just a bad idea?

That circuit has a missing ground connection on the bottom of the coil. Also
the left 10u cap must be in series with the coil. Put also 2 1N4148
antiparallel across the coil, else your circuit might blow. Bad circuit.
Do not fiddle around with live mains without proper insulation. You could
easily blow your scope or soundcard, even kill yourself. Your shunt might
burn up from the inrush current of certain appliances on mains, bad idea.
Salvage a current transformer from an old GFI, or buy one for mains use.

 

[zyxxix]

It is isolated, but I have no means of measuring such a low ac voltage.
As the line is carrying 100W at 230V, it must have over 4 mV across it.

 

[zyxxix]

Chris

Great advice. I'll keep safe and avoid doing the 50Hz dance here
(@230V).

 

[Homer J Simpson]

It is isolated, but I have no means of measuring such a low ac voltage.
As the line is carrying 100W at 230V, it must have over 4 mV across it.

Drive the circuit from an AC source and see what happens. If it works, your
sensor system doesn't.

 

[Bill Bowden]

That circuit has a missing ground connection on the bottom of the coil. Also
the left 10u cap must be in series with the coil. Put also 2 1N4148
antiparallel across the coil, else your circuit might blow. Bad circuit.
Do not fiddle around with live mains without proper insulation. You could
easily blow your scope or soundcard, even kill yourself. Your shunt might
burn up from the inrush current of certain appliances on mains, bad idea.
Salvage a current transformer from an old GFI, or buy one for mains use.

No, it doesn't have a missing ground. If you ground the bottom of the
coil, you will short the 6 volt reference to ground, and it won't work.
Pin 3 of the opamp will be grounded through the coil and there will be
a zero voltage on pin 3. Bad idea.

-Bill