"Jon Elson" wrote in message
...

RogerN wrote:

Anyone here mess with signal conditioning for current transformers?
Seems
that I need a "precision rectifier" circuit and a capacitor to charge up
to the peak, then scale to RMS amps.
No, you don't need such complexity. Put a small bridge rectifier directly
on the transformer winding, then a burden resistor sized to give you a
few Volts at the desired current. Add a capacitor and you have a
voltage approximately proportional to current. Then, rig a simple
comparator to trip at the desired point.

Now, one problem with this scheme is that under some loads
it could start cycling on and off, cutting the heater on and off
every second or so. So, you might need to add some hysteresis to
the comparator.

Jon

I was thinking about the burden resistor on the DC side of a full wave
bridge rectifier, so the voltage drop across the rectifiers doesn't affect
the reading, but I'm not sure how much voltage I should get out of the CT
without causing problems. I was planning to have a small value of burden
resistor to keep the voltage output low.

I can do the comparator and hysteresis, that would be great for the basic ON
and OFF but I was also wanting to use temperature input and am considering
using X-10 to control power to the heater. There are low voltage/contact
modules for X-10 that I could use with a thermostat in series with the
comparator output to shut heat off when the temperature was reached or the
current was above the max.

RogerN