Re: Help interfacing Current Transformers to ADC

beananimal wrote:

John Popelish wrote:

Yuriy K. wrote:

John Popelish wrote:


$6.50 @ qty.20 vs. CSE187L @ $2.34 @ 20 pcs.


Fair enough. What is the turns ratio and burden limit for these?


Google does wonders. :)

http://www.alliedelec.com/Images/Products/Datasheets/967-1100.pdf

Jameco P/N 627591
Mfg TRIAD MAGNETICS
Mfg # CSE187L
RoHS? No
In Stock Yes

10+ 1.81 it will be $36.20 per 20 pcs. Who can beat that?



%00to 1 ratio is quite practical for up to 30 amps (60 mA out). With
a 60 ohm half watt burden, that gives 3.6 volts RMS. I would want to
either use a Schottky bridge with something like a 50 ohm burden or a
silicon bridge with about a 39 ohm burden. Even though the output
does not take up the full 5 volt A/D range, it allows for a bit of
surge current without producing a ridiculous voltage.

Very nice, if 30 amps load current is large enough.


The largest loads will be

1) dual 150W magnetic MH ballast, so figure 450W draw during operation
and somewhat more than that due to the inrush when It powers on.
2) All of the pumps are less than 200W motors, and no more than 2 will
be on any given monitored outlet.
3) 500 watt heaters, 1 per monitored outlet.

So most of the stuff will be well less than 10A during operation,
inrush is a different story.


Inrush is usually handled by having a resistor of, say, several kohm between the rectified and filtered output of your CT circuit and the AD converter (or the uC if it has built-in ADC). Then a diode to the VCC rail and another to GND (BAV99 is a nice dual diode for that). The white-knuckle approach would be to let the internal substrate diodes take care of things after that resistor, something that's done all the time. Just don't exceed abs max values.

Now if the CT circuit output voltage spikes when a lamp or motor turns on the spike is capped.

--
Regards, Joerg

http://www.analogconsultants.com
.

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