Is the current AC or DC? At what level? Clamp-on ammeters are available for both cases. It's then just a matter of amplifying the output to the meter enough to actuate the relay.
How about a minature split core current transformer providing the current is ac. then rectify the output current and use it to drive your relay. It would only give you a low energy output so you might need to use a reed switch or something like that to drive the final relay. If you have not come across split core transformers "Google".
Beware that a current transformer must never be allowed to have an open circuit secondary - that can result in some nasty unsafe voltages.
I can't see any load resistor on the current transformer secondary in your setup. If you are really measuring the *voltage* output of a *current* transformer into a high impedance scope, it isn't giving you a useful representation of the actual current waveform, and indeed the current waveform for the 100W lamp looks wrong. You need to have a relatively low load resistance across the CT secondary, and then measure the current through it by measuring the voltage across it. The value of the resistor depends on the CT turns ratio, CT power rating, and the max current on the primary side.
My bad, I didn't talk about the resistor. The packaged unit I came up (device picture) with has a 1k resistor potted in there. That will screw into a 3/4" knockout in a regular US electric box. That was big enough to provide a load without actually crushing the output. It dropped about half with 100 ohms. If you are sensing with an OP amp it really would not matter that much since they are pretty easy to drive into saturation.
My bad, I didn't talk about the resistor. The packaged unit I came up (device picture) with has a 1k resistor potted in there. That will screw into a 3/4" knockout in a regular US electric box. That was big enough to provide a load without actually crushing the output. It dropped about half with 100 ohms. If you are sensing with an OP amp it really would not matter that much since they are pretty easy to drive into saturation.
Guys, What im trying to do is to open a powered damper when a commercial range hood is turned on.
No silly stuff here...
Im not sure what the actual voltage will be, or the current the motor draws. All I know is that as soon as the hood is turned on, I need to open the damper. I thought that I could do it easily electrically but it looks like using air pressure switches will be much simpler.
So just come off the switch for the range hood and run it to the damper motor. If the voltages are different then run it to a relay or a transformer which will in turn control the damper. It's not that complicated.
How are they turning the hood on? Since it's a commercial hood, there should be a contactor powering the hood so that the fire suppression system has a means for turning the hood off. Right?
The way I view it, the inductance of the transformer (with secondary open circuit) determines the voltage drop there will be across the primary. That voltage drop is multiplied by the turns ratio to get the voltage on the secondary. CTs generally have significant inductance to be able to drive a secondary current proportional to the primary current. Core saturation can also be a limitation. (But magnetics is not my strong suite.)
For gfretwell's CT, it fits in a knockout, doesn't have much inductance, and probably can't produce much secondary open circuit voltage. I think that is why the 100W (if I remember right) waveform is not a sine wave (or saturation?). The CT should be enough to drive a circuit to do what the OP wanted.
I certainly agree, in general, that you want a low resistance load, or short, on the secondary of a CT.
=============== Runway/taxiway lightning at large airports is often series wired with thousands of volts supply. Lights are tapped off with a CT. They must have a voltage limiter or automatic short on the lamp/secondary side for when a lamp burns out.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.