hi forum. my next question is what flexible after market CT clamps can be fitted to the Emonpi please? thanks in advance. leon
ie things like these or ones with compatible connectors.
What sort of emonPi?
If it’s the unnamed but now called emonPi 1, then that Rogowski coil has a 300 mV (at rated current) output and will only ever reach about 30% of the emonPi’s input range. So unless you have a 3 kA supply and use all of it, you’ll be struggling to read anything. And you’d need to remove the internal burden resistor on the emonPi’s input.
If you have an emonPi2, then the position is better, but only 3 times - it would read (almost) full scale (333 mV input) at 3 kA, so realistically you’d still struggle to read anything with any degree of precision.
The catalogue calls it "FCT Series - but they don’t mention any other rated currents. As far as I’m aware, Rogowski coils aren’t suited to relatively low (i.e. domestic vs industrial) current levels.
So I’m afraid it looks like a conventional current transformer will be needed.
hi robert. i just posted that as an example. what im looking for is flexible CT clamps that can monitor up to 100-200A that will fit the latest generation emonpi. if you guys can recommend some that would be great! it just makes it easier when you are dealing with cramped switchboards etc. thanks for your response though.
I think you’re looking at the lower end of the range. Your problem is one of the Rogowski coil’s attributes - air. It’s good for high frequency response, but not for sensitivity. Magnetic flux is rather fond of living in iron, not so much air, so to get down to even 200 A rated current means a lot of amplification as part of the process of integration. You’re almost certainly looking at providing an external power supply for that, which adds a layer of complication for you.
This firm offers integrators down to 100 A, I haven’t dared ask the price.
But spelling out what was implied in my first response, if the integrator offers a 333 mV output, it will work directly into the present emonTx4/emonPi2.
Rogowski coils in the sensitivity range the OP is asking about, aren’t cheap.
e.g.
To top it off, this one has a 1 Amp output, lead time of four weeks, the power
supply is an additional 75 bucks and the lowest cost coil is an addtional 82 bucks.
783 bucks in total.
And then a 1 A, 333 mV shunt to turn the 1 A output into a 333 mV signal for the emonPi2. It’s a bit more complicated if it’s an emonPi1 - it needs 1.1 V and there’s the built-in 22 Ω burden in parallel.