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Measuring difference between current in live and neutral

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cupoftea

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Hi ,
We wish to use this CT for detecting if the current in live and neutral is the same....and if different, how different?
Supposing there was 30mA of difference between live and neutral, then do you know what the output would be of this?

ZCT409 torroid Current transformer
 

Thanks, they look to be excellent devices...

T60404N4641X900


And at sone $30 they are the cheapest on the market...
 
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Hi,

We wish to make a RCD for an EVSE single phase “wall box”. We will use a simple CT for the 30mA imbalance detection. This may get “blinded” by any DC leaking in either line or neutral.

Therefore, we will also have a second CT the same as the first one, but will constantly also inject 30mA AC 50Hz through its aperture with a wire loop. As soon as this second CT does not detect the 30mA , then that means it has been “blinded” by a DC current flow in either line or neutral, so therefore we turn off the relay.

(We will inject the 30mA with constantly alternating polarity.)

Would this pass regulations? Why not? It surely guarantees safety, and is far cheaper than offtheshelf RCDs for 30mA/6mA which are £30 upwards.
 

The installation of a Type B RCD in series with the EV charger is one option to remove the risk of a Type A RCD becoming inoperable, but it can add at least $300 – $400 to an EV charger install.

.the above quote about Type B RCDs in EVSEs costing $300...is this correct?...i thought you could home brew a Type B RCD for a $1 or $2?
 

What happens if you do an RCD fluxgate type current sensor, for a 32Arms mains distribution box, with no feedback, and without a square law core?...ie, with just a "normal" CT core?

...ie, a very simple one, that just pulses into the sense coil to saturate it in one direction then the other.

Why do we need the feedback?
 

Hi,

A fluxgate sensor without feedback is no fluxgate anymore...

A normal CT without burden will create high output voltage, the core will saturate, the output signal will be distorted.

What´s your idea?


Klaus
 
A fluxgate sensor without feedback is no fluxgate anymore...

A normal CT without burden will create high output voltage, the core will saturate, the output signal will be distorted.

What´s your idea?
...Thanks, we will be using a burden res.

The idea is simply to use fluxgate without feedback, and without a proper square law core...it will surely still work?...there is no reason why not?
 

you can drive a square wave into a multi-turn coil on the toroid, and look at the ave voltage on the wdg terminals, this will shift with the DC current thru the main current carrying conductor, so this is one way, albeit with variable accuracy, to measure DC, or slow-ish AC.

One should remember that a small fraction of this applied square wave will appear in the total current of the main conductor.

And also, fast large transient changes in the main conductor will affect the lower power driving circuit.
 
you can drive a square wave into a multi-turn coil on the toroid, and look at the ave voltage on the wdg terminals, this will shift with the DC current thru the main current carrying conductor, so this is one way, albeit with variable accuracy, to measure DC, or slow-ish AC
Thanks, thats right, and the voltage that gets looked at, is simply the voltage across a low value resistor in series with the coil.....(its put in series with the coil "gnd" connection and ground)........and you then see either a symetircal waveform if no DC and no imbalance...or otherwise its non symetircal..........in fact, all you have to do is buffer it, filter it, then read it into an ADC....and its job done. Why is not everybody doing it like this?.....no feedback is needed.
No "square law" core is needed.
So why is nobody doing this?
Why is everyone paying >£30 for an offheshelf RCD

..the way described is inaccurate a bit, but you easily calibrate that out in production.
 
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I think you'll find a square loop core will work better, why are they charging 30 GBP ? - because that is the market. And because extensive internal protection is needed which is often proprietary and not published.
 
you can drive a square wave into a multi-turn coil on the toroid, and look at the ave voltage on the wdg terminals, this will shift with the DC current thru the main current carrying conductor, so this is one way, albeit with variable accuracy, to measure DC, or slow-ish AC.
The average voltage across a transformer winding is zero, unless asymmetrical saturation current and respective voltage drop across the winding resistance causes a DC voltage component. More specifically, saturation can be detected by looking at the 3rd harmonic, which is the usual method applied in fluxgate sensors.

As far as I'm aware of, current sensors based on fluxgate principle are rarely saturating the total core. They have small sensor element with a separate coil placed in a gap of the main core.
 
I think you'll find a square loop core will work better
Thanks..
..We are seeking a "square law" ferrite torroid to use as a fluxgate sensor for imbalance current detection. For 50Hz mains electricity.
No manufacturer seems to make these.
I tried Far-rite, Mag-inc, Ferroxcube and TDK, but no joy. Plenty of high permeability (eg 5000), but no "square law".
We need OD= >35mm, ID = >15mm
Please Do you know of any?
 

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