Spces for a toroid

[bugler]

Hello,

I see that for a toroid size there are different specs and I don't kinow what would be more suitable for a current transformer.

Can you tell me which of these 3 FT240 is better for that?



Thanks.

[gyula]

Depends on how wide range frequency bands you want to cover with the current transformer. The inductance of the secondary coil defines the lowest frequency but you have to consider core saturation and make a trade-off.
The biggest AL value of 2000 (FT240-31) could be used from maybe some kHz frequencies to up some MHz (AL value includes permeability too).

These links serve for starting: http://www.mmgca.com/apps/MMG-ctdesign.pdf
Current Transformer Theory

[bugler]

Thanks for answering.

Rightnow it all sounds foreign to me.

I wanted for the 50Hz of the socket. What would be best sepcs for that?

Is ferrite the best material for the core of a current transformer at 50Hz?

Thanks.

[gyula]

Tutorials can be searched for on building them but have you thought of buying an off the shelf type? Here is some for USD 15.54:
AC Current Sensing Transformers - Toroid Corporation of MD

Also, on ebay you may find even cheaper ones that surely works:

eBay - INSTRUMENT TRANSFORMERS CURRENT TRANSFORMER RATIO 800 5, Similar items search
Out of them here is one for USD 4.99
100:5 current transformer Instrument Transformers Inc. - eBay (item 200555062116 end time Jan-13-11 13:01:16 PST)
If there is ebay in your country or neighbouring countries, and you find one by searcing, postage may be cheaper.

If you really wish to make one for a toroidal core, you would have to wind several hundred turns of wire onto the core to get reasonable accuracy at 50 Hz mains frequency.

EDIT You could use transformer lamination for core, no need for ferrite core.
Even a 30-50W normal mains tranformer is ok if you can wind 1 or 2 turns of heavy insulated wire onto its bobbin (use 1-1.5mm wire), this would serve for the current input/output and the original primary winding of the transformer would serve as the current transformer secondary. You would have to find a correct resistance value for terminating this secondary and build / match a measuring circuit what should be calibrated in Ampers.

[gyula]

There is this link here, selling clamp on AC current meters from USD 16.62 with free shipping worldwide, go down to about the middle of the page:

Electronics :: Multimeters - Electronic digital products and spare parts accessories wholesale goodluckbuy.com

(I have no connection whatsoever with them, I do not know their service.)

You could dig out useful info from this forum here: View topic - Monitoring AC Current • adafruit industries • Customer Support Forums, DIY Electronics, Open Source Hardware, Arduino

for instance this link: Detailed energy monitor system design | OpenEnergyMonitor and Accessories, Jackplug Extra Sensor and OpenEnergyMonitor Current Sensor Calculator (burden resistor=load resistor placed across the current transformer secondary coil as a termination, is a MUST!)

[bugler]

thanks for the info.

I tend not to learn much from tutorials. Next year I will be 100% in electronics.

I need to know which spec would be best for a 50Hz current transformer.

In the image above there are three toroid with different specs like this:
AL=1075 +/- 20 % uH=(AL*Turns2)/1000
Actual measured AL using 10 turns #28 wire

I don't know what it means and what will be best.

Thanks.

[Rubberband]

Torids

ttachment 7435

[Rubberband]

messed up

something messed up last post...I was asking if anyone knew what was up with this torid I pulled from a computer power supply. It is different from most I've used, it is lighter than one like the blue one next to it, also it is only mildly attracted to a neo (1/10 of as the blue one) and the other side is even barely attracted to a neo...Attachment

[gyula]

Hi Rubberband,

I think the permeability of that toroid core is low, compared to the other one. The reason for low permeability must be the high current flowing through that coil and a core with small permeability can better resist to magnetic saturation.

"The other side is barely attracted to Neo" : probably the core of that toroid is made of fine laminations (not solid ferrite) and the plastic house around it keeps a distance at the other side? IF you try to scrape a fine line with a needle into its surface, is it plastic (or ferrite like the other core)? If it is plastic it may be opened at somewhere on its edges and you could see the very thin laminations inside. This is possibility of course.