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Rewinding current transformer

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eslavko:
Hello...

I have a bunch of SCT-13 50A/1V split core current transformers. Now I'm in situation that I need few transformers with 50A/5A ratio. I assume that I can use SCT transformer core and remove windings and wound 10 loops (thick wire) for secondary. Will that work? I assume that core will see same magnetizing current so no risk for saturating. Did I miss something? (I need this for panel meter with standard 5A input)
 

jonpaul:
Impossible to assist as no idea the part mentioned. Please include spec sheet, link or mfg

j

TizianoHV:
In theory should work, but:
-You should use some thick wire (normally CTs should be able to handle twice the nominal current, continuously) and I don't know if there's enough space.
-A 5A analog instrument has high burden, that means that the poor little core could saturate causing errors.

"I assume that core will see same magnetizing current so no risk for saturating" - Remember, this is a current transformer. With directly shorted windings (without ammeter) you'll have minimum saturation. When connecting a load (ex. Ammeter with burden (internal resistance...)) the output voltage will increase and the core will get closer to saturation.

Therefore: for it to work you must not exceed a certain Volts-Per-Turn threshold. Smaller cores have lower V/Turn.
For example if you CT has 1000 turns and 1V nominal output (1mV/Turn) with 10 turns will have 10mV nominal output. By exceeding the nominal output voltage you'll get the core to gradually saturate, loosing accuracy. Usually 5A analog meters have 400mV burden, which is  way over saturation.

In conclusion, such a small core, will barely move the needle of a typical 5A analog meter.

Berni:
5A sounds like a lot of current from a current transformer.Unless it is a pretty large beefy transformer the measurement errors are going to be all over the place.

The 5A panel ammeter you are wanting to use is likely actually a milivolt meter connected across a internal shunt resistor and amps painted into its scale. So you can probably open it up and replace the internal shunt resistor to turn it into a 50mA ammeter.

eslavko:
The CT is like:
https://www.ebay.com/itm/174480352469

And the meter is:
https://www.amazon.de/gp/product/B0BJ5XBPGX/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

I was thinking that primary winding (single loop) will magnetize the core and not secondary.
And I have no idea of meter internal resistance.

As my CT has primary range of 50A I do just assumption to make it 50A/5A.
In reality the meter will be connected over 25A fuse so making range 25A/5A or 32A/5A should be better for meter, but much worse for CT if I understand correctly that not primary but secondary will force core into saturation.

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