Better resolution on ct's



as i got export of data from my heat meter working it starts to make sense to monitor stuff again


i have 3 ct's from the shop but they are 100A and i do not need more than 32A tops... the real number will be lower than this


is there a easy way to enhance the resolution so that it works with V2 boards?

mihailuca's picture

Re: Better resolution on ct's

Yes. You should wind 3 primary turns instead of one. The secondary current will be 3 times larger, so the CT will be 33.3A / 5A instead of 100A / 5A (if you use a standard 100/5 CT)


boelle's picture

Re: Better resolution on ct's

wind 3 primary? 


i have 3 of these:


and the wires from the street are only as long then need so i cant loop them several times nor is there space in the fuse box for it

Robert Wall's picture

Re: Better resolution on ct's

The current transformer is a current source. Provided you do not exceed its VA rating (just like any other transformer), you can increase the voltage you get across the burden resistor by increasing the value of the burden resistor. The penalty is you are increasing the load on the CT (same current, increased voltage = increased power out) and so distortion and errors will start to increase. It would also pay you (unless you are using the emonTx V3 where there is a series resistor to limit the input current to the ADC in the event of fault in the primary circuit being reflected through the CT) to include a series resistor of about 1 kΩ to limit the current in the in-built protection diodes - this won't affect accuracy.

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