CT4 as 100A

I have an EmonTxV3 connected to an EmonPi over RS232. I have no use for the 19A CT4 on the EmonTx, but could use another 100A input.

Can CT4 be used as a 100A output by changing the burden resistor to 22Ohm and configuring the input in EmonHub somehow?


Yes changing the resistor to a 22R or adding a 27R in parallel (with the existing 120R) will make the input similar to the other 3. Ideally the calibration factor for CT4 wants adjusting in the firmware sketch, but yes you could make an adjustment via scales in emonhub.conf instead. Something like scaling the power by 5.453 should do it I think, maybe @Robert.Wall can confirm.

You don’t need to remove the 120 Ω burden resistor - at each end of it you’ll find holes for a wire-ended resistor, just add a 27 Ω (ideally 1%) in parallel, using those holes.

EmonHub won’t need to be changed if you edit the current calibration in your sketch, otherwise you will need to multiply the current by 100 ÷ 18.333 = 5.4545

[Doh! Beaten by milliseconds again!]

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