OpenEnergyMonitor Community

emonTx V3 USA apparent power

Tags: #<Tag:0x00007f1be2010b08>

I have just noticed a bug where USA apparent power mode (when no AC-AC adapter is present), would return incorrect readings if used in the USA on 110V with USA mode enabled.

This has just been fixed with firmware V2.7.0. The emonTx was incorrectly still using 240V as Vrms when USA mode was enabled.

This bug is not an issue if using an AC-AC voltage sensor adapter to enable more accurate Real Power readings. Use of AC-AC adapter is highly recomenended.


The US system voltage is 120-0-120 (L-N-L)

240 Volts across both Lines, 120 Volts across either line and neutral.

The term 110 Volts is a hold-over from long ago.

But it’s the standard UK voltage for industrial portable tools (normally 55-0-55 to earth).

I read that in an article some time ago. But methinks there aren’t many UK power tools in use in the US. :wink:

I think you might be right, there. But 110 V is a common option in a power tools catalogue, and that’s probably where Glyn got 110 V instead of 120 V from. I always have to stop and think because 110 V is also common in control panels here.

Yup, that’s exactly where I got 110V from! Sorry, excuse my ignorance, I’ve never travelled to the US. I should have double checked.

Thanks for letting me know, I’ve corrected the sketch: