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No Voltage sensor but got a inverter that can feed/input voltage in real time

emoncms
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(George) #1

Hi all…
I don’t have a voltage sensor, but just realised I have a Inverter which have real time voltage value.
I’m thinking I can feed this from my inverter to emonPi/emoncms via a mqtt stream via Node-Red.
Would this make sense, would this help improve my power readings/values.
if yes, into what value/field… do i push it ?
G

(Robert Wall) #2

That voltage will only enable you to have apparent power, i.e. voltage × current. That, unless all your loads are purely resistive (i.e. heaters) or have perfect power factor correction, will always be higher than the true value of real power, which is what you pay for. That will give you a small improvement, because without the a.c. adapter, the emonPi also calculates apparent power, but uses the assumed nominal voltage of 120 V (USA setting) or 230 V (EU setting - basically anywhere else).

(George) #3

So… from that I take it it’s apparent power that’s calculated. As I don’t have a voltage sensor installed, to make it worse, South Africa uses a 220V standard, not 230…
and then additionally my inverted which measures and reports this has indicated its actually more like 217-219.
So can I ingest this value into OEM and improve my accuracy? As doing this would be the same as attaching a OEM voltage sensor.
G

(Robert Wall) #4

That’s easily put right with a calibration adjustment in emonhub.conf (But you need to apply the correction to the powers as well as the voltage, because the maths is done in the front end of the emonPi, a long time before the numbers get into emonHub.

Not really, unless of course your system voltage is a very stable 218 V - at all times of the day, every day.

(George) #5

ok, I’m missing something. on norm, a system would have 1 voltage input, that supply real time voltage, either directly connected or connected to a emontx? so instead of having a direct attached unit, I have real time voltage as measured by my inverter, can I not export/supply that from my inverter via a mqtt stream to the emon platform.

Can i not push that into OEM and have that used, instead of a direct or remote attached voltage sensor.
ps: my build is a single raspberry pi running emonpi/emonhub/emoncms all on the same pi, with lechalcal board with multiple CT’s connected.
G

(Bill Thomson) #6

You could.

BUT…

It won’t yield a real power measurement, only apparent power.

The real time sample is needed so the hardware can do a phase comparison between the voltage
and the current to determine power factor and hence be able to calculate real power, which is what
you get billed for.

(George) #7

so, what would be a better solution, importing this real time voltage with it fluctuations (how would I do this), or set the voltage down to 220 instead of 230v, how where can I change this 230->220v
G

(Robert Wall) #8

The real-time voltage will be better than the presumed value of 230 V (or 220 V, or indeed 218 V).

In emonCMS, on the input page, you’ll see a spanner icon where the input processing happens. Because the analogue front end sends you power (already calculated by multiplying current and the nominal 230 V) you need to undo that calculation by dividing the power by 230, the redo it by multiplying by the measured voltage from your inverter, which will come in on another input.

In the left hand drop-down where it says “Log to feed” you’ll find “×”. Multiply by 1/230 = 0.004348, and add this to the list. Then “× input” and select the input where your voltage is, and add that too.
You’ll need to do this to all the powers.
These two processes must be above any other processing of the power in the list of processes.

(If instead you simply want to use your measured 218 V, use “×” and multiply by 218 rather than the other voltage input.)

(George) #9

thanks
G