Could anyone confirm pin polarity, I have plugged my RT in and no voltage is showing, pin is negative??
Can you be more specific about your issue please? Are you using IoTaWatt in an RV? What do you mean by pin polarity, both US and Euro VTs have nopolarity requirement and have non-polarized plugs.
Thankyou, it looks like I have the wrong transformer, so I need a 9volt ac output?
The AC reference input is 9V, but I would not recommend using any 9V transformer. In addition to voltage, there are calibration and phase shift characteristics. The models listed in the configuration list have been tested and their characteristics entered into the tables. If you tell me your country, voltage, and plug type, I may be able to recommend where to get a supported transformer.
Thanks, I am in Australia, 240volt mains
There are two sources in Australia: Jaycar and Radio Parts. References and part numbers are in this listing.
Just a query here: how do you calibrate for phase shift? (Voltage is easy: just use the Inverter O/P voltage, or even better a decent accurate True RMS meter.)
In my case, I have used an old Mobile phone (or old router supply too) supply from my junk box. Crack open the case then remove the board, & wire directly to transformer. (May need to reverse the wires, or compensate in settings) ( The case cracks open with little damage: can easily be re-glued.)
I guess you check the shift with a CRO.
So far, I have not calibrated. I also have a split phase system with only one V ref. The power factor atm seems screwy: Some are pf: 0.5+/- .1, so I think that might be 180 deg out of phase (so will be fixed when the 2nd transformer installed: waiting on a Power outlet to be installed on the 2nd phase.
I calibrate VT phase shift with a standard IoTaWatt. It has the ability to measure the phase difference between two inputs using an undocumented HTTP command. It’s there in the code. You would need a known reference to compare your VT to.
Split-phase, as in the USA, is created using a center tap on a single-phase transformer. The resulting two “legs” are exactly 180° apart. This has absolutely no effect on power factor.
Sometimes, especially in apartments, light commercial, and condo’s, two legs of a true three-phase supply are fed into a conventional split-phase panel. In the US 120V world, both legs are 120V with respect to neutral as in split-phase, but the phase to phase voltage is 208V as in three-phase.
So it’s important to know the phase-to-phase voltage to understand if the two legs are 180° apart (split-phase) or 120° apart ("two-out-of-three phase).
When the two legs are 120° apart and there is a single voltage reference on one leg, a resistive load on the other leg will show up as half the actual power used and the power-factor will be .50 rather than the expected unity (1.00).
Thanks for both answers.
My power system is similar to the US. It is 480v, centre tapped Neutral (180 degrees phase shift).
I do have a transformer of known type (one supplied by Robin for a Solar HW diverter). Except for the Power factor, all working well.
I might even get another unit to monitor the house. Get the first working properly first tho.
I calibrated the 240v off the Solar Edge inverter. Power readings seem OK. I will wire the other V monitoring transformer in the next few days.
I see there are some people who use a bare transformer (that they box up themselves) as a voltage reference.
A tip to ensure the output is wired in phase with the input (mains side) is to temporarily power the mains side with a low voltage transformer on the bench. One side of the secondary is linked to one of the primary pins, then the voltage is measured from the other primary pin to the spare secondary pin. If the voltage rises above the primary voltage, the windings are in phase. If the voltage reduces, the phase is reversed.
(Explanation: we are making a temporary auto transformer. When the windings add to each other they are in phase. If the secondary is reversed, the voltage subtracts. Please do this safely! That is why the test is performed at low voltage (with no bare mains voltage!)
Of course, the phase can also be changed in the settings, but it is nice to be able to check the hardware.