There’s a few “built in” voltage references (in tables.txt version 0.0.8):
They seem pretty different:
{“model”:”DCSS AC910(Aus)”,”mfg”:”Radio Parts”,”cal”:20.72,”p50″:[2.17]},
{“model”:”Powertech MP-3027(Aus)”,”mfg”:”jaycar”,”cal”:23.18,”p50″:[0.92]},
Note the phase shift (2.17, 0.92) and calibration is different.
I’m using different ones:
- PowerTran 12V AC 0.5A M9265A (Altronics import)
- PowerTran 9V AC 1.33A M9233 (Altronics import)
The reference is labelled “9V” but “Most 12V transformers do not exceed 15V no-load, and work fine with IoTaWatt. At the low end, even a 6V signal is fine.”
If I test them using tables.txt edits (see below). I guess the phase shift and calibration but can tweak the calibration to match line voltage later.
Testing against some loads:
| JayCar Powertech | PowerTrans 9V | PowerTrans 12V | |
| Note | Existing in tables.txt, tested by Bob. | Guessed by Brett | Guessed by Brett |
| Heater | 1503W 1.0PF | 1500W 1.0PF | 1501W 1.0PF |
| Aircon Portable | ? | 1270W 0.98PF | 1280W 0.98PF |
| Vacuum | ? | 910W 0.87PF | 910W 0.88PF |
So it seems ok to use these. There is, I recall, a way to test the phase shift of a VT with the IotaWatt. Indeed: see here for Bob’s instructions.
Initially I got 88′ but swapping CT direction gave an expected “small negative”
The phase correction of the CT I’m using ECS1050 is +1.6′ and the measured difference is -4.1
So apparently the VT phase shift is +1.6 – (-4.1)= 3.8 degrees
I used a ECS24200 CT (phase +0.2) and got
500W resistor, 1500W heat gun : PowerTrans12V VT
| CT | CT phase shift from tables.txt | Shift from vtphase on iotawatt | Estimated VT phase shift |
| ECS24200 | +0.2 | -3.5 | 3.7 |
| ECS16100 | +0.6 | -3.3 | 3.9 |
| ECS1050 | +1.6 | -1.5 | 3.1 |
So I’m going with 3.6 degrees for the PowerTrans12V.
500W resistor, 1500W heat gun : PowerTrans9V VT
| CT phase shift from tables.txt | Shift from vtphase on iotawatt | Estimated VT phase shift | |
| ECS24200 | +0.2 | -1.2 | 1.4 |
| ECS16100 | +0.6 | -0.81 | 1.4 |
| ECS1050 | +1.6 | -1.0 | 2.6 (!) |
So I’m going with 1.6 degrees for the PowerTrans9V. It’s much heavier than the 12V unit.
So this (I thought) would work. But it doesn’t. Need to check iotawatt check to determine exact parsing method. The number are right, but need right format. In the meantime, using “generic” VT we can set the phase and cal manually to these values.
{“model”:”PowerTrans12V(Aus)”,”cal”:16.00,”p50″:[3.6]},
{“model”:”PowerTrans9V(Aus)”,”cal”:21.00,”p50″:[1.6]}