TIDM-SINGLEPHASEMETER: Use of Alternate Power Supply with TIDM-SINGLEPHASEMETER Reference Design

Hi Alejandro,

can you provide more details on having "some issues with the readings", please?

1. Are you able to get any readings at all or are those too "far-off" what you'd expect to see?
2. Or do you get "good" = accurate readings and then "bad"=wrong readings or vice versa?
3. Have you build your own HW (but only changed to SMPS)?
4. Are you using our SW without any changes?

Thanks,

Milen

Also, please provide the max. current you need for your system using the SMPS?

You don't say what trouble you are having. I am confused by your description mentioning 120VAC and 240VAC. V1 and V2 in your LTSpice schematic are shown with a phase difference of 120 degrees. As if you are doing a three phase measurement with a delta connection.

I really hope that the as built hardware will use three 330K resistors instead of a single 990K resistor in those dividers. While the resistance is the same the ability to tolerate a single resistor failing to a short in a safe way  vanishes.

1. We are able to get readings, but there was some strange behavior with the stable voltage reading changing under load more than what was measured by the oscilloscope. For example, we would read a small drop (~5VAC) of the line under a 1kW load, which we measured to correspond to a slight change in the PP voltage at V+ of around 50mV, however the reading of the voltage by the meter (stock firmware) would change more significantly.

2. Yes, we had intermittent issues with the quality of the readings as compared to the measured values via oscilloscope. 

3. We have built our own HW, but it is mostly a copy of the Single Phase EVM with small modifications that should not affect this functionality. We are using a stock SMPS from another supplier for this phase, while we finetune the functionality of the entire system. 

4. We are using the stock firmware.

I may have found a solution to my problem, as I have posted below.

We have multiple other systems, including numerous actuators, so the SMPS power system is quite large (200W+)

The readings were all over the place, with significant difficulty to reproduce the same readings under the same conditions.

I guess I use L1/+120VAC and L2/-120VAC interchangeably. I think the core of my concern is still valid, as in the stock configuration, the 'GND' of the EVM is at -120VAC, so I needed to change that to connect this system to our power supply.

We are exploring if we can use the same system when there is 3-phase power available, but we only connect two legs to produce 208VAC, which I may have been playing with when I took the screenshot. Since we are not measuring the current sink through both legs (as we don't have or use the neutral wire) I am under the assumption we can use a singlephase system to measure the power, as the current coming in one leg should be equal to the current going out the other, and we can integrate the voltage delta between the two legs to get the power used by the system. FW needs only a small change to get the right VAC reading with the assumption of a 120º phase shift between the two legs. 

We are using 3 resistors in the HW, they are only conflated in the spice schematic.