Current clamps

Fun! When I first set up the current clamps, I could not make the figures match my electricity meter.

The comments from "the Internet" were "power factor". And so I assumed this was the issue - that the tasmota stuff was giving me reading that I needed to adjust for the power factor (which it also gives me). This did seem to make things match much better.

I believe I was wrong! It looks like the issue is calibration. The instructions for tasmota do say to calibrate, but an initial test I did with a simple hot air gun showed it using about the rating it said it has. So I figured the chips were close enough.

But no. It seems not. And the power factor fudge was wrong, and unnecessary.

So I got a "resistive load" to test. Look them up, they cost thousands. Unless you just get a two bar fire from Screwfix for £14.99...

Having a power factor of 1.00 I was able to more accurately measure voltage and current and confirm the settings and calibrate the power meter. It confirmed that it was about 25% out.

The result is that now, without trying to apply power factor stuff, I get spot on 220W for my network stuff, which is what I added it up to. And the power usage totals over night by the hour match my electricity meter almost spot on.

This makes me happy as the reported power factor for my network stuff was 0.6, which means I was expanding the usage way more. In practice the usage is not bad at only 220W. Yay!


  1. You are aware that domestic customers in the UK only get billed for real power, not reactive?

    Its only industrial/commercial users who get billed in kVA and have to pay additional charges if PF falls too low (below 0.8 IIRC, which I probably don't).

    1. Indeed. My initial work on the clamps sent me down a total rabbit hole. So yes, all makes sense now.

    2. I didn't remember correctly :)

      Seems like industrial/commercial customers start getting charged for kVA(R) if PF falls below 0.95 averaged over the billing period.

      Fair enough I suppose given a bank of suitably sized capacitors to compensate isn't rocket science or all that expensive.

  2. Just spent the afternoon setting up a Shelly em, working from the Web page. Then decided to flash tasmota, with the RevK tasmotiser pcb, looks like I've managed to brick it. Set it to save the shelly firmware, guessed at 4Mb flash size, so no original firmware, & an unresponsive Em. Any help

    1. Very hard to brick, and should be re-flashable.

    2. Oh must pick right tasmota, the SOLO for ESP32

  3. No quite bricked, still had a tasmota ap, but no way to load a Web page, solution was to flash an image for the 4Mb flash. Now just to try & calibrate!

  4. Just spent a couple of frustrating days trying to set the currents using CurrentSet xxxx, xxxx for the 2 clamps.
    Seems on 13.4.0 that is deprecated, usage is now CurrentSet1 & CurrentSet2.


Comments are moderated purely to filter out obvious spam, but it means they may not show immediately.

TOTSCO 66 is guidance, optional

I feel I need to explain this. The TOTSCO call today, first I have been on, and wow! But a key point was TOTSCO bulletin 66, which is actual...