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| Reverse your smart energy meter with this simple trick! |
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| Cyberdragon:
--- Quote from: TheSteve on August 13, 2021, 05:27:41 pm ---I lost one leg of the power coming into my house, the smart meter didn't notice or generate any fault. I'm not convinced they are very smart. --- End quote --- Fun fact, cheap digital meters extract power from only one leg, no redundancies. If you loose that leg, the meter goes out, the remaining leg is free power. ;D :palm: |
| Alti:
The solution could have been to split counting of energy into several harmonics ranges (digitally). Then first counter integrates sub-harmonics, second integrates around main 50Hz, third all other higher harmonics. Then the metering could have been tested for tight <1% errors only around main frequency. Designing a 1% power meter frontend for MHz eBay jammers would have been expensive and unnecessary so maybe let the third meter integrate higher harmonics with +-30% error and just apply higher charge on this counter. This could have been relatively easy to design and to test. |
| Berni:
No need for any fancy FFT or anythyng. You just need to sample the current and voltage about 1000 times per the 50Hz cycle, multiply them together to get instantaneous power then average out the power across the cycle. With some more analysis you can also extract the reactive power and power factor from this. It's just a matter of sampling fast enough to catch all the relevant harmonics while having proper low pass filtering on the voltage and current sense inputs to keep out any high frequency or RF noise. This keeps the noise from perhaps demodulating itself in the current shunt amplifier or alias in the ADC. Test the thing with a large frequency sweep from Hz to high MHz and if the ADC readings don't twitch or move at all then it will be resilient to pretty much anything you could reasonably throw at it (So this does not include pointing a microwave oven magnetron at it) |
| SeanB:
--- Quote from: amyk on August 14, 2021, 02:02:29 am ---Does anyone else get reminded of the old ads in the back of some electronics magazines that told you how to make a device that would cause the meter to run backwards? I always thought those were just scams for the gullible... this was decades ago. --- End quote --- No, those were easy, you just use a iron core welding transformer, or three, which was essentially a near perfect inductive load. The high out of phase current would saturate the current sense coil, and then cause the meter to either not read correctly, or to run backwards as the core came out of saturation and generated a magnetic field that appeared to be a return current flow. The solution from the power companies was to simply include a small non reverse cam and pawl on the meter movement shaft, so it would not run backwards more than a single revolution in this case. For those who were using the arc welders to weld, the meter simply did not move while they were connected but not welding, though when you welded the meter would run forward as usual, as the resistive load overwhelmed the inductive current flow. Modern meters will simply measure the inductive current flow as reactive power, and will ignore it. Also why you need a second meter in series for solar feed in, the flow of reactive power is not counted, only resistive current flow. |
| Alti:
--- Quote from: Berni on August 16, 2021, 07:19:49 am ---You just need to sample the current and voltage about 1000 times per the 50Hz cycle (..) --- End quote --- If the sample is made at that frequency then conditioning circuit starts from anti-aliasing filter (it has to attenuate all frequencies above F/2) otherwise you get junk. At higher frequencies you can happily draw power in between ADC samples. And that is what this dumb eBay jammer does I suspect. I think it (unintentionally) locks fast rising edge with ADC, offset with zero crossing. With this brute force approach and keeping within 1% accuracy you would have to increase sampling to more than 2*some frequencies limited by RLC bandwidth of a piece of cable that separates power meter and jammer. Otherwise a purposely built jammer can be/will be created that locks into ADC sampling and extracts 1.01kWh when ADC counts 1.00kWh (thus defying your concept). That is essentially a proposition of a 1% accurate measurement instrument with DC to tens of MHz bandwidth. |
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