Timeline for Translate voltage between line/neutral potential and ground potential (between primary and secondary side of PSU)
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
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| Feb 18, 2023 at 16:47 | comment | added | bobflux | It would be better to connect "circuit ground" to neutral, but it will work if it's connected to live too: sign of voltage will be inverted, but sign of current will be inverted too, so it will measure the same power. | |
| Feb 18, 2023 at 16:45 | comment | added | bobflux | Yes if the whole circuit is at mains potential you can use a resistor divider for voltage, and a current sense resistor (plus opamp) for current. If you experiment with a 24V transformer then it's safe. When connected to mains, you can't use a USB interface to uploading new code to the micro, but there are other hazards: if it has a LCD or buttons, all the metal bits in these are connected to the circuit too, so they're at high voltage. If it has a serial port to communicate you can isolate it with opto couplers. | |
| Feb 18, 2023 at 12:18 | vote | accept | drzecki | ||
| Feb 18, 2023 at 12:18 | vote | accept | drzecki | ||
| Feb 18, 2023 at 12:18 | |||||
| Feb 18, 2023 at 12:15 | comment | added | drzecki | We will test our circuit with a protective transformer, and 24VAC and if everything works we will place everything inside a 3d printed case and plug it into the grid. Another question: As I understand from your answer, just using a simple voltage divider and placing the whole circuit at mains potential will work without damaging the components as long they are not connected to any external electronics. It's just unsafe. In that case,wouldn't we need to know which which one the neutral wire is, in order to connect it to the ground of our circuit, so both sides are on the same potential? | |
| Feb 18, 2023 at 12:11 | comment | added | bobflux | With the meter you can check your own measurements, and it also has a modbus interface which is nice for data logging. It's not very accurate below 10W though. There are plenty of cheap meters and current clamp transformers sold separately from the meters too. | |
| Feb 18, 2023 at 12:11 | comment | added | bobflux | Yes it can saturate if the current is too high... or rather, if the core isn't properly selected for the current. So it's simpler to just buy a readymade one, you'll get the correct core material (linear, not much hysteresis etc) without headache. I'd recommend buying a Eastron SDM120 CT smartmeter which is not expensive, and a spare current transformer to use for your experiments. | |
| Feb 18, 2023 at 12:09 | vote | accept | drzecki | ||
| Feb 18, 2023 at 12:17 | |||||
| Feb 18, 2023 at 12:04 | comment | added | drzecki | Thank you. Sorry for the inconvenience, I wanted to ask if the current transformer is similar to a current measurement clamp. Wouldn't it be be prone to the hysteresis error resulting from saturation of magnetic force on the flux density v. magnetic force diagram. Anyways, we will probably go with the transformer for voltage measurement and the current transformer + shunt resistor for current measurement. Thank you for helping us. | |
| Feb 18, 2023 at 11:57 | comment | added | bobflux | The "current" transformer is just a transformer, the primary is the mains current carrying wire going through the hole in the middle of a toroid core, which counts as 1 turn. The secondary is N turns on the same core. You need a proper core so it's better to buy it ready-made. It also works as a voltage transformer, Vout=N*Vin, but input voltage is unknown since it's just the voltage drop across the wire that passes through. So it is much more useful to use the transformer equations for current (Iout=Iin/N) and add a resistor on the secondary. It's cheap, safe, and it works. | |
| Feb 18, 2023 at 0:15 | history | answered | bobflux | CC BY-SA 4.0 |