# High voltage DC power meter

I am runing a small diy hydro power turbine, that I would like to eventualy monitor online. I was hoping to use the nodeMcu module that will connect to my home network that is in range. The PMA generator outputs 3phase AC current that I am recitiying to DC for easier connection to a single load (waterheater). The problem I am facing is that once rectified 230VAC (interphase) the output gets about 545VDC ! To complicate things more the voltage range should be at least double accounting for a runaway speed of the turbine in a chance that happens.

Therefore I am in a need for a sensor that will be able to safely measure at least 1100VDC and only a few amps. OR about 460VAC (interphase) if I decide to measure it before converting it to DC via a rectifier (diode bridge).

What are my options?

Thanks!

A <1 minute “high voltage dc meter circuit diagram” search on Google got me to this page which includes a circuit diagram for a volt meter that goes to 1000V, but with an slightly bigger resistor you can easily increase this.

Your hardest problem will be to build this in a safe way.

Buy a secondhand electricity meter and fit in one phase of the AC side . You could then look at putting an optical pickup on the disc and get pulses from that - gives you nice safe isolation and does all the maths for you !! If you do t like that buy a current transformer type transducer - google them , you can get with a DC 4-20mA output , which is again isolated and easy to deal with. Use a small lightly load transformer to get a safe voltage signal ( you will need some electronics to get a DC voltage from that )

The contactless current transformer is what I would preffere yes. I am curious to find only AC-type, although I am sure I have seen DC-types too?
What happens if I run all three phases through a single current transformer? Will it read the sum of all currents, or will I get false readings because of the somewhat opposing currents?
Although I agree measuring one will be sufficient, since the load should be simetrical on all three.

As for reading the voltage I discovered that the generator has an convenient additional output coil that outputs 1/10 the full output voltage for powering auxillary devices. I can use that to measure the voltages easier. Like a transformer + rectifier + voltage divider circuit?

I never studied in the field of electronics so I have limited understanding on the subject, but if I understand correctly measuring on the AC side would only inform me on apparent power (VA) and not true power (W)?
That is an issue that I would not have when measuring on the DC side, correct?

All transformers are AC only. You are confusing it with a hall current sensor, which are usually active devices.

If you go the route of voltage divider for high voltage DC sensor you need to know about resistor voltage ratings, using multiple resistors in series (no single point of failure), potting up of circuits and flash-over. Once you are in the kV range with significant power you absolutely above all else have to avoid any possibility of flash-over, because that will destroy everything and risk lethal electrical shocks and fires.

Finding a commercial high voltage divider probe that's appropriately rated as the basis of a voltage sensing circuit makes sense - the manufacturer knows high voltage and gets it right.

https://electronics.stackexchange.com/questions/235622/measure-high-voltages-with-a-multimeter

DC is more dangerous than AC for the same voltage as it is significantly harder to switch off (standard AC mains fuses will not work reliably on DC for instance). 1kV DC at high power can hold a surprisingly long arc, perhaps 2 to 10cm. Unless you understand the hazards of HVDC, think carefully about such issues, and ensure you have correctly rated connectors and equipment.

I never studied in the field of electronics so I have limited understanding on the subject, but if I understand correctly measuring on the AC side would only inform me on apparent power (VA) and not true power (W)? That is an issue that I would not have when measuring on the DC side, correct?

No, since you are rectifying into a resistive load you know the power factor is 1, so you can measure on the AC side. If the load was capacitive or inductive you'd need to know phase relationship to measure power.

However with rectification you have to correct the AC amplitude to allow for the conduction angle of the rectifier, so actually a true RMS measurement is useful to avoid doing that analysis.

Thank you for the words of caution, didn't know DC could be so hazardus at these levels. The turbine has only seen some mechanical test runs, so luckily I havent done much electrical work. To be safe I will refrain from using DC for now and will rather get a 3phase heater element.

As for the power factor you should be right. A heater element is a resistive load and not inductive, so there is no reactive power to worry about in a pure AC circuit, correct?

Not sure what you mean by adjusting amplitude with rectification? Do you mean the conversion factors applied such as: Single phase: 230VAC=146VDC 3f halfwawe: 230VAC=269VDC 3f fullwave: 230VAC=545VDC

http://www.amelec-uk.com/products/20Amp-DC-Current-Transducer-%252d-ASC020.html

These people do a range of current transducers with a 4-20mA output . If you put all three phases of a balanced load through a CT the result is zero amps. I’d strongly suggest you get a qualified person to make your AC connections -,in fact it’s dangerous to do otherwise

The easiest, safest and most accurate method is to buy a meter and use its pulse output .

http://meters.co.uk/products/three-phase-sc300p/