how can i make my new meter read down to zero

[ME]

I have a PZEM-022 Color ac power meter ,is there a way to get this powered from 220v but give readings from zero volts so it can be fitted to my 220v variac ?

[thephil]

Based on the specs, no. But maybe it's possible to modify the PCB? And/or add a separate supply for the chip... You'll have to take it apart and have a look at the circuit, I guess.

[MrAl]

I have a PZEM-022 Color ac power meter ,is there a way to get this powered from 220v but give readings from zero volts so it can be fitted to my 220v variac ?

Hi,

Why do you need readings at 0v, is it because you want readings down to maybe 1vac or so?
Interesting problem, which I believe comes with power meters that are meant to measure power from a more or less constant voltage source that powers the load.  There's probably no way to modify that unless you have a complete schematic of the internals of the power meter.

I removed my original idea because it's just too risky.  There may be another way though depending on your meter.

Another idea is to use the variac to power the load, measuring the input power to the variac.  Subtract or whatever you need to do to compensate for the variac impedance and possible phase shift.

Does your meter have 4 leads or 3 leads that normally connect to mains voltage and the load?

If it has 4 leads you may be able to use the variac to SUBTRACT its voltage from the mains voltage and thus allow the meter to measure what would look like full power.  You then have to measure the load voltage with a true RMS voltmeter and do some math.
This is a possibility not definite yet.  There is still a possible effect from the variac though.

[Uunoctium]

There already is an thead in this forum, how to connect that meter to an variac. And yes, it also answers to the question, if the meter (after mod) is capable to read down to zero:
https://www.eevblog.com/forum/beginners/power-meter-for-variac/

---------------
Added:
.. or simply follow this condensed "howto":
https://www.instructables.com/Modifying-AC-Power-Meters-to-Read-Down-to-Zero-Vol/
( some traced schematic snippets inside )

[ME]

Thanks for the reply But my meter pcb is totally different! see pic,the model is not the same as the one in the link and post!, see pics.

[ME]

next pic

[MrAl]

next pic

What is so different about your meter?
If it can read power at 220vac then it should work with the variac as the output and load on the variac.

That's unless it cannot natively go down below a certain power level, such as 100 watts, even with a constant 220vac.

There will be some error with the variac on the output, but you may be able to figure that out by running it no load first with the variac turned down to zero.

[Uunoctium]

please inspect your pcb, if there is a connection between the left cap of R15 and R13, as illustrated.
And perform an conductivity test, at which of the screwterminals R15 is connected.

[ME]

please inspect your pcb, if there is a connection between the left cap of R15 and R13, as illustrated.
And perform an conductivity test, at which of the screwterminals R15 is connected.

as per the pic the left side of r13 has continuety with the l/h end of r15 (viewed from the top)  the left hand side of both r13+r15 have continuety with tthe lower screw terminal.

[Uunoctium]

So, here is nothing new or any other way, as the previos threads described. The only thing they had changed is the aux supply for the meter to an transformeless design. Also the numbering of resistors remained.
You have to cut the trace leading to the left solder lug of R13 and conecting an new, mains capable (suitable for 240V AC) wire on it and bring it outside meters housing (drawn red).

That's all.
Final wiring than should look like:

[ME]

Just a quick note to say a big thanks , That posted mod worked a treat thank you.

[Uunoctium]

 

[picburner]

What IC did they use to step-down from the mains voltage?
I can't read the name from the photo.

[ME]

I think it uses a capacitor dropper?,dont know on the ic number as its back together and fitted in my variac, next time i'm in there i will take a note.

[Gyro]

It's an off-line buck regulator, probably some Chinese commodity part with hard to find datasheet. There are other parts though, eg. the TI UCC28881 (not the same pinout)... https://www.ti.com/product/UCC28881