MODIFYING a PZEM-051 (V5.0) Panel meter to read 5v..

[VK5POI]

I have two of these meters. They are V5.0, PZEM-051 pcb's
I want to be able to read 5 V dc, but alas they only go down to 6.5V!!

I will be using a PC PSU for 12v dc and 5v dc. Obviously the 12v readout is ok
12v for a few scanners etc, and 5v for a raspberry pi and USB charge circuits.
I'd really like to make sure I have correct voltage ( even though PC PSU's are incredibly robust)

I have tried all the suggestions, but no luck with an outcome.
Has anyone been able to get the display to read 5v,
Any help sincerely appreciated!
John

[moffy]

Since they are powered by the voltage they are measuring the 6.5V might be the minimum voltage needed to power the unit.

[VK5POI]

Hi Moffy,
No, that is not my issue.
My issue is, the lowest Voltage readout is 6.5 volts.
I want to try and work out a method to get the display to show  lower that 6.5V.
Previous versions of these panel meters may have been modifiable,
and I am looking for information to allow me to read voltages down to ZERO volts.
cheers

[enut11]

Hi @VK5POI
I used a similar meter in my DC electronic load modified to read down to zero volts.
enut11

https://www.eevblog.com/forum/projects/smart-panel-meter-can-it-be-modified-to-read-down-to-zero-volts/msg1540907/#msg1540907

[mikerj]

Hi Moffy,
No, that is not my issue.
My issue is, the lowest Voltage readout is 6.5 volts.

He's giving a very plausible reason why you may have this issue.  Self powered digital meters require some minimum input voltage to work so it's likely that is has a 5v regulator on board and the extra 1.5v is drop out.  Often these cheap import digital panel meters can be configured to be self powered or separately powered by fitting/not fitting specific parts installed on the PCB, so it may be possible to modify the meter to be powered from an external 5v supply.  This would require a small amount of reverse engineering to determine how the meters power is derived, and investigating any unused pads.

[coromonadalix]

this is the issue   

hack it  or choose another panel meter who as a separated supply voltage from the input ... they are cheap, they offer other models witch claim they go to zero volts

Aliexpress Amazon  etc ...

or buy real ones with real dmm chipsets like icl 7106 7107 7135  from 3.5 digits to 4.5 digits, more costly

[VK5POI]

I realise that the input voltage/voltage readout circuits are "tied" together,
That is certain!, However, I want to know if anyone has "Modded", "hacked" or otherwise altered
the circuitry to be able to segregate these inputs!!
The ADC is a MCX11P62 device, of which I cannot find any datasheets for.
Previous versions of this PCB used a different device.
I purchased a pair of these displays not knowing that the pcb circuitry is an updated version.
These cost $80 Aud landed, so its not like I've shrimped on costs guys!
I hear you all, but I would not be wasting anyone's time for no reason.

Thank you ENUT11 for your input, as you know and understand 100 percent what I am trying to achieve here.

KETOTEK KT-D138 Multi Function meter  With a PZEM-051 (V5.0) PCB......

No replies suggesting I bin them please guys, as they are actually a great panel meter.....If you do'nt need to be able the read below that good ol' 6.5 Volts!!

cheers guys
John
Cheers, John

[floobydust]

Post pics of the board, it likely can be done - split up power and voltage-sense.
Examples of doing it with AC mains powered panel meters:
https://www.eevblog.com/forum/projects/using-a-fixed-range-ac-voltmeter-with-variable-input
PZEM-022 https://www.eevblog.com/forum/beginners/power-meter-for-variac