DCM9040 battery monitor

[Barry Fields]

Does anyone have any experience with this unit. My thought was to use it to monitor PV wattage via a 100a 75mv shunt on the lowside return of the combined PV array.

It monitors voltage fine but for the life of me I cannot get the current properly calibrated. I have tried introducing a variable mv source in place of the shunt. I do not frustrate easily, but here I am.

Am I missing something stupid?

[boB]

Does it read zero amps with no load ?

How far is it off ? 

Does it appear to have a gain that is too low or too high ?

[Barry Fields]

Well, some new info. I was able to use my millivolt injector and achieve a decent calibration of the current.
 zero @ zero   25a @ 18.75 mv  50a @ 37.5mv 100a @ 75mv. 

However, when switched back to the shunt, there seems to be a negative offset. It was early morning and the battery bank was charging @ about 100watts but the signal arriving from the shunt to the meter was negative 2mv.

2mv is equivalent to about 3amps X 75volts pv = 225watts negative offset

I do not know where the negative bias is coming from.

The shunt wiring is a shielded twisted pair (old telephone underground 6 conductor cable) that runs about 6 feet.

The controller is a renogy 60a.

[Barry Fields]

As he peers thru the smoke, I came to the determination that the offset was being introduced by the meter itself.

Sooo, I decided to eliminate the 12v feed to the meter and wire it per instructions (page 5 2wire system).

ZAP  apparently the voltage limits (on page 1) are either backwards or inside out.

I will order a hopefully better upgraded version (DCM120100C) and let ya know what happens.

The old unit will be incorporated into my ongoing eclectic sculpture "Technology Fricassee" .

[boB]

Maybe you are measuring the current drawn by the meter itself ?

Or maybe you said that ?

But the meter should not draw but maybe 100 or 200 mA at the most ?

[ClassicCrazy]

As he peers thru the smoke, I came to the determination that the offset was being introduced by the meter itself.

Sooo, I decided to eliminate the 12v feed to the meter and wire it per instructions (page 5 2wire system).

ZAP  apparently the voltage limits (on page 1) are either backwards or inside out.

I will order a hopefully better upgraded version (DCM120100C) and let ya know what happens.

The old unit will be incorporated into my ongoing eclectic sculpture "Technology Fricassee" .

Take a look at Peacefair PZEM-025(built in shunt)  which is a display type - I have two of those .
The PZEM-017( external shunt)  which I also have is just the monitor device with no display and I have it connected to an ESP32 flashed with Tasmota which makes it super easy to interface and then has it's own built in webpage.
I have details of these on various videos on my youtube page.
 https://youtu.be/cKJKUMLyjLM?si=_d_mc22SQZnJ3zWE
https://youtu.be/TbLLrlZ3deI?si=x_Af1dzLublTDVjx
Larry

[boB]

Larry, what do you use to flash your ESP32 ?

What "system"  do you use ?

[ClassicCrazy]

Larry, what do you use to flash your ESP32 ?

What "system"  do you use ?

Any  ESP32 development board ( there are many and they only cost $5 )  you can just plug into its micro usb jack with a regular usb to micro cable. Then just plug it into the computer. They actually made it super easy to flash Tasmota directly from a webpage though you need to use Chrome browser to do that. On some esp boards you need to press a boot button in the board first when flashing .
https://tasmota.github.io/install/
The nice thing about tasmota is it supports so many different sensors - makes life easy ! Once flashed it connects to your router and you have a wifi web page from it.
https://tasmota.github.io/docs/
Larry

[ClassicCrazy]

As he peers thru the smoke, I came to the determination that the offset was being introduced by the meter itself.

Sooo, I decided to eliminate the 12v feed to the meter and wire it per instructions (page 5 2wire system).

ZAP  apparently the voltage limits (on page 1) are either backwards or inside out.

I will order a hopefully better upgraded version (DCM120100C) and let ya know what happens.

The old unit will be incorporated into my ongoing eclectic sculpture "Technology Fricassee" .

Here is the Aliexpress Peacefair store - they have many different DC monitors https://peacefair.aliexpress.com/store/1101058977?spm=a2g0o.detail.1000061.1.7d21tWvdtWvdXJ

[Barry Fields]

Thanks Larry, I appreciate your input. I did look at the pzem-25. It appears to have a built in shunt. Is an external shunt a straightforward implementation.

The biggest problem I have (excluding mental issues) is the dimensions of the unit. Attached is a photo of my living room control panel. I would have to enlarge the lower right hole in that 1/8" aluminum plate to accommodate the pezm-25 unit.

All good info but I will first try the same size DCM120100C.

[ClassicCrazy]

Nice command central you have there Barry ! And nice and neat compared to the mess I have here - ha ha !
Larry

[Barry Fields]

I did look at the pzem-25. It appears to have a built in shunt. Is an external shunt a straightforward implementation?

? external shunt question above.
Thanks Barry

[ClassicCrazy]

I did look at the pzem-25. It appears to have a built in shunt. Is an external shunt a straightforward implementation?

? external shunt question above.
Thanks Barry

I am not understanding your question. Are you asking if pzem-025 has internal shunt - yes.I don't think it takes an external shunt  - just four connections  - 2 for 5 to 12v power to run meter and 2 for the negative power wire running through it.

[Barry Fields]

Thanks Larry,
I needed a meter that could stay in my living room with the shunt mounted 10 ft away in the outside battery enclosure.

[ClassicCrazy]

I can send you a new pzem-017 with shunt  if you pay shipping - but it needs an esp8266 or esp32 , rs485 adapter ( unless you do a mod on it to eliminate rs485  ) , and of course you need to have wifi for it to connect to . But then you can monitor with a phone or computer anywhere in wifi range.
Larry