Warning Note: D85 DC digital ammeter shunt wiring issue

[Kiriakos GR]

This is a warning about one undocumented issue with D85 (no name) digital panel meters.   

This is relative to configuration of using two separate meters, one DC volt meter and one DC ammeter, and this being connected to shunt.

Those meters were my customer choice and selection, I got them from him and I would have to install them in to a high power DC power supply.
No documentation came with them just empty boxes with few external markings.
Picture below of meter and box this is just for you so to identify it.

What I did was to actually assembly this huge power supply, and I did connect the Shunt in to positive side as this looked as reasonable to do.

Power supply for both meters this was one single 12 ACV transformer, everything looked fine and meters did power-on and looked functional with out any voltage running at the circuit.
But as soon voltage was present in the circuit both meters started to play up and behave straggly, up to few DC volts,  voltmeter digits were disappear and only back light was on.
At that point even the ammeter was acting straggly by measuring current when there was no current.

In a way I got trapped by this issue because I discover the problem when my power supply was 98% ready and there is no room for significant design changes.
For several minutes I was unaware of what causing the problem?
All that those meters were sharing, this is 12V AC and nothing else.

Neither Google search help me any because there is not a serious manufacturer behind those anonymous products, and there is no documentation.

My work around and solution this came by adding and a second transformer, and by doing so, now its one panel meter this has it very own isolated  power source.
This solved the problem and finally everything working as it should.

Right now I have no idea how this circuitry would work or behave if I had connected the shunt to negative side.
Honestly right now I do not want to know, I never buy no-name meters for my projects, and this is my suggestion to all.

[giorgos]

The majority of these panels, needs to have seperate power supplies.
I had the same experience too in the past, but I wasnt very lucky, because my panels were damaged so i had to bought new ones.