Working ammeter using same power source of supply

[Allenvik]

Hi there,

I have a project, in which I am building a DC current supply and I am using a panel ammeter for monitoring, however the Chinese ammeter doesn't allow me to use power from the same DC supply to work (When I tried it, the ammeter gets crazy measurements), meaning that it doesn't accept being fed parallel by the same power source that is measuring in the other leg of the circuit, is there a way around this? perhaps a 1:1 transformer isolating coil to supply the ammeter?

My idea later on is to make my own ammeter built-in, to measure the current out put, however it has to work using the same power supply. Anyway, if anyone have a good and simple accurate ammeter circuit to share, please send me the info, I will appreciate very much.

Thank you

 

[AnalogKid]

The way the meter works is that the current being measured is put through a very low value shunt resistor, and the meter tells you the voltage across that resistor, adjusted to display the equivalent amps. At max current the voltage across the shunt resistor is too low to power the meter's electronics. That is why the meter needs a separate power source, and all other current measuring circuits will be essentially the same.

Thanks to Faraday's Law f Induction, you can't put DC through a transformer. I think you're going to have to deal with a separate power source for the circuit.

ak

 

[Allenvik]

Hi AnalogKid,

Thank you very much for taking the time and enlighten me! I am trying to get my head around your explanation still The information makes me conclude that the initial issue is not as easy as I though... reason then, why separate ammeters have to be powered by a separate source, despite my attempts to make it work otherwise. However, the question is, if you had to measure current output of a circuit, with only ONE source of power for both, the main function of the circuit and the measurement function, how would you do it?

Reason I insisted in the same question, is that I am sure of the existence of devices that are powered by only on DC source, and still are able to measure the current output of the device... now how that is achieved in your opinion? It could be the case that the current measurements are made not by an actual built-in ammeter, but a microprocessor of some kind that calculates other aspects and translate the information in current values?

Thank you for your interest and willing to help.

 

[Harald Kapp]

Your options depend on the way the ammeter is constructed. If, as is often the case, the negative input of the ammeter is at ground potential of the ammeter's power supply, you can geet away with this meter by putting it in the negative supply rail of your power supply (instead of the positive supply where I'm confident you putit in the first place. See this diagram: