Help with my Digital Panel Meter

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
Hello! I have recently purchased a Digital Panel Meter to use as an ammeter for a project. I seemed to get it working in its voltage read setting but I'm completely stumped on how to switch it to read current. The manual and the circuit diagrams don't seem to turn anything up for me. It does however say that use as an ammeter is possible (in the manual). A Digital to analogue converter is in use in the circuit. Thanks in advance for any help!

Resources:
Similar circuit
Distributor
Manual
Circuit diagram
Chip diagram
 

dl324

Joined Mar 30, 2015
10,933
Welcome to AAC!

To measure current, you need to use a resistor to sense current. What is the current range you want to measure?
 

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
Let me note the only reason I'm actually posting my life problems are that I have tried EVERY other option I can think of,
Welcome to AAC!

To measure current, you need to use a resistor to sense current. What is the current range you want to measure?
I'd like to be able to sense 0-30Amps worth of current, I read a few things about a so called "shunt resistor" is that what you are referring to? Or are you referring to the formula v=IR?
Thanks for the reply!
 

Dodgydave

Joined Jun 22, 2012
9,200
You need to put another shunt in parallel across the. 01ohm same value will give you 0.05 ohms @20Amps fsd.

Otherwise a separate 0.003 ohms will give you 30Amps fsd.
 
Last edited:

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
You need to put another shunt in parallel across the. 01ohm same value will give you 0.05 ohms @20Amps fsd.

Otherwise a separate 0.033 ohms will give you 30Amps fsd.
Sorry I'm a little confused by what you mean by "another" shunt. Maybe a little more elaboration? I do appreciate the numerical values I'll keep those in mind :)
 

Dodgydave

Joined Jun 22, 2012
9,200
On the Original circuit, it has a 10Amp range, using a 0.01 ohms Shunt, so replace it with a 0.003 ohms one to give 30 amps range, or replace it with a 0.005 ohms one for 20Amps range.
 

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
On the Original circuit, it has a 10Amp range, using a 0.01 ohms Shunt, so replace it with a 0.003 ohms one to give 30 amps range, or replace it with a 0.005 ohms one for 20Amps range.
Ah I see now, you were referring to the "similar circuit". So now that I have the shunt value all sorted out back to the primary issue I'm having (I suppose I may not have been specific enough in my first post). Is there a way to convert the panel that I currently have (labeled "circuit diagram" in resources) to do what the "similar circuit" does? Right now my circuit only measures voltage and I'd like it to measure current. I'd prefer not to have to rewrite my entire board to do so. Apologies as this is my first post. And thank you again for your help so far. Yet the more I'm learning about this topic the more impossible this goal seems. I should probably just order an ammeter online haha.

Cheers
 
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bertus

Joined Apr 5, 2008
20,566
Hello,

The current to voltage converter is for VERY small currents.
Think of nano to micro amperes.
The shunt resistors as @Dodgydave suggested can be adapted to the range you need to measure.

Bertus
 

Alec_t

Joined Sep 17, 2013
11,389
Since your meter has a maximum input voltage rating of 199.9mV, if you want a direct reading of current then the input voltage would need to be 30mV for a sensed 30A current. So the required current shunt would be 30mV/30A = 1mΩ. The meter would then behave as an ammeter with a full-scale reading of 199.9A. You would not need the post #8 circuit.
 

Dodgydave

Joined Jun 22, 2012
9,200
As per my previous post, if your meter has a Fsd of 199.9mV, whatever current shunt you need will need to drop 30Amps giving 30mV, thats a 0.001 ohms shunt (1milliohm)@ 5Watts or higher.

You may need to trim the display preset VR1 for calibration against a working meter.
 

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
Since your meter has a maximum input voltage rating of 199.9mV, if you want a direct reading of current then the input voltage would need to be 30mV for a sensed 30A current. So the required current shunt would be 30mV/30A = 1mΩ. The meter would then behave as an ammeter with a full-scale reading of 199.9A. You would not need the post #8 circuit.
I get that I need a shunt but with how much of a dumb nut I am, I tend to be more visual. I have no idea how to wire it up with a "sensed 30a current". In my head I'm wiring the shunt into my loop, then wiring the meter in parallel but I'm pretty sure I'm missing some knowledge here. If you can either link me to a source to help me learn a tad more or show me a wiring diagram that'd be great! I really do appreciate the time you guys have given me I just can't say it enough.
 

Dodgydave

Joined Jun 22, 2012
9,200
Yes your meter leads will go across the shunt in Parallel with the meter, the shunt effectively shorts out the meter leads, but because of the high current going through it, a small voltage will be dropped across it, which the meter reads as Voltage, but displays it as Amps.
 

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
So I'm going to try to find a 0.001 ohm shunt. one of my final questions is regarding wattage. If I'm running this shunt off of both a 5v 30a line and a 12v 10a line (using a switch) would I need a 150W shunt or is there a different "rule of thumb"?
 

Alec_t

Joined Sep 17, 2013
11,389
The most the shunt will have to cope with is 30A. At that current the voltage drop across the shunt is 30mV and the power wasted (as heat) in the shunt is 30A x 30mV = 900mW = 0.9W. So a 5W shunt, as DD specified in post #11, will do nicely.
 

Thread Starter

Newb Gaming Networks

Joined Apr 17, 2017
16
So a few follow up questions because although all of you have helped me understand the "magic" a shunt resistor can do, you can never know too much when it comes to electronics.

A. Triple checking that "yes, my meter in VOLTAGE mode will measure the voltage drop across the shunt"

B. Is there a shunt that is below 10$ that will accomplish what I need? I've been searching far and wide online and there is very limited stock for these shunts apparently. I don't want to cash out 20$ Just to discover I was looking in the wrong place for a 0.001ohm Shunt resistor.. this definitley hasn't been the easiest part of my project.
 
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