Small project with Ammeter Shunt and Volts - Page 1
Forum section: electronics / projects

author: Pete2103
author_rank: Newbie
timestamp: March 14, 2018, 05:38:04 pm
content: Hello EEVblogTry as I have I just cant find anything relating as to how this little led Ammeter + shunt with volt readings should be wired correctly. There are tons of diagrams and images many contradicting one and another floating around Google but none of them are making any logic.Does anyone on the forum know how this should be wired? From various places around the net Ive read some say a DC/DC isolator is needed? (if so what do I need to look for and on what pins does it need to go on my meter?) or a seperate DC supply and another says no need for either as it has its own isolation.?I am wanting to Run a 13.8v DC power supply which can provide upto 25 Amp when needed. The Power supply uses analoge voltage and amp meters I would like to be able to monitor both volts and amps with a digital meter, I understand I will need a shunt for anything over 10 Amps. Maybe it would make it easier to show you a picture of the volt & Ammeter I have, it looks to me as though its missing a couple of connections, I could be wrong though.I did find a meter on ebay which looks very similar to the one I have but where Ive put Red arrows there is a thick solid copper wire (this maybe would be for 10 Amp) on the other and where the yellow arrows are the other meter had a small connector with 2 thicker wires coming from it. Now I am stuck with what to do next, Sorry for writing a book with my first post but this project has my head battred and stuck for what to try next. Any help would be appreciated. If you read this far, Thank you for your paitence.Thank youPete

author: ledtester
author_rank: Super Contributor
timestamp: April 27, 2018, 10:02:05 pm
content: My guess is that the green and yellow wires are the power supply lines and the blue wire connects to the voltage you want to measure.The 3-pin chip with a tab located near the center bottom is no doubt a voltage regulator. I would expect the green and yellow wires to connect to it. This should allow you to figure out how to connect the power.For instance, have a look at the AP1117 series voltage regulators -http://www.hobbytronics.co.uk/5v-voltage-regulator-ap1117. By performing continuity tests you should be able to figure out which of the green/yellow/blue wires are the positive and negative supply lines. The other one of the three is most likely the voltage sense line - i.e. connect it to the voltage you want to display.As for measuring current I would expect that your shunt is connected between the points you have indicated with the yellow arrows. All of these panel meters seem to implement low-side current sensing. This means that one of those connection points is actually GND, so perform a continuity test to see if that is true.Normally these kind of meters come with a JST header to facilitate connecting the current shunt. It's just a 2-pin version of the same kind of header use for the green/yellow/blue wires.Attached is a pinout of a AP1117 series regulator. I would be interested learning in what you are able to figure out.

author: Pete2103
author_rank: Newbie
timestamp: April 29, 2018, 06:41:04 am
content: Thank you for the reply and help ledtester this did help with progress. The voltage reading are ok and not too far off comparing with multimeter,Different story with Amps I have tried all ways to try and get close under 10 Amp without shunt and over 10 Amp using a 75mv shunt and the readings are a mile off. Maybe typical China QC as it lights up there will probably be small print somewhere saying it's within specRegardsPete

author: ledtester
author_rank: Super Contributor
timestamp: April 30, 2018, 01:54:18 pm
content: Using a shunt are the current readings still linear? - i.e. when you measure twice the current the reading on the ammeter shows twice the value?I'm pretty sure the firmware in the on-board microcontroller has to be coordinated with the value of the shunt you are using. If you see linearity you can compute the value of the shunt it is expecting. As I understand how these things work, one side of the shunt is at GND so all the microcontroller is doing is measuring the voltage at the other end of the shunt and multiplying by some scale factor to give you a current reading.