Arduino or Raspberry Pi or other, Volt and amp meter

[Jeremy450]

Hi there

I'm very very very new to this stuff. I would like to be able to measure volts and + - amps from a 48v Battery and also 240v. But want to do it the easiest way. What is the easiest way to do this? Is there like a USB device that can be used to connect to a computer and can be displayed on a computer? if not what is easiest way to do with a Arduino or Raspberry Pi? (needs to be able to be accessed over a network from a computer)

Amp wise for the 48v battery needs to handle at most 250amps and show both negative and positive amps.

If someone able to make it, that would be good to. I would be happy to pay cant afford too much a $100 - $200

really hope you can help

Regards
Jeremy

[German_EE]

Cheap, accurate, safe, for that price pick any two.

A PC controlled instrument capable of measuring mains voltages and currents up to +/- 250A will be a technical challenge and not one that will fit into your price point unless you're willing to cut corners, and I'm not.

[leblanc]

For this kind of current you're almost definitely looking at a hall-effect type of sensor.

If it's going through a busbar, you can use one of allegro's hall-effect sensors that you just but parallel to the busbar at a known distance. If it's going through a (thick) wire, there are these ring-like current sensors that you slip the wire through.

With allegro's chips, you can just read a small ratiometric voltage (i.e. 0 to 5V) for a current of -250 to +250 (make sure to get a bidirectional one).

As for the voltage, well that should be easy with a simple voltage divider, but don't forget adequate protection. Depending on the nature, it may be best to isolate there exist these isolated opamps, they have a differential input and differential output, isolated from eachother.

[Jeremy450]

hi German_EE

the 250A is for the DC Side not AC. The AC side would be max of 40A.  But i'm more concerned about the DC side right now.

jeremy

[Jeremy450]

Hi leblanc

How hard would that be to be on i'm a total newb when it comes to this stuff. thats why i said the easiest way.

regards
Jeremy

[leblanc]

http://www.digikey.com/product-detail/en/HASS%20400-S/398-1066-ND/1680532
These make it really easy. They're expensive, but for will save you a ton of trouble. You provide a reference voltage and it will output a voltage related to that current. Then you can just measure this voltage whichever way you want (there are thousands of ways of doing this, any acquisition card will do the trick). Labjack makes these cheap national instruments ni-daq clones (https://labjack.com/products/u3), that may be an option. If you don't want to use LabVIEW and you're willing to write some software, they have examples for various languages.

As for isolation of an analog signal, check out http://www.ti.com/lit/ds/symlink/amc1200.pdf.

[theenggprojects]

Raspberry Pi is used in those projects where you want to upload your data on some server or wanna do cloud computing while Arduino is used normally in such projects where you just need to do some stand alone project some measurements or some algo designing. You should have a look at this comparison Arduino Vs Raspberry Pi. It will help you in understanding the difference between the two. As your project is concerned, I think you should go with Arduino.

[rstofer]

In the industrial world, we use 50 mV shunt resistors.  Regardless of full scale amps, the shunt resistor will drop precisely 50 mV at full amperage.  You would need 200A:50 mV.
To this we add a high side sense amplifier, perhaps buffer it with an op amp and then stuff it into an ADC input like those on the Arduino.

I'm not going to get into the AC side but basically, I  would use a current transformer feeding a burden resistor then rectify the result and scale it with an op amp before stuffing it into another ADC input.  We usually use 5A current transformers so, perhaps 50A:5A work.  I have never used a Hall effect device.  They may be a lot easier to use.

Be very careful with current transformers.  Should the secondary become an open circuit, the transformer voltage will rise to a VERY high level.  Suppose your CT had 50A through the primary and was trying to drive 5A through the secondary but the secondary resistance was approaching infinity.  Ohm's law still applies so the voltage across the terminals tries to approach infinity.  There are some limits but none are helpful.

https://openenergymonitor.org/emon/node/842

I stay away from mains stuff.  I'm perfectly content at 50V and lower - usually MUCH lower.  My favorites are 3.3V and 5V.  For the mains, I might just use a clamp-on ammeter connected to a logging DMM.  I would definitely recommend this clamp-on approach for newcomers.  I HATE mains voltages.

[mjkuwp]

Here is a sensor that can read +50A to  -50A

http://www.mikroe.com/click/hall-current/

There is a link on that page to the datasheet of the sensor.

Mikroe makes a good selection of boards that stack onto either Arduino or Raspberry Pi  - by way of an intermediate board.  I have used this sensor with Raspberry pi.

You didn't specify if you needed wireless or wired connection to the network.  Also, what is your desired refresh rate?  do you need to or want to provide your own interface.

Are you doing this as a learning/educational project or is it more important to get straight to the solution?