I want to do a amp meter that is able to measure up to 300amps 48V DC battery bank with devices attached to it, but i dont want to use a shunt if i can get away with it. but at the same being able to get the amp reading from it. i'm Measuring the voltage by using a voltage divider. I want to know what are the best ways to able to measure the amps drawn from the batteries if possible without a shunt with the high amps. If i need to use a shunt i will have to use a shunt.
At the same time i'm a newb so please be gentle LOL
Can anyone help me out with some advice for above?
You are limited in how to do this. Current is measured by the voltage drop on a shunt or by the magnetic field. You may be able to find a Hall effect current sensor suitable for this current.
A shunt does not mean you will damage the Arduino.
A fuse does not mean you won't damage the Arduino. In fact, it has often been said, a semiconductor (such as an IC or transistor) is the best way to protect a fuse! The reason is simple, fuses are very slow devices in general. Also, fusing the negative of the voltage divider is likely to damage the Arduino if it's ground remains connected and the fuse blows. Unless you are saying that you are measuring -48V. Of course, without a schematic it is nearly impossible to say...
Finally, the reason you are not getting replies is likely because you have not really given enough information to reply to. So you need to post the intention of the system you are building, a schematic (hand drawn or block is better than nothing), and it would help if you would explain why there will be surges, if you know.
Have you ready the sticky at the top of the forum on how to post?
You do not add a shunt to existing wiring. You use the wiring itself as the shunt. Without breaking any circuit, you connect sensing wires to each end of a current-carrying wire (usually the ground) making sure that the two sense points are on the same unbroken length of wire and the path between does not include any junction or plug and socket.
You run the (insulated) sense wire held against the wire you are using as the "shunt" except where they leave together to go to your instrumentation amplifier from where they are also run as a pair.
You will naturally need to calibrate this at one point with an accurate current meter, after which you will know your values. The resistance of the wire you use as "shunt" will vary a little with temperature, but this is unlikely to be a real problem (or you can arrange some compensation).
You could use a Hall effect current sensor, such as this one or this one.
They are powered by 5V, and have an output that would connect directly to an Arduino analogue input.
Just pass the wire carrying the current through the hole in the sensor.
The output is at 2.5V, and increases for current flowing in one direction, and decreases for current flowing in the other direction.
JohnLincoln's solution is the only one you should be considering.
These require no electrical connection to the system being measured, can be installed in either supply line, provide total electrical isolation for your arduino and provide a signal output that is ideally suited (0-5 volts) for the arduino.
You can't measure 300A with a Fluke.
In fact, you probably can't measure more than 10. But if you have a scope and a Tek A621 Current Probe you can do it, but that's not what you said.
You will naturally need to calibrate this at one point with an accurate current meter,
Those currents are usually measured with a DC clamp meter.
I would try e.g. an ACS712 breakout board.
And connect the current terminals across a section of the wire that carries the 300Amp.
So two current resistors in parallel. A section of the 300A wire, and the acs712.
So SOME of the current flows over the hall sensor.
Leo..
Not to split hairs but if it doesn't have a Display built in it's called a "probe" or CT , not a "meter". We use clamp-on current meters at work with built in displays and as standalone units or cuurent clamp on scope probes. (like Pearson CTs or Tek A621s.
A DC clamp is basically a ringcore with a small piece cut out. Like the letter "C".
A hall sensor is placed in that gap.
Be prepaired to pay $30 for that current.
The ACS712 is cheap, bi-directional, and can be directly connected to the Arduino.
Leo..
There are two kinds of hall sensor, the ACS712 style with a sensor next to a copper strip, these are
least accurate and pick up magnetic noise more readily, but are cheap and small.
Then you have the ring core sort as used in clamp meters which have higher immunity to
interference and normally use active feedback to null the field, typically these use more power
to run the circuitry, and are larger units. They can be permanently magnetised and misread
if exposed to overcurrent surges, and can exhibit hysteresis, but the split-core sort can be
placed over existing wiring without having to solder anything.
Measuing voltage across a shunt is alas the only low noise and intrinsically accurate measurement
technique, but is not isolated and has real problems with voltage noise on the circuit being
measured.
