I have been searching for a while but besides a few trial setups I cannot find a breakout board that can measure >120A @ 22+V for a longer periode of time (30min+).
Do they even exist or should I park that idea for later on so I can create such a device myself?
This is basically the only one I could find but the author does not seem to be very confident:
The best way is use of shunt resistor.
https://forum.arduino.cc/index.php?topic=349777.0
For DC, you must choose between a shunt based (galvanic) or a hall based (isolated) sensor.
Shunt based sensors can be more accurate and can have a higher resolution,
but for that you must be able to share Arduino ground with the ground of what you're trying to measure.
A breakout board with an INAxxx chip can be used with an external shunt.
The 'shunt' can even be a calculated length of (battery) cable.
Give us more information, so we can advice you better.
Leo..
A shunt resistor for 120A poses a lot of problems - power dissipation and amplifier offset errors being two of them. A 0.5milliohm shunt only gives 60mV full scale, yet dissipates 7W.
Hall sensor is more reasonable at this current level, smaller and more robust to overcurrent too.
The ACS758 is perfectly good chip for this, but the high current terminals need to be clamped securely or soldered to big bus-bars, they cannot be used on a PCB like that module, no PCB can survive the current. The signal side of the chip should be on the breakout board, but the big current terminals (its available in several geometries) aren't for PCBs.
If this is a one off and you want to avoid direct connection hassles, LEM makes some nice +5 volt supply units. Not the cheapest but they certainly meet your requirements for a safe and reliable solution: https://www.digikey.com/product-detail/en/lem-usa-inc/LA-150-P/398-1012-ND/409825
Wawa:
but for that you must be able to share Arduino ground with the ground of what you're trying to measure.
Well, it is actually the situation that made me come up with the idea. I have made a very childish (yes learning KiCad) to show what I am building. I have to integrate a 6S lipo that puts out >120A. Because I already have to share GND, why not measure the Amps/mAh etc. It would be very cool to map throttle position with the Amps or keep track of the time until the lipo is at its bottom level. Also, does the equipment deliver as promised. etc etc. I have this schematic attached (do not laugh, it is rough). Perfect situation would be to measure at the lipo and between lipo and motor.
MarkT:
A shunt resistor for 120A poses a lot of problems - power dissipation and amplifier offset errors being two of them. A 0.5milliohm shunt only gives 60mV full scale, yet dissipates 7W.Hall sensor is more reasonable at this current level, smaller and more robust to overcurrent too.
The ACS758 is perfectly good chip for this, but the high current terminals need to be clamped securely or soldered to big bus-bars, they cannot be used on a PCB like that module, no PCB can survive the current. The signal side of the chip should be on the breakout board, but the big current terminals (its available in several geometries) aren't for PCBs.
That is my fear as well but I am not to familiar with all the parts available. Could you point me towards a parts list?
WattsThat:
If this is a one off and ........
For these kinds of Amps it might be a one off, I dont know. I also have boats that pull a lot of amps. This particular car might even go up to 200A, the boats up to 100A I quess.
Maybe a stupid question but can I use those shunts to also switch 120A or higher? I mean, the amps are going through it, is it also able to break the chain?
Sareno:
Maybe a stupid question but can I use those shunts to also switch 120A or higher? I mean, the amps are going through it, is it also able to break the chain?
Think about the names: "shunt", and "switch". Do they look similar?
Try to design a shunt for 120 amps and higher. What do you come up with? Perhaps a square copper bar 1/4 inch on a side. Then compute the length you need to make the shunt. Then the problem of how to incorporate the shunt into the circuit you are measuring and realize EVERY connection in the circuit will have resistance and will increase the total resistance in the circuit.
It all comes down to how accurate you need to measure the current.
Paul
It was just a thought. If it can measure it, it can disconnect it... But Im wrong.
Thanks!
Sareno:
Maybe a stupid question but can I use those shunts to also switch 120A or higher? I mean, the amps are going through it, is it also able to break the chain?
No. Its a solid bar of copper internally, that runs past an isolated hall-sensor chip, bathing it in the magnetic field from the current.
Sareno:
It was just a thought. If it can measure it, it can disconnect it... But Im wrong.Thanks!
We can measure the chemical composition of a star...
MarkT:
We can measure the chemical composition of a star...
I know! Cool, right?
Density as well?
It is like my two cozens Slim and None You will find a break board in that range. Actually it is as simple as going on line and looking for a shunt for the current you want. I have used them for less then an amp to over 5,000 amps. They have been around a long time and are very reliable. Current Shunt Resistors. Current shunt resistors are low resistance precision resistors used to measure AC or DC electrical currents by the voltage drop those currents create across the resistance. Sometimes called an ammeter shunt, it is a type of current sensor. Use google and try this as a search term: current shunt 150A I got a page of them several less then $25, they are also available on eBay. If you continue with the project pay your life insurance and put the shunt so it is in the ground loop, this keeps the voltages low for the arduino. They also have isolated electronics you can use. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
gilshultz:
It is like my two cozens Slim and None You will find a break board in that range.
I've heard the saying before but I cannot place it in context, please explain.
gilshultz:
If you continue with the project pay your life insurance
Why? If the part exists, why is it so dangerous to use it? I dont mind burning up an Arduino or 2 but please explain the "danger" of using existing stuff. I need to monitor the AMPS to prevent damage to other parts.
Consider a fault where the motor feed opens, you have over 2600 Watts of power stored in it with no voltage limit, that is extremely dangerous if you are not experienced in this area. That amount of energy will kill you. That is a quick approximation, you can calculate it if you like. You can look up inductors and see how they behave. It is like my two cozens Slim and None; becomes your chances are slim to none. This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil
Sorry, I still do not fully understand why this is so dangerous. At this moment I use the device in the attachment to do some reading after driving with the car. The issue is that I want a live feed AND I want the device a bit smaller, without display.
The idea is the same, it will be placed between the lipo and the speedcontroller, just like this one.
Consider a fault where the motor feed opens
What do you mean by this? The connectors will still be the same.
Also, the "big" 6S lipo is already in the Arduino-Group because of common GND
While many folks have life insurance I don't see any relationship to this project.
I see two options I would consider:
Not knowing your wiring plan, you might consider using the existing wiring as a sense resistor. Accuracy would not be the best and you would need an amplifier to allow reading with an arduino. But it is simple and adds no added loss in your system.
I would also consider the ACS758 or similar device. I would not put it on a circuit board, or at least I would not put the measurement current on a circuit board. I would solder or clamp some heavy copper or terminal right to the device leads. I purchased some 0.062 thick copper of one job and it worked out well.
Also you might try passing your current wiring across the ACS758 case. Perhaps the hall device would pick up enough field to give you an indication of current. You would have to do some calibration to know what you are getting out.
John
Hi,
What motor(s) and controller will you be using?
Can you post a link to spec/data please?
Thanks.. Tom.. 
I have a part of the motorsheet attached that I have now. Last season I drove with the 4076 / 2250KV and 4076/1700KV and an almost matching ESC (150A).
Coming season I might upgrade to a motor like this:
It is always a bit of trial and error when choosing the right motor/gearing for a car but for 1 of my boats it is almost certain it wil be something like the one in the link.
Maybe I should keep it with the car and in that case a max of 150 (theoretical) is enough. I just want to make sure my equipment can handle what it can theoretical has to handle.
JohnRob:
While many folks have life insurance I don't see any relationship to this project.I see two options I would consider:
Not knowing your wiring plan, you might consider using the existing wiring as a sense resistor. Accuracy would not be the best and you would need an amplifier to allow reading with an arduino. But it is simple and adds no added loss in your system.
I would also consider the ACS758 or similar device. I would not put it on a circuit board, or at least I would not put the measurement current on a circuit board. I would solder or clamp some heavy copper or terminal right to the device leads. I purchased some 0.062 thick copper of one job and it worked out well.
Also you might try passing your current wiring across the ACS758 case. Perhaps the hall device would pick up enough field to give you an indication of current. You would have to do some calibration to know what you are getting out.John
Thanks. I will try to create a somewhat better schematic as I have now.
