Hi,
I´m going to use this sensor: ACS758ECB-200U-PFF-T (http://www.allegromicro.com/~/Media/Files/Datasheets/ACS758-Datasheet.ashx), and I was wondering if it makes any difference if I place the sensor on the positive or negative side of my motor (130 amp dc). If I could place on the negative side, it would allow for much shorter sensor wires. Thanks
Planned setup is: Battery positive --- motor --- current sensor --- contactor --- mosfets --- battery ground
I don't think that the position of the current sensor matters as long as it is in series with the motor. I might place it between ground and the rest of the motor circuit.
Look up Kirchhoff's current law, Current will be the same whatever side you put the sensor, assuming it doesn't branch off at some point. Make sure you put it in series!
I realize it is counter intuitive But I'd place the sensor in the high side of the motor... because of the possibility of a failure in the power connections to the sensor or the sensor proper. If low side sensing fails then you have full supply voltage on the ground leads.. If high side sensing fails you have no power to the motor, much easier to troubleshoot and much safer to work around. This is one of the reasons why switching grounds is not wise unless it is an absolute last resort -- do-able but inadvisable. Supplies may be switched but it is Always a last resort to switch or sense ground in any high voltage control circuit.
The Allegro ACS series current sensors have a 2KV isolation barrier between sense and sensed conductors so there should be no issues of that nature in using the sensor in the high side of the motor power circuit.
There is little risk of personal injury, as the system is only 24 volts. But I see your points about troubleshooting and also it makes sense to not have permanent power on ground leads. I will have to find the best compromise between physical layout, possible interference and safety. Thank you.
Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion. It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.
afremont:
Since the sensor is not actually carrying any current, it's not going to have any affect on safety either way in my opinion. It's a hall sensor, meaning it magnetically measures the current in the wire, so circuit isolation is very high.
Is this for some kind of RC car?
current does flow through the sensor, on pins 4 and 5 - ip+ and ip-
Oops, I saw the hall effect verbiage and assumed it to be an inductive pickup. I see that it is actually in series with the circuit, sorry about that. I think I'd look for an inductive pickup sensor if it were me.
The motor is 133 amp 24 volt series wound dc. I don´t know what they where intended for (maybe forklift), but i managed to get hold of 6 of them, maybe 10 years old, but unused. I´m converting a lawn tractor to electric with a motor for drive, and a motor for grass cutters. Arduino is at the heart of the operation. I promise to make a ”bragging” post when the project is finished
Recently I bought 15 LEM HAL 300 current transformers as surplus from Ebay (the price was Very Right) and one of these devices would be perfect for your application. The device has a 30? mm (approx) hole in it to pass through the main motor current carrying wire. Due to the inherent losses involved in getting the Allegro device soldered in a suitable PCB (4 Oz Cu?) and connections to the controller and battery, a through hole or pass through device is really called for. The HAL 300's can be found for about $50.00... Mine for considerably less (New on Mfr's shipping material). But I see no easy way to get one to you.
The device can be placed anywhere in the motor power leads, hot or ground as it is totally isolated.The LEM device is spec'd from DC to 50 KHz and has an output similar to the Allegro device however it requires a +/- 12 - 15V split supply to bias the Hall effect circuitry. There are available 12 to 15 V isolated switchers that will supply those voltages. Or in short.. I personally don't think that the Allegro device is ideal for your application. My intent here is NOT to sell current transformers but to point out a more suitable device. I intend to make DC transformers by winding a multi-turn primary so I can use them for more reasonable currents... +/- 30 A = 10T primary. Unfortunately.. I had to buy 15 (at less than the single unit surplus price, much less). It just occurred to me that the motor current is likely going to be considerably less than 130 A since your load will be just the mower and batteries, I should think more like 10 - 20 A which is easier to deal with than the rated full load current and entirely do-able with FR4 PCB material (I would use double sided FR4 laminate and have it plated to 4oz/in with a lot of via's stitching the top and copper together).
afremont: Oops, I saw the hall effect verbiage and assumed it to be an inductive pickup. I see that it is actually in series with the circuit, sorry about that. I think I'd look for an inductive pickup sensor if it were me.