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Current Sensor design

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pikstart

Member
Hi!

I am looking for a way to use a monster current sensor form Allegro the ACS758, a 150Am device.

I wonder on what PCB to place this part or how can Iconnect the power leads to the load. Are there special terminals on PCB fr this?

And what about the copper of the PCB. Can it handle that kind of current?

Its my first on this level of current, so I am afraid a little.

The project is for a water pump current measurement device.

Thanks a lot,
Ioannis
 

bryan1

Well-Known Member
Hi!

I am looking for a way to use a monster current sensor form Allegro the ACS758, a 150Am device.

I wonder on what PCB to place this part or how can Iconnect the power leads to the load. Are there special terminals on PCB fr this?

And what about the copper of the PCB. Can it handle that kind of current?

Its my first on this level of current, so I am afraid a little.

The project is for a water pump current measurement device.

Thanks a lot,
Ioannis

Hi Pikstart,
I have on older version of those sensors and all I did was run the ground wire thru those big legs on the back which was off the circuit board. Now go and have a good read thru the datasheet and it does show the pcb layout off memory. Either that checkout the app note for the device.

Hope this helps

Cheers Bryan
 

pikstart

Member
Thanks Bryan for the reply.

From the datasheet and Ap.Note there are recommendations about pcb layout.

What I am looking for is the connector to put on that pcb and accept the fat cable from my load.

I am not an electrician, but electronics engineer. I wonder why the pump has a 25mm2 cable for the 50A it consumes and the ACS758 has a 4x1,5mm pin.

Best regards,
Ioannis
 

Ubergeek63

Well-Known Member
Thanks Bryan for the reply.

From the datasheet and Ap.Note there are recommendations about pcb layout.

What I am looking for is the connector to put on that pcb and accept the fat cable from my load.

I am not an electrician, but electronics engineer. I wonder why the pump has a 25mm2 cable for the 50A it consumes and the ACS758 has a 4x1,5mm pin.

Best regards,
Ioannis
That depends on the frequency (not a problem), and the copper weight.

I use that family part now but only push 30A into a motor through 2oz copper 0.200" wide traces.

I used fast ons to prototype it. I seem to recall having to open them a little but that was not a problem since it was just a couple units and you did not say if you were looking for a production solution.

BTW I am also an electronic engineer. Integer horse motor controllers are one of the things I design for the company that I work for.

Dan
 

pikstart

Member
Thanks Dan.

It will run on the power line (50Hz) so I suppose there is no problem with that.

And yes is going to be on regular production if ever I design it.

Currently I use ready made solutions like the clamps and Current transformers for my clients or they have their own and just supply me with the measuremens.

Ioannis
 

mstovenour

New Member
I am not an electrician, but electronics engineer. I wonder why the pump has a 25mm2 cable for the 50A it consumes and the ACS758 has a 4x1,5mm pin.
Ioannis for many applications conductor size is selected based on conductor heating and voltage drop. Both heating and voltage drop are a function of current * resistance. Conductor resistance (at power line frequencies) is a directly related to conductor size * length. Very short conductors like the metal going through the current sensor will have very low resistance because well.. the conductor is short. The same can be said for the trace you are trying to size. If it is an inch or two in length it will have a low resistance. If you try to drag it across a 24" PCB then you will need to make it much larger.

Various applications have different constraints. 48V telecom power design is concerned about voltage drop because that represents wasted battery capacity due to efficiency loss in the conductors; this turns out to be the limiting factor vs. the typical AC conductor, like the power line to your motor. AC conductors are normally sized for safety (i.e. to prevent heating that will open the conductor or start a fire) but voltage drop is also an issue. For PCBs, the constraints include heat dissipation of the layout (e.g. internal traces do not self cool as well); since self cooling is important this also means that the ambient temperature is a factor. If you PCB will be used in an air conditioned space the traces might be smaller.

I did a quick search for online calculators and found the one below. I don't know if it is accurate, but it will give you an idea of the constraints that you must consider:
PCB Trace Width Calculator
 
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