Re: Any current sense amps that can handle 0V on one side of shunt?

On Jun 30, 2:42 pm, "Mook Johnson" <m...@xxxxxxxx> wrote:
I am using a brushless motor driver. It has a motor supply input, and
then outputs for the coils. I do not want to just measure current (on
the input of the motor controller) as I want directional information.
So instead, I plan on looking at individual coil currents. So, I plan
on putting shunt resistors on each wire to the motor. Sometimes those
shunts will be on the high end, and other times they'll be on the low
end. Thus I need a device that can handle both. Currently I'm looking
at using the Analog AD628 or AD8210.

-Michael

I dont thinkg you will get directional information if its a true 3 phase
brushless motor. What makes the motor change directions is the phase
sequense which the windings are energized. (say for forward it 1,2,3
and for backwards its (3,2,1).

You can do that by looking at the current in two phases. instead of
just one.

The problem with using a instrument amp is that the common mode signal
(motor
phase voltage) will be very large with lots of high frequency edges.
Compared to the signal you're trying to measure this is huge. You should
put some common mode noise filters before going into the instrument amp.
Then you'll be fine.

you might consider something like this instead

http://www.allegromicro.com/en/Products/Part_Numbers/0712/index.asp

.

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