Any current sense amps that can handle 0V on one side of shunt?
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Posted by Michael on June 29, 2007, 3:37 pm
Please log in for more thread options Hi there - I'm looking to sense currents going through the three lines into a brushless motor. The motor will be operated in both directions, so at some times I'll have something like 49.95 and 50.00 on the two sides of the shunt resistor, and at other times I'll have 0 and 0.05 on the two sides of the shunt resistor. Are there any current sense amplifiers that can handle this? Thanks! -Michael | |||||||||||||
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Posted by Mook Johnson on June 29, 2007, 4:15 pm
Please log in for more thread options Which amps are your looking at and what does you're circuit look like. not clear on what your mean for 49.95 to 50 on two sides? Since resistors for a brushless motor using 6-step should be between the source pins of the low side fets and power return. | |||||||||||||
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Posted by Michael on June 29, 2007, 5:01 pm
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>
> > > Hi there - I'm looking to sense currents going through the three lines
> > into a brushless motor. The motor will be operated in both directions, > > so at some times I'll have something like 49.95 and 50.00 on the two > > sides of the shunt resistor, and at other times I'll have 0 and 0.05 > > on the two sides of the shunt resistor. Are there any current sense > > amplifiers that can handle this? Thanks! >
> > -Michael
>
> Which amps are your looking at and what does you're circuit look like. > > not clear on what your mean for 49.95 to 50 on two sides? > > Since resistors for a brushless motor using 6-step should be between the > source pins of the low side fets and power return. 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 | |||||||||||||
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Posted by Mook Johnson on June 29, 2007, 10:42 pm
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> 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 of the currents are in the 1 A range. | |||||||||||||
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Posted by GPG on June 29, 2007, 10:48 pm
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> > 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
>
you might consider something like this instead
> 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. > http://www.allegromicro.com/en/Products/Part_Numbers/0712/index.asp | |||||||||||||
> into a brushless motor. The motor will be operated in both directions,
> so at some times I'll have something like 49.95 and 50.00 on the two
> sides of the shunt resistor, and at other times I'll have 0 and 0.05
> on the two sides of the shunt resistor. Are there any current sense
> amplifiers that can handle this? Thanks!
>
> -Michael