Summary: I'm ordering "ACS712 Breakout" on a small pcb for $10
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Detail: John Larkin recommends:
- Hall-effect current sensors
- a flying-capacitor thing...
John, I looked at the TI LMP8602 data sheet after seeing your recommendatio n (thanks for the convenient link). Yes I see CMVR -22V-+60V (at Vs=5V). The flying-capacitor is beyond my ability right now. Didn't check Avago yet.
John S recommends Touchstone TS-1101 -- John S, sorry, I didn't explore this yet. I will, though, and thanks for r esponding.
Joerg wonders if I might be wrong about my motor controller outputting a di fferential voltage. Joerg, I don't think so -- my reading of the Maxon LSC 30/2 "Operating Intr uctions" (
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220404.pdf wow, so hard to find this online! Maxon, could you make it easi er?)
Vladimir Vassilevsky suggests measuring voltage on both sides of the shunt, then calculating. Vladimir, let's say I am comfortable losing 1%, or 0.1V of 10V, at the shun t. Won't I be giving up at least 6 bits of the ADCs to the common-mode voltage ? (now two ADCs, to measure both sides) Right now that sounds like a lot to give away.
Spehro Pefhany recommends LEM Hall-effect current sensors. Spehro, I went to the LEM website to explore. I don't doubt that LEM has what I want, but I had a hard time navigating that website to find what I want.
whit3rd asks if one side of the motor is grounded, giving a simple soln, an d with great tact notes that I may have written nonsense about using a coil over a DC current. whit3rd, Thanks for giving me a face-saving gentle reply :) No, the motor is driven by a differential voltage, two leads from the motor controller. At least that's how I read the Maxon doc I reference abo ve.
Jaime describes the current transformer also, Jaime, as whit3rd reminded me, I'm measuring a DC motor, so I'll go with on e of the other options.
Thank you, all, for taking the time to reply. I really appreciate your help. So in conclusion, your suggestions led me to seach more on the Hall-effect sensors, and I found this part... "ACS712 Breakout" on a small pcb for $10
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(See also the "ACS712 Low Current Sensor Breakout" for $15 with op-amp on b oard,
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)
For the $10 item: Description: This is a breakout board for the fully integrated Hall Effect based linear ACS712 current sensor. The sensor gives precise current measur ement for both AC and DC signals. Thick copper conductor and signal traces allows for survival of the device up to 5 times overcurrent conditions.
The ACS712 outputs an analog voltage output signal that varies linearly wit h sensed current. The device requires 5VDC for VCC and a couple of filter c apacitors.
Features:
x05B (5 Amp) version Low noise analog signal path Device bandwidth is set via the FILTER pin
5us output rise time in response to input current
80kHz bandwidth
1.5% output error at 25 degrees C
1.2mOhm internal conductor resistance
2.1 kVRMS minimum isolation voltage from pins 1-4 to pins 5-8
5.0 VDC, single supply operation
66 to 185 mV/A output sensitivity Output voltage proportional to AC or DC currents Factory-trimmed for accuracy Extremely stable output offset voltage Nearly zero magnetic hysteresis Ratiometric output from supply voltage