Esc current sensing
- Thread starter Rcblack79
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It's very common.
You can sense any amount of current you like, by choosing the shunt resistance and the op-amp scaling to stay within the voltage range of the input of whatever MCU or controller chip you're using.
If it weren't so much work and so time consuming, I'd recommend looking at the many existing (ebike/etc) controllers that use shunts (rather than hall sensors like the Allegro series and similar) to measure current, and things like the Cycle Analyst and most other power / watt meters. You'll get some sense of how they do it, and if you also look at the problems experienced with the various designs, you can work out which things to borrow and which to leave out. Schematics will be hard to come by, unfortunately, other than reverse-engineered ones like some here on ES over the years, and a few open-source ones like the VESC, so you may also have to reverse-engineer the controllers / etc to see exactly what they did.
A simpler way would be to check Application Notes for motor controller chips, which may also include circuits like what you want; IIRC the old MC3303x chips had appnotes including a version of a current-monitoring shunt, but it's been so many years since I looked I don't remember.
There's probably also electronics learning / example / etc websites that show how to do it, if you don't want to reverse-engineer existing designs. I'd bet there's a bunch of examples on allaboutcircuits, and various arduino-type sites, etc.
You can sense any amount of current you like, by choosing the shunt resistance and the op-amp scaling to stay within the voltage range of the input of whatever MCU or controller chip you're using.
If it weren't so much work and so time consuming, I'd recommend looking at the many existing (ebike/etc) controllers that use shunts (rather than hall sensors like the Allegro series and similar) to measure current, and things like the Cycle Analyst and most other power / watt meters. You'll get some sense of how they do it, and if you also look at the problems experienced with the various designs, you can work out which things to borrow and which to leave out. Schematics will be hard to come by, unfortunately, other than reverse-engineered ones like some here on ES over the years, and a few open-source ones like the VESC, so you may also have to reverse-engineer the controllers / etc to see exactly what they did.
A simpler way would be to check Application Notes for motor controller chips, which may also include circuits like what you want; IIRC the old MC3303x chips had appnotes including a version of a current-monitoring shunt, but it's been so many years since I looked I don't remember.
There's probably also electronics learning / example / etc websites that show how to do it, if you don't want to reverse-engineer existing designs. I'd bet there's a bunch of examples on allaboutcircuits, and various arduino-type sites, etc.
Thanks for the reply. I have read countless data sheets, app notes and ref designs on SLBLDC motor controller design and construction 85% i fully get and the rest in over my head. Vishay has a .0003 ohm resistor that will put out about 5 watts of heat in my app, well within the soa of the resistor. With so many choices on the market and all my reading im still having trouble sizing a op amp to my app. Thanks so much for the reply.
lizardmech
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What voltage is the controller going be used for?Rcblack79 said:
Typical BLDC controller shunts are around 1 milliohm. Most of them are also made from several SMD resistors (or Manganin wires) in parallel to spread out the heat generated.
A 1mOhm shunt @ 100A will read 100mV across it. Most commonly used op amp is a LM358. Many newer controllers have the op amp built into one of the chips, so not a separate part.
This works great for monitoring the battery current, but not so great for phase current, which will be alternating. For phase current, you could still use a shunt and op-amp, but you would need to use a differential amp that can handle the voltage swing.
Another option is something like the Allergro ACS75xx series. These use a hall effect sensor sitting on the conductor and have practically zero resistance (and heating). At zero current, the output signal is 1/2 the supply voltage and it can work in both directions of current. These would be better for monitoring phase current and they are isolated from the line they are monitoring so you don't have issues with voltage offset.
A 1mOhm shunt @ 100A will read 100mV across it. Most commonly used op amp is a LM358. Many newer controllers have the op amp built into one of the chips, so not a separate part.
This works great for monitoring the battery current, but not so great for phase current, which will be alternating. For phase current, you could still use a shunt and op-amp, but you would need to use a differential amp that can handle the voltage swing.
Another option is something like the Allergro ACS75xx series. These use a hall effect sensor sitting on the conductor and have practically zero resistance (and heating). At zero current, the output signal is 1/2 the supply voltage and it can work in both directions of current. These would be better for monitoring phase current and they are isolated from the line they are monitoring so you don't have issues with voltage offset.
75.6vdc input 200a burst 120a continuons the motor has a Rm of .0245 ohms, 415 kv 58mm/122mm. The esc im planning on building will be a beefed up version of a power tool esc for SL bldc motors. Tms320f28027f is my mcu of choice Switching freq around 50000khz with FOC algorithmes, phase voltage senseing, phase current senseing, dc bus voltage senseing etc. Gate drivers ucc27712D is my first choice driver im using. Both are for power tool, e bike, e scooter, drones and hpev. Fets are even selected based on motor control applications, low rds on good ampacity high temp very fast switching capible etc. Thanks alot for the reply im just looking for information other than what ive read over the past 2 years
lizardmech
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If you can stay under 80V the Ti ina240 is probably the best option. Anything above that and you will need complex isolated shunt sensors or magnetic based sense such as allegro ACS sensors.
tecnologic
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if u are going to use a Tms320f28027f, why not going the extra mile and use a TMS320F280049 with instaspin, as i assume, u want to use by the phase voltage sensing? The 0049 would give u sigma delta decimation filters so that u could use AMC1304s as a ADC with +-50mV input combined with a 0.1mR Resistor u have a range of 500A or use a 0.2mR Resistor for 250A range. Plus u gain a little bit of resolution 
just 2 to 3bits of ENOB.
just 2 to 3bits of ENOB.lizardmech
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They still haven't released the instaspin software for the 280049. It was supposed to be out q2 or q3 2018 now it's q2 2019. 
The 280049 does look pretty good though.
The 280049 does look pretty good though.Thanks so much for the reply all will be considered greatly. Tms320f28027f came in a eval kit that i obtained from TI, i only desire foward/reverse from these escs and of course foc. 250a is more than enough. My motors can operate on 96vdc max but with space im limited to 18s-75.6vdc. Once more im grateful for your replies
tecnologic
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ok, but they are a great design for motor control especially in this price point. The F28379S/Ds are to expensive and no one realy needs the performance of those for just one motor.lizardmech said:They still haven't released the instaspin software for the 280049. It was supposed to be out q2 or q3 2018 now it's q2 2019.
lizardmech
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tecnologic said:ok, but they are a great design for motor control especially in this price point. The F28379S/Ds are to expensive and no one realy needs the performance of those for just one motor.lizardmech said:They still haven't released the instaspin software for the 280049. It was supposed to be out q2 or q3 2018 now it's q2 2019.
Yeah, looks like it will be the best reasonably priced MCU for motor control, only thing it lacks is USB like on the 280069, I just wish they would hurry up with the software, it was supposed to be out when the MCU was released now it's been delayed 3 or 4 times.
tecnologic
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The delay is weird, the peripherals in this thing are just a combination of other c2000s.
There is a LEM DHAB (dual channel, 25A / 200A) hall censor currently on Ebay for 50 bucks. A bit more pricey than a shunt approach, but a lot more straightforward otherwise and fully isolated - you give it 5v power, and read the voltage from one of the two output pins, then calculate the amps.
Thanks to all for replies and comments. I would like to jump back into the senseing. Instaspin foc requires phase voltage and phase current senseing plus a few others. Ina240 for inline current measurment and should i sense the phase voltage before or after the shunt resistor. Thanks everyone again for replies
It shouldn't matter much since there is very little drop across the shunt. I'm measure on the motor side since that's what the FOC algorithm is needing.
lizardmech
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I have always put it before the shunt but it shouldn't matter, just don't do what I did and forget to put the relatively large 0.1uf filter caps on phase voltage sense output, I did that when building an inverter and it stops instaspin from working but it's easy to miss as they don't explain how their observer works.Rcblack79 said:
