How to measure current?

tndr_1

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Hello there :)

I know how to display the current drawn from the batteries to the controller, but I am unsure of how to get the current that is drawn by the motor.

I am using this controller: https://www.aliexpress.com/item/1005004415919350.html

It has some "Display" wire but I am really unsure of what that does and I do not have a display to try it out with... So maybe I need to try a DIY solution with an Arduino or similar...

How do I measure the current that the motor is using while running? If I can get help with that, I am able to put it on a display with a microcontroller :)

/ Oskar
 
tndr_1 said:
Hello there :)

I know how to display the current drawn from the batteries to the controller, but I am unsure of how to get the current that is drawn by the motor.

I am using this controller: https://www.aliexpress.com/item/1005004415919350.html

It has some "Display" wire but I am really unsure of what that does and I do not have a display to try it out with... So maybe I need to try a DIY solution with an Arduino or similar...

How do I measure the current that the motor is using while running? If I can get help with that, I am able to put it on a display with a microcontroller :)

/ Oskar

If you can't get that info from the controller - you'll need to use a shunt to measure the current. I would guess the display wire is to power a display but without the wiring diagram for the controller that's just a guess.
 
Thanks for your reply!

I actually have a shunt to measure from the battery. Would the same type of product work for the motor also?

If so… how would I connect it considering the wiring diagram includes both battery and load. As I have it connected now I have the ESC as “load”!

https://www.amazon.se/dp/B09KLJXDSH?psc=1&ref_=cm_sw_r_apin_dp_2NJ3B88RWMM3XAVT4QHY

B5867515-9D1D-4790-B3FD-0D21220BC4E6.jpeg
 
tndr_1 said:
Thanks for your reply!

I actually have a shunt to measure from the battery. Would the same type of product work for the motor also?

If so… how would I connect it considering the wiring diagram includes both battery and load. As I have it connected now I have the ESC as “load”!

https://www.amazon.se/dp/B09KLJXDSH?psc=1&ref_=cm_sw_r_apin_dp_2NJ3B88RWMM3XAVT4QHY

B5867515-9D1D-4790-B3FD-0D21220BC4E6.jpeg

typically the controller will have three wires that provide 'phase current' to the motor. My knowledge of motor control then gets a bit weak and I'm not sure if the phase currents are the same give or take (just not in phase) so you only need to measure one phase to get the rest or if you need to measure all three... hopefully someone who knows more can fill in the gaps :)

Another possibility is to put a shunt in the common phase ground going to the motor - then you get all the phase currents summed - but again I'm still learning about motor control so this might not be the best solution.

If you were going to do this with an arduino or similar you'd put a shunt in-line in the wire you want to measure current for - then use an ADC pin on the arduino to measure the voltage across the shunt (to then allow you to calculate the current I=V/R where R is the shunt resistance and V the voltage across).
 
Another possibility is to put a shunt in the common phase ground going to the motor - then you get all the phase currents summed - but again I'm still learning about motor control so this might not be the best solution.

There isn’t a ground as such - a three phase motor is either delta or Wye connected, and the power flow is kept completely in the 3 x phase wires. The phase shifts mean eg. current in one phase exits via the other two etc..

A shunt in one of the phases would be one way. Another way would be to derive it… if you know the power going in, measure the voltage on a motor phase, you can calculate the phase current. Assuming there are minimal losses in the controller and it’s acting as a buck converter.
 
tndr_1 said:
How do I measure the current that the motor is using while running? If I can get help with that, I am able to put it on a display with a microcontroller :)

/ Oskar

That's wild AC and it's not easy or straightforward to measure with an onboard device. Why would you want to anyway? Power is power, and you can easily measure that from the battery leads.
 
Chalo said:
That's wild AC and it's not easy or straightforward to measure with an onboard device. Why would you want to anyway? Power is power, and you can easily measure that from the battery leads.

If you want to measure all 3 phases at once, you don't even need to hook up the meter to get an accurate reading. It will read zero amps either way.

If for whatever reason (sheer curiosity?) you want to measure one phase and don't need lot of accuracy (can't think of a reason why you would) you could get the cheapest clamp meter at Harbor Freight for $15.
 
Okey... So maybe I need to pause my query a bit... You have to teach me this... :confused:

The reason is that I want to see how much current the motors draws and from what I can understand that value is not the same as what the ESC draws?
 
tndr_1 said:
Okey... So maybe I need to pause my query a bit... You have to teach me this... :confused:

The reason is that I want to see how much current the motors draws and from what I can understand that value is not the same as what the ESC draws?

Right. But the controller steps current up by delivering a lower voltage than the battery. What really matters, unless you're hot rodding so extravagantly that you risk burning your motor, is total power. Read how much power is flowing from the battery, and about 75% of that value is what you'll put to the ground in optimum conditions. Reading phase current to the motor won't tell you anything noteworthy that you can't read from the battery output power or a thermal sensor.
 
tndr_1 said:
Okey... So maybe I need to pause my query a bit... You have to teach me this... :confused:

The reason is that I want to see how much current the motors draws and from what I can understand that value is not the same as what the ESC draws?

Phase currents can, depending on the load the system is under at that moment, and the system setup, be much higher than the battery currents. But the average voltage is lower at that time than the battery voltage, so the total power is equivalent (minus the losses in the controller due to efficiency of conversions).

Is there is a specific need to know an exact phase current at any particular moment under a specific load (because it won't just be one current value)?


The only easy way to measure the phase currents to the motor is to use a motor controller that actually already has current sensors built into the phase outputs, and directly monitors these for motor phase currents. Any FOC controller should be designed like this; few others will be, if any.

Then for you to access that data, the controller has to have a way for you to connect to it in realtime during use (not just a setup program), either cabled or wirelessly, or with it's own display, and have access to those data.

IIRC the VESC in general will do this, and has software you can use for it to see most info about the system. There are numerous other FOC controllers but I don't know which ones give you access to the data you want. The Phaserunner / Baserunner series should be able to do this; it's likely the ASI controllers they were based on could also do it, but from reading posts about ASI software, it's not easily accessible (requires passwords for various levels of access that you can only get from ASI and only if you buy directly from them). There are also high-end controllers that can do it but they're all OEM-only (some like Sevcon you can buy but you can't get support/etc from the companies on using them or setting them up, and for those it's a very complex tuning process).

The catch with all the FOC controllers I'm aware of is that all of them need to "know" specific things about what motor they're driving; autotuning exists in some of the controllers but it isn't perfect, so you may then need to manually tune the controller further for that motor to make the system run correctly. Those without autotune will need you to input the motor specifics (which are not provided with most motors, so you have to test for these, making things even more complicated in those cases :( ).


Alternately, you can build an arduino (or similar) system that reads current sensors (usually hall-based sensors, rather than shunt types; see the various motor-controller design threads on good sensors to use for this) you would install into at least two of the phase wires between motor and controller. Then program the MCU to read those sensors and display the data for you (or record it for later readout).


I don't know any good way to accurately read the phase current between motor and controller with any of the typical meters you might have--the ones that do read AC are not really intended to read the kind of waveform these have, so I don't know how close the measurement result might be to reality, especially since you need to read current in at least two of the three phases at the same time to accurately tell what is going on between motor and controller (and then do some math to determine the "real" current; this is what the FOC controllers do).
 
Comrade said:
E-HP said:
you could get the cheapest clamp meter at Harbor Freight for $15.

You can. But it won't measuring DC current pulsed at 16+ kHz. :mrgreen:

... and the Harbor Freight clampmeter is certainly not a DC meter.. ( I have two here, they are AC only)... ( my DC clamp meter was signifigantly more expensive) ... and if it is measureing all three on the AC side the reding would be zero current on the balance of the phase RMS current.


All this kind of shizzle.

P is the average power, and V = Vm/√2 and I= Im/√2. Looking at the integral above, and dividing by R, we see that I is equal to the square root of the mean value of i2, so I is called the root-mean-square or RMS value. Similarly, V = Vm/√2 ~ 0.71*Vm is the RMS value of the voltage.

https://www.falstad.com/circuit/circuitjs.html?ctz=CQAgjAzCAMB00IQVhANlgFiYgnBaqGAHEkgOxEgBMG4V01lSApgLRhgBQAZiKzQ3qV2OKtWiUIYsLBRFoPPgPAZaI6apBTwskPM4B3PmFHhT68KgYKjFsFWEmxOVDEPHTVGh7FUkrhQA3PmJBfxD5EBcYGIwGFGsYWU4Acz4IVEo-V1YMrKJKa05g3OhaME1%20OJVaWhQwBBAEmLgILhL8WiElau668EbmiFgKsCRRVCQIJCIcMjwkttT0jLMxXNWvWiLbCFWndLK1t12jg9KuiRPD8vNOmuuLbPTM6nCbHyicvK-HsFdohZoh92K5nk93u52A5jtDKBVtlD7PDzMjxIUkVZYWiDgo0qCGOd-oJvEUSmjuqxCOiQP0GvEYkhYFRpjgiGQyKQ2VQ2ThFu1jDCEXxqcK6YMYlR4DgMBAcEgGiy8CYpvzMdRvKC3gF1WitcDdajXMS3LwqeVKv8HtoZHIFGbqZSrd0bbp9EYTYCrQaPVjwc7IUZiMdg8KPqHTMHuh8rQcI2I8ZZjs7SW5glGrhxfFdxQzCfAMGQTJyFSZJnMArAlun4Zosw9c01YiMCvNoPRC0RUHLoAkq1xfSTyn7A5ZCUKsT6x8msSb7eB7A8TcLXXbFPXuiaXdI3QoADbGMiue5wrRIXxJRDQHA3293%20989hMqgcKxH4iTBxgNwH0-TdaRPcCbwLgD5gTeliYGQCA8hkPKzO2GK-miGBWn%2057UJeoHgQ%20WgyJk-wQNBr6oUQqwggcRJHscFHUVRx5HBRxqmISLHuKxCZaIxUKAYxXGIrYKGxliqE6oOyZ0WxHqSdI1GidcYBycJDDyQoADGLyUICPzPMB34YJgqA8qoZRGSQxDfnACBcAAThEDDaa8wKXlQnB2awoTappXnWPArkAPa0t%201KCGU7IDE0MicWIqFaJwgUoCF4DTIpKD0JFzLgJhKAQPFWVJR24XpQqmUXt%20uVAA&fbclid=IwAR34s8lMMDHd5jpKUPf9r1uQszsqxWcmCUNDhbD7Z4B7Fb1WRGUErhOIQsc
 
Blacklite said:
Another possibility is to put a shunt in the common phase ground going to the motor - then you get all the phase currents summed - but again I'm still learning about motor control so this might not be the best solution.

There isn’t a ground as such - a three phase motor is either delta or Wye connected, and the power flow is kept completely in the 3 x phase wires. The phase shifts mean eg. current in one phase exits via the other two etc..

A shunt in one of the phases would be one way. Another way would be to derive it… if you know the power going in, measure the voltage on a motor phase, you can calculate the phase current. Assuming there are minimal losses in the controller and it’s acting as a buck converter.

Ah i see thanks for that - makes sense now you've pointed it out - I've never seen a big black wire going to the motor! :)
 
Chalo said:
Reading phase current to the motor won't tell you anything noteworthy that you can't read from the battery output power or a thermal sensor.

Wouldnt it show an " unbalanced phase" ?

Just a amateur hobbyist here. How would you read an phase imbalance with only input current? Or a temp sensor?

Wouldnt matter?


Wouldnt it show... unidentified single-phase to ground faults?

Wouldnt matter?

Phase overload is a big probvlem. Veris Industries Hawkeye Phase Shunt Watchdogs exist for just that.. and they are on most industrial motors in a reliability monitoring system. Or something of the nature, to keep from phase overload or underload.
https://www.veris.com/126822/category/current-monitoring

I dont know. Would it matter? On a PWM DCV inverted system? I know they can be implemented on three phase VFD systems,.
Is it possible? That it matters? I dont know.

I do know Kelly Controller " Monitors phase current on all three phases for reliability".. as written in the documentation and sales litterature. Something they seem to feel is a " feature" and worth bragging about.
 
Ah, be a bit supportive to the OP here, there is one excellent reason to want to measure the motor phase current: you want to know your controller manufacturer isn’t lying to you about the controller’s capabilities when it comes to phase current.
 
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