Find current with OScope measuring 3 phase.

Thread Starter

bootloader9800

Joined Jan 12, 2021
27
Hello Folks.
So I am trying to measure the voltage going in to a 3 phase motor using an OScope.
There is a schematic of the setup below.

I am done with the test and I found out the voltage across each phase, with my OScope.
Now, how would I measure the CURRENT going into each phase of the motor?

Thx for the replies.!
signal-2021-01-15-094957.jpeg
 

ronsimpson

Joined Oct 7, 2019
1,236
More information;
Is this a 110, 220, 440 ac power line project? (3.3k resistors? so it must be low voltage)
What is ESC
Is this a 12V stepper motor?
 

MaxHeadRoom

Joined Jul 18, 2013
23,125
ESC (electronic speed control) so I assume it is a RC motor?
Some of these are operated in the BLDC mode, not 3ph AC .
Your DWG doesn't seem to make sense, what is the GND connection and resistors for?
The voltage value would be taken across any two windings
Max.
 

Thread Starter

bootloader9800

Joined Jan 12, 2021
27
ESC (electronic speed control) so I assume it is a RC motor?
Some of these are operated in the BLDC mode, not 3ph AC .
Your DWG doesn't seem to make sense, what is the GND connection and resistors for?
The voltage value would be taken across any two windings
Max.
Hi thx for the reply.
a) Yes, it is a RC motor and it is in 3 PHASE AC mode.
b) The ground connections and reistors are there to make a "star " configuration to measure 3 phase AC using an Oscilloscope.
c) I am looking to find the current going through each phase.
Thank u
 

MaxHeadRoom

Joined Jul 18, 2013
23,125
Presumably each phase would be equal, so measuring one would seem sufficient?
A clamp-on ammeter rather than a 'scope should give it to you, the current for these motors is relatively quite high.
Is there any particular reason for wanting to know?
Max.
 

Thread Starter

bootloader9800

Joined Jan 12, 2021
27
Presumably each phase would be equal, so measuring one would seem sufficient?
A clamp-on ammeter rather than a 'scope should give it to you, the current for these motors is relatively quite high.
Is there any particular reason for wanting to know?
Max.
I wanted to know the current because the MOSFETS on the ESC are burning out -sometimes- . I would like to know if the high current draw is what, that is killing the MOSFETs.

Thank you for your reply.
 

MaxHeadRoom

Joined Jul 18, 2013
23,125
It won't be voltage so current is about the only thing that might cause it.
Just measure the current into the ESC in the 12v supply.
Possibly increase the heat sink, or use forced cooling if possible.
Max.
 

ronsimpson

Joined Oct 7, 2019
1,236
Measure the 12V battery current. Simple DC current meter will get you close. It will measure more average and not peak. If the speed control is doing pulse width modulation you can get a idea of peak current by looking at voltage. Example if the speed control is only on 50% of the time then the motor peak current is 2x the average battery voltage. (not real accurate but close)
 
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