# Voltage spikes calculation

Joined Jan 12, 2021
8
Hi guys, newbie here. Good to see a forum like this.
So here is my first question.

I have an Oscope. I wanted to know the peak current that was being pulled by a DC motor under load.
When I hooked up the Oscope, I was expecting a clean jump on the screen where the voltage line went from 0 to whatever voltage.

What I saw was spikes of all sorts at high resolution of the X - Axis.

Also, the math is showing that the current is 48 Amps, which can't be, since the power supply that was running the motor could give out only a max of 30 Amps.

How would one go about calculating the voltage in this case?
Thx

#### BobTPH

Joined Jun 5, 2013
2,721
Yep, motors cause all kinds of noise. You will never see a clean signal.

Your 30A power supply may well supply a peak current of 45A for a short time.

If you want more, snap a picture of the trace and post it.

Bob

#### andrewmm

Joined Feb 25, 2011
874
How are you measuring the current
a clamp transformer ?

Joined Jan 12, 2021
8
How are you measuring the current
a clamp transformer ?
I am planning on getting the voltage from my scope and then use ohm's law.

Joined Jan 12, 2021
8
Yep, motors cause all kinds of noise. You will never see a clean signal.

Your 30A power supply may well supply a peak current of 45A for a short time.

If you want more, snap a picture of the trace and post it.

Bob
Here is the screenshot. I would like to know how to find the voltage. The voltage is not a straight defined line.

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