# Thread: Confirming PSU spec for steppers.

1. Following from Jonathan's post #99

Transformer Inrush - Open Electrical

2. ## The Following User Says Thank You to EddyCurrent For This Useful Post:

3. Originally Posted by EddyCurrent
Following from Jonathan's post #99

Transformer Inrush - Open Electrical
Good article, but they could have expressed the final equation more clearly to demonstrate their point. Also, it's a bit pointless to solve the differential equation using Laplace transforms when you can trivially separate the variables. This is how I did it:

Seperate variables:

Use sin(A+B) identity to make it easy to integrate:

Integrate:

Use cos(A+B) identity to simplify:
(1)
When the transformer is switched on, we have the initial condition relating to the residual flux:

So substitute this in to (1) to find constant, k:

So the solution is:

So now it's easier to see that the term is a constant, which introduces a DC offset that disappears when the switching angle is ... i.e at the peak voltage.
Last edited by Jonathan; 13-01-2014 at 12:28 AM.

4. I used to like Laplace transforms but that was 40 years ago, I've never needed to use them since

5. Originally Posted by EddyCurrent
I used to like Laplace transforms but that was 40 years ago, I've never needed to use them since
I much prefer the Lapdance performs. . Makes me constant, which introduces a DC offset that disappears when the switching angle is ...at the peak. .

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