Re: Using SSR to switch transformer

cbarn24050@xxxxxxx wrote:
On Mar 25, 7:14 am, Arlet Ottens <usene...@xxxxxxxxxx> wrote:
cbarn24...@xxxxxxx wrote:
On Mar 24, 10:49�pm, Arlet Ottens <usene...@xxxxxxxxxx> wrote:
cbarn24...@xxxxxxx wrote:
Transformer cores do not hold any significant magnetic flux when there
is no current in the windings.
Mine does.
First picture shows current through 3 half cycles, starting and ending
with positive cycle.
http://c-scape.nl/transformer/first.png
Second picture shows same waveform, after a minute of inactivity. Notice
increased current in first half cycle due to core saturation. The effect
is also audible in the transformer.
http://c-scape.nl/transformer/second.png
This happens every time if the waveform starts with same polarity as the
previous one ended, even with considerable time inbetween. I also ran it
starting and ending with negative cycle, and the traces are the same
(but inverted).
Alternating positive and negative bursts shows no extra current.
Without the voltage waveform as well as the current your trace is of
no value. I expect your not triggering quite how you think you are.
I've added a voltage trace (measured across the primary) to the second
waveform:

http://c-scape.nl/transformer/second+v.png

During the current spike, the voltage drops due to current limiting
resistor in series with primary.- Hide quoted text -

- Show quoted text -

You seem to be triggering at the zero crossing point and not on the
voltage peak. How big is your current limiting resistor? How are you
measureing the current waveform?

Yes, for this test I wanted to demonstrate worst case saturation effect, so I'm triggering on the zero crossing point.

If I trigger the SSR on voltage peak, I get similar results, but somewhat lower peak current, as expected.

http://c-scape.nl/transformer/second-peak.png

The series resistor is 33 Ohms. Current trace represents voltage across this resistor. I'm using 3 voltage probes (one side of resistor, between resistor and transformer, and other side of transformer), and tracing the differences between them. Initially, I was using a 0.1 Ohm/10W resistor, but it died with a flash and a bang during a current surge. :) So I decided to pick something bigger.
.

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