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October 26, 2020, 09:52:00 21:52


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Author Topic: Transformer Inrush current  (Read 4301 times)
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metal
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« Reply #50 on: October 14, 2020, 07:12:06 19:12 »

No problem, I am reluctant to changing the topic, is this oscilloscope any good MP720011? if posts become more than 4 for MP720011 I will open a new thread. This one is available in stock, I don't have to wait for a long time to get it. I will use it for SMPS designs and this project, of course.
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« Reply #51 on: October 14, 2020, 07:49:30 19:49 »

also you did not pulse the transformer for some cycles,

There are about 21 pre-mag pulses before switching, that should be enough I think.

Posted on: October 14, 2020, 07:40:37 19:40 - Automerged

You can't complain about the price for sure. I wonder if it is some re-branding of another popular name?
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metal
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« Reply #52 on: October 14, 2020, 08:05:34 20:05 »

Yes, the price is good, I m not sure about rebranding thing, may be other members can shed light on this..
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« Reply #53 on: October 14, 2020, 08:46:36 20:46 »

This is about the best I can set the balance between pre-mag level and inrush-current. It doesn't take much of a variation to flip it either way (too much or too little). I think smaller transformers may be more sensitive. When I get a chance, I will test it on the 1 kVA isolation transformer I have in the lab.
« Last Edit: October 14, 2020, 09:08:29 21:08 by PM3295 » Logged
metal
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« Reply #54 on: October 14, 2020, 10:12:13 22:12 »

How much current at relay engage moment?
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PM3295
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« Reply #55 on: October 14, 2020, 10:56:52 22:56 »

It appears that with no-load, a bit more pre-mag is required than when it is under some load.
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metal
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« Reply #56 on: October 15, 2020, 12:11:07 00:11 »

can you try to see if more pulses at no load can make any difference? also do you know the actual inrush current for the tranfo you are working with?
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« Reply #57 on: October 15, 2020, 01:03:26 01:03 »

If I catch it on the zero crossing it peaks at about 5A, so roughly twice the peak TSR gives me. With the smaller transformers, the copper resistance of the primary winding will help to limit the peak inrush. I expect the difference to be way more with a large transformer due to the low primary resistance.

I will experiment with more pulses to see what difference it makes.
« Last Edit: October 15, 2020, 01:07:27 01:07 by PM3295 » Logged
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