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Old 10th June 2010, 03:53 PM   #1
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Default Current Transformer: New Idea

I recall a long time ago repairing a strobe unit. The Xenon flash tube was not being triggered. The solution that I used for that problem ought also be useful with regard to current sensing transformers in SMPS circuits.

What I did was to use a black phosphor drywall screw as the core for the trigger transformer. It was to boost the capacitive discharge into the several turn primary by means of the secondary consisting of about 100 turns.

If this method will also work for current sensing, it ought to lessen the time and money cost. However, one thing that might happen is a heating effect on the screw core due to the high frequency involved. If so, the idea may still be good using a small ferrite rod that I have seen for sale online. Barring that possibility, I think a Dremel disk could be used to cut a slot into a very small toroid core to greatly speed up the hand winding process.

I should probably add this edit that this idea is not really new. I think it is enough different from what I have been looking at that it seems that way, though!

Last edited by Electrone; 10th June 2010 at 03:56 PM. Reason: Added thought
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Old 10th June 2010, 06:49 PM   #2
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I have a few strobes from which someone has liberated the trigger transformers (for another project). Now I know a cheap easy way to make substituttes. Thanks!
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Old 10th June 2010, 08:07 PM   #3
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Quote:
Originally Posted by Steerpike View Post
I have a few strobes from which someone has liberated the trigger transformers (for another project). Now I know a cheap easy way to make substituttes. Thanks!
Cool, you're welcome! I was thinking that there could be people out there who just might like an easy way to wind a pulse transformer.
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Old 10th June 2010, 10:36 PM   #4
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Ewww...

. . . EWWWW.

...Ferrites are cheap, you know?

I suppose it would be a futile attempt to try explaining why this is wrong, in terminology and practice, on so many levels...

Tim
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Old 10th June 2010, 10:56 PM   #5
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I did say the unconventional core might get hot at SMPS frequencies. But it is not accurate to say that it is categorically wrong. That depends on the application. The different magnetic properties of the screw may offer advantages that aren't apparent at first thought. Don't be afraid to think outside the box. It was an easy way to fix my strobe, for example. So, for low duty cycle, it definitely can be very right.
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Old 11th June 2010, 03:58 PM   #6
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I don't know how many times I've seen people in this group try to use inductors or transformers salvaged from other equipment. It's beyond me why people do this, because if you don't know what the material is or number of turns, etc, you don't have a clue whether it will work.

What's the permeability of the screw? :-)
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Old 11th June 2010, 04:45 PM   #7
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The permeability of the screw is pretty high, containing a high proportion of iron. I've bought almost all the ferrites i use surplus, that makes them more affordable to experiment with. Few of them came with any information except physical dimensions.
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Old 11th June 2010, 11:24 PM   #8
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Considering drywall screws are made from hardened (= magnetizable) steel, I doubt permeability is very high. Magnetization = hysteresis = big loss for AC. Most of that is going to be swamped by the open loop, so you're just as well off using an air cored inductor. Not to forget mechanical reasons, like the sharp threads which may very easily nick enameled wire.

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Old 12th June 2010, 10:23 AM   #9
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A layer of electrical tape goes on first.
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Old 12th June 2010, 06:35 PM   #10
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It'd be nice if the general trend in society of everyone needing to get wording just right were to slacken up a lot. This might still have been a helpful thread, but as it stands now, I am going to ask for it to be deleted since that is the easiest way for it to be handled with the least effort from the mods. It is ugly and shameful. Accolades to the mods for your efforts.
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