Couple SMPS transformer questions

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I recently bough a couple ferrite transformers of differing sizes for making some switching supplies, but I'm having some trouble locating a good source of cheap wire to wind with. There's a few people on Ebay selling it at a reasonable price, but all the ones selling large (>30) gauges only ship to the US.

Does anyone know of a good, inexpensive place to get magnet wire in lower gauges that ships to Canada? Alternately, how much of a PITA would it be to wire the secondaries of a 500-700W transformer using paralleled 30 gauge wire?

Also, I wasn't planning on using it until I had a couple smaller projects under my belt, but the largest core I bought is broken. The two pieces of the broken half match almost perfectly, and they definitely mate better than the two halves of the core do. Would I notice a big drop in performance if I mated them together and still used them?

Thanks guys.
 

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What kinda prices are you looking for?

My local electronics stores seem to have reasonable prices.. I recently bought some wire off ebay, but it probably would have costed the same locally.


Here are some prices (cdn):

30GA 1/4LB SPOOL 785 FEET 7.95
28GA 1/4LB SPOOL 497 FEET 7.45
20GA 1LB SPOOL 315 FEET 17.95

This is the store to see more prices and bulk discounts:

http://www.mainelectronics.com/WireMagnet.htm


Their prices for 14-18 gauge dont seem that cheap. But those are pre-rolled on a plastic bobbin. Theres another parts place few doors down, I bought bulk off a large roll and it was a bit cheaper.


btw where did you get those ferrites from, and what material is it? I couldnt find any large bobbins on ebay, im trying to get a couple 2" toroids though.
 
Mr Teal said:
Alternately, how much of a PITA would it be to wire the secondaries of a 500-700W transformer using paralleled 30 gauge wire?

I have paralleled 18 ga wire -- two strands -- it is a PITA but gets the job done. I would imagine that a bundle made of 30ga wire is going to have much lower skin-effect a la Litz wire --

The number of turns is a function of the core material, switching frequency and min, max and average current demand --

Do you know the core's properties?
 
Cracks in ferrite cores act like small gaps even when glued, they reduce the permeability and increase the saturation current. For ungapped transformer applications the magnetizing current also increases as a side effect of permeability reduction, this may be advantageous or not depending on the circuit but it may be reduced to a minimum extent by tightly glueing the broken pieces

About magnet wire, in my experience diameters above 1mm become quite hard to handle in transformers and also quite lossy even at low operating frequencies ~30Khz. Try to use several ~0.75mm wires in paralell
 
Eva said:
but it may be reduced to a minimum extent by tightly glueing the broken pieces



Don't agee on this one.....some ferrite clamping yokes put a considerable pressure on the side limbs..unless one hard- glues the entire assy......your superglue solution will probably fail sooner than later. As EVA mentioned the permeability will change and so will the EMI. With a fractured core limb with discontinuous operation, the regulation factor will be effected. Try it by all means but personally I'll be looking for a replacemnt.

I've had busted cores from many core vendors......in the earlier days things like this were properly packaged.. it seems component vendors these days are basically customer ignorant.

richj
 
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