Behaviours of a transformer questions.

[khabe]

  High frequency cores are made of many matereials.  These are usually powered down, mixed and formed using an epoxy in the form desired.
Robert

I dont bieleve they are making powder cores using epoxy ... perhaps somewhere in garage or in kitchen
I use often enough Micrometals mix 26 cores, those are machineable, can cut, mill ,drill ... what ever, I have heated, etched - no vestiges about epoxy.
Sand what milling lefts I do collect - then yes - I can use it for some quick-idea experiments mixed with epoxy and press-molded - its good enough, but never so good when real thing.
When more serious projects, then I use Somaloy700. Very hard to find in kilos, more easy when to buy at least 1t. But OK, I have some kilos - then I have to go to factory, to make contract ... they making mould, then pressing, then heat ...
Somaloy its in principle pure Iron - and very good. Added info speaks about Somaloy, there is small precent of lube inside what makes insulation between particles and keeps all together after pressed-heated. For very small parts thats enough if you have 10t press and small good precise(!!!) el.oven with sure timer (!) - I have tried with success.
As you understand Im not much busy with transformers, very seldom, more like motors and generators, but cores anyway
cheers,
khabe

[nwman]

khabe, they do make laminated c cores and are epoxied together. That's what I am using and they seem to work excellent.

Well, I am more confused now. I just built the transformer shown above and it sucks. I'm not sure why but for simplicity reasons if I put one watt in the primary I only get like .2 watts out the secondary. Both sides have 400 turns of 20 AWG wire all nicely packed  and turned. The only difference is that the core inside the primary has been notched out do that the core material is have the thickness as the core inside the secondary.

Am I missing something? Is my construction just crappy? Or does the thickness actually change the functionality of the transformer?

I took the transformer to a  friend of mine and he said that changing the thickness is like making it a step down transformer. The idea is that its not the number of turns but also the size of the circumference of the turns. The larger the size the more wire the field has to interact with. I would estimate the larger secondary has 50% more wire then the primary.


Could there be any other reason why the efficiency suck?

Tim

[gyulasun]

Hi Tim,

I assume the air gap between the C cores was at the minimum possible the core manufacturer matched the touching facing areas with their machining? (I mean you use cores with matching surface areas the manufacturer made the cores to be a matched pair.)
Would you mind saying a few words how you measured the input and output power, what was your load, you used mains frequency (sine wave? ).

Here is a transformer calculation link with formulas that includes cross sectional area for the core, though the cut-out core cannot be the main explanation for the low output power problem: http://en.wikipedia.org/wiki/Transformer_design

rgds,  Gyula

[nwman]

Gyula,

Yes the cores are out of the box condition besides the cut-out area which I made with a large mill. Now I'm not sure if I have the same pair. I bought 3 pairs of them and have only mixed two pairs possibly together. I didn't think it would make a difference? I'll get into more details about the testing later when I have more time to write. I did have a peace of paper between them. Would that small of an air gap cause that much loss? Again, I do not claim to know anything! Thanks for the input.

Tim

[nwman]

I have a newish question. I've ordered a variable power supply [0-30v,0-5A] to power the DC transformer shown in the picture above. To be able to take Amp reading from the secondary coil I need some kind of load. What would be the best setup to achieve a load appropriate to the varying voltage and amperage? Would it be an array of light builds, DC motor [what size], or a capacitor? Preferably something I could find in town would be great.

Tim