[Amps] Transformer material weight

Gene May gene-may at hotmail.com
Tue Sep 13 17:57:13 PDT 2011

It will depend on several matters, such as whether it will be for choke-or capacitor- input, whether it will be for Continuous Commercial Service (CCS) or Intermittent Commercial or Amateur Service (ICAS), and how much temperature rise will be acceptable.  All of these design criteria would permit smaller diameter copper wire (and therefore a lower percentage of copper):  Choke input rather than capacitor input, ICAS rather than CCS, and higher temperature rise.
I was thinking of doing this for two transformers (main power supply and screen supply) one time  It appeared to me that transformer designers aim to have about half of the heat generated in the iron core, and the other half in the copper windings.  Core selection appears to be fixed mainly by the voltage across the primary (so that there is sufficient inductance in the primary) and the peak current that flows (so that the core doesn't saturate).  So designers don't have that much flexibility in iron core selection, implying that they can't vary it as much as they can wire diameter.
I did some research, which was interesting and fun.  Then, I tried to do an "on paper" conservative design, and the thing would have weighed over a hundred pounds if I had made it.  It was also unclear how much money I would have saved after I bought the iron cores at a single-unit price.  I did not have the facilities to bake it or do a decent job of laquering it or making sure that there was sufficient insulation between the primary and secondary.  It also probably would have looked like junk if I had made it.  So after that, I had Peter Dahl make the transfomers (this was a while ago)
The plate transformer he made for me-- 3KVA output, 99 degree F temperature rise for CCS, and capacitive input -- ended up weighing 47 pounds, and I estimate that about 2/3 of that is iron.  I like home-brewing, but I'm glad I did not try it myself.
There is a LOT that goes into making one of them, make sure that you know what you are getting into first.  
Gene May   WB8WKU

> Date: Thu, 8 Sep 2011 14:21:08 -0700
> From: rj3819 at yahoo.com
> To: amps at contesting.com
> Subject: [Amps] Transformer material weight
> Question about transformers .. 
> If I was to buy the laminates and wire to wind
> a 2 KVA transformer and say it weighed 50 lbs.
> What would be a good guess for how much of that
> was iron and how much copper ..?? 
> Side Note.. It seems my acct may have been hacked .. 
> So I changed the password .. 
> I apologize for any spam emails that were a result of that ..
> Randy - N2CUA
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