"I'll call the company monday. I'll ask them what power/cmsq they're toroidal cores can handle. Its just so confusing. Some companies selling 21cmsq toroidal core and advertise them as being 3000va. "
The core size is not really a case of power:size..... if we had copper of zero ohms per foot of whatever size we had in our hand... then very high power transformers could be had very very small.
The magnetising current is fixed for freq and voltage for a core..... you cannot saturate it unless you change the hertz or the voltage.... so core size does not dictate power handling.... sounds wrong I know
So what does?
It is the copper loss that causes us to use bigger cores... we need the real estate to use 3X1.8mm wire and 90mmsq wire of the turns needed to do the job.
The bigger the core, the less turns you need for the same frequency and voltage.... so for the same winding window we get more copper in there... we can make a bigger window and get more copper in there.... and we can see where this is going.... to get more and bigger wire in there, we need to use more core to get more real estate to play with... and better still .... less turns of it too.... so bigger wins.
If we had super conductor wire, then this would be mute. We could use any core for any voltage and freq ( 50-60hz etc), as the wire could be thinner than hair, and carry a 1000 amps, so we could have our 2000 turns on a tiny core, and handle huge power.... remember saturation is not from current or over loading... so once the core is magnetised for that voltage and frequency, all extra amp turns involved with the transforming process do not direct their extra amp turns into saturating the core, but rather using their MMF against each other, and inducing current into the other...but not the core... so if you look at the equations for core saturation.... no mention of current... anywhere.
The little PJ torroids do the job, but their copper loss heats them up too fast to be useful for more than a kw or two, and their sag will be pronounced... so we use a bigger core to allow us to use sensible sized wire to keep the copper loss to a value we can handle heat wise.
Where does this get me?
well core size helps us get to our objective heat wise. If we used silver wire, our core could be smaller, as the R is less for the same power handling.... and losses are I^2R... we need R to be tiny for high currents.... or we burn up.
A big core handles no more power... but allows us to use much more copper to get the losses under control..... then the transformer as a whole handles more power for longer, or if we have enough cooling.... indefinitely.... ie oil cooled, forced air cooled etc.
I guess what I am trying to say is that core size is an indicator, but the copper is where the bulk of loss comes from, particularly in torroids, hysterisis loss is generally small for size, and eddy currents are small, as they use very thin laminate compared to EI ones. They tend to use high grade steel for torroids, as they are very expensive to wind to start with.
Some EI transformers deliberately run in saturation... but these are special cases....particularly ferro resonant ones
PJ boards are just W7 boards in disguise. There are plenty of manufactures on alibaba with virtually identical boards... but getting them to part with them is the problem.
I had a few discussions with several of them, and all will sell you the control cards for very much less than PJ..... if you buy or have one of their inverters... so you can try, $45usd seems to be what they would charge from the discussions I had with them. With PJ, they at least put them on Ebay... cheap at one time , but they have wised up.
Nothing stopping you from trying the others though...... all the LF chinese ones seem to be the pretty much the same.
Some folks here are going to try the EGS002 cards too. 6-10 dollars.
...........oztules