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In Reply to: Bigger core size? posted by nc on June 26, 2006 at 18:03:25:
Hello NC:the first iteration I did I wanted to do on a similar core size to the C-40X which had been recommended. Still I used a larger core size (volume wise) than the C-40X.
And I had already run a sim on a much, much larger core... a choke that would be about a 12.5 pounder.... I will give the details on this later.
I followed up and looked at the C-47U... it appears to be built on an EI 112 with 1.75" of stack if I am reading the mounting dims correctly.
So I ran a sim on this size core... with the following parameters (wanting to keep them close to the first example I posted in this thread)...
L of 300 mh
idc of 125 ma
dcr of less than 3 ohms (in this case)
300 vrms at 100 hz of ripple voltage (assume a choke input)
here are some of the "outcomes"....calculated dcr of 2.25 ohms
calculated L of 359 mh
total flux density of approx 14.6 kg
essentially by going to a much larger core than the 1" by 1" as used in the first example... so far... the main benefit appears to be 2.25 ohms dcr as opposed to 8.5 ohms dcr.now let's look at the copper and core losses...
call this design (design B)....
calc core loss of 7.96 watts (design A was 3.45 watts)
calc copper loss of 4 watts (design A was 10.8 watts)
for a total of 11.96 watts (design A was 14.26 watts)
so... looking at A and B from a loss point of view... the core losses essentially doubles in design B (even though it is the larger core) and the copper losses are cut by more than half in design B vis-a-vis design A. total losses in B are lower but not world's lower....
now let's look at temp rise in design B.calculated coil temp rise of 42 degrees C (versus 126 degrees for design A)
calculated iron temp rise of 46 degrees C (versus 32 degrees C for design A)
total temp rise of 88 degrees C (versus 158 degrees C for design A).
but 88 degrees C is still (in my book) excessive.
the total heating current of design B is 1.34A rms. (design A was 1.47 A rms). this is still very high. Again, if this were a plate choke it would current clip with just 19.93 vrms at 100 hz. Again, this current must be gotten from somewhere... from a source or generator.... if your source or generator is the high voltage secondary of a conventional power transformer designed to deliver 125 mils of dc current... it probably ain't going to be real happy chugging through 1.33 amps rms.... I would expect that it too would have some heating problems...I will try later to post up the EI 175 by 1.75" example I had done... I have enough notes saved to reconstruct it... but I did not initially save the build sheet for it... by memory... it looks a lot better than designs A or B but now we are up to the 12.5 pound territory...
I just don't see how in a conventional power supply design these recommended chokes could serve well as input chokes and carry the 300 vrms at 100 hz ripple voltage that I have assumed for illustrative purposes. And recall... this is with me pulling down the dc current to only a fraction of the published specs for the Triads and Hammonds.
My sense is that these were not ever designed to go into service as a power supply input choke where you have several hundred volts of rms ripple voltage.
msl
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Follow Ups
- Re: Bigger core size? - mqracing 18:50:30 06/26/06 (1)
- allow me to expand... on this one point - mqracing 19:04:19 06/26/06 (0)
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