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is low dcr the holy grail in choosing a choke?

Posted by mqracing (M) on May 23, 2006 at 02:09:16

Hi inmates:

I don't often crosspost messages... but I thought this post has some interesting (and surprised even me) examples to consider. I'd bee interested in your thoughts on this... which would you choose and why?

And we will keep this thread non-combative and respectful of anyone's thoughts\opinions.

Hi XXXX:

You did not give me a complete spec... you said

10 henries with 10 ohms dcr would be nice but did not mention what dc current rating you wanted nor the ac voltage requirements (which effects whether you can use it for a choke input or not)...

but I took some liberty just for the sake of trying....

here is one preliminary candidate... whose design I am about 80% happy with...

10 henries at 125 madc and a calculated dcr of 5 ohms

unit would weigh in at about 11 pounds each

unit is designed to carry 400 vrms at 120 hz which should qualify it for choke input service in a large number of applications.

calculated temperature rise of about 15 degrees C

if your fimiliar with the Dynaco Mk III... this transformer would have the same footprint as the 60 watt output trans on the Mk. III.

dimensions would be

overall height 4.5"
overall width 3.75"
overall depth 4.375"

mounting width 3"
mounting depth 3.3125"

now contrast candidate A with an alternative design...

candidate B

10 henries at 125 madc and 52 ohms of DCR

weight would be approx 2.75 pounds (in channel frame)

unit is designed to carry 400 vrms at 120 hz which should qualify it for choke input service in a large number of applications.

calculate temp rise of 24 degrees C

unit would occupy far less space than candidate A... mounting centers in channel frame is 2.8125" overall height would be approcx 2.5"

so this guy is a turkey compared to candidate A??? Perhaps not...

here is what candidate B has going for it vis-a-vis candidate A....

B actually has a little bit more current clipping headroom than A.

B actually operates at a little bit less overall flux density than A.

B actually produces a smidgen more calculated inductance than A...

the relative perm of B is much, much, much lower... it's relative perm is only 26.6% of the relative perm of candidate A... which is one of the factors that disturbed me with candidate A... and why I gave it a 80 percent approval/confidence rating.

B has a moreso equal distribution of copper and core losses compared to candidate A. Though the copper circuit losses in A were less than the copper losses in B. The iron losses in A were signficantly higher and made up the lions share of it's total losses... whereas candidate B comes very close to a 50/50 distribution of copper and core losses.
And the overall losses in B (calculated in watts) is actually close to 40 percent less than transformer A.... making it more efficient.

And candidate B would cost about half the mullah than candidate A.

I'd be happy to build either unit if there were a sustainable market for either one or both...

but I wonder which one is the better OVERALL performer when you consider a wider range of factors other than just simply dcr as the sole barometer of quality.

be interested in your comments on this XXXX... which one would you pick?

msl

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