From: James Colville
Sent: Saturday, January 16, 2010 7:36 PM
To: Jim Thomson
Cc: amps@contesting.com
Subject: Re: [Amps] KK5DR's ferrite loaded plate chokes.
I just wound an ameritron look alike with #28. It's larger than they use. I
have an original ameritron choke to compare with. I think they must use #29.
My resistance was lower using #28 and it was less uH.
73
Jim W7RY
## Tnx. 29 ga wire will get hot with 2A flowing. I used a test jig
with a variable [ current limited] dc supply,
0-60 vdc @ 5A max, and simply hooked it up to several chokes for testing.
Feed 1-2 vdc to the choke, and then watch the
built in digital ammeter... [ down to 1/10ths] The large 180 uh choke from
the Henry 8-K ultra uses 24 ga wire is fine up to 1.5 A. [warm]
..... then gets really hot at 2A. Remove the power, and quickly measure the
dc resistance, and you will see it has risen a whole bunch.
Of course, with I squared R, the choke gets into thermal runaway...fast!
## next up was 27 ga wire... same deal, but way less current involved.
29 ga will be worse still ! 22 ga is superb for 99% of the heavy
duty applications. I also tested the 20 uh small plate choke from the Henry
8-k ultra [wound with 18 ga]... and of course it ran stone cold
with the max of 5-A my little bench supply could deliver. I don't like stuff
running hot at the best of times. Part of the scenario is the turns are
packed in tight, plus wound on Teflon rods, plus use polyimide insulation, so
any heat developed inside, has a hard time getting out. IE:
it's insulated on 3x sides.
later... Jim VE7RF
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