Topband: Stainless Steel for coil taps.

[Larry-k1uo]

@Tim,  For the sake of my “experiment” I was indeed using the band clamp to hold a small aluminum eyelet soldered onto#14 wire for the tap wire.       The wire used for the coil is solid copper 10 gauge wire.   I found some clips that would work up to #10 wire at DX engineering called coil clips if you are looking.  I believe after I rebuild a coil and tap it “properly” that things will indeed work ok.

Not top dog ok but Home Owners Association ok.

Thanks all for both private and public help with suggestions and helpful information for this old guy…  aren’t we all.

From: Tim Shoppa
Sent: Monday, November 16, 2020 9:25 AM
To: Larry-k1uo
Cc: topband at contesting.com
Subject: Re: Topband: Stainless Steel for coil taps.

Conductivity of Copper: 5.85 x 10^7 mho/m

Conductivity of 301 Stainless: 0.14 x 10^ mho/m

Stainless is 42 times worse conductor than copper.

Larry, was the band clamp holding a copper conductor onto the coil, or was the band clamp actually being relied on for conductivity.

If current was being carried by the hose clamp: Typical 301 stainless band clamp (say one that will accomodate both 1/2" and 3/4" tubing) is .023" thick by 5/16" wide. For an area of 0.007 square inches carrying the current. 

Because copper is 42 times better conductor, a equivalent copper conductor would be just a little more than 0.00017 square inches. So that stainless band clamp is a worse conductor than AWG 26 copper wire.

The tables list 26AWG as having an ampacity of 0.36A. So even at 100W and 50 ohms you are past the limit. Go to legal limit and 50 ohms and you are way past. Go to a high Q circuit and you are way way past.

I would recommend something different for coil tapping for a 10AWG coil: I am a big fan of the Mueller BU-27C copper clip, rated for 40A DC. If you are going onto thick copper tubing, Mueller the BU-27CGW (the "geophone clip") works well.

Tim N3QE

On Sun, Nov 15, 2020 at 6:40 PM Larry-k1uo <k1uo at tds.net> wrote:
Probably everyone but me knew or knows this but it seems it is NOT a good idea to use stainless steel band clamps  as coil taps.  Especially on a large 160M Base coil.     Oh well….   The ss band only got red hot and caused the #10 wire coils underneath it to melt into the pvc form and did not start a fire at least.
Regards  Larry  K1UO

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