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 Joining aluminium in magnetic loop 
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Post Joining aluminium in magnetic loop
Hi, Ive got a Capco AMA 5 magnetic loop that has mechanical joints where the two halves of the loop meet at the bottom. The pieces join with a curved strap either side that bolts through the tube to join and brace them. I know that keeping losses as low as possible is very important in a mag loop. My question is, can I use some very thin copper as a jointing medium to reduce losses, or would it be better to just let the two aluminium surfaces mate with nothing in between?

Thanks

Chris

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Chris MW0MWE


Sat Mar 30, 2013 12:36 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
2e0teg* wrote:
Hi, Ive got a Capco AMA 5 magnetic loop that has mechanical joints where the two halves of the loop meet at the bottom. The pieces join with a curved strap either side that bolts through the tube to join and brace them. I know that keeping losses as low as possible is very important in a mag loop. My question is, can I use some very thin copper as a jointing medium to reduce losses, or would it be better to just let the two aluminium surfaces mate with nothing in between?

Thanks

Chris

Aluminium to copper can give you a problem with electrolysis best stick to aluminium straps and stainless nuts and bolts

Peter GM1CMF


Sat Mar 30, 2013 12:57 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
Thanks Peter, the original straps are aluminium, I just had a brain wave that copper in between would help. Thanks for the reply, I will leave it as is, just give the surfaces a good clean with wire wool.

73's Chris

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Chris MW0MWE


Sat Mar 30, 2013 1:17 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
This info may be of some interest to you:

Electrical Jointing of Aluminium
A particular phenomenon associated with the jointing of aluminium conductors, concerns the
oxide film that forms rapidly on the surface of freshly cleaned aluminium exposed to air. This
oxide film is an insulator and must be removed with a scratch brush in order to achieve a
satisfactory and reliable electrical joint. The problem with aluminium is that the freshly cleaned
surface will quickly re-oxidise, hence it is important to coat the surface with a contact sealant.
Contact Sealants
Various sealant formulations have been developed to provide improved electrical and mechanical
performance as well as environmental protection to the contact area. The use of sealants is
recommended for aluminium to aluminium or aluminium to copper connections. Sealants are also
recommended for copper to copper joints which are subject to severe corrosive environments.
Non-gritted sealants are recommended for flat connections and as a groove sealant in bolted
connectors such as parallel groove clamps. Our gritted sealant is primarily used in compression
connectors. The sharp metallic grit particles provide multi-contact current carrying bridges
through remaining oxide films to ensure superior electrical conductivity.
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Dave G0BHD.


Sat Mar 30, 2013 2:07 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
Here are some common proprietory brand examples, but there are other types available if you ask at an electrical contractor wholesalers:
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Hope the info is useful.

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Dave G0BHD.


Sat Mar 30, 2013 2:10 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
Excellent stuff, thanks Dave, will get down to my local electrical wholesaler and see what is available. :)

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Chris MW0MWE


Sat Mar 30, 2013 3:52 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
Many years of my career with GPO/BT was spent constructing telephone exchanges. It was common to have to make joints in large aluminium bus-bars carrying up to 1000 amps. The procedure was to use a scratch brush (COPPER) bristles and PURE petroleum jelly. The joint was smeared with jelly ad the oxide was removed by vigorous use of the brush. When the oxide was completely removed the joint was QUICKLY wiped clean of oxide/jelly and bolted up. The joint was then testedby passing a test current of 500 amps thru the joint and measuring the volt drop across the joint with a a light-deflecting micro voltmeter.
Roger G0IUW


Sun Mar 31, 2013 6:14 pm
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 Joining aluminium in magnetic loop 
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Post Re: Joining aluminium in magnetic loop
G0IUW wrote:
Many years of my career with GPO/BT was spent constructing telephone exchanges. It was common to have to make joints in large aluminium bus-bars carrying up to 1000 amps. The procedure was to use a scratch brush (COPPER) bristles and PURE petroleum jelly. The joint was smeared with jelly ad the oxide was removed by vigorous use of the brush. When the oxide was completely removed the joint was QUICKLY wiped clean of oxide/jelly and bolted up. The joint was then testedby passing a test current of 500 amps thru the joint and measuring the volt drop across the joint with a a light-deflecting micro voltmeter.
Roger G0IUW

That post took me back a few years Roger! When I first qualified as an electrician, I worked in a large iron and steel foundry. We had quite a few "induction" furnaces, that required large switchable capacitor banks, for power factor correction. The capacitor rooms had very large aluminium bus bars, and connections to and from them, were done with aluminium "strappers".
We also used the pure petroleum jelly/scratch brush method, and tested joints along the lines you just described!
We also used it for copper to copper joints, on outside feeder to trolly wires connections, for the overhead stockyard cranes etc.

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Dave G0BHD.


Mon Apr 01, 2013 1:01 pm
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