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Old 30th December 2011, 08:55 AM   #1
Salar is offline Salar  Germany
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Default Using different Metals for one Case - small Currents likely to flow?

Hello to all,
I am modifying and redesigning a cd-player and amp. The already existing chassis is folded steel,
knobs and front panels will be made from anodized aluminium.
For the bottom and top plates, I would like to use brass, because it can be easily more easily weldered /soldered/painted than aluminium.
But looong time ago, I somehow learned in school, that metals have their own electrical potential (I hope this term is correct).
There should be small currents flowing between the more precious brass /steel to the lesser precious aliminium.
So to say, I am building a weak battery.
Am I correct with this assumption?
Any real world effects?
Even thought the anodizing layer on the aluminium isolates,
there will be electrical connections because of screws.
So all metals will interact.
All the best,

Last edited by Salar; 30th December 2011 at 09:00 AM.
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Old 30th December 2011, 09:08 AM   #2
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You should be Ok provided the contacts are dry. You would need an electrolyte like in batteries or capacitors to get an electrolytic reaction. Lemon juice would work as an example.
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Old 30th December 2011, 01:43 PM   #3
Salar is offline Salar  Germany
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Join Date: Feb 2006
Location: Germany
Hm, somebody described the sound of my amp as "juicy", so I should tke care on that.
O.K, but humming as a likely result, no currents, even in an area lesser than millivolts?

Oh, maybe some real world examples out there, in the field of DIY or off the shelve?
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Old 30th December 2011, 10:22 PM   #4
DF96 is offline DF96  England
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You might set up a small standing potential due to differences in material. You might get a circulating current from differences in temperature at the junctions. Both would be DC, so not audio signals. I don't see a problem.
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Old 31st December 2011, 02:58 PM   #5
tvrgeek is offline tvrgeek  United States
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If the mechanical connection provides sufficient electrical connection, you are not likely to develop any potential. If you lived on the coast and it sat for 20 years. maybe some corrosion. You could always run a length of tape between the joints if you are really concerned.
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Old 31st December 2011, 04:05 PM   #6
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When two dissimilar metals come in contact a process called electrolysis comes into is especially prevalent between copper/brass and other metals. The main effect that I have witnessed is corrosion at the contact point. I don't know how the anodizing process will will affect it inyour situation. I would definetly coat any contacting surfaces. Heat seems to hasten the process. Thermocouples use dissimilar metals in their construction and in their function when heat is applied to them they generate millivolts.
JEREMY M_________________________________
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Last edited by Top Shelf; 31st December 2011 at 04:09 PM.
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Old 1st January 2012, 06:13 PM   #7
tvrgeek is offline tvrgeek  United States
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I would not go through the expense of anodizing, but for general information, anodizing is an aluminum ceramic that is a insulator. A company I worked for in the 80's even went as far as relying on it for heat sinks to transistor case to get extra margin out of the thermal path. Worked in the lab, but was spotty in production. The gentleman's question is solved by nothing more than a strip of packing tape.
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Old 4th January 2012, 04:05 AM   #8
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Conducting paint can be used to give good contact between the metals.
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