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Forest of tabs - corrosion question

 
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heedh23



Joined: 05 Sep 2014
Posts: 4
Location: Washington, USA

PostPosted: Tue Sep 06, 2022 2:43 pm    Post subject: Forest of tabs - corrosion question Reply with quote

Recently on one of the Vans facebook groups, there was a picture of a homemade forest of tabs that another builder made for their electrical system. This led to a discussion on whether the aluminum rivets holding the tabs onto the copper plate would corrode, whether brass rivets were necessary, etc.

My question is this - if aluminum "sacrifices" itself when in contact with copper due to galvanic corrosion, why doesn't the aluminum sheet/structure that contacts a forest of tabs corrode? Is it the presumed lack of an electrolyte? Is it a requirement to use some magic unobtanium alloy of copper?

Thanks in advance for the education.
-Ed


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nuckolls.bob(at)aeroelect
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PostPosted: Wed Sep 07, 2022 8:44 pm    Post subject: Forest of tabs - corrosion question Reply with quote

At 05:43 PM 9/6/2022, you wrote:
Quote:
--> AeroElectric-List message posted by: "heedh23" <heedh23(at)msn.com>

Recently on one of the Vans facebook groups, there was a picture of a homemade forest of tabs that another builder made for their electrical system. This led to a discussion on whether the aluminum rivets holding the tabs onto the copper plate would corrode, whether brass rivets were necessary, etc.

My question is this - if aluminum "sacrifices" itself when in contact with copper due to galvanic corrosion, why doesn't the aluminum sheet/structure that contacts a forest of tabs corrode? Is it the presumed lack of an electrolyte? Is it a requirement to use some magic unobtanium alloy of copper?

Excellent question . . .

The original design I crafted for B&C's products
SOLDERED strips of tabs to the base plate. This
preserves electrical integrity between bus plate
and tabs.

At the time it was designed the target mounting
surfaces were stainless and composite
firewalls.

This assembly can be mounted on an aluminum surface
that stays dry.

Riveted assemblies are not recommended.


Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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Ceengland



Joined: 11 Oct 2020
Posts: 378
Location: MS

PostPosted: Thu Sep 08, 2022 5:14 am    Post subject: Forest of tabs - corrosion question Reply with quote

On 9/6/2022 5:43 PM, heedh23 wrote:
Quote:


Recently on one of the Vans facebook groups, there was a picture of a homemade forest of tabs that another builder made for their electrical system. This led to a discussion on whether the aluminum rivets holding the tabs onto the copper plate would corrode, whether brass rivets were necessary, etc.

My question is this - if aluminum "sacrifices" itself when in contact with copper due to galvanic corrosion, why doesn't the aluminum sheet/structure that contacts a forest of tabs corrode? Is it the presumed lack of an electrolyte? Is it a requirement to use some magic unobtanium alloy of copper?

Thanks in advance for the education.
-Ed
As Bob & others said, riveting is far from optimal for electrical

connections. It's pretty simple to just 'flow solder' the tabs to the
plate by using a propane torch under the plate while adding solder to
the tab/plate intersection.

Charlie

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Charlie
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Eric Page



Joined: 15 Feb 2017
Posts: 241

PostPosted: Thu Sep 08, 2022 6:32 am    Post subject: Re: Forest of tabs - corrosion question Reply with quote

I built mine by setting a brass plate on top of a burner on my gas cooktop. Then I smeared solder paste on the bottom of several 6-way quick-connect tabs and placed them where I wanted them on the plate. Finally, I turned the burner on low and waited for the solder paste to reflow. Photo attached.

If you do it this way, turn the hood fan on high (there's some smoke) and have some sort of heatproof tool handy to nudge the tabs into the desired position as the assembly cools, as they'll move a bit when the paste melts.

I got the brass plate for cheap on eBay and cut it to size. Here's one seller...

http://www.ebay.com/itm/293905310788

The quick-connect tabs are in stock at Digi-Key in 4-way, 6-way and 10-way versions...

4-way: https://www.digikey.com/short/q3pjw0cw
6-way: https://www.digikey.com/short/83hdh0j2
10-way: https://www.digikey.com/short/5br0n7fv

Solder paste is available pretty cheaply on eBay (or you can just feed normal solder wire into the joints once the plate is hot). Here are a couple of U.S. sellers in the $7 range...

http://www.ebay.com/itm/384953664130
http://www.ebay.com/itm/313843925100

Be careful that you don't accidentally buy paste flux; eBay sellers frequently mix up search terms in their listing titles and the packaging is very similar.

Finally, I got brass hardware at Home Depot for mounting it to the firewall and securing the negative cable on the engine side.

1/4-20 x 3" bolt: https://www.homedepot.com/p/204274747
1/4-20 hex nuts: https://www.homedepot.com/p/204274130
1/4" flat washers: https://www.homedepot.com/p/204780701
1/4" stainless lock washers: https://www.homedepot.com/p/204276509


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Forest of Tabs Ground Block.jpg
 Description:
DIY 48-way forest-of-tabs made from 1/8" brass plate and soldered 6-way quick-connect tabs. The through-bolt is secured with washers and two jammed nuts (brass all-metal lock nuts are apparently unobtanium). A stainless rivet will prevent rotation.
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yellowduckduo(at)gmail.co
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PostPosted: Thu Sep 08, 2022 7:24 am    Post subject: Forest of tabs - corrosion question Reply with quote

Steel pop rivets and solder on the tabs.
No corrosion at tabs or on aluminum where it is bolted to structure
after 17 years in an open T hangar.
Ken

On 08-Sep.-22 9:14 a.m., Charlie England wrote:
Quote:

<ceengland7(at)gmail.com>

On 9/6/2022 5:43 PM, heedh23 wrote:
>
>
> Recently on one of the Vans facebook groups, there was a picture of a
> homemade forest of tabs that another builder made for their
> electrical system.  This led to a discussion on whether the aluminum
> rivets holding the tabs onto the copper plate would corrode, whether
> brass rivets were necessary, etc.
>
> My question is this - if aluminum "sacrifices" itself when in contact
> with copper due to galvanic corrosion, why doesn't the aluminum
> sheet/structure that contacts a forest of tabs corrode?  Is it the
> presumed lack of an electrolyte?  Is it a requirement to use some
> magic unobtanium alloy of copper?
>
> Thanks in advance for the education.
> -Ed
As Bob & others said, riveting is far from optimal for electrical
connections. It's pretty simple to just 'flow solder' the tabs to the
plate by using a propane torch under the plate while adding solder to
the tab/plate intersection.

Charlie



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PostPosted: Thu Sep 08, 2022 8:26 am    Post subject: Forest of tabs - corrosion question Reply with quote

At 10:23 AM 9/8/2022, you wrote:
Quote:
--> AeroElectric-List message posted by: C&K <yellowduckduo(at)gmail.com>

Steel pop rivets and solder on the tabs.
No corrosion at tabs or on aluminum where it is bolted to structure after 17 years in an open T hangar.
Ken

Good data point. "Fixtured" with rivets
before soldering. Thanks!



Bob . . .

Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"


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