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Thread: Starter Solenoid/Relay - Battery Terminal Extension

  1. #1
    Out Drivin' Gumball's Avatar
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    Starter Solenoid/Relay - Battery Terminal Extension

    UPDATED - 7/1/16.... Just another TTT for an old how-to thread wherein I was schooled on galvanic corrosion.

    Original post follows.....

    I needed more room than the stud allows on the battery terminal of my starter relay/solenoid, so I decided to add a coupler and a bolt - that way I could put a few of the wires on the stud side and the remainder under the bolt. But, the only couplers I could find commercially were made of steel - not very good for conductivity. So, I made my own using some 1/2" copper hex stock from McMaster-Carr and an aluminum bolt. A few minutes on the lathe and the hex bar was drilled out and tapped. I'll finish it off with a little heat-shrink over it once it's installed for good just to give the electrified surface a little protection. Overall, it will make for a cleaner installation of the various wires I have going to and from that terminal.

    Although I could have accomplished the same thing with a bus bar located nearby or under the dash, I thought this was a simple and functional solution.

    Last edited by Gumball; 07-01-2016 at 10:25 AM.
    Later,
    Chris

    "There are no more monsters to fear, and so, we have to build our own."
    Mk3.1 #7074

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    Out Drivin' Gumball's Avatar
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    Okay, so who would have thought that building a car would be such an incredible learning experience. For a guy who barely made it out of high school so many years ago and later brought shame to his family by becoming a lawyer, I can't believe how much my car hobby has taught me over the years.

    Today's lesson was galvanic action - particularly resulting from the presence of copper and aluminum. The short of it (sorry for the bad pun) is that it's probably one of the worst ideas I've ever had. Although copper is way up there on the electrical conductivity scale, followed just a few elements down the chart by aluminum, the two together with an electrical charge is a big no-no. Further, I learned that copper is best used as a conductor when it's coated by something like tin to reduce corrosion.

    So, thanks again to those who call into question our ideas (in this case, over on the ffcars board) - sometimes such criticism leads to further research and edification.

    Off with the aluminum bolt at a minimum and I'm going to revisit the buss bar idea.
    Later,
    Chris

    "There are no more monsters to fear, and so, we have to build our own."
    Mk3.1 #7074

  3. #3
    Senior Member 68GT500MAN's Avatar
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    You can get silicone-bronze bolts that behave well with copper, similar to the ones used in electrical panels to install the bus bars.
    Doug

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    Quote Originally Posted by 68GT500MAN View Post
    You can get silicone-bronze bolts that behave well with copper, similar to the ones used in electrical panels to install the bus bars.
    Doug
    Thanks - just ordered those from McMaster-Carr... part no. 93516A581 in 5/16" - 18 x 3/4" for $9.53 per box of 10.

    Here's their description:

    Made from Alloy 651 (which contains 96% copper with silicon for added strength), these cap screws are extremely resistant to the corrosive effects of sea water, gases, and sewage. They're also nonmagnetic and good conductors of heat and electricity.
    Later,
    Chris

    "There are no more monsters to fear, and so, we have to build our own."
    Mk3.1 #7074

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    Although the suggestion to use a silicone-bronze or copper fastener is excellent and will essentially eliminate the issue of differential expansion from heat (aluminum "grows" about 33% more than copper), the concern about galvanic corrosion is really a concern only if there is an electrolyte (like salty water) present...please say you don't intend to drive the car in winter on salty roads!!!!

    Dave

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    Out Drivin' Gumball's Avatar
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    Absolutely not!!! No salty roads for this little roadster.
    Later,
    Chris

    "There are no more monsters to fear, and so, we have to build our own."
    Mk3.1 #7074

  7. #7
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    It's a common problem with other cars, too, and the aftermarket supplies junction block studs to add more connections: http://www.summitracing.com/parts/rfw-jb47/overview/

    I've also seen the battery cutoff switch used this way, too.

  8. #8
    Out Drivin' Gumball's Avatar
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    The continuing stream of TTT for old how-to threads. Those of you using the Ford style starter solenoid who are looking for more space on the terminals will likely appreciate this one.
    Later,
    Chris

    "There are no more monsters to fear, and so, we have to build our own."
    Mk3.1 #7074

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