6
$\begingroup$

Copper is around 14 times more conductive than lead according to this source. If this is the case why are car battery terminals and connectors built using Lead? I saw both types of replacement connectors at the automotive store and am interested in the advantages of each? Thanks for any information.

$\endgroup$
1
  • 1
    $\begingroup$ What is the basis for your belief? For that matter, what did the salesperson at the store say about the differences? $\endgroup$ Aug 29 '16 at 13:12
14
$\begingroup$

Yes, copper is more conductive than lead, but that is not necessarily the primary criterion for selecting the connector material.

For car batteries, making sure there's a good connection between the two pieces of metal (the stud on the battery and the connector on the wire) is more important, and lead wins out here because it is so much more malleable (soft) and adapts itself more readily to any mismatch between the shapes of the individual pieces.

A second reason the battery stud is made of lead is that lead is the primary component of all the metal parts of the battery, and there's no compelling reason to use anything else.

$\endgroup$
1
  • $\begingroup$ Great answer! To build on it, Pb has a tensile modulus close to 16 GPa, while copper has a tensile modulus near 117 GPa, meaning that in addition to relatively easy plastic deformation, lead is also an order of magnitude more compressible just in the elastic regime. $\endgroup$
    – wwarriner
    Feb 24 '17 at 16:56
5
$\begingroup$

A lead-acid battery has only lead and acid. If copper was used for the terminal posts galvanic corrosion would eat them. It is better to keep the same metal for the cell plates and the terminals. Also they be cast together during manufacture.

$\endgroup$
1
  • 1
    $\begingroup$ Welcome to Engineering! I've edited your answer to keep it on-topic for the question posed. $\endgroup$
    – Wasabi
    Jun 13 '20 at 0:36
3
$\begingroup$

Lead is more corrosion resistant to sulfuric acid . And copper is more expensive. That is; copper in the battery would dissolve in less than one year.

$\endgroup$
2
$\begingroup$

In regular wet lead batteries, the corrosive environment and the need to have easy connect and disconnect ensures there will be an oxide film at the connection due to the sulphuric acid fumes. While copper metal has a better conductivity than lead metal, lead oxide has a much better conductivity that copper oxides, and the copper oxides tend to form a fluffy mass that doesn't protect the underlying metal. Lead oxidation occurs much more slowly than copper oxidation under those conditions.

As far as the junction from lead to copper wire goes, you want that to be someplace easy to inspect, easy to clean, and easy to replace a small cheap copper part.

In sealed lead acid batteries (SLABs) and sealed vented lead acid batteries (SVLABs), particularly absorbed glass mat types (AGMs), copper flag terminals are common and popular. Any of the fluffy green corrosion on the post means that the seal has been compromised and the battery's days are numbered.

OutBack's new EnergyCell RE High Capacity battery employs a modular design concept with an integral racking system that can be installed more quickly and easily than most Valve Regulated Lead Acid (VRLA) batteries of this size. The Absorbed Glass Mat (AGM) cell design incorporates thick positive plates to extend battery life. Each module (one or two cells depending on cell size) is encased in it's own steel can and features a welded/epoxy dual-post sealed design and large copper posts to enhance performance and safety in high current applications. Unlike flooded batteries, these high capacity AGM cells provide full rated capacity from the first cycle and do not require watering or active venting. The included racking system is deployed with 4 modules per shelf so a 48 VDC system typically uses 6 shelves. Terminals and connecting plates as well as clear safety covers are also included. Standard string terminations are for the top of the rack.

https://www.bluepacificsolar.com/batteries/outback-energycell-1100re.html

$\endgroup$
0
$\begingroup$

Copper also has the tendency to work harden and can crack / split over time.

Yes, lead can also split if it is tightened too much - there are plenty of people that over tighten them.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.