Stupid Question #2: how does an iron frame act as a ground on our cars

[ericr]

Originally Posted by Railcarmover

The perceived dearth of American copper was magnified during WW2,all copper available was diverted to the war effort. Some interesting things about that...we all know about the zinc penny in '43..but did you know the calutrons used to enrich uranium for the bomb used electromagnets wound with pure silver? it was 'borrowed' from the Treasury,and had to be accounted for to the ounce..


Mining and smelting capacity increased by the end of the war,we began using our vast reserves of copper ore..we are currently 4th in the world in production.

A German would appreciate that,they were on the receiving end of most of our copper..

I am sure you are correct but I thought I read in grade school that our copper came from some South American country....

[Bruce of MN]

See https://www.tibtech.com/conductivite.php?lang=en_US

Copper is almost ten times as conductive as steel. The steel frame makes up for it by being more than ten times the cross sectional area.

[Blue-Truck-Nut]

Originally Posted by jrelliott

Note to ericr, Arizona and a lot of other states have abundant supplies of copper. EPA and OSHA and other agencies have made it difficult to mine cost effectively. Smelters put out a lot of undesirable byproducts. Cant get a mine open near Superior, AZ as it is on a sacred site per the native americans.

Here's something fun, at least one of those mines is now owned by Mexico. So they are mining our copper, and selling it back to us.

Sent from my E6810 using Tapatalk

[DannL]

When I was young, 14 or so, I pee'd on an electric fence wire which was surounding our horse lot. It was steel wire, and conducted electricity quite well. Will never foget it.

[alexiskai]

Comparison of square cross-sections of materials having the same conductivity (measured in IACS)

[Kevin in NJ]

Sponsored Links (Register now to hide all advertisements)

Current is carried on the outer edge of the material. That is why larger power lines are hollow to reduce weight. In the end it is just surface area. This is something you get to do the math when you get physics or engineering courses.

With the A it is not the iron that is a problem. It is in understanding the ground paths as they are complicated. When we restore the car we do a lot to cover what would be the ground paths.

So from the engine to the frame you travel from the driveline up through the springs (spring bolts to be exact) to the frame as one major path. You also have the often not installed engine shields. Of course you have to be sure that the various bolts have bit though the paint to make a path.

So in restoring my car. I tinned the area where the pos strap attached to the frame and then put tape on the area so no paint is put there. I made grounding contact paths from the frame through the fender brackets into the headlamp bar and put tape in the sockets for the headlamps before paint.

If you used a thicker paint on some areas then you need to be extra certain the lock washers cut through or maybe cut through the paint first. A little extra care goes a long way to a more reliable car.

[Ranchero50]

Ditto what Kevin said, electrical current travels on the surface of the conductor. There's a bunch of different paths for the current to get from the engine to the frame and battery but a heavy gauge ground strap does it best.

[ericr]

Originally Posted by Kevin in NJ

Current is carried on the outer edge of the material. That is why larger power lines are hollow to reduce weight. In the end it is just surface area. This is something you get to do the math when you get physics or engineering courses.

With the A it is not the iron that is a problem. It is in understanding the ground paths as they are complicated. When we restore the car we do a lot to cover what would be the ground paths.

So from the engine to the frame you travel from the driveline up through the springs (spring bolts to be exact) to the frame as one major path. You also have the often not installed engine shields. Of course you have to be sure that the various bolts have bit though the paint to make a path.

So in restoring my car. I tinned the area where the pos strap attached to the frame and then put tape on the area so no paint is put there. I made grounding contact paths from the frame through the fender brackets into the headlamp bar and put tape in the sockets for the headlamps before paint.

If you used a thicker paint on some areas then you need to be extra certain the lock washers cut through or maybe cut through the paint first. A little extra care goes a long way to a more reliable car.

Kevin sounds like you have the best-grounded Model "A" in America JK.


More seriously, I think it is acknowledged that the Model "A" frame, as it came from the factory, did not really have much of a paint job on it, surely not the thick glossy enamel we like to use.

[Terry, NJ]

Auxillarily grounds can make a surprising difference in the amount of power that gets to the starter. I was always hearing "Ya need an 8 volt battery!" No, I needed a good ground! I put a second ground on it. The old ground cable bolted to the top flange of the frame. Using the same bolt, only the underside. I changed the bolt to a 3/8 brass and ran the cable to one of the starter bolts. The starter spun over with new life, who needs 8v or 12v for that matter. We generally can't get to the ground paths and they've been rusting away for 90 years. Naturally they slowed the current down somewhat.
Terry

[Railcarmover]

the engine pans were the ground path to the engine/driveline.

[ryanheacox]

Originally Posted by Terry, NJ

Auxillarily grounds can make a surprising difference in the amount of power that gets to the starter. I was always hearing "Ya need an 8 volt battery!" No, I needed a good ground! I put a second ground on it. The old ground cable bolted to the top flange of the frame. Using the same bolt, only the underside. I changed the bolt to a 3/8 brass and ran the cable to one of the starter bolts. The starter spun over with new life, who needs 8v or 12v for that matter. We generally can't get to the ground paths and they've been rusting away for 90 years. Naturally they slowed the current down somewhat.
Terry

My car has the main ground cable running right from the battery to the top starter bolt. A 7 year old neglected 6V battery still spins it over like it was new. I use the stock ground on the frame for an auxiliary ground.

[rotorwrench]

Originally Posted by Kevin in NJ

Current is carried on the outer edge of the material. That is why larger power lines are hollow to reduce weight. In the end it is just surface area. This is something you get to do the math when you get physics or engineering courses.

The skin effect only applies to alternating current. Direct current flows equally through a conductor. This is why DC is used a lot for magnetizing ferromagnetic objects for magnaflux inspection and for welding.