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riversidevw
08-22-2011, 07:46 PM
OK, the forum has helped me much by confirming that the pre-'56 6 volt systems typically originally used a flat braided steel ground battery cable. I'm thinking specifically of the '55 Speedster.

I realize that steel has far higher conductive resistance than copper. I've seen references to flat braided cable in 2 gauge and 0 gauge, but I can't find any information regarding the conductive qualities of 0 gauge round insulated stranded copper cable vs 0 gauge flat braided cable. Do the gauge measurements simply refer to physical dimensions? Or to conductivity?

Hot engine restarts are a little sluggish with the current (insulated copper) setup, don't want to make it worse by a switch to more "authentic" flat braided steel.

Thanks.

rockne10
08-22-2011, 08:17 PM
Pretty certain those flat braided ground straps are also made of copper. Steel straps would last about as long as a coarse SOS pad.
Ought gauge in either should be equally conductive. Assuming all connections are tight, I would look at other possible causes for hot engine starts.

Jeff_H
08-22-2011, 08:57 PM
Yes, those braided straps are copper. The strands are tin plated otherwise it would turn green in short order! If it really were steel, the voltage drop would be so bad as to prevent the engine from turning over. You'd also see them rust.

At DC and low frequency AC currents, comparing cable sizes is all about the cross-sectional area. For round cables, there are tables that will give the area of each size (usually in circular mils, but some also in diameter and then you can use geometry to calculate the area A=pi x D^2/4). A flat cable area will be something less than the simple width x thickness since the strands are not 100% of the area (there is air space).

Usually, the braided ground cables seen attached to the battery on cars that have them are at least 1" wide and probably 3/16" thick or so (I have not measured one. Whatever you have should be the same or larger area as the cable from the other battery post going to the starter and that cable will be at least 2 awg for a 6v system but often 0 or even 00.

55 56 PREZ 4D
08-23-2011, 03:23 PM
Install new 1/0 or larger battery cables. Change the location of the connection for the positive cable [ground] to a starter mount bolt. Either the top or bottom bolt. This will give the starter full current. The existing ground strap [between motor and frame] will now be to connect the body/frame. The starter is the largest current draw on the car, it needs the best and biggest cable connections.

riversidevw
08-23-2011, 04:19 PM
As usual, thanks for all the input and patience.

I can get both the 0 gauge flat braided strap and a new large gauge insulated negative cable made up locally. They offer choice of cloth or vinyl insulation for the round cable. Assume that the '55 Speedster used vinyl like rest of the visible harness?

Gil

oldcarfart
08-24-2011, 10:02 AM
The flat straps are available at Tractor Supply.

riversidevw
08-24-2011, 12:31 PM
The flat straps are available at Tractor Supply.

I see them on Tractor Supply website, but says available in store only. Out here, Tractor Supply stores seem (not surprisingly) to be located mostly in aggie areas many hours away. Definitely not worth a summer drive! I can have them made locally (in 0 rather than 2 gauge) for only a bit more.

Thanks.

Gil

oldcarfart
08-24-2011, 05:43 PM
I see them on Tractor Supply website, but says available in store only. Out here, Tractor Supply stores seem (not surprisingly) to be located mostly in aggie areas many hours away. Definitely not worth a summer drive! I can have them made locally (in 0 rather than 2 gauge) for only a bit more.

Thanks.

Gil

Damn shame, but Tractor Supply worth a day trip, they have some great inventory and I find their prices more than fair.

Green53
08-26-2011, 12:43 AM
Go with 2/0 welding cable

Denny L

Dan Timberlake
08-26-2011, 12:48 PM
A voltage drop measurement made while cranking will quickly reveal damaged or undersized cables or bad connections. Any old volt or multimeter set on 1 volt DC would work. From battery + terminal to starter terminal should be something like 0.3 volt or less while cranking. From battery - post to starter housing should be similarly low. If the drop is too high, Measurements made across each connection or component will reveal clearly what needs fixing. Sometimes the answers are surprising. Once a $0.05 cent flat washer added to a bolted cable end prevented the execution of an innocent, honest and hardworking ground cable by providing a little additional clamping right where it was needed. A larger cable would have performed just as badly.

http://www.autotechnician.org/starter-voltage-drop-test-explained-in-plain-english/

riversidevw
08-26-2011, 05:50 PM
Thanks all.

I picked up my cables in Redlands, CA this morning... 1/0 flat braided ground, 2/0 insulated negative cable. They finished the order in about 24 hours. The 2/0 must be about the upper limit for tolerable flexibility. They look great, but real test will be next outing with the car. Documenting the voltage drop is excellent suggestion... when in doubt, know what's actually going on.

Thie component most likely to fail in this weather (about 105 degrees) is me!

Gil

riversidevw
08-30-2011, 01:59 PM
Real world test completed this morning, starter indeed seems to operate more briskly on warm restarts. The new insulated cable and flat braided ground also look good. For those having trouble finding the flat braided item or cloth-covered insulated cables for their 6V cars, the shop does a nice job, offering custom fabrication in variety of gauges for both. They are YnZ Yesterday's Parts, their major line of products seems to be reproduction wiring harnesses (something I haven't needed... yet).

http://www.ynzyesterdaysparts.com/

Gil