Cable size for battery relocation

[bnam]

(reposting as I posted by mistake in the for sale forum)

I've checked a couple of cable design sources and 4Ga cable is rated to 300A over 16ft. That seems plenty for a relocating battery to trunk (assuming normal usage). I currently have 0 gage cable that I don't like. Was thinking when I rewire the car and add a distribution block in front, would go with a narrower gage wire.

Would like to hear from an expert in this area.

B

[RayC911]

http://www.bmw2002faq.com/content/view/42/32/

Here's one for sale now

http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,367544/

[nbcbird]

I think the E30 cable install is clumsy, try this option:

http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,331885/highlight,trunk+battery

[colorobo2002]

I can show you my e30 cable install in my car. And you can find these at any of the local junkyards. Let me know if you're interested in seeing my car in person.

Good luck.

Rob

[c.d.iesel]

BMW E30 cable transplant is dope!

[allbim]

When cranking an engine, you may have peak currents of 300 amps or more for brief periods of time. Average starting current on an M10 engine is probably about 130 amps and depends among other things, on the starter you're using. When selecting the cable size for your application, you have to select a wire gauge that has the needed current carrying capacity (without overheating) and at the same time a resistance low enough to prevent excessive voltage drop. It is important to remember that a 5% voltage drop along the cable will cause a 10% power drop at the starter. If during cranking, you don’t want the car’s electrical system to be subjected to the voltage drop in the big cable coming from the battery, run a separate 10-gauge wire from the battery post to your cars electrical system and use the big cable to supply only the starter. You can see that wire in c.d.iesel's post.

The handy link below will help you make your decision.

http://www.stealth316.com/2-wire-resistance.htm

[c.d.iesel]

did you know that with a diagnostic tester

that can read cranking amperage, and an even better

diagnostic machine that shows cranking amps as each cylinder

cranks - is nearly equal to your compression readings

of each cylinder ?

so if your seeing 130 amps cranking - that means 130 psi

compression tester reading

back to using the BMW E30 cables.

You are assured of proper cable gauge for the task,

the end connectors are already 'factory' soldered on

perfectly, and their quality is the best. Remove them for

nearly free from any pick-n-pull, or order new from any BMWDEALER

for a very reasonable price compared to you sourcing bare wire,

lesser quality connector ends, and your questionable technique of

attaching the ends as well as the 'factory'. It saves time.

Routing from the trunk is easy through a existing hole on the drivers

side of the trunk bulkhead, down under the carper along the drivers rocker box, and then through the firewall to just behind the fuse block on the inner wheel well.

[allbim]

And that's why it's easy to tell if there is something grossly wrong with an engine, just by listening to it crank before it starts.

[Marty]

It's real easy to mesure your voltage drop while starting your car with a multi-meter, just run a 12 to 16 gauge wire from the battery pos. post to the hot side of the solinoid with your metercut into this wire and set to volts dc and also set to record. crank your car over and the reading on the meter will be your voltage drop.

[TobyB]

Racer trick is to go to Home Depot and get aluminum cable for most of the run. Then you can use 2ga or 0 for less weight, too.

You have to use fine strand copper at the ends, but it saves many pounds

in the middle.... those bulkhead fittings from the hot rodders are a good

place/way to transition from/to copper, and solves the grommet problem cleanly.

(stolen brazenly from Guy Selle)

t

[bnam]

When I got the car 3 weeks ago, it was already set up with the battery in the trunk. It was wired with a 0 gauge red cable to the starter, a 0 guage black cable routed from the block (and as I recently found out) -- thru a hole in the bottom of the pedal box under the carpet, thru the back seat wall to the battery, and just a 10Ga wire to ground the block to the body.

Today I replaced the 10Ga ground with a 4Ga ground to the ground point near the relays. This grounding point seems weak and flexes as I tighten. Is this the Factory point for grounding the block?

I removed the 0 ga negative cable that went thru the cabin and put a 2Ga negative cable grounded in the trunk.

I plan to replace the positive cable with the E30 cable and distribution block.

What would a good point be for the E30 distribution block. I have a 74Tii, but don't yet have the air filter housing on so not sure if the firewall next to the timer relay will have sufficient clearance. Would like to hear from other Tii owners on where they've mounted the distribution block.

THx!

Byas