Moving battery: cable sizing, grounding ?'s

On 4 Feb 2006 13:36:54 -0800, > wrote:



>AZ Nomad wrote:

>> Unless you have a three hundred dollar meter with a 4 wire probe (no current
>> through the sense wires), you're going to have a tough time measuring the
>> resistance of a battery cable. Most of the resistance is going to be in
>> corrosion at the connectors. IIRC, a battery cable is typically 4 or 6
>> gauge wire. 6 gauge wire is .47ohms/1000', 4 gauge is 0.24ohms/1000'.

> You could always cheat and pass a known current through the conductor,
>then use Ohm's Law to calculate resistance... but as long as your
>voltage drop wasn't too horrible it wouldn't matter what the resistance
>is, now would it?..<grin>

If you're measuring voltage with a high impedance meter (even cheap meters are
typically 10M), the voltage drop will be negligible.

Get a 0.01 ohm shunt, and wire up the battery cable to a car battery and a
nice load like a headlight. Measure the voltage drop at the 0.01 ohm shunt and
you'll know the current through the entire circuit. Measure the voltage drop
across the battery cable and you'll be able to easily calculate it's
resistance.

On Sat, 4 Feb 2006, bowgus wrote:

> my old VW bug had the battery under the rear seat ... but that was for
> practical reasons

Yeah, it was because those pathetic excuses for cars had no heater to
speak of, so if it was really cold, you just got someone heavy to sit in
the back seat, pushing the seat springs into contact with the battery
terminals. Presto: Instant heat, lots of it, and regardless of engine
temperature.

> wrote in message
. net...

>
> I have used
> www.custombatterycables.com
>
> Vince has a pretty nice site, and you may find a lot of information there.
>
> By the way, his cables were spectacular, and have the price of OEM:


Merde! I hate these autocorrecting routines. They were HALF the price
of an OEM.

"Jim" > wrote in message
nk.net...
>I have a typical nose heavy compact wagon and want to move the battery
>from the engine compartment, to the rear of the vehicle. I have two
>tech details to work out.
>
> 1. What size of batt cable to use. I will be using tinned marine grade
> wire, from Ancor Marine. The run will be no more than 15' long.
> Engine size is 2.5 litre, alternator is 60 amp.
>
> 2. Whether to run the ground from the battery post all the way back to
> the front of the car, or just ground to the body somewhere near the
> battery, or ground to body near battery and also run a smaller gage
> ground all the way forward.
>
>
> In case anyone is concerned about fumes from the battery, I will be
> using a battery that has provisions for adding a vent hose.
>
>
> Jim

CAUTION.

It will work with big cables BUT be very careful of the installation/
INSULATION of the hot wire.
It will be big and run a long way.
If it ever wears thru the insulation the car will be gone before you
smell the smoke.
Because the starter draws large currents there is no practical fuse and
a short of the hot wire to chassis will be deadly.
When the battery is near the starter the unfused wire is very short and
mostly in the air between the battery and the starter solenoid.
--
John G

Wot's Your Real Problem?

Jim wrote:
> I have a typical nose heavy compact wagon and want to move the battery
> from the engine compartment, to the rear of the vehicle. I have two
> tech details to work out.
>
> 1. What size of batt cable to use. I will be using tinned marine grade
> wire, from Ancor Marine. The run will be no more than 15' long. Engine
> size is 2.5 litre, alternator is 60 amp.
>

Your best bet will be running multiple wires. 1 to the starter, 1 to
the fuse panel under the hood. depends on the year of your vehicle.
Also you will need a good strong wire to the alternator since that is
very very important for charging your battery without loosing volts and
efficiency. Of course if you ave room, run the 1-2 jumbo wires back to
the former battery location, thats simplest.

The best is to move the whole fuse panel when you move the battery, but
I don't know the car to say how well/easy this will be.

Without fusing you increase the fire hazard of your vehicle. Will you
run these wires under the carpet in the car? I don't think there is any
inobtrusive place to run these wires.


> 2. Whether to run the ground from the battery post all the way back to
> the front of the car, or just ground to the body somewhere near the
> battery, or ground to body near battery and also run a smaller gage
> ground all the way forward.
>

Didnt tell us the car type or if its truck, unibody, etc. I would say
look at the rear lights and see if they are grounded to frame or to wire
runnign back to front of car. I really need to know the grounding
strategy of the car to give a solid easy answer. without that i have to
recommend treating the ground just like the B+ sans the fuses. Do not
ground the battery at the rear. It could work or you could end up with
ground loop issues in different systems. Safest way is to stick to
existing architecture and simply compensate for voltage drop by using
multiple wires.

>
> In case anyone is concerned about fumes from the battery, I will be
> using a battery that has provisions for adding a vent hose.
>
>

Battery should not be in passenger compartment. Maybe you want to give
more reasons why your doing this and we can give more options.

> Jim



--
Thank you,



"Then said I, Wisdom [is] better than strength: nevertheless the poor
man's wisdom [is] despised, and his words are not heard." Ecclesiastes 9:16

Jim wrote:
> I have a typical nose heavy compact wagon and want to move the battery
> from the engine compartment, to the rear of the vehicle. I have two
> tech details to work out.
>
> 1. What size of batt cable to use. I will be using tinned marine grade
> wire, from Ancor Marine. The run will be no more than 15' long. Engine
> size is 2.5 litre, alternator is 60 amp.
>
> 2. Whether to run the ground from the battery post all the way back to
> the front of the car, or just ground to the body somewhere near the
> battery, or ground to body near battery and also run a smaller gage
> ground all the way forward.
>
>
> In case anyone is concerned about fumes from the battery, I will be
> using a battery that has provisions for adding a vent hose.
>
>

In addition to the details of involving venting of hydrogen gas to the
outside have you provided for some sort of drain?

John S. wrote:
> Jim wrote:
> > I have a typical nose heavy compact wagon and want to move the battery
> > from the engine compartment, to the rear of the vehicle. I have two
> > tech details to work out.
> >
> > 1. What size of batt cable to use. I will be using tinned marine grade
> > wire, from Ancor Marine. The run will be no more than 15' long. Engine
> > size is 2.5 litre, alternator is 60 amp.
> >
> > 2. Whether to run the ground from the battery post all the way back to
> > the front of the car, or just ground to the body somewhere near the
> > battery, or ground to body near battery and also run a smaller gage
> > ground all the way forward.
> >
> >
> > In case anyone is concerned about fumes from the battery, I will be
> > using a battery that has provisions for adding a vent hose.
> >
> >
>
> In addition to the details of involving venting of hydrogen gas to the
> outside have you provided for some sort of drain?

Most battery boxes designed for trunk mounting provide a vent hose
intended to be routed through the trunk floor. There is no drain as
the idea is that the plastic or stainless box will contain any
inadvertant acid spills.

nate

N8N wrote:
> John S. wrote:
> > Jim wrote:
> > > I have a typical nose heavy compact wagon and want to move the battery
> > > from the engine compartment, to the rear of the vehicle. I have two
> > > tech details to work out.
> > >
> > > 1. What size of batt cable to use. I will be using tinned marine grade
> > > wire, from Ancor Marine. The run will be no more than 15' long. Engine
> > > size is 2.5 litre, alternator is 60 amp.
> > >
> > > 2. Whether to run the ground from the battery post all the way back to
> > > the front of the car, or just ground to the body somewhere near the
> > > battery, or ground to body near battery and also run a smaller gage
> > > ground all the way forward.
> > >
> > >
> > > In case anyone is concerned about fumes from the battery, I will be
> > > using a battery that has provisions for adding a vent hose.
> > >
> > >
> >
> > In addition to the details of involving venting of hydrogen gas to the
> > outside have you provided for some sort of drain?
>
> Most battery boxes designed for trunk mounting provide a vent hose
> intended to be routed through the trunk floor. There is no drain as
> the idea is that the plastic or stainless box will contain any
> inadvertant acid spills.
>
> nate

Good point. Which makes me think of another point. He is putting this
in the rear of a wagon. I wonder where he is putting it.....hopefully
not on the storgage compartment floor.

I'm not sure I understand what the problem is that will be solved by
this exercise.

Well, if I really really needed to remove ... and that's remove, not
relocate ... 20 lbs from the front of my jeep, there are smarter
"weighs" do it than relocate the frikken battery.

Jim is answering some of the questions posted:

I want to do it to shorten the braking distance.

It is a brand new compact wagon of Japanese unibody design and US
manufacture. The battery will be inside the rim of the spare tire,
under the rear floor.

Everything, including the rear lights, is grounded thru the body - no
separate ground wires except for a heavy one from the engine block over
to the battery minus terminal.

The proposed positive cable will be under the car, with heavy duty PVC
insulation and covered by the black nylon sheathing typically used for
car wiring. Small sections subject to movement or slight abrasion will
be inside lengths of rubber hose. I have done this before, and have one
installation that is now 20 years old with no abrasion problems.
However, that old vehicle does not have a computer so probably is not
sensitive to the voltage spikes that occur when you shut off the starter
motor. Thus, I am interested in dnoyeB's suggestion to run separate
hot wires to the alternator, computer, and starter. Any idea what gage
each should be? (Would like to keep the weight down.)

Some posters have identified other cars that have the battery in the
rear. Does anyone know if they run separate wires for alt, comp,
starter, or take other precautions?

Jim



bowgus wrote:

>Well, if I really really needed to remove ... and that's remove, not
>relocate ... 20 lbs from the front of my jeep, there are smarter
>"weighs" do it than relocate the frikken battery.
>
>
>