GRND/negative when relocate battery to the trunk

Posted By: Snoddas

GRND/negative when relocate battery to the trunk - 05/11/12 06:42 AM

Hi,
Have started to take care of old (small) irritation problem on my white 64 dodge 330.
When start the car it have been a noice from the starter or some other electrical device.
Yesterday we start measure using an oscilloscope. We found a very big lack on voltage when start the car.
When we had measuring some spots the resultate was about 6 Volts to the starter.
After checking the voltage over starter relay we found that the realy close and open hole time under the starting of engine (that making the noice).

We took the battery and attach it directly at the starter and ground/negative direct on engine and the engine started great and without any bad sounds from start relay or starter.

For info the battery is new and are located in the trunk. The positive cable is 1 gauge and negative is ground in trunk floor (on engine the ground is attach to the firewall).

Its a lack of 2 V ground in chassie when we measured. Adding the lack of voltage in the postive cable and the voltage lack in battery when start/crank the car all that resulting 6 V at the starter.

I'm about route a good ground/negative cable from battery in trunk to the engine.

Strange, almost same battery setup in my 65 coronet havent any problem.

Stay cool.

Posted By: None2Slow

Re: GRND/negative when relocate battery to the trunk - 05/11/12 06:56 AM

When you ground the battery to the trunk, it is trying to transfer current to the engine. The body mounts may limit the current from reaching the starter. Try running the ground to the frame under the trunk. Make sure its clean and tight. Then run a ground from the frame to engine in the engine compartment. This "should" take care of your problem.

Posted By: Snoddas

Re: GRND/negative when relocate battery to the trunk - 05/11/12 07:34 AM

Thanks for the reply. Yes, that would be easier than route a long ground cable from trunk.

Posted By: bb74swngr

Re: GRND/negative when relocate battery to the trunk - 05/11/12 02:05 PM

Quote:

When you ground the battery to the trunk, it is trying to transfer current to the engine. The body mounts may limit the current from reaching the starter. Try running the ground to the frame under the trunk. Make sure its clean and tight. Then run a ground from the frame to engine in the engine compartment. This "should" take care of your problem.

I agree with None2Slow and it worked for me too:)

Posted By: Snoddas

Re: GRND/negative when relocate battery to the trunk - 05/11/12 02:29 PM

The thing is that it works now. I did some improvement on the negative cable where it is attached to the trunk floor.
I also installed a new cable shoe on the positive battery cable. The old one wasent that good installed.

Posted By: Dean_Kuzluzski

Re: GRND/negative when relocate battery to the trunk - 05/11/12 03:21 PM

Sorry to split hairs, but there are no "body mounts" on a early B-body.

The factory engine mount "insulators" provide an electrical insulation too. If you have steel mounts or motor bracket you're good.

The K-member is directly bolted to the "Uni-body" framerails that has innumerable spotwelds tying them into the body.

The thin little "groundstrap" that goes from the engine to the firewall is really for the ignition electronics like distributor spark. Even though it's high voltage, it is actually relatively low amperage and that's where big thick wires are needed elsewhere.

Hence the stock battery ground went straight to the engine block/head and the positive cable went straight to the starter which ground to the block too.

As you add length to the cables, you add resistance, so cable gauge needs to get thicker/bigger (number gets lower).

Adding a remote starter relay further complicates matters. If there's internal resistance from low voltage cranking, burned/pitted contacts you're hosed.

Simple things like the size of the terminal/lugs and quality of the crimping/soldering done to transfer current can strand you. And as most know rust/corrosion and loose connections are bad too.

Keep it simple and go overkill.

Posted By: Snoddas

Re: GRND/negative when relocate battery to the trunk - 05/11/12 04:50 PM

Thanks for good information. We also find that out when measuring. If I remeber right it was about 0.5 Volts lack in the big (and long) postive cable.

Posted By: Dean_Kuzluzski

Re: GRND/negative when relocate battery to the trunk - 05/11/12 09:04 PM

Quote:

If I remeber right it was about 0.5 Volts lack in the big (and long) postive cable.

Ok, you'll always have a little drop due to the length of cable. But, you're only as strong as your weakest link.

Also, the storage/usage of amperage is what is really the means to an end in the automotive starting system. Meaning, the 12-13.8 volts that the battery shows has to have the big amps to crank an engine and keep that level up. That's why MANY racers run TWO batteries in parallel. The current adds while the voltage remains the same.

High compression big block race motors with BIG valvespring pressure take lots of amperage to spin.