Battery Ground Question

[65 Plymouth Satellite 426]

My Satellite Has The Battery In The Trunk Just Like One Of The Old Super Stockers From That Era Were Built With. The Black Ground Wire From The Battery Is Fastened To The Metal Frame Inside Of The Trunk Area. My Question: Is This Safe And Functional? I Had A Garage Owner Tell Me That This Particular Practice Was Unsafe Because Of A Question With Parts Being Welded Or Fused Together By Accident! Most Of The Pics I Saw Of This Set Up Was Done By Grounding It Against The Trunk Frame or Wheel Well. Comments And Or Suggestions?

 

[tpodwdog]

ill never understand the battery in the trunk thing in a street car....but its really no different than grounding the negative (-) to the engine block where it belongs....I.E. the whole car is grounded ( the whole car is also grounded with the battery under the hood via ground cables anyway ). it might not get as good a ground as grounding to the engine block thus creating heat .

now the positive(+) has a much longer distance to travel and could possibly create more resistance causing heat....thus needing a much thicker cable. if it were me, id put the battery under the hood where it belongs....but its your car, not mine!:headbang:

 

[65 Plymouth Satellite 426]

Dave:

I Bought The Car With The Battery In The Trunk! I Have A Pretty Good Idea That The Guy I Bought It From Wanted To Tear Up A Perfectly Good Satellite To Go Racing! We Found Undersized Fan Pulleys On It, An Alumnium Radiator That Had The Radiator Fan On *** Backwards With An Electric Fan To Assist, Etc. Etc. So It Is What It Is! I'm Wading Through It Making Changes. There Is No Battery Box Under The Hood, It Is Gone! I Understand What You Meant About Heating Up The Positive And Negative Cables Because Of The Distance Involved. It Has Size 2 Cables On It. I Just Wanted To Be Sure It Would Not Heat Up And Become A Problem!

 

[440roadrunner]

I don't see the problem

Make sure you have a nice, large (or maybe TWO) straps from the block or trans to the body. Do NOT ground to the K frame, but the body or rear crossmember frame which is part of the body.

If you don't have one (you'll need one to race) seriously consider a battery disconnect. If you rig a "push pull" setup (NHRA requires "push to disconnect") You could make a push setup which would also help anti--theft, IE push the switch off, but you'd have to open the trunk to turn it back on

In my opinion, the best way to hook this all up is to get a 4 terminal (what is called a "2 pole") such as Cole Hersey switch. These have two large, and two small terminals

Use the two large terminals to break the battery POSITIVE lead, NOT the ground

Ground either of the small terminals, and run the remaining small terminal up front with about a no14 wire. Get a good (Bosch) relay, and hook this no14 up front to one of the coil terminals of the Bosch relay. Run your switched ignition wire to the other coil terminal.

Now use the relay contacts to either break the alternator field (blue) wire, or if you have a "one wire" use the contacts to break your ignition.

This is necessary because if you pull the disconnect, the alternator will keep the engine running, NOT acceptable, NHRA

Many guys run a separate no6 or 8 charging wire from the alternator to the battery, and claim this "passes tech" but in my opinion, this does not meet the "spirit" of the rules, and leaves you with a fire hazard. The method I outlined kills ALL power and contains it in the trunk.

The bad side of a "street" trunk mount is venting. If you "actually" use your trunk for clothes, suitcases, etc, it is difficult to completely isolate a battery so far as vents.

 

[RustyRatRod]

There is no problem....as long as there are ample ground wires everywhere else, just like what needs to be on any other car. The only problem I see would be if metal suddenly stopped being a conductor. That's pretty unlikely.

 

[65 Plymouth Satellite 426]

Thanks Guys! Appreciate The Tips!

 

[Ron 73]

there is no problem....as long as there are ample ground wires everywhere else, just like what needs to be on any other car. The only problem i see would be if metal suddenly stopped being a conductor. That's pretty unlikely.

x 2.

 

[tpodwdog]

sounds like someone did to your satty what the did to my belvy. im STILL straightening out a mess. im glad to see youre getting it back to normal. glad to help!

 

[SwedCharger67]

...Use the two large terminals to break the battery POSITIVE lead, NOT the ground...

I don't understand why you shouldn't break the ground connection instead, in my opinion that's safer and better.

If you break the ground connection there is nothing out there in the wiring harness that can cause a short circuit. And you can short the positive battery terminal to ground and nothing happens! Try that with a breaker on the positive battery side!!!

Using the frame as a return lead to engine requires very clean and tight connections, and will cause a certain higher voltage drop due to higher resistance in iron than a in a copper cable. I would use a copper cable to make sure the starter gets all the juice it can.

 

[RustyRatRod]

NHRA mandates the power wire to be broken with a master on/off switch. The reason is because there are usually more grounds connected to the negative side of the battery than just the one main wire. So breaking the main ground wire in some cases would not turn the system completely off, while breaking the power side will.

I don't understand why you shouldn't break the ground connection instead, in my opinion that's safer and better.

If you break the ground connection there is nothing out there in the wiring harness that can cause a short circuit. And you can short the positive battery terminal to ground and nothing happens! Try that with a breaker on the positive battery side!!!

Using the frame as a return lead to engine requires very clean and tight connections, and will cause a certain higher voltage drop due to higher resistance in iron than a in a copper cable. I would use a copper cable to make sure the starter gets all the juice it can.

 

[moparmarks]

If you decide to move the battery back up front just send me your address and I'll send you a battery tray.
Otherwise sounds like your covered.
Be sure that the positive terminal on the battery is covered so the nothing can ground it out.

 

[moparsteve636]

If you're not going to race the car just move the battery back under the hood!The battery tray is available new or i have a good used one with the lower bracket I'll sell!

 

[chattacuda]

my 2 cents. If grounding to the unibody is sufficient, why did Detriot spend the extra money to ground to the engine? if you buy a trunk mount kit from a reputable wiring company like Ron Francis, it comes with 1 guage positive and negative cables to run all the way to the engine as well as a negative terminal pigtail to mount to the unibody at the trunk. You may never have a problem with the set up you have, but Just think about it. That is a lot of amps going thru your unibody/connection when you Are starting your engine. I moved my battery to the trunk just because I needed the room under the hood.

 

[RustyRatRod]

I don't think anybody said grounding to JUST the unibody was sifficient. Why did the factory ground to the engine? Because it and the transmission are both isolated with rubber mounts. Running a ground to JUST the engine would be just as WRONG as grounding only to the inibody. That's why the factory used ground straps. On older cars they were made from flat braided cable. Those are the best ones to use between the engine and chassis.

my 2 cents. If grounding to the unibody is sufficient, why did Detriot spend the extra money to ground to the engine? if you buy a trunk mount kit from a reputable wiring company like Ron Francis, it comes with 1 guage positive and negative cables to run all the way to the engine as well as a negative terminal pigtail to mount to the unibody at the trunk. You may never have a problem with the set up you have, but Just think about it. That is a lot of amps going thru your unibody/connection when you Are starting your engine. I moved my battery to the trunk just because I needed the room under the hood.

 

[440roadrunner]

Rusty is right. You need BOTH the body and engine grounded, but NORMALLY (front mount) the body doesn't have to carry starter current, so a minimal ground, an in my opinion, GM and Ma were both guilty of NOT ENOUGH of a ground from the battery to the body

(I use the unused head holes in the rear of the driver side head to run a starter cable from the head to one of the master cylinder bolts)

So far as the unibody carrying starter current, you have to remember that Mopars ARE unibodys, a singular, welded assembly, and assuming the connections at each end are good, you have a LOT of surface area there, even though just thin sheet metal. LOTS of people have successfully used the unibody as an engine ground path, with no problems.

Another issue with proper grounding is radio noise, and this same "noise" can also cause problems with other modern electronics. A recent thread on another board (where the OP just would not listen) involved an MSD which interacted with the charging system. He'd unhook the regulator, it was fine. Other sensitive gauges, like in over the road trucks ---EGT gauges, electric speedos, the list goes on, can all be affected by ground loops and other unwanted stray voltage "floating around." It's also the reason that breakerless distributor leads should be twisted, and those that remember TV antenna "twinlead" remember that from a LONG time ago.

And today, it's why CAT3, CAT5, etc cable pairs are twisted

 

[HT413]

Is it me or is #2 wire not enough for that run? I've only ever heard of 0 or 00 being used, though i know summit sells a 1 gauge kit.

 

[RustyRatRod]

I've always used 0 gauge welding lead.

That said, moving the battery to the trunk on a street car does NOT mean it's a bad thing. It can be done and done correctly. Nothing wrong with it at all. It is simply how you execute it. What about old Volkswagens with the battery right under the back seat in the passenger compartment? Just because it's not under the hood, doesn't make it wrong.

 

[HT413]

I agree, my dad's 68 vette has the battery behind the driver's seat and it was never a problem.

But if the previous owner was someone who uses 2 wire where 0 wire belongs (2 has about 60% of the cross sectional area of 0 wire) I'm thinkin he wouldnt know a good ground if he tripped and it hit him in the face.

 

[65 Plymouth Satellite 426]

I Talked With John Baughman Here In York Today. He Runs Two Hemi Cars In The NHRA Hemi Clash Series, Which By The Way, Is This Weekend At Maple Grove, And I Brought Up The Topic Of The Trunk Mounted Battery. He Said That That The Best Way To Set This System Up Was To Run The Positive From The Starter To The Battery And Then Run Another 00 Or Welding Cable The Whole Way Back Up Front And Ground It To Something On The Motor. Seems John Has A Problem With Chrysler's Unibody And All Those Welds That Will Not Conduct Currrent Correctly!

- - - Updated - - -

If you decide to move the battery back up front just send me your address and I'll send you a battery tray.
Otherwise sounds like your covered.
Be sure that the positive terminal on the battery is covered so the nothing can ground it out.

Thanks Mark!


Terry

 

[chattacuda]

Rusty, I respect your opinion and was not taking issue. Of course you have to ground the engine to the body just like the factory did and I consider that as a given. I was just stating the factory ran a large negative cable from the battery to the block in addition to the engine to body and battery to body grounds. As I understood the question, the owner does not have a negative cable between the battery and engine and that is what I am commenting about. My opinion is he does need a cable between the battery and the block, in addition to the battery to body and block to body grounds.

I don't think anybody said grounding to JUST the unibody was sifficient. Why did the factory ground to the engine? Because it and the transmission are both isolated with rubber mounts. Running a ground to JUST the engine would be just as WRONG as grounding only to the inibody. That's why the factory used ground straps. On older cars they were made from flat braided cable. Those are the best ones to use between the engine and chassis.