Batt Relocation Lessons?

[Doorkicker]

I need some more room under the hood and considering relocating the batt to the trunk

Looking for advice, lessons learned, things to do and don't do, just overall how should I do it.

Thanks!!

 

[DeltaV]

I believe @Kern Dog has done a few. Maybe he'll chime in.

 

[Kern Dog]

I have actually only done one, my own car. It did work out but at a cost. The additional wiring and thicker cables added weight. I’ve considered the idea of going back to an under hood setup if I can find a lightweight, smaller lithium battery.
I’ll report on it here if I go that way.

 

[DeltaV]

I have actually only done one, my own car. It did work out but at a cost. The additional wiring and thicker cables added weight. I’ve considered the idea of going back to an under hood setup if I can find a lightweight, smaller lithium battery.
I’ll report on it here if I go that way.

Where did you route the cables and where did you ground the negative?

 

[Fran Blacker]

Don't drilla hole in your gas tank! No it didn't happen to me.

 

[Kern Dog]

The main power comes off of the battery and connects to a Ford solenoid in the trunk. The 1/0 cable goes across the axle hump and along the inside above the left rocker panel. From there it rests against the firewall where it crosses over the steering column then goes through a hole above the accelerator pedal. It is a straight shot to the starter there with zero risk of contact with the headers. The main cable is only live while cranking. The starter has a buss bar connecting both terminals together so when the key is twisted, the 1/0 cable is energized and it starts. I have a trigger wire attached to the firewall relay, running back to the Ford solenoid.
I have one ground from the block to the chassis. One ground from the block all the way back to the battery and one from the battery to the rear frame rail. It does work but the move from the engine bay to the trunk must have added 20+ lbs.

I don’t intend to change anyones mind about battery placement but the lightweight and compact lithium batteries would free up space while saving a lot of weight. My battery is 40.5 lbs. If I used a 7 lb lithium battery up front, that 53+ lbs less weight.
My hitch is finding a good size for under $500. I want something with similar power as stock but maybe half the size. Length isn’t a problem but I’d want one narrower and not as tall. Something like 11” long, 4 1/2”wide and 6” tall would be fine. I worked on a buddy’s car awhile back. He had a group 24 size lithium that weighed 7 lbs. That battery-fired up his car much faster than mine does.

 

[gkent]

I wouldn't worry about the added weight unless its a dedicated race car. An easy but very good route is to buy the relo kit from these guys: www.madelectrical.com

One thing to note is that when running the Ford solenoid the main + to the battery is only live when cranking. Therefore you need a seperate lighter + to a) power everything else and b) to charge the battery. The kit from MAD shows how to do that.

 

[70chall440]

I have done a lot of battery relocations (doing one right now on my 71 Charger) and I can say that it can be done a number of ways successfully. The simplest way is to run a large gauge cable (1/0) from the battery to the engine compartment and connect as if the battery was still in the front.

The biggest "down side" or con of this method is that you now have a very large electrically hot cable running the length of the car all the time. This can be mitigated with a battery disconnect so that it can be turned off when the car is not running.

Another method is to use a continuous duty relay (CDR) back at the battery which only energizes the large cable during starting. This then requires a smaller cable (4g) to be run from the charging system back to the battery. This then requires you run a wire from your starter solenoid (the start wire) back to the CDR to initialize it. The pro to this is the method is that the 1/0 cable is only hot when you are starting the car.

As mentioned, there are number of methods and I am sure a simple Google search will yield some good results. As for routing it kind of depends on what model car you are working with because the G3 B bodies have channels on both sides where as the early cars only have a channel on the drivers side.

Of course it is possible to run the cable under the car as well but you need to be very careful to ensure that it is protected and secured. To that end you can use things such as Adel Clamps.

One challenge is always passing the cable through the firewall. You can go with a hole and a grommet or use a pass through battery terminal connector but this requires the cutting of a rather large hole (larger than if you were using a grommet).

Take some time to draw it out and think it through. It is not rocket science but it does need some thought and it is not super cheap. I would not recommend the "kits" you can get from places like Summit or JEGS, IMO the cable is too small and the kit is cheap. You can buy everything individually from places like Amazon or even locally (welding shop for the cable).

 

[gkent]

This then requires you run a wire from your starter solenoid (the start wire) back to the CDR to initialize it.

Nah. You jump the main starter terminal to the solenoid. You run a regular 18ga wire from your ingition switch to the "CDR" or in many cases a Ford starter relay. You completely eliminate the Mopar relay on the firewall.

Its worth noting that if you use an older starter, the solenoid requires a fairly heavy current - hence the 10ga that runs from the battery to the relay and then to the solenoid.

HOWEVER,

If you run a later model Mini-starter a generic 30 amp relay and 18ga wire is sufficient to drive the solenoid. That's all thats used from the factory in all late models utilizing those starters.

FWIW, when the old starters failed it was usually due to toasted contacts on the solenoid - a result of the crazy current being thrown at it.

 

[33 IMP]

If you just want the battery in the trunk, put the switch on the negative side. And then you can put the shutoff anywhere you want. If you put it inside the locking trunk, it can act as an anti-theft device too.
If you need to be nhra legal, the switch has to be accessible on the rear of the car and wired in the positive side (really stupid, imo).
If nhra legal, get the expensive dual pole switch, to shut off the alternator. I had to buy a moroso solenoid to shut it off, that cost MORE than the dual switch.
Greg has a good point about the weight, moving the battery adds weight. But, it removes weight from the front, where most cars are already too heavy, and shifts the great majority of that weight to the rear (or under the center of gravity, in the case of the heavy cable) where it helps weight distribution percentage. That's why the original maxwedge/hemi race package cars had a giant, heavy battery in the trunk.

 

[gkent]

I don't understand the point of switching the negative side.

 

[71Beeper]

I kept my battery in the trunk because my car came like that when I bought it (ex drag car).

I did like 70chall440 said & hooked up the wire for the starter running the existing gauge cable (1/0) from the battery to the engine compartment and connect as if the battery was still in the front.
Here's the Optima battery.

Here's the end of the positive battery cable that's in the engine bay.

I had a starter cable piece that I shortened and put on a big ol butt connector along with some heat sleeving.

I used these big *** crimpers.

Then I extended the smaller 2 wires and ran them back to the starter relay to look factory.

No issues so far.....
Here you can see how I routed the starter wire above the steering column and behind the engine to go to the starter.

 

[gkent]

Years ago when I ran mine I brought the cable across the hump behind the back seat and down through one of the large hole plugs. Wire tied to the brake line to the front crossmember where I slipped it through a piece of hose then through existing frame holes and out pretty close to the starter. If the sucker is going to short, I want it shorting OUTSIDE of the car. Since I'm redoing the car I'll likely follw a similar route but along the frame connector this time. A Ford-style relay at the battery pretty much ensures angainst a major short. A smaller gauge "charge" wire with fusible link at both ends completes the insurance.

 

[Doorkicker]

You guys have been super helpful! Thank you for taking time to share the insights. It's been a big help, sincerely.

 

[65CopCar]

Put a 200 amp fuse on the positive side at the battery (yes - 200A is the correct fuse).

Holder and fuse:

McMaster-Carr
McMaster-Carr

 

[#41]

In addition, stuff can fly around in the trunk, so as far as placement goes advise to put it in an enclosed plastic box with an external vent. Resist the urge to tuck it under the quarter/trunk gutter. Make it easy to remove/replace/service even though it will take up a little more trunk space.

 

[dvw]

Many new cars have the battery located outside of the engine compartment. NONE have solenoids or fuses in line with the main positive cable. None have a separate ground cable to the front of the vehicle. It all comes down to sensible routing. Many newer battteries have a small vent hose that simply goes through a hole in the floor. Or use a gel battery. As far as a legal cut off switch, it must be in the posistive side. It must also kill the engine. The easiest way to do this? use a 4 terminal switch. Wire the feed from the ignition switch to the ignition box through the small seconday terminals. That way the engine shuts off with either the ignition switch or the safety switch. Even if the car isn't raced it's still nice to have at least a main cut off switch for battery disconnect while parked. Doesn't have to be accessable. Nice for working on the car or as a theft device.
Doug

 

[65CopCar]

Many new cars have the battery located outside of the engine compartment. NONE have solenoids or fuses in line with the main positive cable. None have a separate ground cable to the front of the vehicle. It all comes down to sensible routing. Many newer battteries have a small vent hose that simply goes through a hole in the floor. Or use a gel battery. As far as a legal cut off switch, it must be in the posistive side. It must also kill the engine. The easiest way to do this? use a 4 terminal switch. Wire the feed from the ignition switch to the ignition box through the small seconday terminals. That way the engine shuts off with either the ignition switch or the safety switch. Even if the car isn't raced it's still nice to have at least a main cut off switch for battery disconnect while parked. Doesn't have to be accessable. Nice for working on the car or as a theft device.
Doug

I agree that new cars probably don't fuse the positive cable. But that to me is not an accurate argument for our drag cars. Usually the cables are run on the inside or outside of the frame rails in our cars and the batteries have a lot of available energy (more so than most new stock vehicles). In the event of an accident, or in the course of us working on our cars, there is a probability that the cable can get pinched. That is what we are trying to protect against. Its cheap and easy to do. I also fuse at the alternator and the alternator feed wire at the battery.

I have heard the arguments about needing a ground cable to the front of the vehicle. In my experience and testing I just don't see the need for it.

As far as the positive side needing to be the one with the disconnect, that changed over the years. I don't know what decade it was, but I had this conversation with the head NHRA tech guy and he clearly told me that it could be on the negative side. My oldest NHRA book is 2012 and it says positive side.

 

[70bigblockdodge]

I don't understand the point of switching the negative side.

It kills everything. No negative, then positive has nothing to work with. One bad point to negative switched off is if the positive shorts to the car body and you grab the door handle with no shoes in the rain you would be the ground (1/2 amp kills).

 

[gkent]

Here’s my thinking on negative disconnect …

All vehicles run off the alternator - battery is only used for starting. Alternator is grounded through the body.

Our stock wiring runs direct from the battery to starter and from the alternator to the starter relay where it branches to the fuse box and to the battery.

Assuming you relocate the battery to the trunk but maintain the same wiring configuration, a disconnect on the positive battery cable will NOT shut a car off, it will only prevent it from starting. However, in that same configuration it will prevent the battery from receiving any charge current from the alternator.

By the same token, because the alternator is grounded to the engine and subsequently the body, a disconnect on the ground battery cable also will not shut the car off - since the positive current from the alternator is still running through the starter relay.

So in all cases, the "shut off" in either positive of negative battery cable alone will not shut a car off.

So as far as NHRA rules go, there has to be some other component not mentioned that will shut down a running engine and the rest of the electrical system. What is it ???