Battery in the Trunk

[TC]

What do I need to know so that it is NHRA legal.

Do you have to use a Battery Box and can I run the battery cables on the inside of the car.

[Scott Liggett]

Re: Battery in the Trunk

What do I need to know so that it is NHRA legal.

Do you have to use a Battery Box and can I run the battery cables on the inside of the car.

I don't know about the cables, but the box is necessary, as is a exterior cut off switch. At least that's what I could remember from the book.

[squirrel]

Re: Battery in the Trunk

Really helps to have the rulebook....battery needs to be mounted with a certain size of bolts and steel strap, configured a certain way, needs a cutoff switch that will stop the engine, and likely a metal firewall at the back seat opening.

[TC]

Re: Battery in the Trunk

I have the metal divider between the trunk and passenger compartment, so I'm good there. And I knew about the cut off switch.

And your right I should really get a rule book. So does anyone know where I can get one online.

[min301]

Re: Battery in the Trunk

I have the metal divider between the trunk and passenger compartment, so I'm good there. And I knew about the cut off switch.

And your right I should really get a rule book. So does anyone know where I can get one online.

Here.

http://store.nhra.com/

[Loren]

Re: Battery in the Trunk

Two 3/8" bolts, attatched to the frame, in a sealed box vented to the outside unless the trunk compartment is sealed off...again w/ the rulebook, huh...Don't know about the cables either. I wouldn't run 'em inside either way in case there were ever a serious short, like in a collision situation...that copper gets red-hot and frys whatever it's touching even as the battery starts burning, while still providing huge electricity. I have experienced a battery melt-down in a boat, and an explosion in one of my El Caminos (BAM!, then acid everywhere) and "ugh", it's a mess. Something to keep in mind.

[TC]

Re: Battery in the Trunk

Thanks Min for the link.

And I was just asking about running them on the inside because my '71 Camaro has so much bracing on the under side of the car that it's making running the fuel line a bitch, so I can't image the fun I'm going to have routing the battery cables.

[Loren]

Re: Battery in the Trunk

To be honest, we also have a '67 Mustang w/ the battery in the trunk, and I ran the cable inside. But that was before the boat thing...I'd be curious what other people had to say.

[milner351]

Re: Battery in the Trunk

I'd be curious to know what the rule book says about the battery cable routing.

I had a '70 mustang with batt in trunk - steel factory divider was part of the fold down option - so I passed tech with that.

I used 3/8 threaded rod through the trunk floor and rear sub frame, and routed the ground cable to that.

Positive cable (I used welding cable) ran over the wheel well on the inside of the quarter through the door opening, under the sill plate, through the kick panel area, then through the firewall (I used the heater hose hole - it was a race car with no heater box) through a rubber insulator up to the starter.... come to think of it, I didn't have a circuit breaker anywhere in that run, and if that cable would have been shorted to any of that metal I ran it through - the battery would have melted down....

I'd really be interested to know if NHRA / IHRA / etc require some kind of breaker / fuse in that + cable.

[squirrel]

Re: Battery in the Trunk

I don't know of any requirement for a fuse/breaker, and finding one that will handle 500 amps or whatever it is would be fun.

I think the meltdown issue is why I have the battery near the engine in my stuff.

[Huskinhano]

Re: Battery in the Trunk

I don't know of any requirement for a fuse/breaker, and finding one that will handle 500 amps or whatever it is would be fun.

I think the meltdown issue is why I have the battery near the engine in my stuff.

As an electrician what I have to say about a 500 amp fuse is this. Older non permanent magnet starters are what is called a series wound motor. The heavier the load, the more torque, the more electric. also electric motors have what's called Locked Rotor Amps or LRA which means exactly what it says. It's the amount of amps a motor will draw if you were to hold the shaft stationary and turning the motor on. This amount is close to a short circuit and is about 10 times the current of a motor under full load or FLA, Full Load Amps. You can get the picture that you can end up with a really big fuse!

Depending on the type of fuse you can go up to 800% of the full load amps of the motor. While this fuse may seem like it'll never offer protection, the main purpose of a fuse in a motor circuit is not for overload protection of the motor but to protect the wiring on a short circuit. Fuses are excellent in providing short circuit protection even at wildly over sized. Fuses offer far better protection on short circuits then any circuit breaker could hope to. Circuit breakers are limited to their mechanical speed. Fuses and circuit breakers all have inverse time charts for the amount of time it takes to clear an overload vs the amount of overload.

A little tid bit. There are some motors that do not have any short circuit or overload protection and are allowed to run like this. These are fire pump motors for sprinkler systems.

One could always mount a solenoid in the trunk to disconnect the unfused wire to the starter while having a second fused wire supplying power for the fuse block.

[Loren]

Re: Battery in the Trunk


[/quote]
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One could always mount a solenoid in the trunk to disconnect the unfused wire to the starter while having a second fused wire supplying power for the fuse block.
[/quote]

So the big/fat wire is only hot when the starter's going. The other to the fuse box has the usual fusible-link or 50amp fuse like you get with a Painless kit.

Very good answer to the melt-down problem.

[Caddyman]

Re: Battery in the Trunk

I thought everybody did that ^. ???

I've always had a FRod starter sol in the trunk next to the battery (race/hot-rods). The entire batt circuit is opened with the cut-off switch on the ground side, and the big wire to the starter is only hot when "sol" is engaged.

The only "big" wire runs up the rail (or in this case, inside the car) to the starter, which is jumped with a small terminal/big terminal wire to keep the starter sol "engaged" any time the batt post has power from the rear "starter" sol.

It keeps all the "small" wiring (10ga or smaller) inside, usually cleans up the engine bay, and allows for "clean" power away from the generator. You can rewire the start circuit to the trunk, and many times a lot of other wires, too.

You can run an 8-10ga (depending on your loads) wire back to the ignition switch input and/with/or all the way to the trunk to charge the battery, with some jump-offs along the way for other stuff (msd, blower high relay, ect)...which can be mounted inside anyway. I call it my "mainline".

You'd be amazed how much cleaner an engine looks with only a couple wires under the hood, instead of the rats nest of stuff hooked to a starter, gen output, and high-blow relay, along with all the fusible links. All that can be moved elsewhere, inside, to a "hot" post with wires to/from the battery, outputs to the ign switch, fusible links to the fuse box, ect........instead of several fuse links/wires hooked to the back of each the generator and starter, doing the same thing, except for being 4ft longer.

Just look under the hood of a late model.

Theres usually a fusible link box. It works well for the inside installation to make a "hot" post for everything to hook to.

[Huskinhano]

Re: Battery in the Trunk

I thought everybody did that ^. ???

I've always had a FRod starter sol in the trunk next to the battery (race/hot-rods). The entire batt circuit is opened with the cut-off switch on the ground side, and the big wire to the starter is only hot when "sol" is engaged.

The only "big" wire runs up the rail (or in this case, inside the car) to the starter, which is jumped with a small terminal/big terminal wire to keep the starter sol "engaged" any time the batt post has power from the rear "starter" sol.

It keeps all the "small" wiring (10ga or smaller) inside, usually cleans up the engine bay, and allows for "clean" power away from the generator. You can rewire the start circuit to the trunk, and many times a lot of other wires, too.

You can run an 8-10ga (depending on your loads) wire back to the ignition switch input and/with/or all the way to the trunk to charge the battery, with some jump-offs along the way for other stuff (msd, blower high relay, ect)...which can be mounted inside anyway. I call it my "mainline".

You'd be amazed how much cleaner an engine looks with only a couple wires under the hood, instead of the rats nest of stuff hooked to a starter, gen output, and high-blow relay, along with all the fusible links. All that can be moved elsewhere, inside, to a "hot" post with wires to/from the battery, outputs to the ign switch, fusible links to the fuse box, ect........instead of several fuse links/wires hooked to the back of each the generator and starter, doing the same thing, except for being 4ft longer.

Just look under the hood of a late model.

Theres usually a fusible link box. It works well for the inside installation to make a "hot" post for everything to hook to.

I thought that's what a lot of people did too. I only mentioned it because I didn't see anyone else suggest it. I wonder what the OEMs do when they mount the battery in the trunk or other locations?

[squirrel]

Re: Battery in the Trunk

I don't know of too many cars with other battery locations...68-82 vettes have it behind the seat, but there's a lot of fiberglass to route the cable along, and it's not really very far to the starter from there.