One of the common mods to older muscle cars is to relocate the battery to the right side of the trunk. The reason for this is traction. Those cars were front heavy to begin with, so moving 75 pounds from the front to a location right over the tire likely to spin when the driver pops the clutch is a relatively cheap way to improve the 1/4 mile time at a race track.
The issue of safety, primarily fire in the event of a crash, was addressed by the race track sanctioning bodies, the NHRA in the US. Any car having a relocated battery in the trunk is not permitted to race on a NHRA track unless a battery disconnect switch that can be operated from outside the vehicle is installed.
I am not aware of any new production muscle car with the battery in the trunk, but I have not looked at any of the factory hot rods since the mid 2000's, so I don't know how it's done today.
I put the battery in the trunk of my 1973 Challenger using a piece of fat welding cable from the battery to the starter, and a somewhat thinner piece for the ground return in addition to tying the return to the car body at both ends. The Powermaster 1.5 HP starter would draw over 400 amps when attempting to hot start a 7.1 liter V8 with 10:1 compression. I ran the cables underneath the car in semi-flexible PVC tubing made for that purpose
Fuses would be unsafe, as they are prone to other modes of failure, and the battery has critical systems connected to it. In the old days fusible links were used, not sure what the current technology is.
Here's how it's done in my car. A fuse in the rear, I'm not sure if there's a fuse in the front.
RealOEM.com - Online BMW Parts Catalog
What critical systems are you concerned for? If the fuse blow while driving, all systems will still be powered by the alternator.
The last NHRA rule book I had was 2003. I haven't raced since then. The rules only applied if the car had been modified. If the car was "factory stock" it could run on a NHRA track provided it didn't go faster than 12 seconds in the 1/4 mile. In 2003 there weren't too many bone stock cars that fast. Now you can get one at any of the three US manufacturers dealerships provided you are willing to spend some serious $$$$.
My friend used to have a 1999 GMC Yukon SUV (like a Chevy Surburban). It had a large fuse under the hood that was in series with everything on the positive terminal of the battery except the starter. The label on the fuse did not have an amperage rating, only the letters "MEGA."
GM used to have fusible links. They tended to make a mess of the wiring harness when they blew......ditto the resistance wire that fed the ignition coil. Chrysler had the famous white brick ballast resistor on the firewall. At least when it blew you could get home with a paper clip.....then replace the points (OK, I'm an old fart).
Your failure mode isn't the one of concern. The idea was to provide power to emergency lights like brake lights and hazard lights as long as there was any power in the battery at all, hence things like fusible links.
In any case I should have been more precise in my language. I should have said generic fuses are unsafe. I realize modern cars have fuses in critical things like brake lights and so on, but they probably are meeting some automotive specification and design and form factor that allows them to be deemed safe.
Point about rear-mounted car battery - yes the Mini had one from first launch to last build - c.45yrs, from 1959!
as for BMWs since 80s with one: e34 5 series did, c.200A fusible link at the battery end; E39 ('95-03) use(s)(d) an even more complex set-up, with a distributed power architecture, a local , very-high current fusible link console next to the battery feeding major modules from it (few outlinks under 63A each) and a battery +ve connector linked to the SBS system that explosively disconnects the +ve battery connection in case of accident; it is totally reliable (in the sense - it's been out there 23 years, and no-one picks up on it online as a source of failure, not ever; and lord knows how specialist-marque forum owners like to whinge given even half a chance...)
Also helps in both cases the cables run front-rear are double-insulated and positively huge - c.18mm dia core: a lot of copper. In the E39 there's also a short +ve lead from alt+ / starter +ve junction, to a charging/jump +ve terminal in the engine bay; a nice touch.
tl;dr: no issue at all - when done right.
as for BMWs since 80s with one: e34 5 series did, c.200A fusible link at the battery end; E39 ('95-03) use(s)(d) an even more complex set-up, with a distributed power architecture, a local , very-high current fusible link console next to the battery feeding major modules from it (few outlinks under 63A each) and a battery +ve connector linked to the SBS system that explosively disconnects the +ve battery connection in case of accident; it is totally reliable (in the sense - it's been out there 23 years, and no-one picks up on it online as a source of failure, not ever; and lord knows how specialist-marque forum owners like to whinge given even half a chance...)
Also helps in both cases the cables run front-rear are double-insulated and positively huge - c.18mm dia core: a lot of copper. In the E39 there's also a short +ve lead from alt+ / starter +ve junction, to a charging/jump +ve terminal in the engine bay; a nice touch.
tl;dr: no issue at all - when done right.
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I'll go down on monday to the store that I'm getting it done at and ask them what kind of conduit they are going to put the wire into.
I will also ask them if its possible to drill a hole just above the hose which comes out from the air conditioner drain hose, there is some space there which if properly drilled should allow me to run the 70mm2 cable through the firewall and into the cabin. They are really busy however so I don't like my chances on that, might have to get them at a less busy time.
If their conduit is simple plastic and won't handle road rash I'll just do it myself and run it through the firewall with some help from relatives.
Probably a good thing because I do need to get underneath there and wash it all out from the previous owner who left a tappet cover gasket go for too long and a burst power steering hose which the previous owner fixed.
And I get to keep the stands.
I will also ask them if its possible to drill a hole just above the hose which comes out from the air conditioner drain hose, there is some space there which if properly drilled should allow me to run the 70mm2 cable through the firewall and into the cabin. They are really busy however so I don't like my chances on that, might have to get them at a less busy time.
If their conduit is simple plastic and won't handle road rash I'll just do it myself and run it through the firewall with some help from relatives.
Probably a good thing because I do need to get underneath there and wash it all out from the previous owner who left a tappet cover gasket go for too long and a burst power steering hose which the previous owner fixed.
And I get to keep the stands.
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I'm the proud owner of a car with two batteries.. LOL One in the engine compartment and the other in the trunk (boot). E class Mercedes have rather a lot of electronics in them so the second battery provides power for those devices when the engine is not running so that the starting battery cannot get run down. The trunk (boot) battery is about 12AH, and is a wet plate lead acid battery interestingly enough. Not surprisingly the alternator in this car is somewhat big at 180 amps.. I remember when 60A was considered gigantic, guess that dates me a bit.
wow! I can't imagine 12AH could power much over a long period but still wow. wet plate too.
180 amps is rediculous! Mine tops out at 80 amps. 90's cars weren't an entertainment system though they were a transportation device
I've gone down and had a look again at the area where I'm considering cutting a hole for the 70mmSQ cable. But it looks more and more likely that I will probably be relegated to the fact that I cannot run it through the cabin of the car.
I've attached 3 pictures and the 2nd one shows a likely candidate where I would be drilling a hole, just above where the air condenser drain hose currently is.
This area is supposedly free of fuel and brake lines but of course I will need to be 100% sure before I or anyone else does any drilling. Everywhere else on that floor panel is covered in fuel and brake lines which go to the back of the car or the power steering rack gets in the way, not even kidding, its a tight close quarters area in there. And the wheel well is where the exhaust is. So we are literally about 2-3 inches away from the exhaust manifold and catalytic converter, both which run very hot.
In other news the 3rd picture shows a likely spot for placing the 2 channel pioneer amplifier for driving the 2 front speakers. I'm thinking of placing it here and not underneath the seat just so I can keep cables short as possible.
This means that the 2 channel amp will then have its own connection to the battery in the engine bay independent of the subwoofer cable run, which is great for me.
The amount of footwell space taken up by the amp is minimal and shouldn't give anyone issues.
Anyway this is all hypothetical stuff, everything is still in the design stage for now.
I've attached 3 pictures and the 2nd one shows a likely candidate where I would be drilling a hole, just above where the air condenser drain hose currently is.
This area is supposedly free of fuel and brake lines but of course I will need to be 100% sure before I or anyone else does any drilling. Everywhere else on that floor panel is covered in fuel and brake lines which go to the back of the car or the power steering rack gets in the way, not even kidding, its a tight close quarters area in there. And the wheel well is where the exhaust is. So we are literally about 2-3 inches away from the exhaust manifold and catalytic converter, both which run very hot.
In other news the 3rd picture shows a likely spot for placing the 2 channel pioneer amplifier for driving the 2 front speakers. I'm thinking of placing it here and not underneath the seat just so I can keep cables short as possible.
This means that the 2 channel amp will then have its own connection to the battery in the engine bay independent of the subwoofer cable run, which is great for me.
The amount of footwell space taken up by the amp is minimal and shouldn't give anyone issues.
Anyway this is all hypothetical stuff, everything is still in the design stage for now.
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Here I've drawn some lines to detail where its off limits. basically everywhere but the red circles and the immediate area around them are off limits.
Even if I were to run the 70mmSQ cable underneath the car it wouldn't contact the road, there are chassis beams running the entire length of the car going back to the boot which the cable can run up against and be protected by road rash, in addition to this the suspension and steering components are lower than these points. So the likelihood of the cable being damaged is low.
I also intend on raising the car 23mm above the stock ride height.
So things as they are now if I can power the subwoofer independently of the front amplifier AND I add a fusible link in the engine bay AND I don't relocate the battery to the boot AND I put the cable in some reliable conduit it should be safe.
If I run the 70mmSQ cable on the outside of the cabin I can then run a 16mmSQ cable to the 2 channel amplifier underneath the passengers seat from a second hole drilled in the firewall. I highly doubt that I will be able to run both 70mmSQ cable and a 16mmSQ cable and the aircon drain hose all in that area, I will most likely run out of room.
So the plan for monday is to go down and check their conduit out, see if its worth its salt, ask them if they can run it somewhere in the firewall (up behind the dash I'm thinking) then if it is order the parts online and get them to put the 70mmSQ cable in and run it either through the firewall or outside of the car to the boot where it will be used only to power the subwoofer amplifier (yet to be ordered).
Tomorrow I'll take the glovebox back out and see if there is any room up along the vertical part of the firewall where I can run the 70mmSQ cable and not run into things like fuel and brake lines.
Then come back and drill a second small hole for running 16mmSQ cable to the 2 channel amplifier located underneath the passengers seat.
If you are eagle eyed you can also see that I already have a 6mmSQ cable run made out of solar power cable (double insulated, extra thick, much wow) specifically for running ham radio gear which I intend on installing on the passengers side just underneath where the current tom tom GPS is located. Specifically a Yaesu FT-857 transceiver.
Even if I were to run the 70mmSQ cable underneath the car it wouldn't contact the road, there are chassis beams running the entire length of the car going back to the boot which the cable can run up against and be protected by road rash, in addition to this the suspension and steering components are lower than these points. So the likelihood of the cable being damaged is low.
I also intend on raising the car 23mm above the stock ride height.
So things as they are now if I can power the subwoofer independently of the front amplifier AND I add a fusible link in the engine bay AND I don't relocate the battery to the boot AND I put the cable in some reliable conduit it should be safe.
If I run the 70mmSQ cable on the outside of the cabin I can then run a 16mmSQ cable to the 2 channel amplifier underneath the passengers seat from a second hole drilled in the firewall. I highly doubt that I will be able to run both 70mmSQ cable and a 16mmSQ cable and the aircon drain hose all in that area, I will most likely run out of room.
So the plan for monday is to go down and check their conduit out, see if its worth its salt, ask them if they can run it somewhere in the firewall (up behind the dash I'm thinking) then if it is order the parts online and get them to put the 70mmSQ cable in and run it either through the firewall or outside of the car to the boot where it will be used only to power the subwoofer amplifier (yet to be ordered).
Tomorrow I'll take the glovebox back out and see if there is any room up along the vertical part of the firewall where I can run the 70mmSQ cable and not run into things like fuel and brake lines.
Then come back and drill a second small hole for running 16mmSQ cable to the 2 channel amplifier located underneath the passengers seat.
If you are eagle eyed you can also see that I already have a 6mmSQ cable run made out of solar power cable (double insulated, extra thick, much wow) specifically for running ham radio gear which I intend on installing on the passengers side just underneath where the current tom tom GPS is located. Specifically a Yaesu FT-857 transceiver.
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If you fit an additional aux battery in the boot you will have the local 'infinite' DC supply you want.
If this battery is isolated from the main battery by a series diode, or SSR or NO relay contact and this relay is operated from the acc line then you will get away with much lower rated cable that could be routed through the cabin.
The aux battery need not be very high capacity and will provide the solution you want.
A nibbling tool would easily 'customise' the aircon drain/cable hole.
Dan.
BTW, AM DB5 has battery under drivers side passenger seat.
If this battery is isolated from the main battery by a series diode, or SSR or NO relay contact and this relay is operated from the acc line then you will get away with much lower rated cable that could be routed through the cabin.
The aux battery need not be very high capacity and will provide the solution you want.
A nibbling tool would easily 'customise' the aircon drain/cable hole.
Dan.
BTW, AM DB5 has battery under drivers side passenger seat.
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Late 50's / early 60's VW Beetles had the battery under the rear seat on the passenger side. Makes for a hot seat when the sagging seat springs touch the top of the battery.
I believe the car in question was a 1959 bug (very small rear window). Eventually the battery well rotted completely out causing the battery to fall through to the street and break apart.
The car functioned reasonably well without a battery at all for several months. We were high school kids, there were usually several kids stuffed in the car, ample power for push starting. It did get rather tricky driving at night. The lights got dim at idle, so the driver needed to keep the revs up while stopped at a light, and rev it up whenever we saw a cop car.....dim lights were an excuse to be pulled over.
I believe the car in question was a 1959 bug (very small rear window). Eventually the battery well rotted completely out causing the battery to fall through to the street and break apart.
The car functioned reasonably well without a battery at all for several months. We were high school kids, there were usually several kids stuffed in the car, ample power for push starting. It did get rather tricky driving at night. The lights got dim at idle, so the driver needed to keep the revs up while stopped at a light, and rev it up whenever we saw a cop car.....dim lights were an excuse to be pulled over.
lol thanks for sharing tubelab, made me laugh.
I think I'll downgrade the cable from 70mmSQ to 35mmSQ. The sub amp is Class-D so the efficiency is going to be pretty high and I won't be driving my subs at 250 watts each, rather more like 150 watts or less each at most. Which means I can cut a corner and save some money.
The amp is rated for 500 watts RMS at 2 ohms, I intend on paralleling two 4 ohm drivers so that will give me 2 ohms and they are only small so I will be driving them at about 75-150 watts each. So that means most of the time it will be drawing anywhere between 300 watts and 500 watts. Nothing crazy for a 6 meter length of 35mmSQ cable.
Efficiency of Class-D amps drops to 50% at low power levels and increases to anywhere up to 90% at full power, so I'm told by wikipedia. So everything is within operating specifications.
At low power levels: 75 watts per driver x 2 = 150 watts + 50% efficiency = 300 watts.
At high power levels: 150 watts per driver x 2 = 300 watts 66.7% efficiency = 400 watts.
The limit for 35mmSQ at 6 meters and 13v is 540 watts for a 2.5% voltage drop so I'm well within safety margins.
Even if I did punch the amp at the full rated 500 watts RMS output at 2 ohms, I'm assuming that the efficiency will rise to at least 80% (being generous). which means that all I need to do is tack on another 100 watts to 500w output and I will still be underneath the 3% voltage drop rating of the 35mmSQ cable at 2.77% voltage drop for 600 watts drawn at 13 volts (accounting for a sagging alternator and battery output at that power level.)
This might also give me the option of running the cable in through the car and not outside.
I think I'll downgrade the cable from 70mmSQ to 35mmSQ. The sub amp is Class-D so the efficiency is going to be pretty high and I won't be driving my subs at 250 watts each, rather more like 150 watts or less each at most. Which means I can cut a corner and save some money.
The amp is rated for 500 watts RMS at 2 ohms, I intend on paralleling two 4 ohm drivers so that will give me 2 ohms and they are only small so I will be driving them at about 75-150 watts each. So that means most of the time it will be drawing anywhere between 300 watts and 500 watts. Nothing crazy for a 6 meter length of 35mmSQ cable.
Efficiency of Class-D amps drops to 50% at low power levels and increases to anywhere up to 90% at full power, so I'm told by wikipedia. So everything is within operating specifications.
At low power levels: 75 watts per driver x 2 = 150 watts + 50% efficiency = 300 watts.
At high power levels: 150 watts per driver x 2 = 300 watts 66.7% efficiency = 400 watts.
The limit for 35mmSQ at 6 meters and 13v is 540 watts for a 2.5% voltage drop so I'm well within safety margins.
Even if I did punch the amp at the full rated 500 watts RMS output at 2 ohms, I'm assuming that the efficiency will rise to at least 80% (being generous). which means that all I need to do is tack on another 100 watts to 500w output and I will still be underneath the 3% voltage drop rating of the 35mmSQ cable at 2.77% voltage drop for 600 watts drawn at 13 volts (accounting for a sagging alternator and battery output at that power level.)
This might also give me the option of running the cable in through the car and not outside.
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