Battery relocation

[rayray086]

Not really audio-related but my application is, and most of the wiring/electrical gurus are in here. I want to relocate my battery to the boot where it's closer to the amplifier I'll be hooking up. I thought it was a good idea anyway as relocating to the boot yields many advantages (weight distribution, more space in the engine bay, less wiring) and by using maintenance-free batteries, I wouldn't have to worry about gas build-up or acid spills.

So what's really involved? I've been looking up some info and guides on the internet but like most guides, they explain everything as if you already understand how it all works - I don't So my question for now is, (1) how is the battery hooked up? Where do the wires connected to the negative and positive terminals go? I have a faint idea that the negative is connected to the chassis/frame (ground), and the positive is hooked up to the engine, but I see a one or two other wires. Where else do they go, and for what purpose?

My problems are understanding those points and knowing what other components do (distribution block, circuit breakers, different gauge wires etc). I'll ask questions on those once I understand the first bit! Doing the actual install in the boot I'm confident with though.

In need of knowledge! Cheers.

[Tim]

im keen on this one as well.

[Peter Jones]

It's pretty straight forward, but you have to consider your earthing very carefully.

You can run two cables back to the engine bay or you can earth the battery in the boot and run one. If you earth the battery in the boot you should upgrade the chassis to engine block strap.

I have a BMW 318is that has the battery in the boot as standard. It has some pretty neat terminal blocks that could be adapted into a conversion.

The wires off the positive of your battery are

1 Starter solenoid. This is where you should run your cable in the boot to.
2 Alternator you could rerun this to pick up the new battery lead on the starter motor.
3 Power to the fusebox. Also run this to the bolt on the starter motor.
4 All the other stuff (in the case of a MK1) is probably dodgy relays installed by auto sparkys rather than fixing things properly. Again you could pick up battery power from the starter motor.
5 Stuff I've forgotten about like glow plugs etc. Same again.

If you have to extend any cables make sure you use the same diameter cable. A trip to the wreckers would be a good idea, then you can cut matching chunks out of another loom and even match up the colours. The wreckers don't charge much for cable.

I'd not run cable smaller than 35mm. Copper is expensive at the moment so it won't be cheap. Somewhere that sells cable for welding is a good bet. You should get them to crimp copper lugs on the end of the cable too, they'll have the tools to do it.

The engine block should be properly earthed to the chassis with a lead of the same size (35mm). Don't rely on the stock cable they're too small to start with. Make sure the boot earth connection and the engine earth connection are both into the chassis itself and not any removable panel or part. Remove the paint from under the connection, vaseline can be used to seal the joint. A good point to connect the earth cable to the motor is the starter motor mounting bolts.

The cable will also add some weight you may need to consider this for race application.

I saw some cheap battery boxes in Kmart the other day, being sold for boating use I think.

Think about putting in a battery isolation /kill switch, now's the time to do it. As an added bonus you can stick one of those cool blue triangles on your car to show the marshals / fire brigade where it is!

Make sure that the cable is well protected with grommets, heater hose conduit or whatever it takes to make very very sure it can't be shorted out. There were many aircooled VWs lost to back seat fires because cables and battery lids weren't maintained.

Make sure that battery in the boot is mounted rock solid. You don't want it rolling around in there.

Hope this gives you guys some ideas.

Pete

[rayray086]

That's fantastic info Pete. Just some questions/comments on what you've mentioned...

All the wires that run off the positive terminal of the battery - I could get a new distribution block, route a massive wire (0 gauge?) to it, and run all the other wires off that to all the locations that you've mentioned? Like so:



I've read that running a larger diameter wire would be even better in terms of reducing voltage drop. Are there any other disadvantages besides cost, size and weight? I'll be running speaker/sub amps so I'd like to use as thick of a cable as possible.

With the earthing (just to reiterate), I need to connect the negative terminal of the battery to a point on the chassis, AND one from the starter motor to the chassis? Lots of the articles I've seen online use vaseline to prevent rusting around the earthing point, but I have cold gal and fish oil - will either be a good alternative?

I'm well aware (and scared) that a fire would occur due to shorts in such a long winded circuit, and I've read people have put in "circuit breakers" to ensure that doesn't happen. I've read that the issue with a CB is that they might not be able to take high currency, like during engine start. I know that most of these CBs that you can buy nowadays have a 10 second tolerance level to high currency and aren't too troublesome in a daily driver. I know I will have the cables/wires insulated well and tied on to the chassis where chafing is kept to an absolute minimum, but is it still worth getting a CB?

As for the kill switch - I know it's not just as simple as wiring it in series between the positive terminal and starter motor as the car would still be running if you activate it; there's some more wiring involved. Do you happen to know the exact procedure (or know of a DIY article) for implementing a kill switch?

Again, thanks for your help Pete!

Edit: One more question! With a sealed battery, is it still required to have good ventilation? I'd like to either mount the battery in a box, or fab up a small compartment in the boot so that it looks more clean and not exposed.

[rayray086]

Oh, and those that are familiar with the Mk3 2.0L engine bay, this is the distribution block right?

[Peter Jones]

My comments in RED below.

All the wires that run off the positive terminal of the battery - I could get a new distribution block, route a massive wire (0 gauge?) to it, and run all the other wires off that to all the locations that you've mentioned? Like so:

Yep, that's a neat block in the pic below, similar to how BMW do it. Otherwise you could just use the terminal on the starter solenoid to terminate all the positive cables. Gauge 0 equates to about 50mm2 so that should be fine.

I've read that running a larger diameter wire would be even better in terms of reducing voltage drop. Are there any other disadvantages besides cost, size and weight? I'll be running speaker/sub amps so I'd like to use as thick of a cable as possible.

Correct , but you're going to running your amps directly off the battery in the boot. The voltage drop to be concerned about here is the voltage drop to the starter motor. The cable has to be big enough to handle the load of the starter motor. Once the car is running you're also using this same cable to charge the battery, it will be more than big enough to do so if it can start the car ok.

With the earthing (just to reiterate), I need to connect the negative terminal of the battery to a point on the chassis, AND one from the starter motor to the chassis?

YES. Specifically one of the mounting bolts on the starter motor. It would also be a good idea to check that your alternator is also properly earthed to the engine block. Some MK I s have the alternator isolated from the block by the rubber mounts and have to have a small earth strap in place to work properly.

Lots of the articles I've seen online use vaseline to prevent rusting around the earthing point, but I have cold gal and fish oil - will either be a good alternative?

I don't know about the fish oil. You could use just a thin smear of vaseline on the mating surfaces of the joint and then spray over it with the cold gal.

I'm well aware (and scared) that a fire would occur due to shorts in such a long winded circuit, and I've read people have put in "circuit breakers" to ensure that doesn't happen. I've read that the issue with a CB is that they might not be able to take high currency, like during engine start. I know that most of these CBs that you can buy nowadays have a 10 second tolerance level to high currency and aren't too troublesome in a daily driver. I know I will have the cables/wires insulated well and tied on to the chassis where chafing is kept to an absolute minimum, but is it still worth getting a CB?

The trouble is that the starter motor can pull several hundred amps form the battery when it's cranking. You know those CCA numbers on the battery. That's a measure of the Cold Cranking Amps that the battery can supply for one minute. A Golf probably has battery capable of about 300 CCA.

If you can find a 300 amp fuse (They are available) it doesn't really help you much. You'll still be starting fires because so much current is available. Arc welders run at about 80 amps to weld 3mm thick steel. You'll have 300 amps trying to fuse 1mm thick steel. With 50mm2 cable and 300 amps to play with you could probably melt your entire car. The good news is that the battery will go flat or explode long before that happens.

So no a CB probably won't be of any use.

As for the kill switch - I know it's not just as simple as wiring it in series between the positive terminal and starter motor as the car would still be running if you activate it; there's some more wiring involved. Do you happen to know the exact procedure (or know of a DIY article) for implementing a kill switch?

A kill switch should isolate the battery completely. This may not stop all cars from running though - so some battery isolation switches have an auxiliary lower current switch built into them for what ever circuit needs to be isolated.

I'd be pretty surprised if a MK III Golf kept running with it's battery removed from circuit. Typically alternators can't produce power without a battery connected. Early aircooled VWs with generators can run with the battery disconnected as can cars with magneto ignitions.

Again, thanks for your help Pete!

You're welcome!

Edit: One more question! With a sealed battery, is it still required to have good ventilation? I'd like to either mount the battery in a box, or fab up a small compartment in the boot so that it looks more clean and not exposed.

A sealed battery will be OK under normal circumstances. Your enclosure should still be vented though. A small plastic tube to outside the car should be enough. Sealed batteries have safety vents to prevent the battery from exploding under fault conditions such as overcharging or over current due to short circuits. You need to have a way for this pressure to escape your box too.

Pete

[rayray086]

Excellent!

Correct , but you're going to running your amps directly off the battery in the boot. The voltage drop to be concerned about here is the voltage drop to the starter motor. The cable has to be big enough to handle the load of the starter motor. Once the car is running you're also using this same cable to charge the battery, it will be more than big enough to do so if it can start the car ok.

Would an 8 gauge cable be suitable here, or better to use a 4 gauge? Some of the distribution blocks I see have 8 gauge thickness outs.

The trouble is that the starter motor can pull several hundred amps form the battery when it's cranking. You know those CCA numbers on the battery. That's a measure of the Cold Cranking Amps that the battery can supply for one minute. A Golf probably has battery capable of about 300 CCA.

If you can find a 300 amp fuse (They are available) it doesn't really help you much. You'll still be starting fires because so much current is available. Arc welders run at about 80 amps to weld 3mm thick steel. You'll have 300 amps trying to fuse 1mm thick steel. With 50mm2 cable and 300 amps to play with you could probably melt your entire car. The good news is that the battery will go flat or explode long before that happens.

So no a CB probably won't be of any use.

OK, seems like I'll save on not putting a CB in. However, I have heard from other people that there are CBs out there rated at 140A but have a mechanism whereby it can sustain high amps (300+) for a short period of time, like 10 seconds, to allow for high surges like during setup. I'd like to know if these are suitable?

A kill switch should isolate the battery completely. This may not stop all cars from running though - so some battery isolation switches have an auxiliary lower current switch built into them for what ever circuit needs to be isolated.

So, the kill switch will simply be implemented in the cable that connects the battery to the starter motor? Where is usually a suitable position to mount a battery kill switch? In the cabin near the driver's control, or at the back?

Cheers!

[Peter Jones]

Would an 8 gauge cable be suitable here, or better to use a 4 gauge? Some of the distribution blocks I see have 8 gauge thickness outs.

Whatever fits in the Amp I guess. Mostly it's cosmetic. People generally run much bigger cabling than they really need for stereos. 8 Gauge equates to about 8.4mm2 which is pretty large cable. 4 Gauge is around 21mm2. Most houses only have 16mm2 lead in cables from the street for their mains power!

The battery to Starter motor cabling needs to be at least 35mm2.

OK, seems like I'll save on not putting a CB in. However, I have heard from other people that there are CBs out there rated at 140A but have a mechanism whereby it can sustain high amps (300+) for a short period of time, like 10 seconds, to allow for high surges like during setup. I'd like to know if these are suitable?

Maybe but 140 amps is still enough to weld with! Most car manufacturers don't fuse their batteries. It would be very hard to actually blow a 140 amp CB in a Car. You could load up the electrical system and get there but a fault to ground may not trip it out. Whatever the cable shorted against would probably blow before the fuse.

So, the kill switch will simply be implemented in the cable that connects the battery to the starter motor? Where is usually a suitable position to mount a battery kill switch? In the cabin near the driver's control, or at the back?

The kill switch is connected directly to the positive battery terminal. Everything else is connected to the kill switch. If you're racing it should be accessible from outside the car. If it's a street car I wouldn't do that because a pedestrian could turn your car off! Putting it next to the battery in the boot is easy. Some people have them on the dash or under the bonnet. I'd probably mount it next to your battery. It's not usually something you need while you're driving along and you wouldn't want your passenger to say "what's this do" and turn your car off while you're mid corner on the freeway.

They typically have a big red key which can be removed as a security feature but the the stereo you're considering remember that actually using it will need any security codes etc to be re-programmed.

Here's a typical switch. They're usually rated around 2500 amp for 10 seconds , so they'll have no problems with starter currents. You'll have to choose one that will cope with your total system load. 100 amps seems typical of these switches.


I did a bit more reading and it seems that some cars WILL run on their alternator with the battery disconnected, so you would need to have the alternator wiring setup through the auxiliary contacts on the kill switch. We're probably headed into auto-electrician territory here. Without actually seeing the car and how it's all wired up there's probably not much more advice I can give other than to see an auto-electrician to make sure it's done properly.

Pete

[rayray086]

They typically have a big red key which can be removed as a security feature but the the stereo you're considering remember that actually using it will need any security codes etc to be re-programmed.

Here's a typical switch. They're usually rated around 2500 amp for 10 seconds , so they'll have no problems with starter currents. You'll have to choose one that will cope with your total system load. 100 amps seems typical of these switches.

Oh yes! Saw those today at Repco when I was window shopping around for the parts. Think I'll be picking one of those up.

I did a bit more reading and it seems that some cars WILL run on their alternator with the battery disconnected, so you would need to have the alternator wiring setup through the auxiliary contacts on the kill switch. We're probably headed into auto-electrician territory here. Without actually seeing the car and how it's all wired up there's probably not much more advice I can give other than to see an auto-electrician to make sure it's done properly.

Should I just wire in the kill switch for the moment, and have an auto-electrician check it and make the necessary adjustments? Like you said before, since I'm doing the relocation I might as well implement it in so I don't have to fork out more money to get more cables (yes they're not cheap - $14/m for 2 gauge)

Thanks again Pete, you've been a fantastic help with answering my questions. I will be writing a DIY later on to document my relocation - it'd be great if you could glance it over for me to see if I did anything wrong!

[rayray086]

Just a few more things that I'm doubtful over.

My plan is to run a 2 gauge cable from the battery (in the boot), to the dist. block (in the engine bay). It will then branch off to two 4 gauge cable; one to the starter motor and another to the alternator. Other components of the electrical system (fusebox and anything else) will be connected via the starter motor, using 8 gauge. Is this OK?

And now the EARTHING!
I will run 2 gauge cable to earth the negative terminal on the battery to the chassis (boot), and engine block to the chassis.
I will have to earth the starter motor to the chassis, and alternator to the engine block, is that correct? Can I just run 8 gauge cable for this? Does the alternator have to be earthed to the chassis?
With earthing, do we use the same mounting points as used to connect to battery positive/dist. block/other components of the electrical system? Do we have to earth all the components of the electrical system, like the fusebox too?

Yes some are very noobish questions but I can never wrap my head around electrical wiring stuff!