toby69

Was wondering if anybody could advise of what size of fuse to use.

I'm planning relocating the battery to the boot.

Car is a 2002 bugeye

Thanks

alcazar

iTrader: (2)

I don't think you can fuse everything like that. The average modern starter can draw up to 600Amps for a cold start and no-one makes fuses THAT big.

Your best bet is to relocate, and run cables thick enough to take the current, back to the original connectors, which will split to fused and unfused circuits.

Remember that longer cables can cause volts drop, (lost voltage due to resistance in the cables), so use thicker than is already there.

I have seen folk use one positive cable and do the rest through the car bodywork.
Personally I wouldn't do that, I'd run a pair of cables, one to positive and one to negative. 600Amps etc is a HELL of a current to run through a bodywork connection!

toby69

Ok thanks for that, really wanted to stick a fuse as close to the battery as possible, just incase there is any issues later that may cause a short. I do plan to run positive and negative front to back

alcazar

iTrader: (2)

You could run them in like braided sheeths, but TBH, so long as you are careful where they run, use decent thick cable with decent insulation, you'll be fine.

MOST shorts or problems are caused by chafing, or loose wires, so run wiring through grommets, and solder all joins.

THIS: http://www.vehicle-wiring-products.e...e/homepage.php is an excellent site for all wiring needs. Not the cheapest, but quality stuff.

Wyorksautoectrical

Run a cable for the feed side, use 25mm and get the really flexi stuff ( get it from your nearest auto electrical place. On the negative side use same size and bolt it to the nearest place to where your going to fit your battery.
Any auto electrician you ask would not run the earth all the way back to the front it's absolutely pointless. All you would be doing is increasing volt drop.
The only time you would have to a earth wire all the way back would be on what you call a earth return vehicle ( petrol tankers) which don't have any earths to the body or chassis so if the get any wiring rubbing through to the body or chassis you don't get any shorts ( sparks) causing boooom if you know what I mean.

alcazar

iTrader: (2)

Whilst I value your opinion, I must take you up on volts drop......

There is likely to be FAR less volts drop running a single cable from battery to original connector, than trying to get a decent contact through the bodywork in two places.

With car electrics, ESPECIALLY Subaru earths, which are dodgy, do it once: do it right.

FMJ

iTrader: (2)

Big fuses for you:

http://www.ebay.co.uk/bhp/mega-fuse

They go up to about 500amps. Not sure which you will need and would quite like to know myself.

alcazar

iTrader: (2)

it would be worth knowing the current draw of the Subaru starter.
Could be as much as 600A instantaneous current.

bmposer

iTrader: (3)

I think 600A is a bit much, on a cold diesel car/small van iv only ever seen them draw up to around 150A.

If you wanted to fuse I would go for a 300A

FMJ

iTrader: (2)

After reading a few threads I am going 150amp and if it blows I will try 200amp. Will be doing it in a few weeks so will update.

alcazar

iTrader: (2)

Can I ask how you "saw" that?

Woooops........here's one, about 1/3 way down, that takes an intantaneous current of over SEVEN HUNDRED Amps.

OK, it's an Aston martin V12, but an Astra diesel at the bottom has instantaneous current of over 600A.

Wyorksautoectrical

I think you need to stop digging your hole now, I have been an auto electrician for over 25 year now and you don't ever see a starter motor on a car drawing the amps you have stated.
And also you say ESPECIALY earths on subaru cars?????? Which I can tell you they are a lot better than a lot of cars which we work on everyday at the Bosch auto electrical garage in which I work.
Like I said in my earlier reply ask any auto electrician if they would run a complete length of earth wire all the way from front to back rather than straight to the body.
The table below is easily found on the Internet, people like you are dangerous and you should stop guessing answers which I have read of yours and it makes it so clear that you don't really know what your talking about when it comes to auto electrical work.
• 4 cylinder gas engine -typically draws up to 160 amps
• 4 cylinder diesel -typically draws up to 350 amps.
• 6 cylinder gas engine -typically draws up to 210 amps.
• 6 cylinder diesel -typically draws up to 450 amps.
• 8 cylinder gas -typically draws up to 250 amps.
• 8 cylinder diesel -typically draws up to 650 amps.

alcazar

iTrader: (2)

I don't know what I'm talking about? I was wiring cars before you were a twinkle in your dad's eye.

The two graphs I posted were off the internet, all I did was Google starter motor current. Do you deny either is correct?

Do you further deny that LOADS of folk have had to fit special earthing kits to Subarus because the earth through the bodywork etc is so poor? Even poor enough that special kits are sold for it?

I don't really care about your 25 years fiddling with a Bosch machine that tells you want to do. I have a degree in Physics and know more about electricity than you could ever think of learning.

Start by explaining the difference between instantaneous and continuous current draw. THEN go on to explain what causes instantaneous current to be much higher than continuous current. Don't forget to mention the difference between EMF, Back EMF, Potential Difference and Voltage, will you? No searching Google....do it from your own extensive knowledge.......

Stick to replacing batteries and starters for exorbitant prices, and leave proper electrics to your betters.

Now.........how does THAT feel?

Next time you want to reply to someone, TRY not to be rude, eh? You'll only get it back in spades.

Jimbob

iTrader: (13)

Right can I get this back on track???

If someone wants to do the relocation mod, can people state;
What is the optimum cable (diameter/construction/length)?
Is it worth fitting a cut of switch (with permanent +ve for stereo/alarm/tracker etc)?
Would you be best to box the battery in??

And afaik isn't the earth issue to do with galvanic corrosion over time between the ally alloy parts and the steel bolts/chassis, and the 12v DC through it?? Same reason why my 1972 Landy has corrosion around every steel nut and bolt. And this corrosion inhibits the flow of electricity, so the only earth issue is between the engine/gearbox and the chassis, once on the chassis it should be ok?? Or am I barking up the wrong tree??

alcazar

iTrader: (2)

I'm going to leave it to Mr. Expert above to answer.

TBH, I'm sick of giving advice and help on here only to have some ill-mannered newby come on and slag me off.
Sorry.

Jimbob

iTrader: (13)

Fair enough bud, but for the one know it all, there are a few wanting to learn, or discuss things properly.

What gets me are the people who claim to know this and that, but when it comes down to it they cant change a bulb without a 40 page discussion, and then claim that their £4000 bulb is better, then get a back street garage to fit it as they have no actual ability.

alcazar

iTrader: (2)

He doesn't seem to want to come on and help, only have a go at my attempts to help.

To try and answer your questions:

Cable size:I'd fit the best and thickest you can a) get in, and b) afford. The better/thicker the less volts drop, and the lower will be the heating effect. Remember that the heat generated in a cable is a product of it's resistance, the SQUARE of the current being passed and the time it passes for. You can't change either the time, or the current, so use better wire with a lower resistance.

Cut-off switch: I would. If you have space, and can find somewhere to fit it. Remember to fit a decent one so as to keep resistance at a minimum.

Boxing in: the least you want is a tray with a lip, and if possible a plastic liner, to cope with any acid drips from the battery. Modern sealed batteries etc shouldn't drip, but I've actually witnessed a battery explode........
And a tiny crack could weep. You don't want acid on the car/you/wiring.
for the above reason, of paramount importance is to have the battery firmly held in place wherever it is.

This: http://www.vehicle-wiring-products.e...e/homepage.php is where I tend to get my electrical stuff. Not the cheapest, but the best.

They will also give advice if you ask while you ring through an order.

HTH.

Jimbob

iTrader: (13)

Cheers mate, great advise as always.

toby69

Thanks for all the input so far