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 Post subject: aaaarrrrhhh what fuse
PostPosted: Sat Sep 22, 2012 12:52 pm 
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Group N

Joined: Fri May 28, 2010 11:55 am
Posts: 310
Location: launceston cornwall
Car Model: None
got a battery re-location kit and want to know what size fuse i need

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PostPosted: Sat Sep 22, 2012 3:21 pm 
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Joined: Thu Jul 14, 2005 12:44 pm
Posts: 4067
Location: drinking devil fuel
Car Model: ST205
Somewhere in the region of 100amps for a normal fuse or nearer 150 for a resetable one


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PostPosted: Sat Sep 22, 2012 6:41 pm 
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Group N

Joined: Fri May 28, 2010 11:55 am
Posts: 310
Location: launceston cornwall
Car Model: None
thans just orderd a 100amp

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PostPosted: Sun Sep 23, 2012 12:28 am 
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Group N

Joined: Mon May 26, 2008 2:33 pm
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Location: Wellington, New Zealand
Car Model: ST185
I normally advise at least a 150A. The fuse is the line protection and still needs to be able to draw power through for starting duties. One of these days I'll chuck a clamp meter on the starter and figure out the current draw

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PostPosted: Sun Sep 23, 2012 10:55 am 
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Group B
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Joined: Sat Sep 02, 2006 3:13 pm
Posts: 3679
Location: Bournemouth
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There's a good guide on Kris & Lucy's site.

http://www.gtfours.co.uk/
How to -> Relocate the battery.

I particularly favour the battery terminal with built in fuse reccomended on there. Failing that, put the fuse as close to the battery terminal as you can get it as any short to body between terminal and fuse will probably cause a fire.

http://rswww.com
342-0205 - Bracket
342-0198 - Insulating nut (buy 2 or 3 as they crumble easily)
337-7959 - 150A fuse

For safety, ensure the cable you use is rated at least as high as the fuse, otherwise the cable can catch fire before the fuse blows. The rating depends on how the cable is run.

e.g. 35mm sq is rated for 181A horizontal, free air or 99A enclosed in conduit in thermally insulating wall (rough equivalent running under carpet). This is probably the minimum I would go for. You could probably get away with 25mm sq if not run under carpet, but I would go for 100A fuse.

Fuse rating has a bit of mystique around it as a 100A fuse won't blow at 101A, or even 110A. The rating refers to the current you can draw all day long, including heat cycling on & off and the fuse won't blow. In a single overload condition, the actual blowing current is much higher, the bigger the current flow, the quicker the blow. For example, the quoted fuse will take up to 60 seconds to blow at double it's current rating. This means the fuse can handle short surges much greater than the fuse rating.

http://docs-europe.electrocomponents.co ... 02c95a.pdf

My clamp meter only goes up to 30A so I'm unable to measure starter current, however I'm led to believe that it's normally less than 100A once the engine is turning over, the only surges being the initial pull in and first compression stroke plus any kick-back from the engine if the ignition is a bit over-advanced at cranking speed. I've tweaked a couple of maps now which suffered this problem. I don't understand how mappers can think the mixture needs to be ignited 20 or 30 degrees early below 500RPM, but I suppose it gives a nice smooth looking3D graph when it has a linear RPM scale.

As far as relocation goes, I'm not a huge fan of moving the battery out of the bay unless absolutely necessary, or for a competioin build for weight distribution. Batteries are hazardous things and they contain poisonous and corrosive chemicals and give off explosive gasses - even gel ones.
Leaving asisde the fact my last rally car was written off by the battery leaking into a chassis rail, most people put the battery in a sealed box in the boot. This is the perfect recipe for a bomb as hydrogen and oxygen are produced in perfect proportion for combustion. Even the gel batteries have warnings in the data sheets to use in a ventilated area.

I would always favour relocating within the engine bay, even if it means going to a smaller battery.

http://en.wikipedia.org/wiki/Lead%E2%80%93acid_battery

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