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K9F



Member Since: 12 Nov 2009
Location: Bournemouth
Posts: 9610

United Kingdom 2008 Defender 90 Puma 2.4 XS CSW Stornoway Grey
As a sparky you should not take the positive directly off the battery. Either take it off the mega fuse or independently protect it as soon as you can after connecting it to the battery with a fuse or you will have no circuit protection.
Thumbs Up If you go through life with your head in the sand....all people will see is an ar5e!!

Treat every day as if it is your last....one day you will be right!!
Post #401396 23rd Feb 2015 2:56pm
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JWL



Member Since: 26 Oct 2011
Location: Hereford
Posts: 3443

England 2002 Defender 110 Td5 SW Coniston Green
I took my Anderson connector outside and bolted it to the front bumper next to my winch mainly so I can get closer to what needs power, I don't need to have the door open to access the connection which avoids disturbing passengers etc. Having to put jumpleads to the side of your motor is often a pain, far easier on the front or back(when I've got round to fitting what is sat on the shelf at home) plus if you're up to your neck in the dirty stuff it's a lot cleaner on the inside of your motor Whistle
As it happens mine were in use this morning, helping a mate tip his Ifor trailer as the battery was flat on the trailer and he hadn't got the patch lead with him, just drove up to the side of the trailer and put the jump leads into the connector on the trailer and got him sorted. Yes it could be done from the passenger door but far easier from the front.
Post #401402 23rd Feb 2015 3:13pm
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AndrewS



Member Since: 10 Apr 2007
Location: Hereford
Posts: 3707

United Kingdom 2013 Defender 130 Puma 2.2 SW Rimini Red
K9F wrote:
As a sparky you should not take the positive directly off the battery. Either take it off the mega fuse or independently protect it as soon as you can after connecting it to the battery with a fuse or you will have no circuit protection.
Thumbs Up


A question o wise one Bow down

Here is the scenario:- Live cable from battery via and isolation switch connected to an Anderson connector.

The red plastic coating rubs through and the now bare cable between the switch and the connector starts to earth out.

Lets say there is a 400 amp mega fuse in the line between the isolation switch and battery connection...... how hot will the cable get before the fuse blows? or wont it get hot at all? 130's have feeling's as well you know Smile
Post #401487 23rd Feb 2015 8:05pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 17240

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
Arc welders are generally low voltage high current machines, eg 40V and 180A. They get pretty hot!

A 12V 400A supply could easily be used for arc welding without blowing the fuse!

A dead short to ground (such as might happen in an accident) will probably blow the fuse. Insulation chafing through will incinerate the vehicle before the fuse blows.
Post #401504 23rd Feb 2015 9:09pm
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AndrewS



Member Since: 10 Apr 2007
Location: Hereford
Posts: 3707

United Kingdom 2013 Defender 130 Puma 2.2 SW Rimini Red
Thumbs Up Bow down

So how does one protect the vehicle in the chafing situation? 130's have feeling's as well you know Smile
Post #401576 23rd Feb 2015 11:36pm
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blackwolf



Member Since: 03 Nov 2009
Location: South West England
Posts: 17240

United Kingdom 2007 Defender 110 Puma 2.4 DCPU Stornoway Grey
Realistically the only way is to make sure that heavy current cables are protected from chafing. If you look at any heavy engineering product with a similar problem, eg a railway locomotive, you'll find that the electrical installation is designed so that it won't happen. You'll also find fire suppression systems etc as a backup.

For something like battery cables to a jump-start connector, I would fit a cut-off switch as near the vehicle battery as possible, so the +ve lead isn't live except when needed. If you then find you get fireworks when you switch on, switch off quick!

There is a risk that in this situation the switch contacts will either weld closed or arc continuously but you are in a much better situation than without the switch (and I do note you're fitting a switch in your question).

Bottom line is that a megafuse has to supply a huge current without blowing, and for it to blow then something catastrophic is already happening.

A battery cut-off switch to isolate the vehicle battery or batteries is a good idea. If you have a fault which is discharging say 100A to ground and generating heat, smoke, and flames, the megafuse won't blow but you can at least easily shut off the juice. It's ironic perhaps that such switches were commonplace 50 years ago, when vehicle wiring was really simple, but are almost unheard of now vehicles are monstrously complex and electrical fires are at an all-time high.
Post #401589 24th Feb 2015 12:44am
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K9F



Member Since: 12 Nov 2009
Location: Bournemouth
Posts: 9610

United Kingdom 2008 Defender 90 Puma 2.4 XS CSW Stornoway Grey
Best practice and sensibility must prevail. With regards to your 400 amp megafuse thermal theory why not give it a go. I'll lend you my work Isyris Thermal Imager. Why would you fit a 400 amp fuse on a 12 volt car battery for normal or even jump starting use? As stated the protection as a rule of thumb should be placed as soon as practical after the connection to the battery. Amperage should be one and a half times your anticipated maximum draw or reduce the protection to a closer figure by fitting anti-surge fuses. If you go through life with your head in the sand....all people will see is an ar5e!!

Treat every day as if it is your last....one day you will be right!!
Post #401631 24th Feb 2015 10:14am
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leeds



Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8579

United Kingdom 
There are some vastly different numbers about fires in road vehicles.

Official data would suggest that road vehicle fires are decreasing look here page 50

[quoteChapter 4 – Road Vehicle Fires
Introduction (Table 16)
4.1 Road vehicle fires in 2011-12 totalled 28,000 in 2011-12, down by 14% from 32,600 in
2010-11. The 2011-12 total represented the lowest in more than a decade and declined by
nearly three quarters from its peak in 2001/02.
4.2 A breakdown of the road vehicles figure shows that the majority (65%) of fires occurred in
cars, 10% were in vans, 4% were in lorries and 2% in buses or minibuses. The number of
car fires was 17% lower than in 2010-11 and 79% lower than in 2001-02.

Casualties (Table 6)
4.3 The number of fatalities in road vehicle fires in 2011-12 was 37, down by 7 from 44 in
2010-11. This equates to 1.3 fatalities per 1,000 fires and contrasts with a fatality rate for
dwellings of 6.6 fatalities per 1,000 fires. Time series data shows that road vehicle fire
fatalities have been declined by nearly a half in over a decade[/quote]





It is not possible to say from those official figures the cause of the vehicle fires be it arson, faulty electrics, physical damage due to a collision etc.

Carrying a decent fire extinguisher would also be good practise.



Brendan
Post #401636 24th Feb 2015 10:28am
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Supacat



Member Since: 16 Oct 2012
Location: West Yorkshire
Posts: 11018

United Kingdom 2013 Defender 110 Puma 2.2 XS DCPU Keswick Green
What an amazing decrease in just the last decade or so.
Post #401639 24th Feb 2015 10:48am
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AndrewS



Member Since: 10 Apr 2007
Location: Hereford
Posts: 3707

United Kingdom 2013 Defender 130 Puma 2.2 SW Rimini Red
K9F wrote:
Why would you fit a 400 amp fuse on a 12 volt car battery.


Err.... That was to describe a scenario that led to my question. Thumbs Up 130's have feeling's as well you know Smile
Post #401742 24th Feb 2015 6:14pm
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Supacat



Member Since: 16 Oct 2012
Location: West Yorkshire
Posts: 11018

United Kingdom 2013 Defender 110 Puma 2.2 XS DCPU Keswick Green


Admin note: this post has had its images recovered from a money grabbing photo hosting site and reinstated Mr. Green
Post #405181 6th Mar 2015 10:05pm
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leeds



Member Since: 28 Dec 2009
Location: West Yorkshire
Posts: 8579

United Kingdom 
Oi, I could shout copyright infringement! Razz

One of my photos in the Baltic countries with our red 110 in the background Thumbs Up


Brendan
Post #405217 7th Mar 2015 12:57am
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Supacat



Member Since: 16 Oct 2012
Location: West Yorkshire
Posts: 11018

United Kingdom 2013 Defender 110 Puma 2.2 XS DCPU Keswick Green
I did wonder when i nicked it from that other site and saw the posters name Whistle ; but then i thought if it was you, you'd have posted it above in an effort to be helpful; unless you'd completely forgotten about it... Thumbs Up

Do you remember how it was kept closed - it's not obvious from the photo & looks like it would flap about as you drove along?
Post #405263 7th Mar 2015 12:06pm
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