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Towing Electrics Fuses
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D4mation
 


Member Since: 29 Jul 2011
Location: Ruralshire
Posts: 593

United Kingdom 2012 Discovery 4 3.0 SDV6 HSE Auto Ipanema SandDiscovery 4
Towing Electrics Fuses

According to my owners handbook and what I've discovered on the web the fuse for charging a caravan battery should be 30 amps. I had to replace mine yesterday because it had blown, but it's only a 15 amp fuse. I've had the car from new and the fusebox is virgin - not touched since coming out of the factory. I had to google how to drop the glove box down to get at the fuse board.

I noticed the blown fuse when trying to charge the car battery through the towing socket, with the charger failing to see the battery.
Prior to this I had discovered that my caravan battery was knackered and my theory is that this, together with the caravan AL-KO ATC startup routine was too much for the 15 amp fuse. The caravan battery has now been replaced.

Anyone know what cabling is used for this battery charging circuit and whether I could replace the fuse with say a 25 amp fuse. It's fuse 48 in the linked diagram.
http://knigaproavto.ru/shemy/en/land-rover...92016.html
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Post #197547219th Aug 2018 6:03 pm
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al cope
 


Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10289

England 

the ATC 12v supply is from the permanent 12v pin, whereas the 12v for charging and the 'van fridge is from the switched 12v, so not from the same supply.

Al
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Post #197560920th Aug 2018 7:13 am
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Martin
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Member Since: 06 Nov 2004
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United Kingdom 2006 Discovery 3 TDV6 SE Manual Buckingham BlueDiscovery 3

The permanent supply fuse 48P changes according to the model year Rolling Eyes

2014MY: 15A
2010MY: 30A

Both model years use 2.5mm² cable from the fuse to the socket, and there are SOME other uses of 30A fuses with 2.5mm² cable on the D4.

However, technically, a 2.5mm² thinwall cable is rated for 29 Amps in free air, so a fuse with a continuous rating of 30A is under-spec really.

There are lots of uses of 25A fuses with 2.5mm² cable though.

Presumably there is an engineering reason for the big drop from a 30A fuse specified at 2010MY to the 15A at 2012MY. Rolling Eyes

I would step up the fuse from 15A to 20A and see if that sorts it, with the option to go to 25A. And keep some spares Thumbs Up

al cope (him above) did this back in 2013:

https://www.disco3.co.uk/forum/atc-system-...p;start=15
https://www.disco3.co.uk/forum/d4-towing-e...=alko+fuse

Al, did the 20A fuse sort it?
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Any issues with the site let me know! 
 
Post #197565620th Aug 2018 9:49 am
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al cope
 


Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10289

England 

Blimey Martin - I forgot I did that, and yes the it did resolve it. Bow down

Al
 Volvo XC90 B5 Plus Dark
Gone - MY18 D5 HSE - Corris on 22's with Black Pack
Now gone - MY16 D4 SE Tech, Loire Blue, Almond Leather, Privacy, plus some other goodies.
Old - MY12 D4 SDV6 XS Auto - Ipanema Sand with Almond Leather - Plus other niceties, and D4.com sticker
Older - D3 TDV6 XS Auto - Lugano Teal with Almond Leather, 20" Stormers, Shiny Tailpipes, DVD/TV - and obligatory D3 sticker
Ancient - D3 TDV6 S - Tonga with Ebony, 20" Stormers, satnav & DVD 
 
Post #197567120th Aug 2018 10:48 am
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D4mation
 


Member Since: 29 Jul 2011
Location: Ruralshire
Posts: 593

United Kingdom 2012 Discovery 4 3.0 SDV6 HSE Auto Ipanema SandDiscovery 4

al cope wrote:
the ATC 12v supply is from the permanent 12v pin, whereas the 12v for charging and the 'van fridge is from the switched 12v, so not from the same supply.

Al


The trailer ignition feed to the caravan is via fuse 54, again 15 amps, and supplies pin 10. Again this fuse seems a bit low for purpose.

I thought the permanent feed on pin 9 supplied the ATC, and also charged the van battery when the habitation relay is activated.
Pin 10 activates the habitation relay, and supplies the fridge when the engine is running.

After fuse 48 had blown I noticed that with the car ignition on that the ATC still went through it's noisy startup routine when I plugged the van into the tow socket. How could this be I asked myself if there's no power to pin 9.
It seems that the ignition on activates the habitation relay and connects the caravan battery to pin 9 ready for charging from the car and consequently connects to the ATC - the caravan battery powers the ATC.

I found Simon Barlows website very useful in educating my thicko head on towing electrics.

https://caravanchronicles.com/guides/under...electrics/
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Post #197568020th Aug 2018 10:56 am
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al cope
 


Member Since: 08 Nov 2005
Location: Oldbury, WM
Posts: 10289

England 

not sure thats correct as the ATC on mine activates without having the battery in the 'van, so its cant be being run from that.

Al
 Volvo XC90 B5 Plus Dark
Gone - MY18 D5 HSE - Corris on 22's with Black Pack
Now gone - MY16 D4 SE Tech, Loire Blue, Almond Leather, Privacy, plus some other goodies.
Old - MY12 D4 SDV6 XS Auto - Ipanema Sand with Almond Leather - Plus other niceties, and D4.com sticker
Older - D3 TDV6 XS Auto - Lugano Teal with Almond Leather, 20" Stormers, Shiny Tailpipes, DVD/TV - and obligatory D3 sticker
Ancient - D3 TDV6 S - Tonga with Ebony, 20" Stormers, satnav & DVD 
 
Post #197568420th Aug 2018 11:03 am
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D4mation
 


Member Since: 29 Jul 2011
Location: Ruralshire
Posts: 593

United Kingdom 2012 Discovery 4 3.0 SDV6 HSE Auto Ipanema SandDiscovery 4

Martin wrote:
The permanent supply fuse 48P changes according to the model year Rolling Eyes

2014MY: 15A
2010MY: 30A

Both model years use 2.5mm² cable from the fuse to the socket, and there are SOME other uses of 30A fuses with 2.5mm² cable on the D4.

However, technically, a 2.5mm² thinwall cable is rated for 29 Amps in free air, so a fuse with a continuous rating of 30A is under-spec really.

There are lots of uses of 25A fuses with 2.5mm² cable though.

Presumably there is an engineering reason for the big drop from a 30A fuse specified at 2010MY to the 15A at 2012MY. Rolling Eyes

I would step up the fuse from 15A to 20A and see if that sorts it, with the option to go to 25A. And keep some spares Thumbs Up

al cope (him above) did this back in 2013:

https://www.disco3.co.uk/forum/atc-system-...p;start=15
https://www.disco3.co.uk/forum/d4-towing-e...=alko+fuse

Al, did the 20A fuse sort it?


Thanks Martin, very useful information especially the 2.5mm² bit.
As I struggled to get my sausage fingers into the fuse board area and my knees aren't as good as they once were, I decided to use the 15 amp spare from the board whilst I was down there, before seeking advice.

Should I go for genuine fuses, or will eBay fuses be OK ?
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Post #197569820th Aug 2018 11:18 am
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D4mation
 


Member Since: 29 Jul 2011
Location: Ruralshire
Posts: 593

United Kingdom 2012 Discovery 4 3.0 SDV6 HSE Auto Ipanema SandDiscovery 4

al cope wrote:
not sure thats correct as the ATC on mine activates without having the battery in the 'van, so its cant be being run from that.

Al


But .... I bet it wouldn't work if you pulled out fuse 48 Shocked

Edit: As I said, with a blown fuse 48 the ATC fires up if the car ignition is on and so is getting its supply from the van battery.
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Post #197570320th Aug 2018 11:22 am
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Martin
Site Admin and Owner 


Member Since: 06 Nov 2004
Location: Hook Norton
Posts: 18439

United Kingdom 2006 Discovery 3 TDV6 SE Manual Buckingham BlueDiscovery 3

D4mation wrote:

Should I go for genuine fuses, or will eBay fuses be OK ?


Genuine not necessary (Land Rover don't make fuses...or much) but a good quality fuse is - not cheapest eBay ones.

Littelfuse are likely the OEM, or MTA for aftermarket. However finding a seller who will tell you who the manufacturer of a fuse is might be tricky.
 06 D3 SE / 15 LR D90 XS SW / 88 LR 90 Td5 / 68 BMW 2000 ti
Any issues with the site let me know! 
 
Post #197571220th Aug 2018 11:58 am
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D4mation
 


Member Since: 29 Jul 2011
Location: Ruralshire
Posts: 593

United Kingdom 2012 Discovery 4 3.0 SDV6 HSE Auto Ipanema SandDiscovery 4

I went for a mixed bunch of Littlefuse minis from Farnell - thanks for the pointer.
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Post #197575720th Aug 2018 2:19 pm
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