fuse rating

[fazzer]

ive now got a leisure battery fitted,but when ive been driving the van the fuse by the leisure battery blows,(15amp) so changed it to a 20amp and the fuse on the cranking battery blew(20 amp)ive looked on web but cant get a definitive answer to which fuse rating I should be using, don't want to go to high as worried about fire.

[windydubber]

I've got a 25amp in mine! It's one of those relays with a fuse holder in it. Hope this helps?

[CJH]

... the fuse by the leisure battery blows,(15amp)... ... the fuse on the cranking battery blew(20 amp)...

Golden rule - these fuses have to have a lower rating than the cable's current carrying capacity, and the relay's rating. They are there to protect the circuit from heating up, melting and potentially catching fire. So don't be tempted to just keep increasing the fuse rating - find out what the cable rating is, and stay below that (this can be tricky, as the outside diameter is not always a good guide, since thinwall cable has become more commonplace).

But... the main reason for a lot of current flowing down the split charge circuit is probably because your leisure battery is flat, while your starter battery is full. If the leisure battery is low it will draw a lot of current from the alternator and the starter battery as soon as the relay closes and joins the two batteries - do your fuses blow quite quickly when you start the engine? If you give your leisure battery a good charge from a mains charger it will draw less charging current and will probably stop blowing 20A fuses in the split charge circuit.

[CovKid]

Aye, my setup is 80amp cable, a 40amp relay and 30amp strip fuses in cases. I used to have a bare-bones approach to building things but having worked with my stepfather on various projects including some made from timber, I adopted a more heavyweight approach to designing/building everything, and this has paid off.

I always used to think his projects were overkill in construction but I have to say, his stuff still stands today where everyone elses has long since disappeared. He always gets the last laugh I'm sure but is consistently modest. I am a huge admirer of his thought processes. Sadly Chinese built stuff falls into the "will just do" category which is why much of it doesn't last beyond a year. Now when I upgrade anything on a T25, I work out what will meet spec then double it. Its the old-school British way I think.

[fazzer]

Leisure battery is new and fully charged,

[CovKid]

What gauge cable, and what is the relay rated at?

[CJH]

Leisure battery is new and fully charged,

I guess it could also happen the other way round - if the leisure battery is full and the starter battery is depleted, then there'll be a lot of current flowing between them when they are first connected via the relay. What state is your starter battery in?

[California Dreamin]

ive now got a leisure battery fitted,but when ive been driving the van the fuse by the leisure battery blows,(15amp) so changed it to a 20amp and the fuse on the cranking battery blew(20 amp)ive looked on web but cant get a definitive answer to which fuse rating I should be using, don't want to go to high as worried about fire.

The fuse blew whilst cranking!!!! indicates that the batteries are connected during 'cranking' which is WRONG! I'm guessing that some plonker has wired up your split charge relay to switch from an 'ignition live' and not the exciter feed to the alternator (as it should be).

So what is happening is: the starter motor is drawing from both batteries when this shouldn't be able to happen.

Fuse rating wise: I would say a GREEN 30amp as long as your wiring is 4.5mm2 or heavier (35amp or more)

Martin

[CovKid]

Agree. I run with these type of fuses (at 30amp) mostly for security of connectors although you could use blade too:

http://www.ebay.co.uk/itm/STRIP-MIDI-FU ... 43d8d215e7" onclick="window.open(this.href);return false;