Split charger blowing fuse

[el sketcho]

Does anyone know why this is happening?

[1664]

Could be your leisure battery is so flat it's pulling more current from the alternator than the fuse was rated at - does it on mine occassionally if I really run it down. If I think it might have run it too flat I remove the fuse, start the van, chuck a set of jump leads between the two batteries and go for a drive. Even the jump leads can get warm so a leisure battery can suck a fair bit when they're hungry.

I really must get round to putting a larger cable, relay and fuse in..........

[el sketcho]

If the fuse blows would it leave an open circuit? The starter battery was flat this morning and had to charge it up before I could start it. Once it had some charge in it I turned the engine off and remove the earth cable from the Starter battery so I could check for any drain, there wasn't anything coming off the battery but I had replaced the fuse in the split charger.

[Oldiebut goodie]

Does anyone know why this is happening?

It's because people insist on installing underrated split charge systems!
You need a minimum of 80A rated system to avoid this scenario - people keep poo-pooing this as too much but you have just shewn why it should be beefed up.If you think about it, depending upon your alternator the leisure battery could be asking for 50/65/90A from it.
What are you running - a 15A or 30A system?
Did you mean would it leave a short circuit not open circuit?
I run a 100A system on mine and 120A on my big Merc van.

[el sketcho]

It's one of the hella units that JK sell. Oldie but goodie when you say an 80amp rated system do you mean the unit or the wiring? Coz the wiring is very thin.

[Oldiebut goodie]

Split charge unit and wiring. Long thin wiring will lead to voltage drop and undercharging of the leisure battery.
I used a 15A voltage switching unit(which can then be used to power the fridge whist the alternator is running only) to switch a 180A(because it was cheap!) relay with 140A wiring fused to 120A on my Merc.
A 100A relay switched by a voltage sensing relay with 100A wiring fused to 80A will do. The reason for overrating the system is that you then avoid voltage drop which leads to undercharging of your leisure battery and you don't keep blowing fuses after you have run your leisure battery down too much.(lets face it, we all do it occasionally).
You can run a lower spec. system but the 15 and 30A relays really are not suitable for the demands placed on them with the number of electrical items that we tend to try to run from our leisure batteries.