12 Volt Electrics - appropriate fuses

[Harry Lissimore]

As my electricial knowledge is limited a little, I am hoping that someone can help/explain to me the protection of electrical circuits in my 2002 Tvan.

While camping by the Lions Rd in the QLD/NSW border ranges last weekend, I plugged a friends 12V fluoro light  into one of the merit sockets.  The fluoro light had frayed wires (which weren't particular heavy duty) where they went into the light, and consequently shorted.  After about 5 seconds wondering why the light hadn't come on, I noticed that the wires to the light were fairly hot maybe about 50 degrees centigrade and rising.  I disconnected immediately. 

I wonder why the  fuse on the front chassis did not blow.  I had already changed that fuse from 30A to 20A some time ago, and it didn't blow.

Is there something I am missing here?  Tvan wiring is supposed to be rated at 10A.  Does that mean that the fuse should only be 10A.  I would have liked to put a 10A large blade fuse in place of the 30A, but I don't know whether they are available.  Supercheap didn't have them.  The smallest I could get was 20A.  The current (not intended as a pun!) system doesn't seem to offer much protection.

The next question is.... does everything I plug in to a merit socket need to have its own fuse.  Most applications that are plugged in eg lights, chargers, TV etc dont have their own fuses.

Any comments? I would sure like to sort this out for peace of mind.

Harry

[peterjantvan]

Harry
I have a 2011 tvan so it is different to yours.
I remember a question like yours some time ago.
Possible Craig will chip in to be accurate.

From what I remember I think the front fuse only protects the charge circuit from the vehicle.
All other circuits for sockets and lights have no fuses for protection.
I think others have had to put fuses in for these circuits.

Hope someone has the exact answer for you.

Peter

[Harry Lissimore]

Hi Peter,

I think Craig said that the early Tvans had no fuse protecting the anderson plug cable that plugs into the car, but they do have a 30A maxiblade fuse that protects all other wiring (lights,pump, merit sockets, voltmeter).  I sort of confirmed that by pulling the fuse before installing switches on a few of the merit plugs and the power was disconnected.

I have 3 adapters that adapt merit sockets to cigarette lighter sockets - I have now installed 8A in line fuses in them and any application that I have that has a merit plug, I have ensured that the merit plug has a built in 8A fuse.  That should cover most things for the moment.

I am thinking that I will install some sort of fuse/circuit breaker on each wire just after it leaves the positive battery terminal (ie in the battery box) to fuse the anderson plug cable (charging from the car) and the accessories (pump, merit sockets etc).  I consider that the fuse mounted on the chassis is too far from the battery and too close to the chassis.  However, I am unsure what sort of fuses to use as I dont have a detailed knowledge of them.

Any help would be appreciated.

Harry 

[peterjantvan]

Hi Harry

I think you are right about the fuses.
If you look in the technical section electrical and wiring
You will find a post called mark3 wiring harness
The last two documents show the battery bad and power box for a mark 3.
This is where it has all evolved to.
It will give you done clues as to how to do yours.

10 amp fuses on the individual feeds

Have a look and ask any more questions - happy to talk on the phone just
Send me your number

Peter

[The Hueys]

MkI and MkII Tvans only had the one fuse on the front which covered everything in the van. They were originally 30amp. After a bit of recalculation it was decided to send out 20amp fuses to all the owners we were able to get in contact with (this was one of the most painful and time consuming things I ever had to do at Track, because we just didn't have everyones details). The loom in the MkII was then upgraded with a chassis earth and they continued to use 30amp fuses. Vans without a chassis earth (one at the battery and one at the right hand rear corner under the powerbox to the chassis) should only use 20amp fuses.

That said the scenario as described with a very small short can sometimes not be enough to blow the fuse but should not be sufficient to damage the Tvans wiring. The faulty device on the other hand may go into melt down, the resulting damage to the device may then make the short big enough to blow the Tvan fuse. Most plug in 12 volt devices are not fused and rely on the cars fuse (which is where most are initially intended to be used).

Looking back in hindsight, the wiring loom in the MkI and MkII is a bit simple and if it was done now would be done differently which is why the MkIII ones are so complicated, but that is how looms were often done in the late '90's when it was designed.

[Harry Lissimore]

Thanks Craig,

I'm not the expert but I sure could see that the 30A fuse was too big.  Thats why I installed a 20A.  I also think that 20A is too big but I haven't been able to find a maxiblade 10 or 15A fuse.  To me , 15A would be perfect as long as any inverter was plugged directly into the battery, not the Tvan electrics.

So with my 2002 Tvan, should I be earthing the battery to the chassis as an extra earth point? Again,  I'm not the expert but everything in the Tvan has negative wiring going back to the negative side of the battery (I think!)

Harry