2012-10-26: Make your mind up time

In this build diary, we’re trying to track our progress in converting the van. But sometimes progress is incomplete. And today, we have a pile of incomplete jobs in the van, so I’m just going to write about one of those: the 12V distribution box.This is a cabinet that takes 12V power from the battery into a fuse box, and then distributes it out via switches to all the 12V circuits in the van (lights, USB sockets, fridge, heater, water pump, fan, etc.). In many vans, this is right next to the battery, or the solar charger, or an invertor for AC power. But those things are all just big heavy lumps that you don’t need to interact with on a regular basis. So we decided to separate out the distribution box from these other components. Originally we tried putting it down on the floor behind the drivers seat.

But while this was a good use of dead space, it was far too fiddly to reach the switches for each circuit. We played with the idea of using part of the overhead shelf in the cab, and mounting the switches on the partial bulkhead we fitted as part of that project, but it we couldn’ figure out a good way of running the wiring in and out.

Our third plan was to fit a dedicated box on the wall behind the drivers seat, at about chest height. That worked pretty well,but was a poor use of space. So our current plan is to mount it a little higher, as part of the overhead cabinet that will run along the whole length of the drivers side of the van, occupying the space directly behind the bulkhead. This is the empty box pictured at the top of this post (the one below it is the remains of the previous attempt).

It currently exists as a rough version made of scrap ply, but if this works functionally, I’ll make a proper version out of nice wood. It’s time to make a decision and live with it.

One more thing

One of the key considerations — and something that may be news to anyone, like me, working with 12V power for the first time — is voltage drop.

Power run at low voltage over even just a few metres of wire, can lose a significant voltage over the run. That’s inefficient, but can also affect the functioning of anything you plug in the other end. If a device is expecting 12V but only gets, say, 10V, it may not work.

There are plenty of calculators that let you work out voltage drop, but there’s no escaping the fact that the van is long, so if you want to run 12V from the front to the back, and perhaps from one side of the van to the other, you might be looking at a run of 4–8 metres each way. For a remotely high power drain, that means using very thick cable, which is very spendy.

Moving the fusebox can have a dramatic impact on these cable lengths, and is worth thinking about when you’re doing these nice early stage sketches, before the inconvenient realities of conversion start spoiling your fun!

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