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Fuse box safety question. Answered

I am currently working on turning my van into a full-time home and I'm throwing the rule book out of the window. I have 600W of solar and 180Ah of batteries and I'm working on the wiring

Normally, the high current lead runs from the batteries to a fuse box and then around multiple circuits with a fuse to match the demand in that circuit. I'm looking to decentralise the fuse box so that the main cable has a 50A fuse and runs around the entire van feeding junction boxes and modules. Each module contains its own fuse, an ethernet connection, possibly a buck converter and whatever it needs to do its job. Every module is, therefore, able to report faults and output to any other module that's interested. If a fuse blows, a simple ping across the network will tell you which module is not responding and, therefore, which fuse needs replacing.

Is there a safety issue I've not thought of with this approach?




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1 year ago

Genearally I see nothing too wrong with your approach.
However you need to consider the entire system as a whole.
That means first you have to be able to fully isolate the solar part (switch and fuse).
From the battery to your setup you can go with a single fuse for a single cable just fine.
-With a downside though:
12V is a bitch to work with if you need real amps.
The more you need, the thicker the cable needs to be to prevent voltage drop.
It is no problem to loose over 2V from the battery to the last consumer on the long cable!
Interference can be a big issue as well when using voltage converters.

You have a freezer, fridge, TV and then some hot water system or whatever.
Usually they would never run all at the same time but you still need to cater for this event in terms of fuses and wire gauge for your supply.
These days it can actually be much cheaper to use multiple cables to supply power to your individual consumers/fuse boxes.
Light is LED and does not need much, so even speaker cable works fine here.
For the rest check what amps are used at max and check what size wire you need (online charts and such).
Calculate if it is really much cheaper to use a single, thick cable instead several thinner ones ;)
Best feature of going with individual lines IMHO is that upgrading is much simpler.
It really is easier to work with thin wires ;)


Reply 1 year ago

Funnily enough, I've stumbled across some interesting solutions to some of these points. I'm still assembling the battery (in a Black and Decker, 19" tool box - £20 from Homebase) and I've put a couple of switches in the housing. One uses a DPDT switch to reverse the polarity of the middle of 3 batteries which should, in theory, go from 3 x 12V in parallel to 3x12V in series = 36V. I'm protecting that switch under a safety hood! I also ran the negative lines of the 3 balancing boards through a 3 circuit switch since the boards are rated for 50A, not the kind of welding amps. It's a simple little thing but I might post an instructable because the result is so pretty!
Now I've got to figure out a way of creating an alterative route for unbalanced cell use which doesn't interfere with the balancing.


1 year ago

How do you know your enemy? You study, you send in a few probing attacks and you *ask questions* - especially when trying out a new tactic. I couldn't see why it wouldn't work, I just figured it was better to ask stupid questions than to make stupid mistakes. Electricity and I have had a few minor skirmishes in the past, like the martians in War of the Worlds, it has released its black smoke!
The upcoming battle has more at stake with 600W of 24V solar, 180Ah of 12V batteries, a 50W charge controller, 3 balancing boards and a 5KW inverter. While none of these are on my side, I am hoping to set them up to tame each other without too much killing involved (minus to minus, plus to plus, in the desperate and optimistic hope of possible resurrection).

I've lived in RVs for the past 13 years and the wiring is a nightmare - thick bundles of thin wires buried in the walls and under floors making tracking down breaks an absolute mess, even with a circuit diagram (which you never get).

Thinner wires may be cheaper but they run everywhere, there's the voltage loss problem and they break more readily, usually in the most inaccessible place. DownUnder makes a good point, though, and so two lines running from the back down either side of heavy gauge cable should minimize the power loss. With junction boxes every, say, 250 or 500 cm, I should be able to hook in wherever I need to using thinner, short lengths of wire. Of course, keeping everything easily accessible without disassembling the entire vehicle.

There is no circuit diagram because I'm building a framework (subduing the locals) for whatever I decide to add later on.As my ex once said "a software engineer's project is never completed - you just have to take it away from them".


Jack A Lopez
Jack A Lopez

1 year ago

"If you know your enemy, and you know yourself, you need not fear the outcome of 100 battles."

That is a quote from Sun Tzu,

and it is only a partial translation. The full version considers all four binary permutations; i.e. "know" and "not know", regarding "your enemy" and "yourself."

The GI-Joe (Hasbro) version of this quote is even shorter, condensed to simply: "Knowing is half the battle."

The interesting thing to me about this quote is, this ancient Chinese military commander apparently thought about probability the same way modern gamblers and insurance companies do, using percentages, i.e. a proper fraction with 100 as the denominator; e.g. 0/100, 50/100, 100/100.

Anyway, the fact that you are asking this forum, to make a judgement ("Is there a safety issue I've not thought of with this approach?") about your system, plus uncertain language, like "possibly a buck converter" and "whatever it needs to do its job." These statements say to me, that you need to do more studying, of your enemy.

I suppose this forum can help you with your homework, but for us to do that, it would help a lot if we knew more about your enemy.

You know: A wiring diagram for your setup? The maxium voltage present? A link to manuals for your photovoltaic modules? Or even mention of which modules you are using?

I mean you will have to give us some hints, otherwise it is kind of hard for us to guess what is going on with your setup.

Although, I guess I could make some vague pronouncements about safety (or conversely danger), just based on the amount of power involved. At 600 watts, maximum power output, I think these modules, working together in full sun, are likely less dangerous than the van, with its engine running.

Moreover, the van with its engine running, is likely less dangerous than a fission reactor, with sticky, hand-adjustable, control rods.