Thought of some other options plus explanations of attitudes held. Don't know what your experience of camping (sic?) is so starting from the beginning.[You must be registered and logged in to see this link.]
A good basic guide. I might disagree slightly with.
Yes it is but apart from the use of inverters that cause a massive current demand I'd say that the really dangerous overload is an accidental one. A short circuit. These demand massive amounts of power cause cables to get white hot and can even cause the battery to burn or explode. I know of one dandy user who had a short and was within moments of a bad fire. Hence we're keen on fuses as close to any battery as possible.
The main hazard is from overloading supply cables. This causes heat to be generated and could lead to a fire.
Short thread on [You must be registered and logged in to see this link.]
Very long thread with much of the thought on 12S wiring negated by the link to the Caravan Club Fact Sheet [You must be registered and logged in to see this link.]
I included in my previous post. Still it shows how we got here.
Being of more delicate sensibilities I'm sure Mrs jh might like a tap. So other ways to skin a cat:
If all you wanted to do was run the tap then a small transformer would allow this [You must be registered and logged in to see this link.]
it would power either the lights or the pump. With fused outputs the 12V would be safe.
Battery power for the pump; a small motorcycle battery, two 6V lamp batteries (4R25 or PJ996) wired in series but these are expensive and not rechargeable or a pack of 8 1.5V AA batteries like this.[You must be registered and logged in to see this image.]
There are several battery holders on this theme you could use rechargeables but at charge of 2,900 mAh per battery http://www.kodak.com/eknec/documents/f4/0900688a8019d7f4/KAA.pdf you have what is roughly a one time use 3Ah battery for £1.33 or a 1Ah battery for £0.73 [You must be registered and logged in to see this link.] [You must be registered and logged in to see this link.] [You must be registered and logged in to see this link.]
Note to get the energy outut of the batterys you have to select "Technical Information" and the PDF will be downloaded.
One stage short of using a Leisure battery I normally regard these as junk but I can see a place for them here. [You must be registered and logged in to see this image.]
Why am I considering the use of a battery pack when it's the same price or possibly more than a leisure battery? It's a convenience. If you are on an EHU once plugged in it can provide a smoothed 12V supply for the fluorescent lights and the water pump.
If you fancy the odd night away without EHU it would give you enough power for one night: N.B. I've only looked at 2 power packs with 17Ah batteries. As always you don't want to discharge the battery by more than 50% so you are looking at a useable 8.5Ah Say just short of 3 hours of both lights or both lights for an hour and one light for four hours. This should be adequate for summer. Obviously the light times are less if the pump is used.
The battery pack can then be plugged into your car when you go out the following day to recharge but this could take four hours however they are light and portable. If going out for lunch or a couple of drinks ask can you plug it in as you're off mains at the moment.
Why is this different than just buying a very small capacity battery? If you remember our fondness for putting fuses near the battery terminals. Well on this the 2 12V outputs are fused so it's simpler than wiring up a battery. It has a usb port for charging phones and it has the light and compressor functions which could always come in useful. Not forgetting that once charged it can be used as an aid to starting though I'm not convinced that these are every very competent at this task.
Auto Express' review of power packs then links to descriptions of the two best performers. [You must be registered and logged in to see this link.] [You must be registered and logged in to see this link.] [You must be registered and logged in to see this link.]
Though I'm not sure I've presented it successfully this was meant to give a sliding scale of the possibilities of providing 12V power to your Dandy.The next step of attaching your Dandy to your car battery via the 12S or 13 pin connector requires more of an effort to check through wiring and the ultimate step of using a Leisure battery requires you to wire up the Dandy. You then get to questions about how you charge that battery if you're not on EHU (As stated previously if generally on EHU why the battery) do you remove the battery daily, or every trip or every other trip to recharge in the car or do you consider the ever cheaper solar panels.
I'm sure someone could tidy this up and i'm curious if anyone can think of more possible ways to provide 12V.
At least it's a bit more positive about options than my 1st post.