Simple 12v Installation - Notes..

 If you filter on label "12v" in the blog, and read from the last post forwards you'll get more detail on this, but in summary, the following was how I built the basic 12v system on "Sparrow". I had a completely clean sheet for this - there was nothing on her, when I bought her

So basic requirements at this 1st stage was nothing more than:
  1. battery
  2. isolator switch
  3. bus bar
  4. switch panel
  5. solar
 ...working towards the following....

Click to "embiggen" - this diagram shamelessly ripped off from the "Sailing Around" blog (now sadly gone)

1. Battery

The original battery was an old one*, donated by a mate as he didn't need it anymore - lead acid, car battery type

Some basics - the battery dimensions were 13cm by 19cm by 24cm (W/L/H - battery dimensions are important to get the right size battery box), and it was 40 AMPH's - so not huge, but suitable to my purposes at this stage..  BEWARE - lead acid batteries are sold/advertised as "sealed unit's" but you can't turn it over or upside down with impunity while getting it into position as they have breather holes to allow any gasses to get out, so be careful when installing..

It will be in a battery box to protect against battery getting wet, or if it leaks, etcetc, which will then be either:
  • bolted between the sides of the quarter berths, just behind the cockpit drains and under the cockpit sole....  or..
  • bolted to the lip of the opening for the same space
The opening is 22cm high so everything will fit through in one dimension or the other...  I also have limited access to that space from above via the quarter berths - for the installation, I:
  1. trimmed part of the carrying handle on the battery box so that the handle then sat comfortably on the lip, and then 
  2. cut a wooden batten the width of the inside of the box to act a strengthening brace
  3. clamped the whole lot in place - batten inside box to lip
  4. drilled through the lip, box, and batten twice - once at each end to provide lateral bracing
  5. bolted through with M6 stainless bolts/nuts - I used some butterfly nuts to make it easier to remove in future should I need to...
..and after...  you can just see the hex heads of the M6 bolts behind the cockpit sole..
* the battery died soon after (voltage of 9.4 when I checked it, and despite 24 hours on charge, no difference afterwards.... 😏) so I replaced it with the following (£45 delivered) - note also I went for a Leisure Battery rather than a car/starter battery - there's lots of stuff on Google explaining the difference, but a Leisure battery is used to supply steady power over a period, as opposed to a starter battery which is designed to give a big oomph once ...

Leisure Battery 12V 50AH SuperBatt LM50 Battery Caravan Campervan Marine Boat
Brand: SuperBatt
Voltage 12 Volts
Item dimensions L x W x H 20.7 x 17.5 x 17.5 centimetres
Number of cells 6
Resistance 30 Milliohms
Terminal Marine Terminal

2. Isolator/master switch

Any number of these are available on eBay and the like, I am an electrical novice, but I had one of these on a previous boat and if it was good enough there, it's good enough for Sparrow..  this is the master switch to the whole system, if this is off, there's no power to any of the devices in the boat... I switch everything off with this switch when leaving the boat and if I'm doing any work on the boat 12v (attaching devices/fixing stuff etc etc).

The studs underneath are M10 - one will be connected via cable to the positive on the battery, the other connects via cable to a switch panel (see below)..

For cables I've bought a set of car jump leads - yes, I know tinned cable would be better, but they are four or more times the cost. From what I can tell these were/are 16mm2 (they are 100Amp capacity so plenty of oomph), with 8mm outside diameter and approx. 2mtrs long. The planned cable run will be short, no more than a metre, maybe a metre and a half.

For connectivity at the battery, I already have quick release cable clamps (you can get bolt on one's, but I had quick release previously so I'm falling back on duplicating what I know and am comfortable with.
Once connected to the clamps:

  • The other end of the positive cable has a copper tube terminal; it was approx. 16mm2 cable so I used a Copper Tube Wire Terminal / Lugs - Crimp type (picture above) - it was 35mm with a 10mm opening (to match the stud on the isolator switch it needs to fit on). Once the lug is firmly crimped/attached (use a hammer, or mole grips if you don't have one of them dedicated tools), wrap the lug end in amalgamating tape to protect, leaving just the ring opening umcovered...
  • I trimmed the cable to length once I saw where the switch physically was going to be. 
  • Connect it to the "in" (battery) side of the isolator switch.
  • The other end of the negative cable will go direct to the switch panel and the connector so the other end will depend on the fitting in the switch panel
  • Goes without saying keep the two cables well apart while they are connected to the battery, and not connected to anything else 😏
On my boat the switch is positioned just under the step into the cabin as it is out of the way there, adjacent to battery and switch box, protected by the step, and easy to get to - I used a 22mm flat drill bit to make the hole for the key shaft and then through bolted the base of the switch from behind...  

3. Bus bar

So.... thus far we have battery, in a box, bolted to boat (via battery box/ply board), with 16mm2 copper cables attached to the battery using quick release clamps - one positive/one negative. The positive one connected to the "in" side of the isolator switch, the negative one not currently connected to anything...

On the positive cable we have the isolator switch wired in, but on the negative side currently just the bare cable length. This (negative) cable I will connect to a 12v bus bar so I have a common negative for anything I want to attach to the switch panel...  you could use a power distribution post (like a big bolt) but a bus bar allows you to work on each device without having to take everything off the post to get at the cable you want (probably the one at the bottom!)

Seems stupid, but it was a bit of a eureka moment for me when I realised that all devices on the boat are switched on and off only via the positive really - all the negatives go to a common source which in essence is inert/static - any device on the boat can use any other devices negative, providing that negative is connected back to the switch panels negative.

You can buy a pukka bus bar, but they are 6 times the cost of the following which was recommended to me by the guys on the Practical Boat Owner web forum - this is a stainless steel 8 Way Earth Terminal Block...

You may want to jump to #5. ("Switch panel mounting box") at this point as you'll need somewhere to put this bus bar and it makes sense to do that, before you then connect the negative cable from the battery to one end of the bus bar using a crimp that is a suitable size for the connection - once the lug is firmly crimped/attached, wrap the lug end in amalgamating tape to protect leaving just the ring opening..

...and on to the next step in the puzzle..

4. Switch panel

So.... thus far we have battery, in box, bolted to boat (via battery box/ply board), with 16mm2 copper cables attached to the battery using quick release clamps - one positive/one negative. The positive one connected to the "in" side of the isolator switch, the negative (black) runs direct from the battery to a bus bar/earthing block. 

Now I need the thing to allow me to turn individual devices off and on - that's the switch panel....

These switch panels are available in a bewildering number of styles & prices, and are a bit of a Godsend as they come pre-wired, and with fuses...  I chose a 6 switch (6 gang) panel as my requirements will always be pretty simple, and I plan to combine some devices on a single switch anyway (nav lights for example) - I've also chose one where the light comes on when the switch is turned on (so at least you know there's power there when you see the light 😏)

The wiring basics for the switch are as follows:

  • first, switch power off at the isolator switch
  • we need power for the switch panel - using the same type jump lead cable as previously, measure off a length of red/positive cable enough to reach from the isolator switch to the switch panel. It will need the same 10mm opening crimped lug on one end to match the stud on the isolator switch.  Attach this positive cable to the isolator switch - it will go on the other stud to the one already being used, the "out" (power) side of the switch.
  • The other end of this positive will need a lug to match whatever the positive input on the switch panel is - connect it up.
  • the battery negative is already attached to the bus bar but as the switch panel is a device in its own right (as the switches light up when they are on), it also needs a negative - using the same type of jump lead cable as previously, attach it to the top of the bus bar at one end, and the switch panel at the other.
If everything is connected up, and the isolator switch is off (ie. power is on), then the lights in the switches will now work when you click them...  

All the subsequent things I'm going to connect to the switches on the panel (VHF/nav lights etc.) will then have their negatives screwed into the bus bar and their positives to the required switch on the panel.. 

5. Switch panel mounting box

So.... thus far we have battery, in box, bolted to boat (via battery box/ply board), with 16mm2 copper cables attached to the battery using quick release clamps - one positive/one negative. The positive one connected to the "in" side of the isolator switch, with a similar but separate cable connected to the "out" side providing power to a switch panel. The negative (black) runs direct from the battery to a bus bar/earthing block. The switch panel is connected to the bus bar, so when power is on via the isolator switch the panel is active....

I needed a cupboard or box to keep it all in, and rather than make one (which I could do, but it wouldn't be as nice) I ordered one of these from eBay - the quality is superb. I'll give it a coat of preservative, and then cut the holes for the switch panel/master switch/anything else in the lid (which is hinged, and has a catch for access to wiring)

My plan was to position it here - red or blue (which I went with in the end) depending on whether I put it in upright or on its side - the dark wood you can see is the lip to a shelf, I took the lip off so that the box sits directly on the shelf, cables will be fed from the battery up the inside of the bulkhead and through two drilled holes in the shelf/box into the bottom of the box itself....

Like this:

Over the preceding week I gave it two or 3 coats of wood preservative, then made the cut out for the switch panel with a jig saw and mounted the panel - power cables connect at the top of the board which is why it isn't central - I wanted to leave room to route cables...  on the left I had plans for a battery monitor, a cigarette/12v charger socket and/or a USB charger. Inside the box I have a glued a wooden batten on the left to mount the earthing block.

The box now sits on the shelf, in a cut out to the lip (jig saw again), I have two M4 stainless bolts through the bottom of the box and shelf holding it in place (they're 70mm long!). I used a 22mm flat drill bit to make the hole for the power cables to get "into" the box, drilling up through the shelf and into the box... 

6. Connecting it all up

For anyone coming along afterwards - see picture following:
  • at the bottom middle - the thick red is the positive from master/isolator switch; it connects to the common positive on the switch panel
  • at the bottom middle - the thick black is the negative direct from the battery attached to bottom of the bus bar/block on the left
  • the thick black negative from top of switching block connects to common negative on the switch panel
  • thin black negatives from the voltmeter and dual USB to the switching block (see later)
  • thin red positives from the voltmeter and dual USB to the relevant positives for each switch on the switch panel...
  • all spades/pins etc covered with amalgamating tape to keep damp out...
That's it - the system is ready - any devices you want to install simply require a negative cable to the bus bar, and a positive cable to the switch you are attaching them to on the panel 

Combine (or not) common devices (ie. things you want to come on at the same times as each other eg. cabin lights) by simply combining positives on a single switch - either via a clever spade connection or just twisting the wires together and putting them in a single standard spade connector. 

Negatives from multiple devices can share a single connection if needed, even if they are devices that don't need to be on at the same time, as the negative is inert/static. If you have already have a device installed near where you are installing a new device you can use the negative from that device as it saves cable runs, again twist the wires together or just use a clever spade connector.

7. Solar panel

My boat lives on a mooring in the summer with no access to mains power, so I need a way of keeping the battery topped up. On my previous boat I used to use two of the little tiny trickle chargers (1.5W) they sell for car dashboards - I put one in each window inside the cabin and they'd keep the battery topped up for the whole summer (I had very light needs on power - just a bit of VHF, and power for a small stereo amplifier) - this time round I've bought a fully weather proofed 5W panel from a recommended supplier on eBay (Friendly Green Giant)

I follow the "10% rule" when figuring out whether I need a solar charge controller or not - if the output of the panel in Watts is less than or equal to 10% of the capacity of the battery in Amp hours - then you're OK to do without. In my case 5 Watt panel/50Ah battery so, bang on "10%"

  • I replaced those tiny cables that came with the panel with a longer more robust one.. I used  1.5mm2 two core cable (5 mtrs), and I also bought myself a soldering iron from Toolstation as the existing cable was soldered on...  fired it up and when it was hot applied the end to the existing solder and removed the cable, I also removed the old alligator clips and put them to one side, I was planning to re-use them.
  • I then carefully laid a blob of solder on the new cable ends attaching it to the terminals on the panel. To finish I put the panel in the window and tested with a multimeter to ensure all was as it should be - it was...
  • Last job was to run some amalgamating tape round the junction box on the back of the panel to give some additional water proofing...

Connection to the battery was simply a matter of crimping those alligator clips to the other end(s) of the new two core, and then putting a small feeder cable to each quick release clamp on the battery which I could then attach the alligator clips to (the clips stopped the quick releases from closing when attached directly). 

  • Digital voltmeter and a dual USB charging port.. 

Need a way of seeing how the battery is doing, and the USB chargers are useful for phone's... 

Drilled two mahoosive holes in the fascia of the switch box in order to take the new voltmeter, and dual USB charger - happily it went largely OK, but a 28mm spade drill into thin plywood is never going to be entirely pretty. A sand down, and coat of wood treatment did wonders though and once on the boat, four M4 bolts hold the fascia panel, and the units were slid in and attached from behind...

Next job was to wire them in, and I decided to wire them independently, just because I could, and I had the switches available...  if I run out in the future then I can daisy chain them to one switch if I need to (I have subsequently done this)..   positive to the switch, negative to the bus bar using 11A 0.5mm2 single cable in red and black

Having done that, it was time to test - master switch on, Aux 1 flicked (lit up good) check voltmeter, 12.8 and working, flicked on Aux 2, and lifted the cover, USB's also lit up... triple success... 

  • Lights:
I bought four of these :

...for less than a tenner (twelve dollars in old money ) from a very helpful eBay'er in China - seriously - all four cost less than £7 delivered - from China - how on earth do they do it???! Either way I figured that for some cheap lighting these were second to none - they were bright and very easy to string together.

I use them as downlighters under the shelves that run down the sides of the cabin...

First pair rough fitted - once they were proved good I taped the electric joins with amalgamating tape, and then secured the wires more neatly with some cable clips.. I used spade terminals for connections because I can't help thinking that at the price I paid I need a solution where I can easily disconnect to replace

Spot soldered additional connection cables to the far end of the one on the left above, and then fed the wires through to the fore cabin where I daisy chained a third above the door...

Fourth one (a single) went in under the shelf on the starboard side - the shelf is shorter on that side to take account of the galley.

All were wired into the switch panel using 11A 0.5mm2 single cable in red and black and joints were all taped for support and damp proofing...  the positives are combined for port and starboard side, I used one of these (following) to be able to attach both positives to the single switch on the panel

"Female Spade Terminal with Piggy Back Male"...  apparently... 😏 

  • Tiller pilot power...
I've fitted a DriPlug 2-Pin socket in the cockpit to provide power for the tiller pilot...  not sure you can even get these anymore - other options are available..
Piccie courtesy Gael Force Marine [clicky]

Socket (back of it) is on the left in the picture above, two small terminals with a threaded screw to hold the wire, no room for normal terminals and mine didn't come with those rather handy looking terminals..  cable from the back of that goes to the power source.

I wired in an inline fuse as my original set up* was to wire the tiller pilot wiring direct to the battery, albeit I wired the positive to the switch panel (up) side of the isolator switch so that when that's off, there was also no power to the tiller pilot socket/circuit...

The inline fuse currently had a 15 amp fuse in it, Raymarine recommend 12 amp, and will provide some protection to the circuit. The cable I'm using is 2.5mm² two core tinned (marine grade) thin wall so is rated for up to 27 amps.
The cable run is likely to be no more than 2 mtrs so 2.5mm is over-spec but as Raymarine say in their manual (extract above) when in doubt err on the heavier side, so I went heavier..

* since the initial build I have simplified this installation massively, and the cable now goes to the switch panel in the same way as any of the other devices and without the additional in line fuse...

  • VHF:
The easy job was to connect it to power - used the usual 11A 0.5mm2 single cable in red and black - black/negative to the bar, red to the switch on the panel I was going to use - tested and it worked.

Being DSC I had two more jobs to do though - one simple one to program in the MMSI that I got from Ofcom when I registered the radio, but then the job that turned out to be infinitely more a pain in the ar*e - connecting my Garmin GPS 72 (which is truly old, but continues to work and therefore I am reluctant to upgrade) so I can send GPS data for the DSC function on the radio.

It's not directly related to installing a 12v system so more detail on how I fixed the DSC issue here [clicky] 

  • Anchor light
(NB. The following assumes one, your mast is wired, two, has an anchor light on top of it, and three, you have already installed a deck plug to provide power to the light when you connect it up to the boats 12v)

Feed wires through the deck from the cabin - I used the usual 11A 0.5mm2 single cable in red and black - and connected them to the deck plug. Double secured the wires in the socket fitting (red arrow above - I don't want to have to do this again for a while) - refitted the socket within the metal housing (with a smear of grease to help removal in the event I need to do it again, refit the deck fitting. 

I had a cunning plan to save wiring, which worked, and that was to use the negative from the forward cabin light as a common negative... at some point I'll probably fit a small bus bar somewhere unobtrusive up forward as a remote negative will assist greatly in cable runs for devices forward in the boat.

More detail on how I installed power to the light here [clicky] 


Just in case anyone is interested - here's the basic costs so far...
  1. Battery (75aH "Leisure") - £45 (Amazon)
  2. Battery box - £15.99 (eBay)
  3. Jump leads for battery cables - £4.90(eBay)
  4. Isolator switch - £4.99 (eBay)
  5. Bus bar - 8 Way Earth Terminal Block - £2.27 (Screwfix)
  6. Switch panel - £18.95 (eBay)
  7. 20 mtrs of 11A (0.5mm) single core wire (half red/half black) - £7 (Amazon)
  8. Dual USB Charger and Voltmeter - £10.50 (eBay)
  9. 5w solar panel - £11 (eBay)
  10. Lights - £7 (eBay)

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