12 volt circuits

[Moley]

At the moment, my boat electrics are a bit of a mess, and I'm not keen on these ceramic fuse holders.

 

 

I'm trying to get my head around what went where, how to improve things, and what I need to fit, and think I might be heading in this direction:

 

http://www.ekmpowershop.com/ekmps/shops/gs...LAYCAT&catid=34

 

Does that seem reasonable to you, dear readers, and how many circuits should I allow for.

 

I am fitting a very basic (2 socket) 240v supply. Fridge will be gas or 240v, cooker will be gas only with battery ignitor.

But what about the 12 volt? As I see it, it should be quite a simple installation, but what fused supplies do I need?

 

In no particular order:

1. Engine electrics via ignition switch

2. Wall lighting, Port

3. Wall lighting, Starboard

4. Ceiling lighting

5. Headlight

6. Bilge pump

7. Water pump

8. Horn

9. Appliances, Port (toilet etc.)

10. Appliances, Starboard (TV, radio etc.)

 

So is 10-way enough, or am I missing anything?

 

Thanks,

Ade.

[dor]

Keep it simple!

 

I would think that 10 way is more than enough - some can be combined, e.g. horn & headlight.

 

The bilge pump does not want to be fused through your main panel, but should be fed directly from the leisure battery through an in-line fuse. Halfords do a fuse holder that takes blade fuses and is waterproof.

[stuart]

Think about it as 3 parts. The 240v (keep completely seperate from 12v), switched 12v for your lighting, water pumps etc. and a perm. 12v circuit for bilge pump, c/heating pump, cd/radio memory etc.

 

I have 10 switched 12v circuits, some of the lighting is joined together on a room by room basis but dont put all your lights in one circuit, if thr fuse blows at night your in complete darkness!

 

All my electrics are housed in a cupboard so I've also got a small 12v light in the cupboard running off the perm. 12v circuit so that when I turn off the main supply I can still see what I'm doing!

[John Orentas]

Hi Ade.

 

If anything I think you have overdone it a bit 2 lighting circuits are enough and there is nothing wrong with doubling up on similar power appliances, for example only one circuit is required for all pumps and similar for horn and tunnel light. Yes ceramic fuses are rubbish, the automotive blade types are far better, though I prefer cartridge type industrial fuses.

 

To terminate the inevitable large numbers of wires of the same connection arrange for some kind of bus-bar system you can make them yourself from brass bar or angle or you can buy them.

 

Include some instrumentation so you can see what is going on volt meter and shunt type ammeter.

 

Fit wire numbers to at least the more important conductors.

 

Most important draw a good intelligible wiring diagram.

 

Dont use those modern automotive isolators (removable red key) unless you get the very big ones 300 amps upwards.

[Denis R]

Hi Moley,

Just a few thoughts on aesthetics. I think that every panel has the potential to become a cluttered 'bird's nest'. At the same time it can be made to look workmanlike without a lot of extra effort. If the individual wires are routed through decent cable trunking, in-comers are retained with cable glands and connections are made with 'proper' terminations rather than chocolate block and a bit of an effort is made to identify the wires and make their connections tidy, the whole thing takes on a totally different feel. Hopefully then if something does give a problem, the first thought won't be 'where the hell do I start to look in this lot?'....

[Moley]

Thanks for the comments folks, keep 'em coming.

 

OK, I'm already realising anomalies with existing wiring. At the moment there's a fused supply to bilge pump switch (top row, 4th from left, white wires), but as these wires go nowhere near the actual bilge pump, this can be disregarded. Not actually sure where they go, I seem to have a lot of taped-up loose ends.

 

I love the way some of these connections are made, and particularly like the horn connection (yellow wire twisted together between fuse blocks).

 

It's no real surprise that my temperature guage is a bit 'twitchy' and the voltmeter doesn't seem to do much.

 

Incidentally, if I've got a pair of wires running the length of the cabin for a lighting branch, what's the preferred method for tapping in to those wires (chocblock seems like a few too many screw connections and I don't like Scotclocks). Am I right in thinking watts over volts equals amps, so 10amps = 6 x 20w lamps?

[John Orentas]

Hi Ade.

 

I would certainly reccomend to keep connection of wiring other that at your distribution panel to a minimum.

 

For lighting take a 1.5mm cable (+12v) to each light switch and a 1.5 (0v) to each fitting and a wire between them try to use sensible colours black or blue for 0v red or brown for +12v. Don't bother with sheathed cable for 12 volt systems.

 

In a simallar way wire all 12v sockets right back to the panel, 2.5 cable will be usually OK perhaps up to 6mm for the fridge, but no more. Earths are not required.

 

You will end up with a lot of wires back at the distribution panel label them as you go along, but it will be simple and straightforward. If you are concerned about volt drop for a specific application let me know. Will need current rating and there and back wiring length.

 

Yes, each 20w 12v light = 1.66 amps. 10 lights = 16.6 amps

 

I would fuse in lots of max 5 lights use 15 amp fuse.

[dor]

If you have a 12V TV at the front of the boat, I would run a 10mm pair up to a dedicated socket. This is because most TVs will drop out when the voltage drops below a certain level, and this can easily happen as the TV will probably draw 3 - 4 amps and the there could be getting on for 30 metres or more of wire. 6mm wire would probably be ok if the TV is flat panel.

[John Orentas]

4 amp TV 12 volts 30 metres of 2.5 cable Volt drop = 0.84 volts.

 

Given that the system will have approx 12.5 volt supply. That is perfectly Ok.

[dor]

As you so often say John, theory is all very well, but experience counts for much. I replaced my 2.5 mm tv supply with 6mm as I got fed up with the TV dropping out at 10pm. The 6mm cured it, and if I was doing it again I would use 10mm so i could run my dvd player at the same time when the battereis were less than full.

 

If the system was supplying at 12.5 volts, then 2.5 might well do, but do we all sit down in the evening with fully topped up batteries?

[Moley]

So for an early 80's boat, and given that all lighting, pumps and appliances will be individually switched, do I actually need a fancy, fused, switched distribution panel, or am I OK with a simple blade fuse carrier and bus bar return.

 

In which case, anyone suggest suppliers?

[John Orentas]

So for an early 80's boat, and given that all lighting, pumps and appliances will be individually switched, do I actually need a fancy, fused, switched distribution panel, or am I OK with a simple blade fuse carrier and bus bar return.

 

In which case, anyone suggest suppliers?

 

 

You can get everything you need from an electrical wholesaler including wire, tie wraps trunking and all the other bits an bats you will need, remember too you will have heavy cables coming from the batteries. I would have a preference to having as much as possible of all this in the cabin area so it stays clean and dry, don't hide it away to much you will need to access it at night in a hurry. As you will no doubt have a split charge system I would also have two separate isolators one for the domestics say 40 amps and a heavy duty job for the engine starter* say 150 amps.

 

Depending on your engine and battery layout it is good to have even the engine isolator and split charge system in the cabin but you need to keep starter cable lengths down to a minimum, but even then you can double the length if you double the size. The feed cable to my starter is probably 3 metres, 35mm.

 

*You do have a few options for the engine isolator an industrial 3 pole, 50 amp per pole type makes a neat job, you need to parallel the switches keeping the conductors big.

[Maffi]

The good old Hercules C130 work horse has a lot of lighting circuits at the rear. Despite having about 24 Sq ft of CB and fuse panels on the flight deck a secondary CB panel is located near the rear para doors for all the rear lighting. This utilises a huge length of 6mm diameter cable travelling about 60ft down the fuselage from the flight deck.

 

Given that main lighting needs would be in the Galley and living room (assuming they are at the front of the boat) this might be a good idea to use in a narrow boat. Get all the volts drop done and dusted in one piece of large cable to a small secondary CB/fuse panel up in the Galley. The resulting cables to the lights could then be smaller and more manageable. Yes/No?

 

Just thinking out loud

[Guest]

As you so often say John, theory is all very well, but experience counts for much. I replaced my 2.5 mm tv supply with 6mm as I got fed up with the TV dropping out at 10pm. The 6mm cured it, and if I was doing it again I would use 10mm so i could run my dvd player at the same time when the battereis were less than full.

 

If the system was supplying at 12.5 volts, then 2.5 might well do, but do we all sit down in the evening with fully topped up batteries?

In theory, theory and practice are the same. In practice however they are different.

[david and julie]

Moley wrote.

Does that seem reasonable to you, dear readers, and how many circuits should I allow for.

 

I bought the 10 way unit you show on the link and have all you mention plus a macerator toilet. You mention fuses but these units actually come with a selection of differently rated circuit breakers (which, I am sure you meant).

 

I got my unit from Midland Chandlers but it is the same thing. They come with a slip of paper telling you the rating and position of the fitted breakers, some of the breakers may be no use to you but they do sell replacements in whatever sizes you need.

 

The supply for mine comes from the domestic batteries-isolator-70 amp main fuse(sterling gold).it is in 10mm cable.

 

I found it cheaper to buy 2 rolls of 10mm cable(black/red) and this did both telly, fridge, (separately)and the power and earth to the breaker boards. I got my cables from vehicle wiring supplies. The thinwall is slighly dearer, but far easier to work with.

 

IMHO, the best way, for the lighting cables really is to strip them back and then twist together, soldier then tape up. Choc blocks are to big and scotch or the piggyback type are also big and a bit unreliable.

[DHutch]

...remember too you will have heavy cables coming from the batteries...

For this we used arc/mig welding earth cable.

- Its about 16mm diameter, we used it between the batteries, and from the batterys to the dis board.

- I Beleave we got it quite cheaply as well.

 

 

Daniel

[Guest]

Mine from memory (bad) is something like this:

 

10way domestic dis board with standard 10 amp breakers (bsc man actually liked this! )

 

4 x lighting circuits

2 x 12 volt socket circuits

1 x sump pump

1 x water pump

1 x feed to tunnel lamp/horn/nav lights

 

That is in fact only nine, but you get the idea. All cables of course are well in excess of 10 amp breaker rating. Cables feeding dis board are rated at and fused at 100amps (overkill).

[DHutch]

10way domestic dis board with standard 10 amp breakers (bsc man actually liked this! )

Yeah, 'we' also used a 240v dis board (MK sentry) with a load of 6A breakers.

 

We have:

Navlights

Bildge pumps (x2)

Lights-Daycabin/galley

Lights-Forward

Lights-Aft

Skts Port

Skts Stbd (inc tunnel light)

Fridge

Shower Pump

Water Pump

And four spare (inc one 16a)

 

 

 

 

Daniel

[ChrisPy]

A couple of posts about using domestic panels for low voltage applications. I have read that using AC rated switchgear is unsuitable for DC. Any truth in that?

[bottle]

A couple of posts about using domestic panels for low voltage applications. I have read that using AC rated switchgear is unsuitable for DC. Any truth in that?

 

Yes

 

The 'problem' is the speed and distance (gap) of the contacts. DC (volts) are more likely to create and maintain an arc, especially at high load.

[Moley]

Hang on, let me get this straight:

 

So Catweasel and Dan are saying that a domestic 240v AC distribution board can be used on 12v DC, hence a 10amp breaker (2400W @ 240v) will do the same job on DC (120W @ 12v), but Chris and Bottle reckon it's dodgy?

 

Ever asked a question and wished you hadn't?

I'm tending to think I might stick with the ceramic fuses.

 

Presumably, the switched breaker board I linked to at the start has to be wired from the back, is this a pain in the posterior?

[John Orentas]

Hang on, let me get this straight:

 

So Catweasel and Dan are saying that a domestic 240v AC distribution board can be used on 12v DC, hence a 10amp breaker (2400W @ 240v) will do the same job on DC (120W @ 12v), but Chris and Bottle reckon it's dodgy?

 

Ever asked a question and wished you hadn't?

I'm tending to think I might stick with the ceramic fuses.

 

Presumably, the switched breaker board I linked to at the start has to be wired from the back, is this a pain in the posterior?

 

 

Hi Moley.

 

They are both sort of correct, you can get circuit breakers which have an AC and a DC rating on them but they are all much the same. Having said that I would stick with fuses, but not those ceramic ones they are lousy.

 

(Breakers are always rated in amps, not watts)

[Moley]

Having said that I would stick with fuses, but not those ceramic ones they are lousy.

 

So where can I get a nice new blade fuse carrier panel? I've tried googling and drawn a blank.

 

Actually, strike that, I think I've found what I need

http://www.autoelectricsupplies.co.uk/prod...?product_id=215

 

(Breakers are always rated in amps, not watts)

 

Yes, that's what I think I said, whether you're drawing 2400W @ 240v AC or 120W @ 12v DC, 10 amps is 10 amps?

Edited January 10, 2006 by Moley

[david and julie]

Presumably, the switched breaker board I linked to at the start has to be wired from the back, is this a pain in the posterior?

 

I can only speak for the one I bought from Midland Chandlers, which is indentical to look at and more or less the same price, so I presume they are the same.

 

The board comes fully wired ready to fit. The only part I disliked, which is not that much of an issue, is that there is not a dedicated terminal on the back for the 10mm cable. The unit consists of banks of piggy back spade terminals linking the live inputs together, these are pre wired for you, there are 2 terminals left blank(1 each bank) for you to connect your 10mm cable too. Obviously such large cable wont take small spades. What I did was to mount a choc block close by with the 10mm cable in one side and two thinner cables coming out, one to each bank. Hope you follow my hopeless description. Basically all you have to do is mount the unit fit an incomming live then take your appliance lives to their(correctly rated) terminals.Flags made of masking tape are good enough for marking the cables although plastic numbers look more professional.

 

Also the stickers mainly relate to salty boats and most are no use

[alan_fincher]

Yes

 

The 'problem' is the speed and distance (gap) of the contacts. DC (volts) are more likely to create and maintain an arc, especially at high load.

 

I understand this argument....

 

But, unless you throw the switch when a lot of current is being drawn, I can't see it being a big issue.

 

Our boat also came using a 240 volt fuse box for 12volts, (from memory probably a Wylex one), with 8 fuses, each wired with good old fashioned fuse wire.

 

As I tend to ensure everthing on board is switched off before thrown any master switches, I can't see why this should give any trouble. I'm assuming it's as old as the boat, and seems to do the trick.

 

Similarly, I wouldn't plan to pull the fuses out with current actually passing through them.

 

Of course the other argument is that if you use 240 volt equipment for 12 volts, and also have 240 volts aboard, then the two can get mixed up. I believe you can meet any requirements in this area by sticking big 240 volt and 12 volt labels on each

 

What I would definitely NOT recommend is using 13A square pin sockets to supply 12 volts, as we also have aboard. This means you would have 12 volt equipment with a 240 volt plug on, (we don't !), and the possible consequences of that should be obvious. At such point as I need to plug any 12 volt equipment in, I'll certainly change this unsatisfactory arrangement !