12v Electrics

[Liam]

We've recently bought a CB Radio for the boat. It's 12v and just has what looks like spade connectors on the end of the 2ft or so of cable which comes out of the back of the unit.

 

My question is, how would I go about hooking this upto the boats exisiting 12v system? The boat is a trad style, with the engine room forward of the back cabin. The batteries are by the side of the engine in the engine room, with ammeter, voltmeter etc. The main fuses for the internal lights, bilge pump, headlight and nav lights etc is in a cupboard forward of the engine room in the calorifier cupboard. Whether it makes any different or not I don't know but the ignition, water temp guage and switches for the bilge pump and headlight/nav lights are to the right of the footboard at the back. We'd like to have the CB up near the back aswell in the hatches.

 

I appreciate that there could be no straight answer to this as I've not explained the setup on the boat in any detail, so any ideas or comments would be great.

[John Orentas]

Hi Liam.

 

It goes without saying it is always best to keep things simple, if you have a bank of fuses it is best to make wiring connections from there. Any kind of radio is something of a special case in that you should avoid sharing wiring with florescent lights, motors or anything that might be a source of interference.

 

Locate the main feed from your isolator to the fuses and make the connection from that and fit a dedicated fuse, a 5 amp fuse and 1.5mm cable will be OK but avoid running even alongside those other cables for more than a couple of feet, the same goes for the 0 volts wire keep it all simple and separate.

 

If you are still bugged with interference of any kind you may need to beef up the main battery feeds or it you must wire back to the batteries with an in line fuse but this is bad practise. Keep the aerial cable well away from any other wiring.

Edited June 14, 2007 by John Orentas

[Liam]

Hi Liam.

 

It goes without saying it is always best to keep things simple, if you have a bank of fuses it is best to make wiring connections from there. Any kind of radio is something of a special case in that you should avoid sharing wiring with florescent lights, motors or anything that might be a source of interference.

 

Locate the main feed from your isolator to the fuses and make the connection from that and fit a dedicated fuse, a 5 amp fuse and 1.5mm cable will be OK but avoid running even alongside those other cables for more than a couple of feet, the same goes for the 0 volts wire keep it all simple and separate.

 

If you are still bugged with interference of any kind you may need to beef up the main battery feeds or it you must wire back to the batteries with an in line fuse but this is bad practise. Keep the aerial cable well away from any other wiring.

Hi John,

 

The 2ft length of 12v cable which comes out from the back does have an inline fuse built in so should I still hook this upto the main feed to the fuses? Also, when you say avoid running the cable alongside other cables for more than a couple of feet, is this due to interference? And does the same apply for the aerial cable?

 

Thank you kindly

[NB Phoenix]

Hi Liam

 

Another question is what type of antenna are you going to use? If it's a magmount that should be OK, but if you intended to drill through the steel roof and use a conventional aerial, you may find problems with an additional "battery negative" bonded to the hull.

 

Dam did I say bonded?

 

Oops!

 

Tin hat on and digging fox hole as we speak!

[Liam]

Hi Phoenix,

 

The aerial we've got, and going to use is a standard magmount one.

[John Orentas]

Hi Liam.

 

Yes, best to avoid other cables for reason of possible interference, fridge supply cables seem to be the worst, personally I don't like in-line fuses I would cut it off and install things in a permanent manner, connect to a plug and socket so you can take it out. Same thing with the aerial cable. In practise CB radios work very well on narrowboats you have a massive ground plane which people who know about these things consider important.

 

I could occasionally get an 8 mile range, I don't know why more people don't have Cb's on their boats, ideal for keeping in touch with fellow cruisers.

Edited June 14, 2007 by John Orentas

[Tortoise]

The 2ft length of 12v cable which comes out from the back does have an inline fuse built in so should I still hook this upto the main feed to the fuses?

 

No - the inline fuse by the equipment itself protects the radio, but not the cable.

 

The fuses at the distribution point protect the cables, in that the fuse/circuit breakers should be rated LESS than the current capacity of the cable - that way if there's a short in the cable run, the fuse goes, and your boat doesn't catch fire.

 

So you'll need to run the power supply from a spare way on the fuseboard, and make sure you have the lowest rated fuse on that point you can get away with.

[John Orentas]

No - the inline fuse by the equipment itself protects the radio, but not the cable.

 

The fuses at the distribution point protect the cables, in that the fuse/circuit breakers should be rated LESS than the current capacity of the cable - that way if there's a short in the cable run, the fuse goes, and your boat doesn't catch fire.

 

So you'll need to run the power supply from a spare way on the fuseboard, and make sure you have the lowest rated fuse on that point you can get away with.

 

 

I wish people would stop talking in these terms. Fuses are not there to stop your boat catching fire and a fuse never protected any equipment, there are other ways to do that.

[Liam]

Thanks for all your help.. I shall do the following over the weekend..

 

Run the cable from one of the free points within the fuse board just forward of the engine room, to the back end within the hatches making sure it's seperated from the rest of the cable run towards the back end. Put a permanent plug on the end of the cable at the back end in the 'control panel' with the nav light switch, etc. which will enable me to plug/unplug the CB when it's being used/not being used. The magmount aerial is directly attached to the CB with the cable attached to it. This will just be sat on the roof when the CB is being used.

[Tortoise]

I wish people would stop talking in these terms. Fuses are not there to stop your boat catching fire and a fuse never protected any equipment, there are other ways to do that.

 

apologies if I was a little forthright... but fuses are there to stop an overcurrent fault causing further damage, to equipment or cable, and do so. Please expand on your answer, though?

[John Orentas]

apologies if I was a little forthright... but fuses are there to stop an overcurrent fault causing further damage, to equipment or cable, and do so. Please expand on your answer, though?

 

 

Hi Torty.

 

It has always been an accepted practise to opt for a fuse that will protect the cables hence the original concept of the 13 amp plugs that we have got used too, originally it was the accepted thing with a few exceptions to fit a 13 amp fuse in all plugs on the grounds that flexible cables would always be 1.5mm or bigger.

 

It is hard to think of a piece of equipment that a fuse could be expected to protect, for example a defective component in a TV set will invariably kill the set long before a current rise can be detected by a fuse or even a circuit breaker, (that will be about a year in electronic terms) all you can rely on is that the fuse when it eventually goes will cut off the power to the set.

[Tortoise]

Hi Torty.

 

It has always been an accepted practise to opt for a fuse that will protect the cables hence the original concept of the 13 amp plugs that we have got used too, originally it was the accepted thing with a few exceptions to fit a 13 amp fuse in all plugs on the grounds that flexible cables would always be 1.5mm or bigger.

 

It is hard to think of a piece of equipment that a fuse could be expected to protect, for example a defective component in a TV set will invariably kill the set long before a current rise can be detected by a fuse or even a circuit breaker, (that will be about a year in electronic terms) all you can rely on is that the fuse when it eventually goes will cut off the power to the set.

 

Not quite what your previous comment said, then... ;-)

 

It has, in my experience, never been 'accepted practise' to fit 13A fuse in 'all' domestic mains plugs - the correct practise is to use the minimum appropriate fuse for the equipment & cable. When I talk about protecting the cable, it is essential that the fuse goes before the cable overheats...

 

... and that's especially important in 12v systems, where large currents are potentially available. Any distribution fuse/circuit breaker should fail in the event of a short in the equipment or along the length of the cable - possibly likely on some boats. I do know of a near-fatal fire on a boat where the cable between the battery and distribution point shorted, melting the cable, releasing poisonous fumes into the cabin - that's what happens when you don't have cable protection. Such fuses protecting this line aren't standard, but I intend to fit one even though the distribution panel will be only a couple of feet from the batteries - the joys of redesigning a boat.

 

Incidentally, I'm not here to prove how much I know, or do anyone else down - but to learn from others, and offer help where I think I can. I suspect we're both trying to say the same thing, but even if a safety device isn't perfect, it's worth having, and in the correct place, that's all. My original comment to the original question was that even if the equipment is fused, the cable feeding it also needs to be fused at the feed end - this could be a cable running the length of the boat, after all.

[Tony Brooks]

Hi Torty.

 

It has always been an accepted practise to opt for a fuse that will protect the cables hence the original concept of the 13 amp plugs that we have got used too, originally it was the accepted thing with a few exceptions to fit a 13 amp fuse in all plugs on the grounds that flexible cables would always be 1.5mm or bigger.

 

It is hard to think of a piece of equipment that a fuse could be expected to protect, for example a defective component in a TV set will invariably kill the set long before a current rise can be detected by a fuse or even a circuit breaker, (that will be about a year in electronic terms) all you can rely on is that the fuse when it eventually goes will cut off the power to the set.

 

 

Anyone care to explain the "funny" fuese that we used to find mounted on TV circuit boards when we ignored the warnings and removed the back?

 

:-)

 

Tony Brooks

[John Orentas]

Anyone care to explain the "funny" fuese that we used to find mounted on TV circuit boards when we ignored the warnings and removed the back?

 

:-)

 

Tony Brooks

 

 

Very odd the TV industry, have you ever noticed that the resistors scattered liberally all over the circuit boards were always 'dead sized' or in other words a bit of circuit that carries 20 watts will always have resistors rated at 20 watts and very often they will blow. I used to wonder why they did that when a 50 watt one would cost no more and would probably last 100 times longer before it overheated and blew. I have a theory that the TV manufacturers used the resistors as fuses to save money or for some other reason. Very easy to repair though, look for a burned out resistor, replace it and odds on the tele worked again.

 

On the other hand I now have a wide screen jobby (built it myself but thats another story). Amazing contraption, not one resistor variable or otherwise, not a single capacitor other one or two big ones with the power supply. In fact nothing in there except an HT transformer with it's associated bits and two massive CPU's with about 100 pins on each. Really it's a computer with a screen tacked on to it.