Wiring a new lamp.

[real_vibes]

I have a new lamp for my boat. There is quite a lot of 12v wiring up the front end I could use to power it but I am a bit worried about drawing too much from one set of leads. Currently the radio cuts out if you turn all the over head lights in the kitchen on but not other lights!

 

Running new cables from the engine room is going to be a real pain though. How can I tell if I can get away with linking the new headlamp from the current wiring?

[ditchcrawler]

I have a new lamp for my boat. There is quite a lot of 12v wiring up the front end I could use to power it but I am a bit worried about drawing too much from one set of leads. Currently the radio cuts out if you turn all the over head lights in the kitchen on but not other lights!

 

Running new cables from the engine room is going to be a real pain though. How can I tell if I can get away with linking the new headlamp from the current wiring?

I would suggest you have other wiring problems that you should sort out before adding more to the system.

[duztee]

Are the lights in the kitchen LED's since some poor quality ones can have this effect on the radio signal, so check if it is only the sound which is going, if the actual radio is going off then i agree with the above and you have a problem to find and solve first.

[Chalky]

If you have an electrical background I suggest that you start by drawing a circuit diagram of what you already have and put on it the wire lengths, cable sizes and fusing. You should then have enough info to work out where to add the new circuit. Doing this will help work out what's going on and sort out your "interesting functionality".

If you're not electrically minded it would be worth finding some one who is to help you since as ditchcrawler says you need to sort out the existing issues before adding anything else.

[NMEA]

Get a decent multimeter, measure the voltage at the house bank, then turn on all your stuff at the front and go around measuring the voltage at each load to get an idea of the voltage drop, in the abence of a full and accurate schematic with all cabling sizes specified there is no other way of being certain. It may well pay you to run some heavy cables

(say 10mm2 conductor)terminating in a distribution point at the bow end so you will be able to add future stuff if you do have to run new cables, instead of just adequate for the lamp. If the voltage drop exeeds 10% even for for non critical aplications you need more cable.

Edited February 20, 2012 by NMEA

[ditchcrawler]

Get a decent multimeter, measure the voltage at the house bank, then turn on all your stuff at the front and go around measuring the voltage at each load to get an idea of the voltage drop, in the abence of a full and accurate schematic with all cabling sizes specified there is no other way of being certain. It may well pay you to run some heavy cables

(say 10mm2 conductor)terminating in a distribution point at the bow end so you will be able to add future stuff if you do have to run new cables, instead of just adequate for the lamp. If the voltage drop exeeds 10% even for for non critical aplications you need more cable.

10% that's 1.2 volts on a 12 volt system. I wouldn't want to be anywhere near that low.

[Arthur Brown]

First you already seem to have a problem lights vs radio, so don't add more til you know what you really have. Settle down and work out the wiring diagram and cable sizing of your boat. Yes I'd consider that pulling in an extra cable pair is the best answer to your headlight query. Your headlight is likely 60w so at 12v that will draw 5a so over a long caple you will lose volts.

[Radiomariner]

10% that's 1.2 volts on a 12 volt system. I wouldn't want to be anywhere near that low.

Think you might have misread NMEA's post. I would be concerned but not over worried about a 1.2V drop with a circuit on a full load. Such a drop on a circuit with say 4 20W lamps in circuit would mean a line resistance of about 0.18 ohms.

 

I agree that the OP must however look into that radio/lighting problem

Edited February 20, 2012 by Radiomariner

[Bob18]

It reads as if the radio is fed from the same wires as feed the overhead lights and they are "too thin for the job", or they are on a common negative, which is too thin...

 

A couple of things, it is not the best of practice to have the lights and a radio fed from the same circuit - you don't want a fault on the radio to leave you in the dark. (Or a lighting fault to leave you without entertainment....)

 

Start at the fuse board - How many fuses are there? Are they labelled? Are they labelled correctly? Are there any fuses that have no obvious function? What rating are the fuses? How thick are the wires going out from the fuse board? Is the wiring "tidy", or "messy"? Are wires labelled correctly? How are the negative wires brought back (to a common point/battery)? How thick are those wires?

 

(OK I know some these may be hard to do, but answering some of the questions is better than none, and the more answers the easier to sort you out (well that's the theory)

(I've used the word "fuse", but it might be a circuit breaker...)

 

Once you know what goes where its now a case of working out the best place for adding any required new wires, not forgetting on a boat you should really have an "out" and a "back" wire for each circuit

[ditchcrawler]

It reads as if the radio is fed from the same wires as feed the overhead lights and they are "too thin for the job", or they are on a common negative, which is too thin...

 

 

Or it could be his radio is using the lights as a neutral and when he switches them on its gone. There is no way you can second guess this with the limited information given.

[Bob18]

I'd go with that, as you say - too little info and too many possible bits of "silly" wiring...

 

One thing is sure and certain, there is at least one problem that needs to be sorted before the OP puts any more lights on the boat - and I'd go for "more than one" problem given the comment about "lots of wires to choose from"...

[Chris Pink]

I have a new lamp for my boat. There is quite a lot of 12v wiring up the front end I could use to power it but I am a bit worried about drawing too much from one set of leads. Currently the radio cuts out if you turn all the over head lights in the kitchen on but not other lights!

 

Running new cables from the engine room is going to be a real pain though. How can I tell if I can get away with linking the new headlamp from the current wiring?

 

Wading through all the grumbling I see no-one has asked whether you mean a headlamp (tunnel light) or cabin lighting?

 

if it's a tunnel light then perhaps there is some existing wiring there? It doesn't need to be particularly fat as most tunnel lamps are too bright and a bit of voltage drop wont do any harm. It is likely that the original wiring for a tunnel light is there somewhere, can you identify it as a switch near the controls at the rear of the boat? Then get someone with a meter trying each wire up the front until one changes voltage when you switch the switch.

 

If it's an interior light, try it and see, you'll soon find out through a bit of experimentation.

 

I am guessing that the reason you are asking these questions is that your electrical knowledge isn't great so I've tried a less technical approach.

 

I think the situation with radio and kitchen lights is a red herring - or if you prefer another problem altogether.

[NMEA]

10% that's 1.2 volts on a 12 volt system. I wouldn't want to be anywhere near that low.

 

Perhaps you could give me a rationale for that, ABYC, NMEA0400 standard, BSI, EU standards et al that boat builders worldwide and trained & certified tech's like me work to all use maximum 10% for non criticalsystems and equipment manufacturers also design to that standard. Of course we use 3% for critical systems but that has no bearing on any canal based vesselI've ever worked on, even nav lights don't really have to give the specified lumens that a 3% drop is needed for on offshore vessels. No coms, autopilot, sensitive nav kit to worry about so 10% is accceptable. Possibly bilge pumps, but again even with a small drop they are not a critical system as most I've seen on narrowboats are so small as to be suited to clearing minor drips and would never stop a sinking no matter how many volts you shoved up them.

Edited February 22, 2012 by NMEA

[ditchcrawler]

Perhaps you could give me a rationale for that, ABYC, NMEA0400 standard, BSI, EU standards et al that boat builders worldwide and trained & certified tech's like me work to all use maximum 10% for non criticalsystems and equipment manufacturers also design to that standard. Of course we use 3% for critical systems but that has no bearing on any canal based vesselI've ever worked on, even nav lights don't really have to give the specified lumens that a 3% drop is needed for on offshore vessels. No coms, autopiot, sensitive nav kit to worry about so 10% is accceptable.

Yes. I don't want that sort of volt drop on my boat

Edit

Sorry that was a rather rude and uncalled for reply.

I want to have minimum volt drop on any circuit on my boat, I realise that zero is impossible. It is far better to head for the highest standard than to what is the minimum and acceptable. Why walk on the edge when you can just as easily walk in the middle of the path.

Edited February 23, 2012 by ditchcrawler

[PaulG]

I have a new lamp for my boat. There is quite a lot of 12v wiring up the front end I could use to power it but I am a bit worried about drawing too much from one set of leads. Currently the radio cuts out if you turn all the over head lights in the kitchen on but not other lights!

 

Running new cables from the engine room is going to be a real pain though. How can I tell if I can get away with linking the new headlamp from the current wiring?

If you don't run a cable from the engine room area, how is the steerer going to switch it on when it's needed?

[Grace and Favour]

If you don't run a cable from the engine room area, how is the steerer going to switch it on when it's needed?

 

He could always use a wireless send/receiver and relay - - - however- I strongly suspect that consensus indicates that OP checks through the existing wiring before doing anything else

[NMEA]

Yes. I don't want that sort of volt drop on my boat

Edit

Sorry that was a rather rude and uncalled for reply.

I want to have minimum volt drop on any circuit on my boat, I realise that zero is impossible. It is far better to head for the highest standard than to what is the minimum and acceptable. Why walk on the edge when you can just as easily walk in the middle of the path.

 

 

Not an issue, I didn't think it rude, just uniformative and not addressing the question, as indeed is the edit. 10% is not walking on the edge, it's where most equipment is designed to operate, that is unarguable, just look at the tech spec. Perhaps an example may illustrate my point better; let's take a 7a load which could be anything from a largish lighting circuit to a bilge pump, then let's assume a 10% voltage drop under load, to support that would require 4mm2 cabling over a 15m round trip battery positive to battery negative. Now lets go for a 3% drop, to support that would require 16mm2 cable from battery positive to battery negative, that is extremely heavy cable and I doubt it is what is present on any non critical circuit using on such loads, certainly I have yet to see it despite many years experience.Most,if not all narrow boats I have worked on it is more common to find 2.5mm2 supplying such circuits which really is small, I reiterate 10% is not on the edge because that's what most 12vdc (so called)equipment is designed to operate at. Even the falacy that heaters require loads of volts to start is a nonsense, most are designed with an operating voltage of 10.8v before problems occur, it's usually the heater, not the voltage, or a bit of both. BTW, a zero voltage drop is not impossible, it's just that it would require 70mm2 cable to support my example. Many believe that doubling the cable size will halve the voltage drop, it simply aint so.

Edited February 23, 2012 by NMEA

[bottle]

Mmmmm.

 

I wonder, ref volt drop. one was talking under load and one was talking no load.

[NMEA]

Mmmmm.

 

I wonder, ref volt drop. one was talking under load and one was talking no load.

 

The only way to meaningfuly measure volt drop is under load otherwise it will show very little drop, not only load but the specific load that the circuit is required to service, that's why 0400 standards require volt meters to be tapped from loads or distribution panels rather than direct to the battery as they are in many cases.