12 v horn problem

[Tony Brooks]

12 minutes ago, Greg & Jax said:

Thanks again .

I  will now go and see about swapping it for another 10 amp breaker .

Cheers Greg 

If that is the horn breaker then it might not be such a bright idea because from the 150W your new horn draws over 10 amps (say ab0ut 12). That may be why the old breaker failed - long term over loading. Also be aware that if that 150W is a continuous rating the horn is likely to draw more by way of an initial surge before the contacts start making and breaking.

 

Just to complicate the issue you can't simply put a higher rated breaker in until you assure yourself that the cable currant is at or higher than the breaker rating. Luckily with such a long cable run it probably will be because it would have been specified (I hope) to minimise volt drop but that's a guess and it depends upon any new breakers current rating.

[Sir Nibble]

11 minutes ago, Tony Brooks said:

If that is the horn breaker then it might not be such a bright idea because from the 150W your new horn draws over 10 amps (say ab0ut 12). That may be why the old breaker failed - long term over loading. Also be aware that if that 150W is a continuous rating the horn is likely to draw more by way of an initial surge before the contacts start making and breaking.

 

Just to complicate the issue you can't simply put a higher rated breaker in until you assure yourself that the cable currant is at or higher than the breaker rating. Luckily with such a long cable run it probably will be because it would have been specified (I hope) to minimise volt drop but that's a guess and it depends upon any new breakers current rating.

Hear hear. The 12A is an average drawn when the horn is operating, the coil may well be drawing 30 plus when the contacts are closed.

[Alan de Enfield]

22 minutes ago, Sir Nibble said:

Hear hear. The 12A is an average drawn when the horn is operating, the coil may well be drawing 30 plus when the contacts are closed.

And we don't know if the 'much quieter' (old) horn actually draws anything like 12 amps.

[Greg & Jax]

Hi guys .

I tried the other 10 amp breaker and it doesn't work the horn but  when I use the 15 amp breaker it works fine . 

Regards Greg .

[Tony Brooks]

15 minutes ago, Greg & Jax said:

Hi guys .

I tried the other 10 amp breaker and it doesn't work the horn but  when I use the 15 amp breaker it works fine . 

Regards Greg .

Greg - do you not understand what you are told?

 

You simply can not put a higher rated fuse or circuit breaker into a circuit unless you are sure the cable is also rated for at least that current.

 

I get the feeling the existing cable may well be of marginal capacity so might no have sufficient current capacity.

[Greg & Jax]

Hi Tony. 

I get what you and Alan ment .

I need to up the breaker to 15 amp that will run the horn  , but I need to make sure the cable will be thick enough to wire it permanently.  

I only used it as a way of testing if it all worked as it should . 

I've now disconnected the horn and will find out the rating of the cable before reconnecting with a bigger breaker .

Regards greg .

[Keeping Up]

First, is there any way you can find out the size of the existing cable, to determine what size breaker is satisfactory? If necessary lay the end on a ruler (to show the scale) and take a photo.

 

Another thought, does the horn have an adjustment screw? I have often found it necessary to adjust the screw slightly to ensure that the horn operates at the end of a long cable.

[Alan de Enfield]

35 minutes ago, Greg & Jax said:

Hi Tony. 

I get what you and Alan ment .

I need to up the breaker to 15 amp that will run the horn  , but I need to make sure the cable will be thick enough to wire it permanently.  

I only used it as a way of testing if it all worked as it should . 

I've now disconnected the horn and will find out the rating of the cable before reconnecting with a bigger breaker .

Regards greg .

 

Try and find the CSA (cross sectional area) of the cable.

The current rating of the cable should be well 'overspecified' to accommodate a 17 metre length volt drop.

 

As I showed earlier drawing 12+ amps over 15 metres require very thick cable (16mm2 +) because of the volt drop, NOT the current carrying capacity.

 

2.5mm2 will more than carry the necessary current, but 2.5mm2 will mean that you only get about 10 volts out of the end of the cable.

Edited May 30, 2020 by Alan de Enfield

[Greg & Jax]

Hi guys .

After have another look at the wiring etc it seems the original horn was on a 6 amp breaker and the headlight was on a 10 amp breaker . As Alan suggested I swapped them round .

The horn still doesn't work on the 10 amp breaker but does if I fit the  15 amp breaker I have bought .

Now the cable for the headlamp is  thicker than the horn cable but  it's still not as thick as Tony suggested 16 mm2 .

Is it still advisable to run a thicker cable .

Do the pos and neg cable need to be the same thickness ? .

Cheers guys  Greg. 

 

[WotEver]

6 minutes ago, Greg & Jax said:

Is it still advisable to run a thicker cable

What size is the existing cable? You can compare it with some cable of a known size or you can count and measure the strands, but the latter requires a micrometer.  Note that it's the copper core that you need to compare, not the outside diameter of the insulation.

8 minutes ago, Greg & Jax said:

Do the pos and neg cable need to be the same thickness ? .

Yes, although it wouldn't hurt if the negative was thicker.

 

As a real rough-and-ready calculation, strip a bit of the cable, measure as accurately as you can what the diameter is, then use pi x r² x 0.8.

[Tony Brooks]

It was Alan that mentioned 16 sq mm CCSA not me.

 

It won't hurt if either or both cables were larger than the theoretical requirement apart from the OPs wallet.

 

Just had a naughty bodgy type thought. If the horn and headlamp negatives were joined at the front of the boat it might reduce the negative cable resistance enough to allow the horn to work. This won't work if either use double pole switching but I doubt they do.

 

 

[Joe Bourke]

I'd be tempted to use a relay. ?

[Tracy D'arth]

Could I refer you back to posts 35 and 65 in this thread?

TD'

[Tony Brooks]

1 minute ago, Joe Bourke said:

I'd be tempted to use a relay. ?

 

How would that solve any issues? The OP will still have to run more cables. Thick ones to carry the horn current via the relay contacts and at thin one to feed the coil.

[Greg & Jax]

Hi guys . 

Thanks for the reply,s .

I will run new thicker cables to be on the safe side , it not so much the cost just 're routing the cable to the front is going to be a pain . 

Cheers Greg. 

[TheBiscuits]

3 minutes ago, Greg & Jax said:

I will run new thicker cables to be on the safe side , it not so much the cost just 're routing the cable to the front is going to be a pain . 

 

At this point I think you should just buy another horn of lower power instead of rewiring the boat.  It's only because you bought an oversized horn that it needs so much juice, so get a smaller one.

 

 

 

[Slim]

18 minutes ago, Greg & Jax said:

Hi guys . 

Thanks for the reply,s .

I will run new thicker cables to be on the safe side , it not so much the cost just 're routing the cable to the front is going to be a pain . 

Cheers Greg. 

76 posts discussing a non working horn! Yes, I know it's because most people aren't boating and there's a limit to how much one can say/read about Covid19. ? To the OP. Rather than ripping half the boat apart to run thicker wires why don't you just buy an air horn? When I fitted my boat out 25 years ago I ran the cables and fitted the button etc but just could not find a suitable horn, size , appearance etc. Short term I got an air horn that I use to this day.. It has the advantage that you can point it in the direction of 'interest' and is far more effective than a squeaky electric horn. Overall running costs are tiny and not really a consideration. 

Edited June 5, 2020 by Slim

[Joe Bourke]

Regarding the relay. Couldn't you use the existing cables to the relay and bigger supply cable from somewhere like a pump or whatever in that area?

[WotEver]

39 minutes ago, Tony Brooks said:

Just had a naughty bodgy type thought. If the horn and headlamp negatives were joined at the front of the boat it might reduce the negative cable resistance enough to allow the horn to work.

I had the same thought but then I figured if OP was running a new pos then it's just as easy to run a new neg at the same time  

[Greg & Jax]

To be honest the ones I have had in the past were cheap ones an not very loud .

I bought this stainless one because it said 12 v  low current , it's just not so low 

It's also become a bit of a mission now .

[WotEver]

3 minutes ago, Joe Bourke said:

Regarding the relay. Couldn't you use the existing cables to the relay and bigger supply cable from somewhere like a pump or whatever in that area?

The problem with this is the 'whatever' bit.  Pump feed won't necessarily be live all the time...

1 minute ago, Greg & Jax said:

To be honest the ones I have had in the past were cheap ones an not very loud .

I bought this stainless one because it said 12 v  low current , it's just not so low 

It's also become a bit of a mission now .

[Tracy D'arth]

Soon we will not need any horns if C&RT have their way.

 

See

https://narrowboatworld.com/12328-harecastle-tunnel-on-part-time

 

Thin end of a very big wedge?

 

TD'

 

[Tony Brooks]

27 minutes ago, WotEver said:

I had the same thought but then I figured if OP was running a new pos then it's just as easy to run a new neg at the same time  

My thought was that reducing the voltdrop on just the negative might be enough to let the horn work on the existing positive.

 

As a proper beam is not vital for the headlamp maybe the lamp could be modified to accept a 21 watt bulb and the two sets of wires swapped over - may be a big favour to oncoming boats.

[tehmarks]

Quote

And don't attempt it if either your light or horn does not work—you will not be allowed through and no longer will you be loaned them either as in the past.

I had to temporarily bodge-wire in my horn at the stern this morning as I discovered yesterday that I've developed a similar cable fault to the OP, and the air horn I bought can't do a long blast. 200m into the tunnel my headlamp tripped the power to the entire switch panel - headlamp, nav lights and horn. Did pretty much all of the tunnel without either ?

[Tony Brooks]

14 minutes ago, tehmarks said:

I had to temporarily bodge-wire in my horn at the stern this morning as I discovered yesterday that I've developed a similar cable fault to the OP, and the air horn I bought can't do a long blast. 200m into the tunnel my headlamp tripped the power to the entire switch panel - headlamp, nav lights and horn. Did pretty much all of the tunnel without either ?

In your case the horn mechanism may have seized/stiffened or the contacts burned/got dirty so it no longer works with whatever voltdrop is along the wiring. Although i suspect a new horn will cure your problem some advise that you try twiddling the adjustment screw in the horn but in my experience its rarely a long term fix.