Parallel return?

[George and Dragon]

I'm having a little problem with my horn. Essentially it works once and then not for several hours. I've tested to see that there's 12V at the terminals when the button is pressed. I expect I'm going to have to buy another but before I do I want to be sure the fault is in the horn rather than the wiring.

 

Fortunately the tunnel lamp and horn share a joint box at the front of the boat. Tunnel lamp works fine. Both have been wired in 2 core flex (maybe 0.75 mm2). The obvious test is to swap the positive supplies (that's where the switches should be?) in the joint box and see if pressing the horn turns on the tunnel light and vice versa. Would it matter if I didn't also swap the returns? Both run from the same battery bank but the supply to the light is switched at a different panel from the supply to the horn. Or can I just join the two returns together in the joint box?

 

 

[Tony Brooks]

20 minutes ago, George and Dragon said:

I'm having a little problem with my horn. Essentially it works once and then not for several hours. I've tested to see that there's 12V at the terminals when the button is pressed. I expect I'm going to have to buy another but before I do I want to be sure the fault is in the horn rather than the wiring.

 

Fortunately the tunnel lamp and horn share a joint box at the front of the boat. Tunnel lamp works fine. Both have been wired in 2 core flex (maybe 0.75 mm2). The obvious test is to swap the positive supplies (that's where the switches should be?) in the joint box and see if pressing the horn turns on the tunnel light and vice versa. Would it matter if I didn't also swap the returns? Both run from the same battery bank but the supply to the light is switched at a different panel from the supply to the horn. Or can I just join the two returns together in the joint box?

 

 

No it won't matter

 

If that is 12V at the HORN terminals with the horn still CONNECTED then fine but if the horn was disconnected or it was at the push button then its an invalid test as far as the wiring run goes.

 

If the cable really is 0.75 sq mm CCSA twin flex than that could well be the trouble. Excess volt drop down the cable. Without doing any calculations I would want at least 2sq mm CCSA and on a longer boat even more.

 

As A test join the two feeds and also the returns at both ends and see if that helps. It it does then it needs thicker cables.

Edited October 10, 2020 by Tony Brooks

[George and Dragon]

I'd better have another look at the horn circuit then.

[Keeping Up]

If the horn has an adjustment screw you may be able to fix the problem by giving it a half turn one way or the other.

[George and Dragon]

It worked until I took down the cratch board for repairs. But I don't know what current it draws... I think more hefty cable can't do any harm.

[Iain_S]

As Tony has said, 0.75mmsq is a bit on the small side. Might get some improvement by joining the two negatives at the junction box.

[Onewheeler]

Horns, in my experience, need to be treated as disposable and need replacing every few years. Maybe the weather or the spiders inside.

[George and Dragon]

On 10/10/2020 at 20:10, Iain_S said:

As Tony has said, 0.75mmsq is a bit on the small side. Might get some improvement by joining the two negatives at the junction box.

I need to investigate where the circuit runs and how feasible it would be to install heavier duty cables. Perhaps a solid state relay at the front of the boat is called for.

 

23 hours ago, Onewheeler said:

Horns, in my experience, need to be treated as disposable and need replacing every few years. Maybe the weather or the spiders inside.

That's worth knowing, thank you.

[Tony Brooks]

51 minutes ago, George and Dragon said:

I need to investigate where the circuit runs and how feasible it would be to install heavier duty cables. Perhaps a solid state relay at the front of the boat is called for.

A relay needs four wires. Two for the coil and two for the main current supply but the two negatives can be common leaving three cables. How will a relay help unless you run a pair of heavy cables?

[Jen-in-Wellies]

1 hour ago, Tony Brooks said:

A relay needs four wires. Two for the coil and two for the main current supply but the two negatives can be common leaving three cables. How will a relay help unless you run a pair of heavy cables?

Does the OP have a bow thruster by any chance? If there is a bow thruster battery at the bow, then a relay could use the existing wire as a signal to close the relay and use the bow thruster batt to provide the oomph. If no battery, then heavy cables are the answer, in which case, you don't need a relay.

Another option would be to relocate the horn to the stern. This would give only a short run and minimal voltage drop with thin wires.

Jen

Edited October 12, 2020 by Jen-in-Wellies

[Alan de Enfield]

For the very infrequent use that horns seem to get, why not just get one of these :

 

  

 

£9.99 from Screwfix (less than the cost of running 'fat' cables to the front of the boat).

[cuthound]

1 hour ago, Alan de Enfield said:

For the very infrequent use that horns seem to get, why not just get one of these :

 

  

 

£9.99 from Screwfix (less than the cost of running 'fat' cables to the front of the boat).

 

I use the rechargeable version.

 

https://www.tcschandlery.co.uk/mobile/ecoblast-rechargeable-air-horn/p7055

[Richard10002]

On 10/10/2020 at 19:12, George and Dragon said:

It worked until I took down the cratch board for repairs. But I don't know what current it draws... I think more hefty cable can't do any harm.

If the horn worked fine before removing the cratch board, the wiring to the cratch board area was fine.

 

Have you tested whether the horn still works? You could connect it to a 12v supply near to the batteries and see.

 

Did you test it on the tunnel light cable, and the tunnel light in the horn cable? I may have missed that.

[George and Dragon]

5 hours ago, Jen-in-Wellies said:

Does the OP have a bow thruster by any chance? If there is a bow thruster battery at the bow, then a relay could use the existing wire as a signal to close the relay and use the bow thruster batt to provide the oomph. If no battery, then heavy cables are the answer, in which case, you don't need a relay.

Another option would be to relocate the horn to the stern. This would give only a short run and minimal voltage drop with thin wires.

No bow thruster. I'll reluctantly consider relocating the horn if there's no easy way of getting heavier duty cable in. The horn really needs to be at the bow in my opinion - no point deafening myself. If it's at the front and I don't hear it sound then it probably didn't.

 

[Tony Brooks]

3 hours ago, Richard10002 said:

If the horn worked fine before removing the cratch board, the wiring to the cratch board area was fine.

 

Have you tested whether the horn still works? You could connect it to a 12v supply near to the batteries and see.

 

Did you test it on the tunnel light cable, and the tunnel light in the horn cable? I may have missed that.

Er, no. Only if the conditions of the then and now test were the same.

 

Most people don't go blowing the horn when moored up so it is fair t assume that the horn worked OK when the engine was running and charging. That means it had up to 14.5 volts at the battery so even if the wires suffered 2V of volt drop the horn would still receive 12 volts or more.

 

I get the impression the OP tested the horn when he refitted the cratch board so it is likely the engine was not running so that 2V of volt drop reduces the voltage at the horn to maybe 10.3 volts or so. If this is the case no wonder it does not work so the OP needs t try it with the engine revving with well charged batteries.

[Keeping Up]

As I suggested earlier, has the OP tried adjusting it? My return wiring is a bit thin and I have to adjust my horn about once a year (usually every springtime) to make it easier to start by reducing the distance it has to travel before breaking the internal contact.

[Tony Brooks]

1 minute ago, Keeping Up said:

As I suggested earlier, has the OP tried adjusting it? My return wiring is a bit thin and I have to adjust my horn about once a year (usually every springtime) to make it easier to start by reducing the distance it has to travel before breaking the internal contact.

I think the so called adjustment is for tone during manufacture and although messing with it can make it work I usually does not last as you explained.

[Keeping Up]

46 minutes ago, Tony Brooks said:

I think the so called adjustment is for tone during manufacture and although messing with it can make it work I usually does not last as you explained.

I can assure you, on mine (and many others) that is EXACTLY how it works. Definitely!

 

ETA: screw mine a couple of turns one way and the horn takes no current. Screw it back then a couple of turns the other way and it just goes "click" and takes a continuous heavy current. Find the right point between and it makes a noise.

Edited October 12, 2020 by Keeping Up

[Tony Brooks]

26 minutes ago, Keeping Up said:

I can assure you, on mine (and many others) that is EXACTLY how it works. Definitely!

 

ETA: screw mine a couple of turns one way and the horn takes no current. Screw it back then a couple of turns the other way and it just goes "click" and takes a continuous heavy current. Find the right point between and it makes a noise.

I never said that messing with the "adjustment" would not work, in fact i sad it may appear to but it does not last long - you said it needs redong about every year so you tend to confirm what I said. I could never advise anyone with a horn probelm to mess with the adjustment because its all too easy to burn the coil out.

[Keeping Up]

6 minutes ago, Tony Brooks said:

 I could never advise anyone with a horn probelm to mess with the adjustment because its all too easy to burn the coil out.

Then we must agree to differ because I would advise anyone with a problem such as this to try adjusting it. Turn it half a turn one way and press the button for a moment. If it doesn't then work, turn it back the half turn and continue for another half turn before pressing the button for a moment again. If that doesn't work, you can return the adjustment to it's original position and only then consider rewiring or replacement etc. In the highly unlikely event of burning out the coil (and in fact you might actually SAVE the coil by making the adjustment) then you replace the horn which is what you were about to do anyway!

[TheBiscuits]

38 minutes ago, Keeping Up said:

Then we must agree to differ because I would advise anyone with a problem such as this to try adjusting it. Turn it half a turn one way and press the button for a moment. If it doesn't then work, turn it back the half turn and continue for another half turn before pressing the button for a moment again. If that doesn't work, you can return the adjustment to it's original position and only then consider rewiring or replacement etc. In the highly unlikely event of burning out the coil (and in fact you might actually SAVE the coil by making the adjustment) then you replace the horn which is what you were about to do anyway!

 

It's not often I disagree with @Tony Brooks on technical matters, but this is one of them.

 

Horn doesn't work, it's going in the bin.  Poking it with a screwdriver to see if it will start again? No brainer!

 

(I bought a new one, because poking it didn't work.  But I tried it first!)

[Chewbacka]

On 12/10/2020 at 22:29, TheBiscuits said:

 

It's not often I disagree with @Tony Brooks on technical matters, but this is one of them.

 

Horn doesn't work, it's going in the bin.  Poking it with a screwdriver to see if it will start again? No brainer!

 

(I bought a new one, because poking it didn't work.  But I tried it first!)

The problem with ‘adjusting’ every season as per post #16 is that sooner or later it won’t work when you really wished it did........

[Tony Brooks]

49 minutes ago, Chewbacka said:

The problem with ‘adjusting’ every season as per post #16 is that sooner or later it won’t work when you really wished it did........

That is precisely my point. It may or may not make the horn work but it is very rarely a long term fix. It is not for nothing that manufacturers hide the "adjustment" under compound or a plastic cap. It is also instructive to study the language in the online pieces that advise this repair. they don't seem as technical as one would expect from the manufacturers.

 

I suspect moving the adjustment has the effect of removing a small amount of corrosion from the contacts so they are conductive again but only for a short while.

 

If the adjustment is overdone the contacts may be jammed shut and then the coil will burn out. The horn coil is a bit like a motor in that is draws a high current until the contacts pen and the the effective current is far lower because it keeps turning on and off.