12 v horn problem

[Greg & Jax]

Hi guys a quick look at the blurb of the horn revealed it ops on 408 hertz. 

Cheers 

[Alan de Enfield]

11 minutes ago, Greg & Jax said:

ce just contacted the seller and the horn is a 12 v low current . 150 watt horn .

I wouldn't call 12+ amps 'low current', that pretty high current for boaty stuff.

A 12v fridge for example is probably around 5 amps

 

The MAXIMUM a cigarette lighter socket will take before melting is normally 10 amps

[WotEver]

2 minutes ago, Greg & Jax said:

Hi guys a quick look at the blurb of the horn revealed it ops on 408 hertz. 

Cheers 

Yup, a pretty standard low frequency. Irrelevant to your issues

[Alan de Enfield]

Cut out all possible failure points.

 

Get 2x 50 feet bits of cable, (sized to minimise Volt-Drop. Attach one end to the + & - on the battery, connect the other end to the horn - does it work ?

 

If it works the fault is in the boat wiring.

If it doesn't work, the fault is in the horn 

[ditchcrawler]

10 minutes ago, Alan de Enfield said:

I wouldn't call 12+ amps 'low current', that pretty high current for boaty stuff.

A 12v fridge for example is probably around 5 amps

 

The MAXIMUM a cigarette lighter socket will take before melting is normally 10 amps

That was my point. When the OP said he tested on the terminals, was that the terminals of the horn or a junction box?

[Greg & Jax]

Hi guys

Would a length or arctic blue mains  cable do to test it that is  the only cable I have that would be long enough ? 

Regards Greg. 

I tested at the terminals at the horn .

Cheers 

Edited May 29, 2020 by Greg & Jax

[ditchcrawler]

4 minutes ago, Greg & Jax said:

Hi guys

Would a length or arctic blue mains  cable do to test it that is  the only cable I have that would be long enough ? 

Regards Greg. 

I tested at the terminals at the horn .

Cheers 

Did you check the polarity?

 

[Tony Brooks]

2 minutes ago, Greg & Jax said:

Hi guys

Would a length or arctic blue mains  cable do to test it that is  the only cable I have that would be long enough ? 

Regards Greg. 

I tested at the terminals at the horn .

Cheers 

 

But which part of the terminal and what sort of terminals are you using.  The voltmeter needs to be connected to

a metal piece that is part of the horn, not the terminal on the end of the cable.

 

If the horn has blade terminals then try to connect to the swage that holds the terminal blade onto the horn.

 

Arctic cable comes in a variety of different conductor sizes so  we can't really answer until we know what conductor size your cable has. My gut feeling is possibly not a larger enough conductor CCSA to be sure.

 

[Greg & Jax]

My understanding of the 12 v dc is not the best so not sure how to check the polarity if I'm honest .

Cheers .

[Tracy D'arth]

Give up and buy an air horn with a gas canister.

[Greg & Jax]

Hi guys the cable is a 16 amp hook up cable that I use as a spare .

That's the only thing I have that's long enough .

Cheers 

[Tony Brooks]

2 minutes ago, Greg & Jax said:

My understanding of the 12 v dc is not the best so not sure how to check the polarity if I'm honest .

Cheers .

If it is polarity conscious then the terminals should be marked. Put a digital multimeter on the horn and test the voltage, reverse the meter connections and the reading that puts a minus in the front of the reading is the wrong way round so ignore that connection pattern. Then with no minus sign the red meter lead will be connected to the positive cable and the black the negative.

[Alan de Enfield]

3 minutes ago, Greg & Jax said:

Hi guys the cable is a 16 amp hook up cable that I use as a spare .

That's the only thing I have that's long enough .

Cheers 

Its probably 2.5mm2 so not ideal, If it works it shows that it is the boat wiring, if it doesn't work it could be that the horn has a problem, OR, ir could be due to volt-drop.

 

Try it and see - nothing to loose.

[Tony Brooks]

5 minutes ago, Greg & Jax said:

Hi guys the cable is a 16 amp hook up cable that I use as a spare .

That's the only thing I have that's long enough .

Cheers 

 

If that is all you can tell us then any answer will be a guess. We need to calculate the volt drop along 100ft of cable and for that we need the cable conductor's cross sectional area. A 10% volt drop at 240V is 24 volts which is  all but nothing. At 12V its 1.2 volts so it only leaves 10.8 volts to work the horn.

[Greg & Jax]

Hi guys .

Than you for all the help and reply,s I will be home soon and will look at all the ideas and suggestions. 

See if we can sort this between us all 

? regards Greg. 

[Alan de Enfield]

49 minutes ago, Greg & Jax said:

Hi guys .

Than you for all the help and reply,s I will be home soon and will look at all the ideas and suggestions. 

See if we can sort this between us all 

? regards Greg. 

 

Calculating using :

12 amp current draw and 17 metres cable length.

 

Having checked, and assuming your mains-lead is the standard 2.5mm2 then it will NOT do.

 

The volt drop over 17 metres would be a 23.25% volt drop.

The normal  'acceptable' volt drop is  3 to 4%

To get that you will need 16mm2 - 25mm2 (is you boat wiring that big ?) to give you a comparison - battery cables are normally 25mm2

 

 

Maybe the old horn was drawing a much lower current. If the old horn was drawing only 1 amp then 2.5mm2 wiring would only give a volt drop of 1.9% if it was drawing 2 amps then the volt drop would be 3.9%

 

You maybe the suffering the consequences of buying 'a louder horn'.

 

Edited May 29, 2020 by Alan de Enfield

[ditchcrawler]

1 hour ago, Greg & Jax said:

My understanding of the 12 v dc is not the best so not sure how to check the polarity if I'm honest .

Cheers .

What Tony said, just put your volt meter on the terminals and if you have the positive lead of the meter on the positive lead of the horn it should have a positive reading

[dmr]

2 hours ago, WotEver said:

Corrected that.

 

By your logic voltage and current are unconnected.  They're not.  If the device (horn in this instance) attempts to pull the required current but is unable to because of resistance in the circuit then the voltage will be pulled down as determined by the circuit resistance and the current flowing. 

 

 

 

 

Ive seen and struggled with a possibly similar issue with DC DC converters failing to start. Measuring the input voltage with a DVM suggests its fine but when you look with a 'scope there are very short negative spikes where the voltage transiently drops significantly as the converter tries to take a quick gulp of current. Inductance can be a bad thing.

 

...................Dave

[WotEver]

12 minutes ago, dmr said:

Ive seen and struggled with a possibly similar issue with DC DC converters failing to start. Measuring the input voltage with a DVM suggests its fine but when you look with a 'scope there are very short negative spikes where the voltage transiently drops significantly as the converter tries to take a quick gulp of current. Inductance can be a bad thing.

 

...................Dave

Yes for electronics but not for something as basic as a buzzer (which is all a horn is, fundamentally) 

[Alan de Enfield]

4 minutes ago, WotEver said:

Yes for electronics but not for something as basic as a buzzer (which is all a horn is, fundamentally) 

I've got the bit between my teeth on 'volt drop'.

 

OP is not measuring the voltage correctly at the horn end of the cabling, when, the horn is activated.

Horns works OK on thin cable when adjacent to battery.

Horn doesn't work when 17 metres away on thin (typical horn) cable

 

Horn is draws many times the current of the old horn.

[David Mack]

3 hours ago, dmr said:

 

Years ago I fitted a cheap horn to my VW camper and it would only work when the engine was running.

When the CRT guy was checking Belfast over before I could go through Harecastle Tunnel, the horn didn't work. "Try it with the engine running" he said. That worked. So I was OK to go, as long as the engine didn't fail in the tunnel!

[dmr]

1 minute ago, David Mack said:

When the CRT guy was checking Belfast over before I could go through Harecastle Tunnel, the horn didn't work. "Try it with the engine running" he said. That worked. So I was OK to go, as long as the engine didn't fail in the tunnel!

and when might you need to sound the horn in a tunnel ?

 

.................Dave

 

 

[David Mack]

2 minutes ago, dmr said:

and when might you need to sound the horn in a tunnel ?

 

.................Dave

 

 

Quite.

I do need to replace the loudspeaker cable that currently feeds the horn with something a little more substantial!

[TheBiscuits]

1 minute ago, David Mack said:

Quite.

I do need to replace the loudspeaker cable that currently feeds the horn with something a little more substantial!

 

I have been known to swap tunnel lamp and horn cables over if the lamp cable is thicker.

 

Obviously replacing the bulb for a lower power one helps at this point!

 

Add a bit:

 

Or you could use the skinny horn cable to run a relay fed off the usually thicker water pump cable, but this is a bodge.

[ditchcrawler]

19 minutes ago, TheBiscuits said:

 

 

 

Or you could use the skinny horn cable to run a relay fed off the usually thicker water pump cable, but this is a bodge.

Now if boats had 2 batteries installed in the bows?