Horn Relay

Ok, I shall try this tomorrow. What if it doesn't work? Obviously a bad/faulty horn

but if it does work, then what the hell am I doing wrong!? :'(

[yorkie_chris]

Most air horns need to spin correct way. You should usually check +ve/-ve is correct before applying power to electrics.

Re. non-start I'm not sure, you must have disturbed something else.

Originally Posted by yorkie_chris

Most air horns need to spin correct way. You should usually check +ve/-ve is correct before applying power to electrics.

Re. non-start I'm not sure, you must have disturbed something else.

Yup, I can confirm that this horn is faulty. I just grabbed another one of Halfords (exact same type of horn) and it worked straight away when I connected -ve and +ve to the battery, then I wired everything up and worked brilliantly and loudly once more.

I shall return the original one that I bought (of ebay)

Originally Posted by Baph

Come then, out with it. The only change to the entire system, was that I changed the length of one wire (to match the length of the other). Heypresto, it worked. I even used the same spade connectors (bar one) as I chopped the wire & put a new spade on it.

As a geeky electronicsy person I've read this wire length thing with some interest... One thing which I don't think has been mentioned is reactive impedance. It's not the change in path length that'll make the difference to the phase angle but the longer wire's larger inductance. This will reduce the RMS power of anything which draws pulses of current (in this case a DC motor) by offsetting the phase of current and voltage, an effect of the increased back EMF generated by an inductor.

In the case of the horn this would proabably change the motor rotation rate / air pressure / note(?), stopping the noise cancelling effect, a point not in contention!

I'd be happy to try and calculate the reactive impedance of a given bit of wire operating at a certain frequency but it's the day after the night before and I'd have to find my textbooks :S I'm probably talking a load of b*lls anyway. Please, if I am, shoot me down.

Baph, what sort of beat frequency do you get out of the two Magnums? 1Hz? 10Hz? Also, do you know if these Magnum horns have some sort of electronic control, or is it just 12v > motor? I'm gonna do a horn conversion soon and am curious!

[yorkie_chris]

Originally Posted by 85jas

This will reduce the RMS power of anything which draws pulses of current (in this case a DC motor) by offsetting the phase of current and voltage, an effect of the increased back EMF generated by an inductor.

Baph, what sort of beat frequency do you get out of the two Magnums? 1Hz? 10Hz? Also, do you know if these Magnum horns have some sort of electronic control, or is it just 12v > motor? I'm gonna do a horn conversion soon and am curious!

Have you ever put oscilloscope across a running motor to see what it is drawing?

Magnums are just 12v>motor.

a quick update on my progress -

I completed the fitting of my new horn yesterday, thank you all that helped! It was very simple. I added an inline fuse to the circuit as a precautionary measure because the wires I used were 15amp and the relay provided was 30amp, so I installed a 10am inline fuse for the circuit.

Sounds awesome and I made a quick video here to show the comparison!

http://www.youtube.com/watch?v=6OrW89AUb3A

Originally Posted by yorkie_chris

Have you ever put oscilloscope across a running motor to see what it is drawing?

I've not actually looked at a brushed DC motor myself, mostly I end up playing with AC induction motors - when I've got a moment I'll have a rummage and see if I can find a (brushed?) DC motor anywhere, measure the V I traces. Should probably then start playing with lengths of wire etc... noooo!

Originally Posted by musne

a quick update on my progress -
Sounds awesome and I made a quick video here to show the comparison!

http://www.youtube.com/watch?v=6OrW89AUb3A

That is sh*t-the-bed loud!! Definitely gonna be the new year project for me now. Well done!

Thank you! Do update us on your progress once you start!