Boat Horn inner workings

[robertmee]

Okay, I'm feeling dense as I don't quite understand how the internal mechanisms of a working boat horn are supposed to operate. The horn in question is similar to this:

http://www.firstchoicemarine.com/p-1...orn-10035.aspx

Mine is not working so I took it apart. I get how there's a magnetic coil inside that vibrates a disk against another disk to create the chatter. What I don't get is mine has a small make/break contact above the Negative side winding. It's made by tension of the contact spring only. I don't see what could break it and what function it would even serve.

I have good winding resistance on the magnet, so the coil is good. What I don't have is continuity between the Common side connection and the common side magnet lead. So, obviously, the magnet is not firing. I actually got it to fire one time, but none since. But I don't know the path from the common connection to this magnet lead. It goes through a stacked electrode with an insulator between this contact and the winding. Unless you've taken one of these apart, none of this may make sense, so I'm hoping someone has taken one apart before and sees this.

Anyway, I hate to buy another one for $25 + Shipping if I can get mine working. Plus it is original to the boat which is always a plus to me.

EDIT: Eureka moment. Okay, I think I understand the purpose of the contact. As the disk deflects due to the magnet, it opens this contact, releasing the disk which makes the contact. Rinse and repeat which gives the chatter. Makes sense. So, I guess for some reason, I don't have continuity between the magnet and the negative contact. I wonder if the gap on this contact is too great or corroded. Time to get out the emory board.

[robertmee]

Well, for those interested or for future posterity....

I cleaned the contact and the horn worked....Momentarily. I think the winding insulation is breaking down because the magnet got really hot, very fast (due to decreased resistance from inner windings touching and shortening the overall path). Now it doesn't work again, and I think I'm reading open resistance on the windings. Probably toasted it enough where a weak spot gave way.

Guess I'll use a portable air horn for now till I get a replacement.

[Captmikestarrett]

Small DC motor spins a squirrel cage

The air forced thru the squirrel cage is forced out the horns orfice.

Those little motors bind all the time and stop working.

Never had one yet that could handle salt air.

Air can is the most dependible and a whistle attached to each life vest..

Capt Mike

[robertmee]

Originally Posted by Captmikestarrett

Small DC motor spins a squirrel cage

The air forced thru the squirrel cage is forced out the horns orfice.

Those little motors bind all the time and stop working.

Never had one yet that could handle salt air.

Air can is the most dependible and a whistle attached to each life vest..

Capt Mike

That's the airhorn type...The type I'm dealing with uses a magnetized coil to suck a metallic disk against another disk. The displacement of the disk releases a contact which breaks the magnetizing circuit, releases the disk, only to repeat again once the contact makes again. The 'chatter' of disk to disk's frequency is controlled by a tension spring and the gap of the contacts which subsequently controls the pitch of the horn....Higher pitch = smaller gap = faster chatter.

Really a pretty slick engineering design for simplicity. The problem is when due to age the insulation of the magnet's windings begin to break down, the resistance changes, the windings heat up more which only breaks the insulation down further.

[Jackl]

Cause and effect,chain of events.
All this chaos makes perfect sense.
When your spinning 'round, things come undone.
Welcome to earth, third rock from the sun!!!

JackL

[Rebbasser]

Had the same problem with mine. Bought a new one but didn't need it. Replaced the wiring and good as new. Speaker wire works great for this.