iksbob
New Member
Hi. Newbie here - been hunting for a decent cam but thought I'd chime in.
It's not necessarily the electrical load that's the problem - it's the horn itself. Cheap horns aren't just audibly noisy, they produce a lot of electrical and RF noise as well.
Explanation if you care to read it: The heart of a simple puck-type horn isn't much different from an electrical relay: an electromagnet coil and some switch contacts. If you're not familiar with relays, the coil moves the contacts, which lets you use a small amount of power (operate the coil) to control a higher power device (wired to the switch contacts). In the case of the horn, a high power coil is used which moves both the switch contacts and the bell (the dome-shaped part on the front) of the horn. The contacts are "normally closed" which means when at rest the contacts are touching so electrical power can flow through them. The power to the coil is wired through the switch contacts - when power is applied (you push the horn button) the coil (and horn bell, and switch contacts) jerks forward. That pushes the switch contacts open (breaking the circuit) which cuts off power to the coil. A strong spring pulls the bell/coil/contact assembly back to its resting point which closes the contacts and the cycle repeats. That cycle happens hundreds of times a second, giving you the buzzy element of your horn sound, with the ringing coming from the horn bell resonating. You can turn a relay into a buzzer by wiring it up the same way: power (whatever voltage the coil is rated for) to one side of the coil, the other side to switch common, normally closed to ground.
Coils (thanks to the magnetic field they produce and absorb) like to smooth out changes in current (electrical flow) and will produce spikes in voltage (electrical force or pressure) to make that happen - it's like they add momentum to the flow of electricity. When a set of switch contacts goes from closed (current flowing) to open (current stopped) it will produce a spark, its size depending on the voltage present. When the switch opens and current tries to slam to a stop, the coil tries to keep current moving across those switch contacts by ramping up the voltage, maintaining the spark. A spark gap is one of the earliest and crudest forms of radio transmitter - IIRC, that's how radio was discovered. Most of that radio noise gets dumped into your motorcycle's electrical system, wreaking havoc with any sensitive electronics.
Old engines with points-condenser ignition systems have a similar construction electrically speaking and similar spark gap issues. One partial-solution is to put a capacitor (condenser, which acts like an electrical spring) in the circuit to soak up the voltage spike from the coil. You're giving the momentum of the coil some padding. In this case, the capacitor goes in parallel with the horn - positive to positive, negative to negative. You can further improve things by adding an inductor (a coil that doesn't do anything mechanical) to the positive (negative will work too) wire feeding your horn/capacitor combo. Together, you've created an LC (L for inductance, C for capacitance) electrical filter. Unless you've got electronics components just laying around, it's much easier to just buy a filter from an auto-parts store.
It's not necessarily the electrical load that's the problem - it's the horn itself. Cheap horns aren't just audibly noisy, they produce a lot of electrical and RF noise as well.
Explanation if you care to read it: The heart of a simple puck-type horn isn't much different from an electrical relay: an electromagnet coil and some switch contacts. If you're not familiar with relays, the coil moves the contacts, which lets you use a small amount of power (operate the coil) to control a higher power device (wired to the switch contacts). In the case of the horn, a high power coil is used which moves both the switch contacts and the bell (the dome-shaped part on the front) of the horn. The contacts are "normally closed" which means when at rest the contacts are touching so electrical power can flow through them. The power to the coil is wired through the switch contacts - when power is applied (you push the horn button) the coil (and horn bell, and switch contacts) jerks forward. That pushes the switch contacts open (breaking the circuit) which cuts off power to the coil. A strong spring pulls the bell/coil/contact assembly back to its resting point which closes the contacts and the cycle repeats. That cycle happens hundreds of times a second, giving you the buzzy element of your horn sound, with the ringing coming from the horn bell resonating. You can turn a relay into a buzzer by wiring it up the same way: power (whatever voltage the coil is rated for) to one side of the coil, the other side to switch common, normally closed to ground.
Coils (thanks to the magnetic field they produce and absorb) like to smooth out changes in current (electrical flow) and will produce spikes in voltage (electrical force or pressure) to make that happen - it's like they add momentum to the flow of electricity. When a set of switch contacts goes from closed (current flowing) to open (current stopped) it will produce a spark, its size depending on the voltage present. When the switch opens and current tries to slam to a stop, the coil tries to keep current moving across those switch contacts by ramping up the voltage, maintaining the spark. A spark gap is one of the earliest and crudest forms of radio transmitter - IIRC, that's how radio was discovered. Most of that radio noise gets dumped into your motorcycle's electrical system, wreaking havoc with any sensitive electronics.
Old engines with points-condenser ignition systems have a similar construction electrically speaking and similar spark gap issues. One partial-solution is to put a capacitor (condenser, which acts like an electrical spring) in the circuit to soak up the voltage spike from the coil. You're giving the momentum of the coil some padding. In this case, the capacitor goes in parallel with the horn - positive to positive, negative to negative. You can further improve things by adding an inductor (a coil that doesn't do anything mechanical) to the positive (negative will work too) wire feeding your horn/capacitor combo. Together, you've created an LC (L for inductance, C for capacitance) electrical filter. Unless you've got electronics components just laying around, it's much easier to just buy a filter from an auto-parts store.
