Louder horn acquired, do I use a mosfet or SSR to activate?

[N8!]

Good Day/Evening,

My bike came with a sad little 2.5v piezo buzzer for a horn, not loud and not useful for alerting cross traffic. Most cyclists here ride with police whistles as the local drivers are very distracted. I like the electric railway horn method better.

I acquired a nice 12v 130db horn but I'm not sure which parts to use to power it. Putting out 12v is not the problem, I don't know if I should use a mosfet or Solid State Relay or which type to use.

The horn button activates a 2.5v circuit, I'm handy enough with electricity to make the circuit to be switched by that but I'm just not educated on how to determine which parts to use for the switching.

help?

 

[kuromaku]

either would work. most of those motorcycle horns are very inductive and draw a few tens of watts, so an RCD clamp would be a good idea to prevent damage.

 

[harrisonpatm]

You said you have a 12v power source. Does that mean that you'd be able to replace your current 2.5v button, with a 12v handlebar switch, to just manually switch the horn on and off? Or at least, purchase/make a 12v handlebar switch?

 

[N8!]

You said you have a 12v power source. Does that mean that you'd be able to replace your current 2.5v button, with a 12v handlebar switch, to just manually switch the horn on and off? Or at least, purchase/make a 12v handlebar switch?

See that nice weather resistant combo switch for the horn and headlight in the photo? It has nice waterproof connectors on the 4 wires to the combo headlight/horn device. The horn part has already been modified to have the 2.5v relay leads sticking out the back in a less weather resistant manner. I just need a relay or mosfet the triggers at 2.5v and I don't know which one(s) to order.

There are 22,706 different mosfets on the mouser website, but I don't know which one I need

https://www.mouser.pr/c/semiconductors/discrete-semiconductors/transistors/mosfet/

there are only 7,456 types of ssr's listed, but still don't know how to read the data to know what I need there either.

 

[Chalo]

The horn button activates a 2.5v circuit, I'm handy enough with electricity to make the circuit to be switched by that but I'm just not educated on how to determine which parts to use for the switching.

In my casual observation, SSRs that are made to switch DC loads all specify 3V-30V on the control line. Maybe 2.5V works, maybe it doesn't.

 

[harrisonpatm]

See that nice weather resistant combo switch for the horn and headlight in the photo? It has nice waterproof connectors on the 4 wires to the combo headlight/horn device. The horn part has already been modified to have the 2.5v relay leads sticking out the back in a less weather resistant manner. I just need a relay or mosfet the triggers at 2.5v and I don't know which one(s) to order.

There are 22,706 different mosfets on the mouser website, but I don't know which one I need

https://www.mouser.pr/c/semiconductors/discrete-semiconductors/transistors/mosfet/

there are only 7,456 types of ssr's listed, but still don't know how to read the data to know what I need there either.

View attachment 353424

Gotcha, that's fair. And @Chalo is probably correct, that 2.5v would probably work for a 3v relay, but it's hard to know for sure.

Have you tested how many amps your new horn uses @ 12V?

I'm partial to mechanical relays. This one is good for 10A @ 28v. This one is good for 2A. Not hard to waterproof those either. I like to pull relays like that off scrap circuitboards for reuse and 3d print sleeves with mounting points for them.

 

[fill]

Fwiw the horn that draws 3a @12v ive fitted works a treat fed off a supply dropped down off the main bike 36v battery via an ebay m/cycle lights/horn button set as do the lights drawing over 6a total Front and rear/brake (diy light bars made from led/neon strips)
Just wires and switches post the DC-DC converter. No contact sparks, pops or anything.. get a genuine honda suzuki etc part not a generic plastic m/cyle style part and you should be fine..

**edit "switchset" is the keyword for a search iirc,

 

[Chalo]

Just wires and switches post the DC-DC converter. No contact sparks, pops or anything.. get a genuine honda suzuki etc part not a generic plastic m/cyle style part and you should be fine..

The only reason I don't do it this way is because a DC-DC converter draws a small current when it's not doing anything. Sooner or later I think I'd regret that if it's on by default. I prefer to switch upstream from the voltage converter, even though a 48V spark is much more destructive than a 12V spark.

 

[N8!]

It has occurred to me that the horn wires may be conducting a Pulse Wide Modulated (PWM) signal instead of analog DC current, originally the wire were directly soldered to a piezo buzzer.

I have no desire to patch a micro-controller into the horn, I may have to just put a big fat 10amp push button on the handlebars after all.

it's going to have to be on the throttle side, I'm out of space.