Hella Horns Install question

[canuck37]

Question for all running Hella Super or Sharptone horns: I see lots of pros/cons to using with or without the relay setup. Has anyone had any bad experiences NOT using the relay? Seems to me that for the short amount of time they are in actual use, overheating stock wiring seems unlikely, but I'm no electrician.......Thoughts either way?? Thanks,

[sfeather11]

Hey there,
I've had horns installed for well over 5 years now and have never had a problem or needed a relay. I just unplugged the old horn and installed the hellas. I think I had to create a simple splitter to connect the 2nd horn, but did NOT use any type of relay, just snipped the old connector off and crimp a new one on. I never did figure out why others say a relay is needed??

Peace!
Scott

[canuck37]

Hey there,
I've had horns installed for well over 5 years now and have never had a problem or needed a relay. I just unplugged the old horn and installed the hellas. I think I had to create a simple splitter to connect the 2nd horn, but did NOT use any type of relay, just snipped the old connector off and crimp a new one on. I never did figure out why others say a relay is needed??

Peace!
Scott

Thanks, Scott - didn't make sense to me either given their amp draw and the existing 15 amp fuse, etc.....maybe they include the relay for vehicles with a less robust stock fuse setup?

[w.rohr]

The relay is there because most cars use 14ish gauge wire and the horns consume 8 amps each so 16 ams for two. The stock wire wont provide the power to get the full 118db so the relay is there to wire the horns to the battery. I mean the hellas are loud regardless but if you wire them to the battery the are about 2x louder.

[sfeather11]

Ahh, finally a good explanation! I didn't realize the wire size would affect current that much. I'm a mechanical nerd and just figured as long as they got 12V, they would work. I might have to try this as an experiment!!

Peace!
Scott

[kamesama980]

Ahh, finally a good explanation! I didn't realize the wire size would affect current that much. I'm a mechanical nerd and just figured as long as they got 12V, they would work. I might have to try this as an experiment!!

Peace!
Scott

Thus the magic of electricity. Sort of like hydraulics through too small of a hose: when everything's stationary, you have the same pressure (voltage) everywhere. once you open a valve and it starts to flow, if the hose is too small, not enough fluid can flow to whatever work is being done and it slows down. Electrically wire is too small, voltage drops, amps increase (since wattage is a constant), causing the wire to heat and resistance to increase causing more problems in a vicious circle. If you do it right (or wrong, depending on the goal of the experiment) you can heat the wire up enough to melt the insulation off. It's the same concept as an electric oven or furnace: amps and resistance leads to heat.

There are two ways to check if the wire's already too small: just put the voltmeter on the device, turn it on, and see how much the voltage changes, or much better way is a volt drop test: put one meter lead on the battery + post and the other on the + side of the device with the meter on Volts then turn the device on. Whatever voltage is displayed on the meter is how much you're losing on the wire. Most common automotive use is to test the starter lead because the starter normally pulls 100-250 Amps depending on the engine size and system design. V=IR: When volts are low and amps are high (12v, 200A) a fraction of an Ohm of resistance matters and most consumer meters aren't precise enough with that low of resistance to just Ohm out the system.

Because I, also, am a huge nerd in many fields and have an IR camera that plugs into my phone for the fun of it and randomly decided to take a pic of my car just after startup, I'll give you a great example you can even see. This is my Firebird, the big orange areas are the exhaust manifold, alternator, and water pump. The little orange squiggly line in the green box is the battery positive cable. It's had occasional issues starting (weak cranking usually) and I think I know where to check next (don't worry, I got closer and it's only about 10f warmer than the fender next to it, but still something to check.)