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Discussion Starter #1
Installing a louder horn on a Burgman is a common modification. The hardest part is hiding the horn without cutting “Exterior Components” (as Suzuki calls tupperware) or making too many irreversible changes to the scooter. I describe how I have successfully hidden the very loud Denali Soundbomb Split Dual Tone Air Horn on my 2018 Burgman 650 Executive consistent with these goals. The “split” designation is the key. Denali has separated the horn into two components: the “compressor” and the “acoustic unit”. They are connected by a flexible tube enabling the compressor to activate the horn. This greatly simplifies the problem, but each part is still not small.

The attached PDF file describes my installation.

...damocles
 

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Nicely done!
 

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Installing a louder horn on a Burgman is a common modification. The hardest part is hiding the horn without cutting “Exterior Components” (as Suzuki calls tupperware) or making too many irreversible changes to the scooter. I describe how I have successfully hidden the very loud Denali Soundbomb Split Dual Tone Air Horn on my 2018 Burgman 650 Executive consistent with these goals. The “split” designation is the key. Denali has separated the horn into two components: the “compressor” and the “acoustic unit”. They are connected by a flexible tube enabling the compressor to activate the horn. This greatly simplifies the problem, but each part is still not small.

The attached PDF file describes my installation.

...damocles
1) Very nice work and documentation.

2) You mention ditching the supplied relay.

You might want to suggest using a relay with a built-in diode to prevent back-EMF. I leave that up to you, as you're much more qualified than I am in such matters in general, and I don't know whether this is relevant on the Big Burgers.

Some notes on all of this:

A) A few years ago, I changed out the relay on an air horn I had installed on a Victory bagger. I was unaware of this issue until I read a Victory-forum post on it. And then I verified that my turn-signal lights blinked when the horn was used -- I seldom use the horn, and I had never looked at the dash turn-signal indicator when I did so.

B) I discuss this a bit in this thread here on the forum, from 2018, which I don't know whether you had stumbled across:


See post 24 (page 2) for a brief discussion and the parts source that I used (twice now).

3) I can't tell from your pics (and not owning the 2013+ model of the 650), but I would recommend that the trumpets face down. Is this the case on your mounting solution?

Stebel, for instance, suggests some recommended downward angle, somewhere on their web site. On my '07 and '08 Execs, I mounted one-piece Stebels, but on my '00 Honda Valkyrie I had a separate compressor/horn setup like you now have:



On that setup -- which didn't have any downward tilt, to allow moisture to drain -- I had to periodically squirt WD40 and suchlike in the horns periodically, because I was unaware of that. On my Execs, I made sure that the trumpets faced down, and didn't have a problem. Same thing on my Victory (and no trumpet problem for the five years I owned that):



Just some thoughts ...
 

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When that huge electro magnet of a motor charges up to blow the horn its all OK. When the power to the motor is cut off and that magnitic field colapes it could send a high voltage spike back to the wiring harness. Where the relay with the diode built in does its job is it stops the back charge and bleeds it off to ground..... Could...
 

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Discussion Starter #5
You mention ditching the supplied relay. You might want to suggest using a relay with a built-in diode to prevent back-EMF. I leave that up to you, as you're much more qualified than I am in such matters in general, and I don't know whether this is relevant on the Big Burgers.

I can't tell from your pics (and not owning the 2013+ model of the 650), but I would recommend that the trumpets face down. Is this the case on your mounting solution?

Just some thoughts ...
Good catch on both accounts!

I ditched the supplied relay and used another. Neither have flyback diodes built in. My bad. I will add one. I have a Schottky diode which is exactly what is required in this application. Schottkys have a low forward voltage and are very fast. I should have known better. Thanks for the reminder. I will mount it right at the relay. Here is a link to a little primer on flyback diodes: flyback diode primer

Unfortunately, as mounted the horn's trumpet is tipped up. But it is also underneath the front panel, tucked way up there, and I hope it will survive out of the elements. I was aware of this issue at install time, but alas, I just couldn't get the horn to fit in the tight space with the horn trumpet tipped down. So I took what I could get, and I will see how it fairs in time.

...damocles
 

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Discussion Starter #6
Both members wspollack and Dave_J took me to task about not used a flyback diode in my horn install. wspollack suggested using a flyback diode across the relay coil; Dave_J suggested possibly using one across the compressor as well (if I have understood him correctly). So I set about to better understand the theory and practice of suppressing the negative voltage spike that happens when a relay coil is de-energized.

While I am an electrical engineer, my training is not in power electronics or similar, and so, I was relying on schooling memories from 45 years ago to guide my thinking. My career as a “theorist” made me cook up some models and calculations and I wrote it all up, with the thought of sharing. Upon further reflection, I realized it was interesting only to me. Old habits die hard. So instead, I did some measurements on my scooter. Actual data…I had managed to avoid this my whole career, but not now.

The Hella 007794301 automotive relay I used to switch on the compressor of the horn has something called a “coil suppression resistor” built in, which is a 680 Ohm resistor across the relay coil. Interesting. But no built in diode.

Before I go any further, here are two excellent links:

“The application of relay coil suppression with DC relays”

https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3311_AppNote&DocType=CS&DocLang=EN

“Coil Suppression Can Reduce Relay Life”

https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=13C3264_AppNote&DocType=CS&DocLang=EN

The first article has a table on page 2, which lists eight different suppression techniques and their relative effectiveness compared to no suppression. The bottom line: unsuppressed = worst; flyback diode = best in terms of suppression of the voltage spike. But there are always tradeoffs. The flyback diode also has a bad effect: when the relay coil is de-energized the flyback diode slows down the opening of the relay contacts. This can actually result in wear to the relay contacts, and in the worst case, they can become welded together. So other suppression techniques are considered, which are faster than a flyback diode with less voltage spike than no suppression. I note the use of a Schottky diode (which I extolled) is much worse than a regular diode as a flyback diode because the forward voltage is ~0.2 V instead of the silicon diode’s ~0.7 V. Shows you what I know.

One in-between suppression technique explored is the use of a resistor across the relay’s coil, like what Hella supplied. So now I see why Hella made this choice.

Anyway, let’s look at some actual measurements. The oscilloscope trace I show was hard for me to get and of low quality because my ‘scope is crap. Figure 1 is the plot of voltage across the relay coil versus time showing the negative voltage spike at turn-off. Three relay turnoff events are shown. The picture shows the event lasts about 5 ms, and the peak negative voltage is at least -60 V. It is very hard to tell how far down the spike extends. This image has been Photoshop enhanced to the max, and I think I see the rightmost trace reaches down 6 boxes vertically, so -60 V. It could go further. The aforementioned table in the first link measured a -120 V spike for their relay as tested with a 680 Ohm resistor. The circuit modeling I did (not shown) using my relay’s electrical parameters gave a result of -96 V. So I conclude: suppression of the relay coil is very important. I unwittingly included a “coil suppression resistor” of 680 Ohm thanks to Hella. I might very well install the “diode + 24V Zener” suppression arrangement on my scooter, if I can find something close to a 24 V Zener diode in my stash.

I have no idea if the relay supplied by Denali has any suppression built in. It is not marked as having any.

Is suppression needed in the compressor circuit? Do I need a flyback diode, or a resistor, or something across the compressor’s terminal? I took a look at the voltage waveforms as the horn was blown and released, both across the relay and across the compressor. There are no ugly spikes to report in either case.

…damocles
 

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So far I haven't used relays with diodes or resisters. With an isolated power supply for all my farkles I haven't noted any issues with lights flashing or flickering unintended. My horns are electric, not air horns, this time around so no motor to throw back a voltage spike. My horn hook up uses the OEM horn wires to trigger the relay for the louder horns, and are still connected to the OEM horn also, so don't know if that helps reduce any potential feedback from the relay trigger coil. The only other item using a relay is the LED flashing brake light bar I am in the process of installing along with the new-to-me Suzuki branded top case (really a Kappa K49, 47Liter case) and Suzuki mounting plate. The relays I use these days are mini relays since they only need to handle very low current (120 ma at full intensity with running and brake LEDs on) and fit better in tight spaces. I know that the power used at pin 87 of the relay is not what's at issue with reverse EMF but rather the effect of the trigger coil in the relay when the signal voltage is removed (across pins 85-86). Not saying it wouldn't be a good idea. Sounds like the resister is a better option.

The resistor or diode across the trigger coil inside a relay only takes care of bleeding reverse EMF on the relay trigger signal, at relay pins 85-86. The air horn compressor is not attached to that part of the relay... or better not be. So another resistor or diode across relay pins 30 (power input) and 87 (relay power output) is what would be needed to manage the spike coming from the compressor motor.
 

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Discussion Starter #8
So another resistor or diode across relay pins 30 (power input) and 87 (relay power output) is what would be needed to manage the spike coming from the compressor motor.
As I stated, I examined the switching waveform across the compressor terminals of my Denali setup. No spikes, no troubles, no suppression needed.

I only asset that I found a negative voltage spike at the coil of the relay controlling the compressor when the coil is de-activated. Any relay coil which looks electrically like an inductor (so not a solid-state relay) will have this issue, and the spike should be suppressed in some manner. The links I provided give the details and the tradeoffs.

...damocles
 

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Discussion Starter #9
Is suppression needed in the compressor circuit? Do I need a flyback diode, or a resistor, or something across the compressor’s terminal? I took a look at the voltage waveforms as the horn was blown and released, both across the relay and across the compressor. There are no ugly spikes to report in either case.
I was lazy in writing this last paragraph of a prior post. I will atone by expanding on the issues raised here.

Fig 1 shows how I wired the Denali Soundbomb Split horn. As stated, this picture hardly differs from the manufacturer’s instructions. However, I wanted to make sure a few items were clear. First, the location of the 680 Ohm “coil suppression resistor” built into the relay is indicated. Second, the actual voltages as measured while the horn was blasting are shown on the schematic. This makes clear the role of voltage drops across the relay contact and in the wires of the compressor circuit. Since the compressor draws 16 A, voltage drops can add up. I used 10 AWG wire (shown in red) which has a resistance of about 0.0011 Ohm/foot, which results in a voltage drop of 0.0011 x 16 ~ 0.02 V/foot of wire. For 16 AWG, the numbers are 0.004 Ohm/foot x 16 A ~ 0.06 V/foot.

Fig 2 shows the voltage across the relay as the horn is sounded versus time. As the horn button is pressed, the voltage drops to near 0 V. When released, the voltage returns to ~12 V in ~0.14 s. The transition is smooth with no voltage spikes, positive or negative, in sight.

Fig. 3 shows the voltage across the compressor as the horn is sounded versus time. Here, the voltage climbs to just short of 12 V quickly, the falls back to zero in ~0.14 s when the horn button is released. Thankfully, no spikes are in evidence here either, so no suppression is required.

As a sanity check, the two waveforms should add up to the constant battery voltage, minus wiring drops, and they do.

I suspect the compressor has some internal components to reduce switching spikes. If so, it was well designed.

…damocles
 

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That's some REALLY hefty wires. WAY more than practical for this application. I would have gone with the 16ga wire, or more likely 14ga wire, for 2 reasons. Most electrically trained mechanics and technicians seem to adhere to the electrical code for wire size for HOUSE WIRE which is solid core. Automotive and motorcycle wiring is stranded so can handle slightly more current and the drop is less over the same distance for any given wire size as a result. The other reason is that you are dealing with very short distances compared to what is of concern with house wiring so any drop due to using smaller wire size becomes insignificant over just a few feet vs. the distances for wiring a house. OK, 3 reasons, 16ga wire is a lot less $$$. Opps, 4 reasons, I think smaller wire size is easier to work with IMO. I use this chart for selecting wire size when I add electrical farkles on my bikes since it is adjusted for 12 volt DC systems with stranded wire. For heavy amp systems like incandescent headlights and air horns I consider using one size larger than indicated.
12v gage-distance-amps stranded wire.jpeg

Oh, and just wondering one thing with your setup... Does the Denali air horn compressor really use 10 amps more than the Stebel Nautilus horn? I seem to remember the Stebel horn only really needed a 15 amp fuse. Maybe 20 amp if really worried about current but that would mean something else is wrong with that compressor and I'd rather have the fuse blow before something else causes a problem.
 

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That's some REALLY hefty wires. WAY more than practical for this application. I would have gone with the 16ga wire, or more likely 14ga wire, for 2 reasons.
You give four reasons to use smaller stranded wire: 1. smaller AWG wire is more practical and stranded can handle more current than solid core of the same size; 2. wiring is of only a short length; 3. cost of large AWG wire too high; 4. easier to work with smaller AWG wire.
My $0.02 worth in replay:
1. "practical" is in the eye of the beholder. Solid core wire has a slightly lower resistance per foot, and so can pass a slightly higher current with the same voltage drop than stranded wire. Look it up.
2. I show the voltage drops for 10 AWG stranded in my Fig 1 of my prior post. I computed in the same post that voltage drops for 16 AWG would have been 4x larger. Still small enough. Still 4x larger.
3. I clearly stated I had the 10 AWG stranded in my basement and so I used this without regard to cost. I likely would have used 16 AWG had I had to buy it outright.
4. Yes, AWG 10 stranded is harder to work with. But not impossible.

Oh, and just wondering one thing with your setup... Does the Denali air horn compressor really use 10 amps more than the Stebel Nautilus horn? I seem to remember the Stebel horn only really needed a 15 amp fuse. Maybe 20 amp if really worried about current but that would mean something else is wrong with that compressor and I'd rather have the fuse blow before something else causes a problem.
The Denali instruction show a 30 A fuse. See https://www.revzilla.com/assets/0002/0399/denali_soundbomb_split_dual_tone_air_horn.pdf. I measured (and stated multiple times that I measured) a 16 A current draw. I fused mine at 25 A; could have used 20 A I suppose.

...damocles
 

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I tend to always up one wire gauge when I do anything. I then fuse to the Amp draw plus 10%. This has always worked well.
It seems that the American Wire Gauge (AWG) is a bit different from 1965 till now. Almost every stranded wire on my 1965 Barracuda has been found to be almost 1 wire gauge UNDER what the wiring diagram states. I have stripped the wire and checked them with a spec grade wire gauge scale.
When the book says the headlight wires are 16 gauge I have found then to be between 20 and 18 gauge and the headlights are dim. I then run a new set of wires and put a relay set on with it hard wired to a 10 Gauge feed and ground. The OEM wires are then used just for the relay trigger. I never cut out the old wiring if I don't need to so the car can be returned to OEM in short time.
In the past I have made over 50 of these harness's for other friends with other brand of cars. Till about 5 years ago there were no kits to do this but the China markets have started making good kits These kits are what I am modifying to fit our Burgmans to get some of the 130 Watts of draw off the Ignition switch. Anyone can make these kits.
Relays 2.jpg
 

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I do not have a 'O' scope any longer. I wish at times I had a inexpensive one to do some testing.
We had a few other Electrical Engineers as members on here but they have ether moved on or have passed away. I am not an engineer.

Back in my old life I used a lot of real good test gear. My first meter to grab off the truck was an anolog VOM with a 3rd wire to ground *. I would look at the wires to get an idea of what to grab next off the truck. I had 3 different 'Time Domain Reflectometer' (TDR) that would let me look at the wires for many different faults. But you had to know something about the wire, like Velocity of Propagation (Vp) .....

VOM with 3 leads for ground fault testing.
Sidekick 7B.JPG
 
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