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Adding a horn to an 01 WR

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Hi all, im getting a bit desperate now :cry: I bought my 01 WR nearly three months ago and still haven't been able to use it!?! :cry:

To take it out I need to make it street legal. I've got a switch gear from a 02 KTM 200 EXC, which is perfect for what I need (hi/lo/off, kill & horn - no turn signals!).

The headlight has been wired up for high/lo beam, hydraulic brake switches front and rear, and a number plate assembly/light, all works a treat.

The last stumbling block is the horn. I got one of these from Hein Gericke, but cant get it to work with the bike. I know for sure that the horn works, but the bike just doesn't produce enough juice to power it.

So what I need to know is what alternatives are available? Im pretty sure the law over here (uk) says no compressed-air types and definatley no old style meep-meep hand horns.

Rooster, I saw a post of yours where you mention an electronic horn from Baja Designs, but I cant find it on there site anywhere.

Please help!

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just buy a standard yaaha item for it, al 01 wr250fs came out with them so gettin a stock item shouldnt be to hard.

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I might be being a bit thick, but wouldn't the standard yamaha horn just be a normal 12v horn like the one I tried? The problem seems to be that the bike cant produce enough power for the horn *and* everything else.

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i have the same horn and the same bike.

you need to convert the AC output from the '01 WRF's electrical system to DC which is needed by the horn. otherwise these types of "old-fashioned, non-electronic" horns won't work or they just squeak a bit.

for my bike i built a simple half-wave rectifier, consisting of a single power diode (1N4001 type is fine, 1N4004 is preferred) and a 3300uF/35V electrolytic capacitor, which is about 1.25" [30mm] X 0.5" [12mm]. the larger the value cap (in uF) the better. if needed, you can use several smaller caps in parallel, e.g. three 1000uF. but be sure the rated voltage of any cap you get is 35V or greater.

this half wave rectifier circuit produces the DC you need. the diode goes in series with the power lead to the horn. the "arrow" in the diode symbol points towards the horn. the capacitor goes from the rectified side of the diode to ground (or in other words, across the horn's DC inputs). be sure to obey the capacitor's polarity markings as electrolytics do not take kindly to reverse polarity. most electrolytics are marked with a (-) stripe up one side -- that's the side that goes to ground.

<font class="small">Code:<hr /><pre>

diode

---power lead---->|------------ HORN+

|+

--- capacitor

---

|

---ground----------------------- HORN-

</pre><hr />

you can get these parts at most any electronics store; for example in the USA Radio Shack carries these parts. they cost just a few US dollars. to assemble, ideally you just solder them up. but if you are not handy with a hot iron, just get a small terminal strip (aka barrier strip or terminal block) while you are at the electronics store. then you can just screw it all together and make the connections to the horn. cover the whole assembly with insulating tape (or better yet heat shrink tubing) to prevent shorts.

you can also use 4 diodes to build a full wave "bridge" rectifier, which in turn reduces the size of the capacitor that you need. but the half wave works fine and requires a minimum of connections.

jim aka the wrooster

'01 wr250f

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Hey wrooster. I'll freely admit that I'm a dope when it comes to electronics, so if this is a stupid question feel free to do your Jonny Storm impersonation.

Shouldn't the charging circuit on the WR already be DC? If so, couldn't he tap into that for 12V for the horn? The horn wouldn't work unless the bike was running but that shouldn't be an issue. Isn't there already a rectifier/regulator in the circuit?

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I've already have tapped into the bike, but the sound out of the horn can bearly be heard. Also, pressing the horn takes power from the engine (which makes it cut out).

Im not bothered about having no horn when the bike isn't running.

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Shouldn't the charging circuit on the WR already be DC? If so, couldn't he tap into that for 12V for the horn? Isn't there already a rectifier/regulator in the circuit?

yes/yes/yes, but only for an '03 or later WRF. prior to '03, the WRF had a novel starting system which consisted of a foot operated lever and a spring loaded pinion gear which engaged a ring gear on the crank. there is no battery, no charging system, and no rectifier. thus, the electrical system on an '01 or '02 WRF is very primitive, and indeed the lights et al are run from unregulated AC power. adding a component -- like the horn above -- which requires DC power requires some sort of rectifier, such as the simple half wave type that i described above.

as you can see from this diagram,

http://losdos.dyndns.org:8080/public/motomisc/wrf-wiring_sm.jpg

the entirety of the electrical system on "early" F's is hanging directly off of the stator's secondary winding. there is a voltage regulator (item 3, in parallel with the loads) and it's job is to prevent the AC voltage from exceeding some reasonable value, say 15V. but there is no rectifier, and no large capacitor (read: battery).

jim aka the wrooster

'01 wr250f

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Flip...

I've also used the KTM switch on my '01 WR and had the same horn issues. It took me a while to suss out that its going to need a DC supply but ive been assured that you can buy an AC horn and slap it straight on.

Interseting to see you posting again, i replied to you when you just got your bike but i suppose you never went back too the thread. Only reason being im in the same neck of the woods and ride the same bike as you.

Best of luck and let me know how you go.

Mat

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Shouldn't the charging circuit on the WR already be DC? If so, couldn't he tap into that for 12V for the horn? Isn't there already a rectifier/regulator in the circuit?

yes/yes/yes, but only for an '03 or later WRF. prior to '03, the WRF had a novel starting system which consisted of a foot operated lever and a spring loaded pinion gear which engaged a ring gear on the crank. there is no battery, no charging system, and no rectifier.

DOH! :cry: Of course you're right. Thanks for straightening out my temporary(?) brainlesssness. :cry:

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Wrooster, im a complete electical novice so I've one last stupid question (promise).

I picked up the bits I need for the rectifier last night. They didn't have any 3300uF/35V capacitors, so I got 3 * 1000uF/35V.

The question is, how can I find out which is the positive and negative terminals on the diode and capacitors?

Thanks in advance

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The question is, how can I find out which is the positive and negative terminals on the diode and capacitors?

the negative side of the capacitor body will have a contrasting stripe on it, usually with the "-" symbol repeated in it.

in this picture, the large black electrolytics have such a stripe:

http://www.niccomp.com/Images/LDDmix2.jpg

also see

http://www.chemi-con.com/guide/pg3.php

as for the diode -- the cathode of the diode will have a band around it, usually it is a white or light colored band on the dark body. this is the side that goes towards the horn. the other end (anode) connects to the horn power feed, coming from the pushbutton switch.

the datasheet for the 1N400x series diodes is here:

http://www.fairchildsemi.com/ds/1N/1N4001.pdf

jim aka the wrooster

'01 wr250f

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Wrooster, unfortunately the half-wave recitifer doesn't seem to be the answer.

The noise from the horn is a *little* louder but still cant be heard much over the exhaust. Also, pressing the horn makes the lights dim, (which is a definate test fail over here).

Does anyone know where I can pick up an AC horn from in the UK, and more importantly, will it work with the WR?

Thanks in advance

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flip_lmb,

hmmmmmm. i don't know what the problem could be but i do have a warning... the power required by the AC horn will be on par with the DC horn. so if you are having a problem driving the DC horn, you will likely have the same problem with the AC horn. that is, the sound output level will be low and the headlight will dim etc.

that said, i would look into an "electronic horn" that has a speaker rather than a mechanical horn like you (and i) have now. the power requirements for an electronic type are far less than the "old fashioned" mechanical type -- and thus i'd bet you'll have better luck with the e-type.

the electronic horn will likely require DC, but with the half-wave rectfier in place you're already set up for it.

good luck,

jim aka the wrooster

'01 wr250f

ps

are there any markings etc on your horn? my unit came from a USA shop, www.fourstrokesonly.com and requires around 1A at 12Vdc. your WRF should be able to drive a 12W load just fine.

mine is item 44-0032 at the botton left of

http://fourstrokesonly.com/HornKit.html

note that these guys don't actually sell AC horns, they just package a DC horn with what they call a "diode cap thinge" -- guess what that is? :cry:

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phil,

just check you wired the capacitors in parallel and not series. They dont add up like resistors do.

mat

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