Why not one of those aerosol boating/sports event noisemaker horns? They're pretty loud!

Actually, where's Rube Goldberg when you need him?

Tree Farmer

 

If you have a Radio Shack near you then go there and buy a full-wave rectifier(if not any local electronic supply will carry them). It will cost less than $5.00, you will keep your ground seperate from the negative DC power.
it will have the following connections:
~ hook this to your ac supply or ground
~ hook this to your ground or ac supply
- negative dc power out put
*(plus sign) positive dc power output

This should fix your problem

 

If I go full wave rectifier like that, then is there no need for a capacitor? Would I only need a capacitor if I used a 1/2 bridge rectifier?

 

No I would not use a capacitor because it will up the voltage. The reason capacitors increase voltage is they store the highest amount of voltage in the circuit. I know you think your bike is only makeing 12volts but really it will be much higher. If you understand what a AC sine wave is than this will be easier to grasp.When you put your voltage meter on your bike and it reads 12volts what it is saying is you have a average of 12volts over the sine wave. What this means is it averages the peak voltages with the 0 voltage at the base of the sine wave. but this average changes as you speed up the motor and change the frequency of the sine wave. Higher RPM's will increase frequency and when you inrease the frequency it takes a higher peak voltage to average 12volts.And even though you have a rectifier to make DC it will have the same humps as the ac voltage, rectifiers don't condition electric they only take the ac sine wave and keep it positive.This is a very crude explanation so please read a basic electricity book to fully understand.What does all this jibberish mean, if you put a capacitor on your bike weather it is a halfwave or a fullwave rectifier you will have a capacitor with 30-40 volts, that if big enough will have enough amps to fry your horn. The reason you should use a full wave rectifier it will give a cleaner dc voltage because you are using both ends of the sine wave. this should work for a horn but if it doesn't than it may not have enough watt output from the stator, before buying a larger stator unhook your lights and try the horn if it works now than you know you need a larger output stator

 

rsss396, that was a good faith response in an attempt to help out a fellow ATVer, but I'm afraid that you are incorrect on some minor details. You have the correct ideas, but just not about the capacitor storing voltage and a few other minor points.

Trust me MaxAz, you need a capacitor. First of all a capacitor will not "store the highest voltage". A capacitor as used in an AC to DC rectifier is used to smooth out the pulsating DC that will be produced by the full-wave bridge rectifier. Don't worry about the voltage levels anyway because everything electrical on your bike gets it's power from the voltage regulator which shouldn't let the voltage get above about 14 volts or so. I would still be more worried about the current draw from the horn; you don't want to burn up anything like your voltage regulator or stator windings. When I put one of these on a quad I couldn't believe how much current they draw. Go with the battery powered solution this is a can of worms.

 

wyorider, If you take a dc capacitor and connect it between the positive terminal and the negative terminal of the rectifier you will see a large increase in voltage. I have been there and done it. I have not tried using a ac capacitor on my bike but plan on experimenting because ac capacitors will cause the sine wave to lag and not peak as high. I am not a expert in designing circuits I just know what I have tried. A capacitor would be great to help clean up the dirty DC but it will charge until it reachs the highest value of the DC ripple coming from the rectifier. The 120volts in your house is not measured at the peak of the sine wave if it was it would be more than 120volts, the same is true on the magneto voltage off your bike. I have seen the voltage as high as 40volts DC at the capacitor and have blown up a couple of soild state regulators (max rated voltage of 35v) I was using to charge the MSD ignition 7.2v battery on my bike. I have seen fullwave rectifers run neon lights on a snowmobile with no battery so i would think it would also run a simple vibrateing coil in a horn. good luck

 

dc capacitor?? ac capacitor?? Don't think the designations apply. The impedance of a capacitor varies inversely with the signal's frequency, thus DC to capacitor is an open circuit, if I remember correctly.

ac/dc capacitors - kind of makes me think of right/left-handed screwdrivers and metric/standard crescent wrenches.

 

when the electroltic capacitor is polarized, it can only be used in circuits containing fluctuating dc voltages, where the polarity does not change.When voltage is applied in the other direction the oxide film is broken down and the capacitor conducts like a low ohm resistor.Thus if an elecrolytic capacitor is connected in the circuit backwards, it could blow up because of the high current that could flow through it. meaning if you hold it in your right hand while it is hooked up backwards you just might be shopping for a left handed screwdriver
and yes there are non polorized capacitors for both ac or dc circuits.

 

First off, thanks again everyone for all the information. I decided to start simple and just install a full wave bridge rectifier figuring I could add a capacitor later if needed. Anyhow, it seems to work just fine with only the rectifier installed. I put a volt meter on it and found that my rectifier is eating enough power that my idle voltage is about 8V and when revved it peaks immediately at about 8.5V. It appears the factory voltage regulator is doing a pretty good job as my anolog meter held very steady during tests. I also tried this with the headlamp disconnected and got basically the same readings. Since the voltage is a little low for the 12V horn, I called the shop I got it at and they are ordering a 6V horn and will swap it out. Then I think it should sound pretty good. As it is, I got my bike through the vehicle inspection this morning and after a call to my insurance agent I'll be ready to roll. I don't plan on doing anything else to it since I never really planned on having to use it. It's just to make it road legal. With the switch installed before the rectifer and horn, I don't think I'll ever have any troubles. By the way, this horn is made by NIKKO Horns and is no bigger than a chewing tobacco can. That's what I like about doing it this way. It's light, the batteries won't run down or corrode, and it's so small you don't even notice it. Thanks again! Max

 

That's great. I'm glad that worked out for you. It's good to know you can do this without the capacitor. Apparently the horn doesn't care if the DC is pulsating... Now, maybe I can get rid of that squeeze bulb horn on my Banshee....