Sachs Suburban 1980 horn funny business

Dan (high idle) Conway /

hey everyone,

i’ve got a sachs suburban, everything works except the horn. This setup has the zener diode and the horn powered off the ignition lol. Whenever the horn is pressed the ignition is cut. I’ve tried several different horns, wiring has not been tampered with anywhere on the bike.

I tested the diode simply labled “se 30” and one side is around 450k and the other side is over 2 Mega ohms. The horn switch functions as it should, tested with a meter.

Somehow the horn is draining the ignition? Any advice much appreciated, this is just a funny sachs problem.


Re: Sachs Suburban 1980 horn funny business

huh, never had a horn, i can yell louder anyway. have you tried just wiring the horn off the lights? It'd probably kill the lights but the bike'd still run and it should work. or off the brakelight circuit, it'd be the same power source just the other side

Re: Sachs Suburban 1980 horn funny business

Dan (high idle) Conway /

So, I did actually try that Will. What happened was when I hit the horn everything went dead and the horn didn’t do anything. I think it offsets the balance too much. I am positive this 6v horn works too.

Like I said, wiring is clean and wasn’t touched by anyone it seems. Maybe I just should drop the horn? Or try a new diode for the hell of it?

Not sure what that zener diode is actually rated at anyways

Re: Sachs Suburban 1980 horn funny business

I, the great electrical engineer, studied the schematic you posted rather carefully, for the screwy arrangement seems very similar to the wiring of my Trac Clipper, which is a Korean Batavus.

I am fairly confident that your diode is not a zener diode, but a plain rectifier diode. That's because a zener diode is almost invariably connected in series with a considerable resistance--generally a resistor--to limit the current through the device when it conducts 'backward.'

It looks to me that the purpose of the diode is to allow the horn to be run off the flywheel magneto's ignition coil. That poor coil has three duties: to supply a large impulse of sharply-cut-off current to the spark coil for the spark, to run the stop light, and to run the horn.

I assume you know the following, but I have to get it straight in my own head. The bike's ignition, or any flywheel magneto, pushes a large current through both the flywheel coil and the primary of the spark coil (actually a transformer) as the strong flywheel magnet approaches the flywheel coil. When the ignition points open, that current is instantly (approximately) stopped, as is the magnetic field produced by that current in the spark coil's primary winding. Since the large secondary coil--the one connected to the spark plug--is also subject to this same suddenly-cut-off magnetic field, the rapid change in magnetism through that secondary coil gives us our 30,000v spark. (Rapid change in amount of magnetism through a coil produces a prodigious voltage across the ends of that coil, or V=d phi / dt.

But our flywheel ignition coil just sits idle for the rest of the time. As the flywheel magnet goes past this coil, it develops a large opposite voltage across its ends, a voltage that could drive current through accessories like the horn.

And so we connect our horn to the flywheel ignition coil. But then if we push the horn button, current from our flywheel ignition coil will happily travel through the horn's internal coil, down through the horn switch, and thence to ground, thus preventing any current from flowing through our spark coil. And the engine will stop.

And so we add a diode, which will only conduct current in one direction, in series with our horn. This will prevent the positive-going current produced when the flywheel magnet is approaching the magneto ignition coil from flowing anywhere but through the spark coil's primary. When the magnet passes by our magneto ignition coil, though, the current changes direction and thus can, when the horn button is pressed, flow through the horn and produce a horrible croaking beep due to the weird current waveform thus produced.

I would guess that you'll want to replace that diode with any silicon rectifier diode capable of conducting, say, 10 amperes of current. The PIV (peak inverse voltage) rating is not so critical, but since we're dealing with ignition voltages here, something greater than 200 volts might be in order.

Don't connect two diodes in parallel in an effort to increase the current rating, for while it's tempting to do so, it doesn't work: one of the diodes always hogs all the current and then burns out for its trouble.

Corrections are invited here, for I've rapidly come to understand that moped wiring is awfully strange. The reason is that they're trying to squeeze all the electric power they can out of that tiny magneto and that tiny engine.

if the parts ever come I'll try building a half-wave voltage doubler to increase the lighting coil's output to 12v DC and thus maybe run some LED lights.

Re: Sachs Suburban 1980 horn funny business

howd you test the horn? it's the original horn? If it works when you test it on a battery then it's not the right horn

Re: Sachs Suburban 1980 horn funny business

I read that electrical stuff carefully, interesting. Waves and magnetisim and pos/neg stuff, so how do you explain those bikes that run without a resistor or zenor diode. All I know is external ignition ground to power usually brake light, but it's always connected to the ground side.

forgot, it' s always about the grounds. check clean all grounds.

Re: Sachs Suburban 1980 horn funny business

Good question. For one thing, additional lighting, some required by law, has added extra load to the feeble electrical systems on these bikes. My 1963(?) Peugeot had no brake light and an AC horn that ran off the lighting coil and extinguished the headlight when you tried to sound it. So you had to turn off the headlight to honk the horn.

My Trac Clipper is a 1984, but if there's a horn diode in there I can't find it. It ran right off the ignition coil like yours, and stopped the engine, like yours. The diode might have been removed at some point. I'll stick an ammeter on the horn (do I have an AC ammeter somewhere?) to find the current.

The deal with current, voltage and magnetism is as follows:

(1) when electric current flows through a wire, the wire becomes magnetic. This effect is magnified many times when the wire is very long and wound into a coil with many turns. We get even more magnetism if that coil is wound around a piece of iron or steel. This device is known as an 'electromagnet.'

(2) Conversely, if we have a coil like that described above, we might bring something magnetized close to it. We could say that it then has magnetism--we call it a 'magnetic field'--running through it. Now, if we happened to change the amount of magnetism flowing near that coil--say, we pushed the magnet closer or took it away or flipped it over--then we'd see a voltage, or electrical pressure, generated at the ends of that coil's wire. A large, fast change in magnetism near the coil will produce a large voltage across the ends of its wire. Then, if there's a path for it to take, a current will flow from one end of the coil wire to the other. This is an electric generator.

So: an electric current flow will produce magnetism in a coil, and a change in magnetism near a coil will produce a voltage and, if the path for it is complete, a current.

Now connect an electric generator consisting of our flywheel magneto coil to an electromagnet, which is one of the two separate coils (the 'primary') inside our spark coil assembly. The magnet on the flywheel rapidly approaches the magneto coil, which rapidly changes the amount of magnetism through that coil. This generates a large current through both both the magneto coil and the primary coil. Hence we get a lot of magnetism through the primary coil _and_ through the secondary coil.

When the points open, the amount of magnetism through all coils drops from a lot down to zero in a very short time. This rapid change in magnetism creates a very large voltage across the ends of the secondary coil, and this is applied to the spark plug.

Only the abrupt change in magnetism caused by the opening of the points can generate enough voltage in the secondary of the spark coil to arc the spark plug gap.

M Kinsler

Re: Sachs Suburban 1980 horn funny business

Dan (high idle) Conway /

So basically i should just move the coil closer to the flywheel if i have the space Mark?

Re: Sachs Suburban 1980 horn funny business

In any motor or generator it always helps to minimize the air gap that the magnetic field must traverse, but I think the moped manufacturers have pretty much optimized this: you do not want your magnet to hit your coil's armature under any circumstances, so I'd leave it alone.

(The air gaps in the generators at electric power plants are extremely narrow, so narrow that a good deal of excess heat is created because air gets compressed when the molecules are dragged by surface adhesion into the space between the rotor and the stator. And so instead of air, the generator case is filled with hydrogen gas, which is far more slippery than air. The rotor spins at 3600 rpm, driven by a shaft that's maybe two feet in diameter. About half a million horsepower is involved in the larger generators.)

What you probably do want to do is trace wires to see if any previous patriot has tried to improve the wiring arrangement. On my bike you can arrange those connectors any which way, and the screw slot in the headlight has a suspicious amount of wear.

I'm going on another diode-hunting expedition as soon as I get done replacing the ancient crankshaft seal that's letting fuel vapor coat my clutch plates. (It's really great: bike stalls, and then the clutch slips so you can't restart it.)

Re: Sachs Suburban 1980 horn funny business

Moped horns are simply lousy, but: If you apply a six-volt battery across the terminals you should be able to hear a single click sound as the horn diaphragm is pulled back onto the electromagnet. You'll hear another click when you disconnect the battery, which lets the diaphragm snap back into its original position. That said, you can purchase electronic bicycle horns which contain their own batteries and which will scare the heck out of you when you push the button.

Mark Kinsler

Re: Sachs Suburban 1980 horn funny business

yea, they won't go "beep" on a DC current from a battery. if it does beep on a battery, it wont on an AC bike.

Re: Sachs Suburban 1980 horn funny business

Dan (high idle) Conway /

So i totally missed something thats kinda wild... someone changed out the magneto with a batavus magneto and hid the other wires under the frame. I removed the brakelight switches (both broken anyways) and wired the horn into the light circuit, Everything is working! I could have sworn everything was stock but they did a good job hiding those wires.

I changed the carb to a 15 bing clone today (nicest new treats one) and its great. Thing idles for days, I changed out the front tire today, tomorrow ill do the rear and take it off the lift for a spin.

I got a hitch carrier for my forester, this bike is coming up north for some field/ trail adventures. I love the 5051/d for off road mopedding because its geared so low

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