Horn Circuit

[jOe]

Hmmm...Radio noise suppression. I would have thought that it would be addressed in the ignition system (magneto) and not the lighting system, but since they use the same ground, it's possible .I dunno, did the factory consider that an issue back then?
Mid '60s Corvettes came with a complete shield over the distributor and plug wires on small blocks for that, while standard passenger cars did not. A steel firewall vs. a fiberglass firewall with the radio about a foot away.
The button is as good as it gets- I tested it with and external power supply. I suppose there's only so much you can expect from a half century old Delco horn.

[hennesse]

If you mean the little capacitor going to the regulator, that is there for radio noise suppression. It takes the switching spikes out of the regulator relays and keeps radiation down.

The 32727-63 capacitor is listed in the 1965 and 1967 parts books as fitting 1963 to * XLCH (above engine number 63XL-3015). V-Twin says it is a 500 mfd 25 volt (if we can believe them). I kinda agree with jOe about radio supression. Modern spark plugs and plug wires are radio-supression, but I don't think the early 1960s were. And XLCHs didn't come with radios either! I kinda think these capacitors were used to provide a little extra oomph to get the horn started at low engine rpm / low generator output on the battery-less XLCH, kinda like starting capacitors on electric motors. No, they don't store much juice, but maybe just enough to overcome horn inertia. If they were really for radio-supression, wouldn't they have been used on XLH also?

The V-Twin replica can be had for about $25 these days, so it might be worth a try. http://www.motoparthub.com/32_7784_VTwi ... _Capacitor
I think I looked it up a couple of years ago, and they were outrageously priced (like over $100). My 1962 XLCH horn works great on a battery, but on the XLCH, it's kinda hit or miss whether it beeps or not when I press the button. But I consider it just to be there for show. Like the factory-stock squeeze-bulb horn on my 1955 Hummer.

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My 1954 Ford NAA tractor has solid-core spark plug wires. My wife complains that it screws up the TV when I'm mowing near the house. (Yes, we still have over-the-air TV). Haven't had any complaints about the XLCH. Of course, she can't hear the TV when I'm revving up the XLCH either.

[mikeslemmon]

most XLCH horns didn.t work when they were new (lights were marginal until 19,65 for some reason the XLH horn and lights were fairly reliable the only difference is the battery

[sportsterpaul]

500mfd (microFarads) is pretty big for just radio suppression, so the capacitor must also smooth the alternator output a little and lets the Bosch regulator be more accurate and less temperamental. 500mfd sounds big but there is that "micro" in there, it can not hold any appreciable charge. It keeps the generator voltage from going to zero when the brushes pass over the commutator segments. It just smooths the generator output a bit and makes the regulator's job easier. You can determine how little a capacitor of this size holds by connecting to a 12V battery. And then take it off the battery and connect it to the horn. It will discharge in a few microseconds.

A VW bug does not need the capacitor since it has a battery. That means the Bosch regulator is happier and more accurate with this capacitor on the generator output. Tell you what, I have a generator test rig sitting in the second bedroom, still unpacked from when I moved to Florida. I can hook a Bosch regulator to it, and see what happens with 500mfd and without.

The horn is sensitive to voltage, so a battery is 12V, but a working generator is closer to 14V. So it is no surprise you have to twiddle the screw to get it to work. Too bad the 5-dollar suppression caps are smaller value, it looks like V-Twin is the only game in town, I could not find a cheap substitute.

[jOe]

So after a check ride today, the damn thing is feebly working. The capacitor is OEM and original to the bike and I'd rather keep it, but anyone who's dealt with vintage electronics knows that aging capacitors are prone to leaking and drying out. I think the theory was that the discharge from the cap kicks the horn into initially oscillating and then the generator current sustains it. That there is an adjustment to the diaphragm would vouch for the unit's sensitivity to the amount of current. Combine this with whatever corrosion, rust, dirt, and small birds that may have accumulated in a 50 year old Delco horn and it's a wonderment that it works at all.
I think a good capacitor and dialing in the adjustment knob would probably bring it up to a normal operational standard , whatever that was.
As it is, I'll put some more miles on it and see if the cap comes back any any more. It may, it hasn't felt any sort of charge in decades. Who knows?

[hennesse]

Hey guys,

I wrote up a Technical article on our favorite condensor.

http://www.harleykmodel.com/technical/c ... index.html

Comments? Especially SportsterPaul !!!

[John R]

Hi Dave, Comments requested, so here are a couple. A condensor in a points ignition system is more than to suppress arcing, it sends a reverse current through the coil windings as the points open. This causes a much more rapid collapse of the magentic field. The effect is a higher voltage output from the coil. You'll barely get a high-tension spark with a dud condensor.

I hadn't thought before, but could the condensor in circuit with a horn help reduce internal point burning (which horns are prone to) and even cause a more rapid collapse of the magnetic field for a more freely vibrating diaphram? Should think the latter effect would be minimal.

[dr dick]

if your insight is satisfied with "a cap keeps your ignition points alive", or "allows your horn to operate better at low generator speeds" thats cool.
but its never gonna allow you to really understand whats happening.

take a look how mechanical energy is turned into electrical energy in our no battery bikes AND vice versa.
without a clear understanding of that, the role of a capacitor cant be understood.

all xlch use a coil of wire wrapped around a magnetic core to turn mechanical energy into electrical potential.
in the generator circuit breakers (brushes) commutate this into a rectified, but wavering unidirectional output.
the output is linked to the generator rpm.
the force that connects the mechanical motion to electrical potential is magnetism.

to regulate the generator output the regulator wraps a coil of wire around a steel core that creates magnetism that controls another circuit breaker-- the regulating point set.

in the horn a coil of wire (attached to the diaphragm) is wrapped around a steel core too. its movement when energized also operates a circuit breaker thru magnetic attraction.

what is common in all these systems is the basic principle.
mechanical motion thru magnetism creates electrical potential.
and
electrical potential creates mechanical movement thru magnetism.
think about that in your generator-regulator- horn.

once you have a grasp of that--
what is usually not considered is what happens when the circuit breaker opens the circuit.
to understand that you need to understand:
1) inductance. and what circuit elements are involved.
2) capacitance. and what circuit elements are involved.
3) reactance. and what circuit elements are involved.
4) reluctance. and what circuit elements are involved.
5) frequency. and what circuit elements are involved.

95% of us can explain what happens when the circuit breaker opens, but very few can describe what happens in the circuit AFTER the circuit is broken.
a capacitor operates in this realm.
but this realm is populated with circuit elements.

this is basic electrical knowledge.
there are tons of ways to understand it out there in googleville.

[sportsterpaul]

Excellent point John R about ignition condensers, the spark does not happen without one. Sure, it reduces pitting on the points, but its also used to make a resonant aka "tank" circuit with the coil. That is what sustains the arc during the so-called "firing line" part of the spark event. Current is rushing in and out of the coil and condenser, dumping that initial condenser energy into the spark.

Speaking of condenser energy, the 500mfd "horn" capacitor charged up to 6V holds 0.009 Joules of energy. A Joule is a Watt-second. So that 500mfd capacitor can supply one watt for 9 milliseconds. More likely its supplying 9 Watts for 1 millisecond. That ain't gonna run the horn very long or give much of a boost.

I note my 1965 parts book shows the "horn" capacitor on the ignition page. Also note that nothing changed in 1963 with the capacitor running change at bike serial # 3015. Same regular, same horn pack, same generator. I thought the factory might be "getting ready" for the 12V Bosch regulator used on 65 and later XLCH, but a better explanation is given by a guy on the AMCA forum that says "The horn capacitor was added to the XLCH to fulfill Federal requirements that stated the horn must blow at any time which it would not do at slow RPMs due to the batteryless system. The capacitor held enough charge to allow it to honk, once... "

I can find no "Federal" requirement, the FMVSS (Federal motor vehicle safety standards) that require the horn to work at idle. There is an Ohio requirement, "Every motor vehicle shall be equipped with a horn which is in good working order and capable of emitting sound audible, under normal conditions, for a distance of not less than two hundred feet." So maybe "in good working order" was interpreted to be "at idle" by some lawyer. The fact that the capacitor was a running change does imply something made Harley do it, it was not something they wanted to do.

In the tradition of "a little right, a little wrong" on the internet, the capacitor cannot hold near enough charge to get the horn "to honk." Like I said, hook it to 6V battery, than remove it and touch the wire to the horn and I would be very surprised if the horn did anything. As usual, Dr Dick is on the right track. What the capacitor does is smooth over the regulated armature voltage. There are two periodic things going on-- the "bumps" in voltage that come off the generator commutator, and those vary with engine speed. Then the horn is a periodic thing, with its frequency dependent on applied voltage. So at low RPM its likely the two things interact, that the bumps in the generator output interfere with the operation of the horn.

The capacitor smooths out the generator voltage bumps and probably makes the regulator work better. I have tried for 25 years to make a Harley voltage regulator that works with no battery and no load and no capacitor. I gave up. Its really ugly. When the relay (or a transistor like I was using) open to turn off the generator field, the energy in the field has nowhere to go, no battery, no lights no load at all. So with a "catch" diode it dumps into the armature, making a 120V spike. With no diode, like a old mechanical regular, its only the field coil that snaps up to 120V or so. I have dozens of 12V generators, and I think I can run the 6V generator on my 1952 K on my test bench to see exactly what is going on.

Another AMCA forum thread maintains the capacitor was used to keep the lights from flickering at idle. That might be true as well, but once again, I can't see 1 watt for 9msec doing much to power the headlight, it probably just stabilizes the voltage between commutator segments, just enough so you can't notice the flicker.

As to the problems of the OP, yes, this capacitor will help your horn problems. Electrolytic capacitors like this one are the worst reliability components in electrical engineering. As they age they dry out and stop holding charge. So please drop 25 bucks for the V-Twin replacement one to see if it helps.

I will get my generator tester set back up now that I am getting settled in Florida. I will look at the effect of this capacitor, and I can at least look at re-pop horn packs to see how they act.

[hennesse]

Hi Dave, Comments requested, so here are a couple. A condensor in a points ignition system is more than to suppress arcing, it sends a reverse current through the coil windings as the points open. This causes a much more rapid collapse of the magentic field. The effect is a higher voltage output from the coil. You'll barely get a high-tension spark with a dud condensor.

I hadn't thought before, but could the condensor in circuit with a horn help reduce internal point burning (which horns are prone to) and even cause a more rapid collapse of the magnetic field for a more freely vibrating diaphram? Should think the latter effect would be minimal.

John, you are correct - the instantaneous discharge of the condensor as (after) the points open does cause the effect you mention. It probably does help the coil in the horn to "reset" as its points open, and get ready for the next "vibe". Unfortunately, I was too dumb to pursue EE and went for CS instead. So my explanations may be technically naive.

Dr. Dick - when I mention "whoopie" to my wife, I am sometimes met with "reluctance". Let's drink a few beers at Oley and discuss these terms more fully...