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Antique Gas Engine Discussion

Make Your Own Buzz Coil

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Old 12-07-2017, 12:14:43 PM
joegeds joegeds is offline
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Default Make Your Own Buzz Coil

Having decided that spending $200+ on a Wico EK magneto was not in the cards, I decided to do some internet research and make my own buzz coil - at least so I can see/hear my Hercules 2 HP engine run. It is made very cheaply, from parts most of us have lying around the garage. Ingredients:
1) Simple 12-volt coil from any vehicle
2) 30-Amp Bosch 5-pin relay
3) Condenser
4) Spark plug and spark plug wire
5) Micro switch
6) 3-4 ft of 14 gauge wire
7) Wire connectors (male/female spades, ring connectors, etc)

See the diagram to make the following connections:

From positive post of coil:
- to spade 87a of relay
- to spade 85 of relay
- To bracket of condenser

From negative post of coil:
- to base of spark plug (ie, ground to engine)
- to spade 86 of relay

Connect spade 30 of relay as well as one side of switch to the end of the condenser wire.

Connect other side of switch to the positive terminal on battery.

Connect negative post on battery to base of spark plug (ie, ground to engine)

Connect spark plug wire from top of coil to top of spark plug.

That's it!! Activate the switch for your own super-hot blue spark. All you have to do now is figure out how to time the switch activation to the trip finger on your engine, and it should spark at the correct timing mark.
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Old 12-11-2017, 03:44:23 PM
Daniel Dorece Daniel Dorece is offline
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Default Re: Make your own buzz coil

I have a little problem with your wiring diagram. On all the Bosch relays of this type that I have seen the 86 and 30 terminals are in reverse positions.

Iron Wolf ( Dan )
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Old 12-11-2017, 03:58:17 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Make your own buzz coil

Diagram is correct, numbers are reversed.
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Old 10-16-2018, 09:54:31 AM
DOC0455 DOC0455 is offline
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Default Re: Make Your Own Buzz Coil

Well I ordered some cheap relays and attempted to make a buzz coil but couldn't get them to work. So I figured what do I have to lose so I opened one up to see. Seems the spring pressure on the contacts was to strong and the magnetic coil was to cheap to react fast enough for them to work. So I did a little tweaking and made the gap between the magnetic coil and contact carrier about half and bent down the normal open contact to get it out of the way and now they work like a charm.

Here is a video of the process:

Here is a video of me playing with one that I did the mod to making a small Jacobs Ladder:
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Old 10-16-2018, 10:47:31 AM
DustyBar DustyBar is offline
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Default Re: Make Your Own Buzz Coil

Your circuit is about the same as the one I send out.

I have a schematic for another circuit that prevents discharging the battery if the engine ever stops with the points closed. It limits power to the coil to to no more than 1/2 second. The problem with that circuit is I need help deciphering the missing wiring. I need help, three wires run off the drawing and I don't know how they should connect. Maybe there is someone who can look at it and tell me how to use that circuit. Following is the reply I got...

This is a very common problem with circuits that handle significant current and/or power. If the oscillation stops — which is mechanical, in this case — the circuit is left in the high current state. This can drain batteries or damage contacts or coil windings. There is no “correct” solution, but I’m going to try one that should work. Since I don’t have the exact setup to test with, I’m going to guess a bit. I think the general idea should work, however.

I’ve annotated Figure 1 in blue with points on the circuit that I will use. Point A will give us access to the timing points. Points B and C will allow us to control the relay coil and primary coil power supply, only energizing it if the system is oscillating. We’ll break the circuit where the blue X is — not the red X as in your original diagram — to allow us to control the relay and stop the buzzing, but also to de-energize the ignition coil that is draining your battery.

The idea I have for controlling the behavior is to sense when the timing points are opened and closed, and use that to reset a little RC (resistor-capacitor) timer. When the timing points are closed, point A will be at circuit ground potential. We will exploit that fact to make our RC timer discharge. When there is some buzzing of the ignition coil primary, we’ll rectify and steal a little energy from there to charge up our RC timer.

We don’t care very much whether the timer is linear or not; just that it can sense when things haven’t been moving for a few seconds. It does rely on the coil primary waveform having some positive voltage swing with respect to the common when it’s oscillating with the relay shown in Figure 1.

The RC timer voltage is a rough measure of the activity of the timing points. We can use that voltage to switch a transistor that can then be used to control a second relay that will cut off the first relay (the one on the original schematic) when no activity has been detected. The transistor allows us to amplify the voltage and current available from the RC network in order to switch the secondary relay in Figure 2.

There is one important consideration that kept me thinking about this circuit for a while before I decided that it was likely to work. That consideration is how the circuit will start up. This is particularly important when we consider oscillating circuits, or even those that will work with something else that oscillates. Some are initially metastable, so small perturbations will make them go. Others — like this one — are mostly bistable, but it’s important to make sure that the circuit will be in a state where it can work at all when the timer points are either open or closed.

Let’s look at each state. When the points are open, R3 will pull point A up, charging the RC timer (R1, C1) through D2 and R2. This will eventually switch Q1 on, energizing the relay, K1. That will enable the circuit. R3 is required to bootstrap the circuit into the on state where K1 is engaged. In that point’s open state, though, not much should happen then since the timing points being open keeps the ignition system from oscillating.

When the timing points are closed for a long time, no current will flow into the RC timer. So, Q1 will eventually turn off and K1 will become open. That disables the circuit. A little bit of current (approximately 1 mA) will flow when the circuit is in the disabled state with the timing points closed. K1’s relay coil current will flow when it stops in the point’s open state for a long time. That should drain the battery very slowly. The circuit should recover if the timing points are open for a few seconds. Probably spinning the motor during starting will get it to go.

A couple of notes about the components. Diode D2 should be able to handle 100V or so reversed, just in case there is significant flyback voltage from the ignition coil. Q1 should similarly be a medium sized transistor that can handle a little excess base current — at least momentarily. Maybe something like a TIP29. The RC time constant of R1 and C1 may have to be adjusted until the relay stays on for long enough; 10 µF might be a good starting point for C1. If it’s a polar capacitor, the + side goes closer to the transistor base. Of course, I will admit that I have not tried this circuit, nor have I simulated it. So, I can’t guarantee that it will work. If I had a setup, it would be fun to make sure that this all performs as I think it does. If you build it, let me know how it goes and send in any corrections or discoveries."
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Last edited by DustyBar; 10-16-2018 at 11:09:09 AM.
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