Viewing Spike On O-Scope

[osuri7]

Hi everyone,

I've been a bit MIA lately but good to be back at it.

Novice issue here:

I've got my SS SSG set up and have been trying to get a good view of the spike. I'm using a Tektronix 2246 100MHz O-Scope (I know, old) but works great.
You'll see in the attached photos the following:
1 - O-Scope Setting Panel (x10 probe)
2 - O-Scope Screen Shot
3 - Back side of my circuit (with Patrick's cap/diode mod, though you can't see them in the photo)
4 - Charge battery (small Harley Davidson 12V 10Ah battery). You can see I am taking the spike reading directly from the battery terminals. I noticed if I put the probe directly on the output point coming from the circuit board, I get a larger spike reading (the 17.4V seen in the scope screen shot).
5 - Setup (input is a power rail 16V, 0.6A. I know, power rails aren't ideal as the signal needs to bounce between charge and input batteries, but I'm still at the testing stage for now). The multimeter is not hooked up to anything, hence the nul reading.

In the full setup you'll see my 3 coils, circuit, power supply and charge battery. The coil in the center is the drive coil (haven't separated the trigger) and the other two are power coils (8 filer, 18AWG, 150foot windings, same but 9 filer for the trigger coil).

You'll see in my scope shot that the peak voltage of the spike is only around 17.4V. But I have filled a 450V, 470uF cap to just over 180V with this system so I do believe I am getting a proper spike. To do this, I just switched the charging battery for the cap. I know the cap isn't the proper way to measure the spike level, but I thought it would be a good indicator whether I'm getting a proper spike or not.

Anybody have any idea why I can't see the spike on the scope? Is the scope just not up to the task?

Let me know if any clarifications are needed. Grateful for any advice or thoughts.

Chris

PS - In my setup image, you can see some iron pipe sections at the top left. I took these (10mm thick) pieces and placed them around the two power coils and the spike increased about 8% (focusing the em fields I believe: Master Class DVD from Bedini). Putting one around the drive coil seems to interfere with the trigger resulting in a slight drop in the max spike.

[osuri7]

Hi all,

I worry my question is either too novice or unanswerable with the information I've given.
Any advice at all would be greatly appreciated.

Many thanks,

Chris

[Michael Luton]

Your battery or cap is loading the spike when tested at those points. Try looking at the transistor collector. look at the transistor base to see the switching mechanism.

Michael

[sephiroth]

Hi osuri7,

Your spikes look fine to me. The output from a collapsing field is self regauging ( or self impedance matching ) so that the voltage output will increase to whatever voltage neccessary across the load (within reason) to allow sufficient current through the coil to maintain the present state of the magnetic field. This means that if you put a 12v battery on the back end as a load the voltage output will be just above the battery's voltage for the majority of the collapse. If you put a small capacitor in place of the battery then as it charges the voltage output by the field collapse will constantly increase with each pulse up to the maximum voltage attainable which is normally up to 200v with our standard coils and a 12v source.

Another way to look at it would be if you put a small impedance on the back end, like a one ohm resistor, the voltage output by the coil will be very low, but then if you put a very high impedance on the back end, like a 10kohm resistor, the voltage will skyrocket.

When we discharge the coil into a lead acid battery something very interesting happens. The lead ions in the battery are very heavy and so do not want to move immediatley when voltage is applied across the terminals. So when the field starts to collapse, the first thing it sees is a very high impedance load where the battery is which restricts current, and so the field collapses very quickly. Because voltage induced in a coil is dependant on the rate of change of the magnetic field, this induces a very high voltage initially. This is our spike. But then the ions in the battery begin moving and the impedance of the battery drops and current begins to flow. Once current starts flowing through the coil, this maintains the magnetic field and slows the rate of collapse. I like to think of it as a parachute opening up. So now the magnetic field is collapsing at a slower rate, and as we know the voltage induced is dependent on the rate of change, the induced voltage drops down to just above the battery voltage.

This is why we don't usually see the 200v spikes which the coil is capable of generating when it is charging a battery. The battery only impedes current for a very short time and it is not usually long enough to let the voltage induced by the collapsing field to reach such high levels.

Hope that makes sense