Note: at any picture you can click and magnify to 1024 x 768 pix
I was make simple spark gap with two mini doorknobs, ceramic insulator for trigger electrode,
and only simple setup for testing working distance (without housing). For triggering test in #1
case, I was use car's ignition coil. For test #2 it will be same SG, but different triggering coil.
 |
| Power supply for this test is
15.5 kV with ground at middle, so no one end was grounded.
Triggering circuit is powered with power line rectified voltage of
-300V. Spark gap operate in "C" mode, which mean - negative voltage at adjacent electrode, positive voltage at opposite electrode and positive triggering pulse. |
Choice of ceramic sleeve for triggering pin:
 |
| Here is two choices: or TV diode
(need to be removed caps and inner diode), or spark ignition trigger
pin for gas heaters. My choice is ignition spark pin (I was cut this
pin to equalize with ceramic surface). |
Now, how looks this simple spark gap:
 |
 |
 |
| Because of weird body shape of
doorknob, I was make connection to adjacent electrode at side with
little screw. |
Dimensions of whole things is
not so important. Distance between triggering pin and adjacent
electrode is about 2 mm. |
How looks spark from triggering
pin to adjacent electrode. |
Now, how look measurement setup:
 |
 |
| Self triggered = 5 mm (no
trigger pulse). |
Triggered spark at "working
distance". |
Next is few results of comparison tests. I was change distance between electrodes,
charging capacitor for triggering unit at primary coil signed as "Cp" in diagram at top of page
(for comparison of pulse power in milli Joules for trigger electrode). I was make a lot of
pictures, but all looks similar as two pictures above, so I will describe only results.
(without photos):
| "Cp"
capacitance (at 300 V) |
Triggering
power in milli Joules at primary coil |
maximum
working distance with 100 % success of fires |
maximum
working distance with 50% success of fires |
| 500 nF |
22.5 mJ |
9 mm |
10 mm |
| 1 uF |
45 mJ |
10 mm |
12 mm |
| 2 uF |
90 mJ |
10 mm |
12 mm |
| 20 uF |
900 mJ |
10 mm |
12 mm |
The Conclusion: I was expect with more power at primary coil more working distance, but seems to
me that car's ignition coil have "limited" transfer energy of about 50 mJ. From 45 mJ to 900 mJ spark
at triggering pin have same brightness. Only with 22.5 mJ is little weaker. My next spark gap tests #2
will be with different triggering coil, but with same setup of electrodes and measurements.