Spark Gap Triggers
Truthfully spark gaps are one of my favourites as they are so cheap. When something costs virtually nothing that’s always good.
Spark gaps don’t look pretty but they are cheap.
These are also easy to adjust by making the two metal strip contacts further apart or closer together. By adjusting this spark gap distance you can adjust trigger voltage.
The Spark Gap is not as reliable over time as the other two devices, after so many
weeks of pulse fire between the contacts it corrodes or destroys small layers of
the metal strips. It is only two strips of metal crossing over each other on a small
piece of PCB board and adjustable by opening or closing the distance between the
metal strips. At lower voltages 400 -
Spark Gap Distance
Sparks jump between distances at certain voltages, for instance:
1000v to 2000v will be appox 1mm.
2000v to 3000v will be 2mm
3000 to 4000v will be 3mm and so on.
So if you want a 1000 volt to 2000v trigger limit open the gap between the two metal strips to 1mm.
If you want an approx 500v trigger set to a gap of ½ mm.
The lower power that your driver circuit and T1 generates the lower voltage your trigger will have to be to get a fast repetitive spark fire rate.
It is best to just get a good T1 so you dont have the problem
(Xgen2000v Ultra Power T1)
Spark distance to voltage can vary due to many factors:
Air humidity, temperature, gas mixture in the air, and other factors.
Both pictures above:SG with the Xgen38 mounted inside. 4.3cm Spark distance.
Pic : 2009
Old Model XGen 38 PTT
The lower your trigger fire voltage is the less distance your T2 spark distance will become.
Always start with your T2 probes close together and then widen them gradually to find out your maximum distance but don’t ever exceed your data sheet specifications or the exercise could become very expensive.
When your circuit is tuned everything then depends upon your T2’s voltage performance levels and insulating factors to deliver your final spark distance.
T2 Ultra miniature transformer design size here can be a massive disadvantage because of internal arking within your T2’s internal design structure. To clear a 3.8cm gap with solid reliability is asking a massive amount for a miniature high KV transformer.
This takes miniature transformer design right to it’s very limits.
I know that a 3.8 cm or 38 mm spark distance is unrealistic for a stun gun as you don’t need this big distance for SG but this information is good to know.
My advice is to start small.
Build your design and start with a 600v 25ka or 1000v 10Ka gas discharge tube as your voltage trigger and close the Pulse Transformer probes real close together to start with to about 8mm apart or even smaller.
Get real small sparks going first then you can make small changes to your design to increase its power then you can increase the spark distances between your probes until you end up with 3cm spark or wider.
Different designs or multiplier stages can require different sized voltage triggers to reach their maximum potential.
This takes experimentation with your trigger voltage or gap size. If your voltage gap is to big your fire discharge rate will become less frequent but have good power. If your voltage trigger is to low it can fire more rapidly but with less power, or it might not even have enough voltage or energy to trigger a sufficient discharge of your T2.
XRS Design systems is not related to the Sgscience Website
The SCR Silicone Controlled Rectifier is very good device and the trigger voltage can be controlled with this device.
SCR’s are usually very reliable however there are some draw backs.
The main problem is to control the gate of the SCR so you can control the voltage level at which it triggers. An advanced builder may not have a problem with this but for a beginner it can be difficult.
Another problem is the voltages required for SG’s are very high and SCRs at high voltages are very hard to find especially at high amp ratings.
Cost is also a factor with these. These can be quite expensive and understanding the data sheets for SCR’s can be complicated especially for beginners.
Silicone Controlled Rectifier (SCR)
The Surge Arrester or Gas Discharge Tube is very good and reliable although it is fixed at a certain voltage.
Another small problem is that these can have a percentage factor where the voltage is out slightly. For instance a 600v GDT can really be anything from approx 550v to as far as 900v and if you join two of these in series together the gap then obviously grows even bigger. So if you join two together in series you could end up with a 1800v trigger when really you want 1200v. This means your spark will be more powerful but will fire slower. When using GDT’s you may have to buy a few spares and have a play to get your fire speed just how you want it.
The cost of a GDT is also a factor, it depends where you buy.
These can be a slight pain to find at the correct high voltages on Ebay but remember that you can join GDT’s together, they must be joined inline in series with each other.
Gas Discharge Tube
This Section looks at stun gun triggers, silicone controlled rectifiers and surge arresters discharge tubes and spark gaps.
The trigger system can be a problem for some people. However there are three main types to choose from SCR Silicone Controlled Rectifier, Surge Arrester (Gas Discharge Tube) or the Spark Gap.
All three have their draw backs:
The voltage trigger is used to fire energy in to the Pulse Trigger Transformer.
The higher the voltage of the trigger the more energy then enters the Pulse Trigger Transformer.
The higher the voltage of the trigger the larger spark distance is achievable by the XGen pulse trigger transformer.
However the higher the voltage rating of the trigger the more charge time is required by the circuit to charge up to that voltage level making the fire speed of your circuit slower.
The T1 is the engine supplying the energy to the charging circuit capacitor.
By entering more power more quickly in to the charging circuit we can overcome the charging time problem caused by using a high trigger voltage. This is done by using a good T1.
Gas Discharge Tubes
Stun Gun Triggers