Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 85 users online :: 4 registered, 0 hidden and 81 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

ignition system

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
Sponsored 
  • Author
    Message

ignition system

Unread postAuthor: jct0064 » Sat May 16, 2009 1:44 pm

I am going to put a ignition with three spark gaps, and was wondering if a 100 kv stun gun would be enough. Also i already have a piezoelectric ignitor and I did not think that it would be enough, but if you think other wise just say so.
  • 0


jct0064
Private
Private
 
Posts: 9
Joined: Thu Mar 19, 2009 11:20 pm
Reputation: 0

Unread postAuthor: jimmy101 » Sun May 17, 2009 12:10 pm

A "100KV" stun gun should be fine, heck it should be OK with a couple more gaps. The stun gun should jump a total gap of more than an inch since that is what the default gap probably is. As long as the sum of all your gaps is less than an inch or so it'll work.

Piezos can often do two narrow gaps but three is probably pushing it. The piezo may have the voltage but not the energy needed for three gaps. You need a millijoule or two per gap to ignite propane in air. The total output from the piezo is divided up across the gaps so even if you can get the spark to jump you may drop the energy/gap below the minimum needed for ignition.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3127
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Unread postAuthor: Biopyro » Sun May 17, 2009 12:17 pm

Don't forget, that the length of the spark will add nothing really. Three 1/3" spark gaps will give the same performance as three 1/5" spark gaps.

Don't try and squeeze too much out of your stun gun, if anything go for four or five much smaller gaps.

I don't think you'll get 3 gaps from a cigarette lighter piezo, but a good BBQ piezo might be up to the job.
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: jct0064 » Sun May 17, 2009 1:41 pm

Thank you for the info. I probably should have mentioned this but the chamber is 24 inches of 4 inch pipe. How many spark gaps would you recommend.
  • 0


jct0064
Private
Private
 
Posts: 9
Joined: Thu Mar 19, 2009 11:20 pm
Reputation: 0

Unread postAuthor: Biopyro » Sun May 17, 2009 1:50 pm

(One spark gap per chamber diameter) minus 1. so 5 would be optimum for you.
Make sure they're evenly spaced.
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: jct0064 » Sun May 17, 2009 3:37 pm

I may just not get it but I do not see how "(One spark gap per chamber diameter) minus 1" works? Do you mean one spark gap per 4" of chamber minus 1? By the way I have not purchased a stun gun yet, so what voltage would you recommend.
  • 0


jct0064
Private
Private
 
Posts: 9
Joined: Thu Mar 19, 2009 11:20 pm
Reputation: 0

Unread postAuthor: jimmy101 » Sun May 17, 2009 4:17 pm

Measure the length of the chamber.
Measure the diameter of the chamber.
Divide the first number by the second.
Subtract one from the result.
That is the number of spark gaps.

First gap is at one half the chamber diameter from the breech.
The second gap is at 1.5x the chamber diameter from the breech.
The third gap is at 2.5x the chamber diameter from the breech.
...

Or, save time and use a single spark gap at the center of the chamber. Difference in performance of one gap versus several is significant but not huge.

Stungun voltage really doesn't matter a heck of a lot. "50KV", "100KV" are all really pretty much the same. (The quote marks are because the actual voltage is almost certainly a lot less than what the maker claims.)
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3127
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Sponsored

Sponsor
 


Unread postAuthor: Hotwired » Sun May 17, 2009 5:39 pm

The output voltage is a little bit more than the voltage needed to jump the fixed spark gap on the stungun.

So about 20-40Kv

If you take those away and try to stretch the spark out, it just won't. What will happen is, instead of the energy pulses being lost through a spark the coil starts sending back reverse pulses back towards the circuit board. Which kills it after a bit.

The higher "voltage" stunguns, there are two other things they can do:

1 - increase the energy dumped per spark - but not too much or sparks become dangerous.

2 - increase the spark rate

Apart from that... yeah... load of garbage that somehow is allowed to be printed.

Tasers only have 50kV at their terminals but that's a properly measured 50kV, you're not going to get many manufacturers willing to get independent tests to prove their little pocket stunguns can put out twice that.
  • 0

User avatar
Hotwired
Lieutenant General
Lieutenant General
 
Posts: 2599
Joined: Fri Oct 13, 2006 5:51 am
Location: UK
Reputation: 0

Unread postAuthor: jimmy101 » Mon May 18, 2009 10:25 am

Hotwired wrote:The output voltage is a little bit more than the voltage needed to jump the fixed spark gap on the stungun.

So about 20-40Kv

And, the actual output voltage is basically whatever is required to jump the gap(s). If you use say three 1mm spark gaps (in series, with sharp points) the output voltage of the stun gun will be about 3KV, regardless of what the stungun is rated at. The default gap won't be used and once the spark gap(s) start to break down the stungun's output voltage stops rising.

The total energy output of the stungun will be about the same. The power (energy released/unit time) will be probably be different since the spark duration will probably be different.
  • 0

Image

jimmy101
Lieutenant General
Lieutenant General
 
Posts: 3127
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Country: United States (us)
Reputation: 7

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Google Adsense [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'