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Registered Member #1430
Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102
hey everyone. i have built this coil driver:
and i works great but only for a while. when i use it sparks get shorter and shorter over time(3 minutes) until it almost cant spark. i think my 555 is being killed by back-emf(i can feel a constant shocking/tingling sensation when i hold the leads onto a 9 volt battery) i read somewhere that a "snubber" would stop the back-emf from getting to the 555 chip, can you help me build one?
maybe you could even make the driver and the coil to run on seperate power sources?(that would be great)
EDIT: i forgot to say that im running this thing no a 9volt battery
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Solidacid wrote ...
and i works great but only for a while. when i use it sparks get shorter and shorter over time(3 minutes) until it almost cant spark. ... EDIT: i forgot to say that im running this thing no a 9volt battery
Your 9V battery is discharging, this circuit pulls fair amount of currents which discharges the little battery in a few minutes. Get a better power supply with 12V and at least 4A.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Solidacid wrote ...
the spark gets shorter if i use an AC power supply too
Well, this is absolutely weird. I've never had a silicon component die like this, it either works or does not work. Are you absolutely sure? Can you try it again?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
The tingling sensation is because the high voltage at the output creates an intense electric field around it, and induces a current between the circuit and you that is probably serving as ground. Ground the circuit as shown in the schematic at this will almost disappear. A snubber can be a capacitor across the transistor. Probably several tens of nF, rated to 250 V or more. A 100 Ohms resistor (big) in series with it may help. It will prevent excessive voltage over the transistor when it is turned off. Put a filter between the power supply for the coil and the 555 supply. A resistor with a few Ohms and a big capacitor to ground. It's also good to add pairs of diodes to ground and to the power supply at the pins of the 555 that go to the potentiometers. This would protect it if a spark happens between the pots and you when you touch them.
Registered Member #1403
Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968
I have had problems with this circuit, the 2N3055 seems to draw a bigger current than some 555 can handle, so I have a C547B transistor between the 555 and 2n3055 to ease the stress. (in my schematic I use a mosfet instead of the 2n3055, a 2n3055 fits fine, mosfet just give a tiny extra spark and work better a higher frequencies)
I posted my schematics and there is abit about the troubles I had with kickbacks.
Registered Member #1430
Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102
thanks for the feedback everyone :D, for some reason it stop getting weaker and it's workingjust fine now(max 10mm spark is fine not great :( ) i think i will try making a more powerfull driver soon so if you have any links or suggestions for drivers that would be great.
it's nice to know im not the only dane doing stuff like this :D
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