Ignition circuit suggestions?

loco · Post by **loco** » Mon May 21, 2007 11:57 am

Hi all,

I've recently had some bad luck with my ignition circuit. My coil was from an old car that was producing a weak spark. I first made a circuit which was simply an indicator flasher unit connected to a coil. The spark provided was weak and intermittent which was a bit of a nightmare when it came to firing up the engine.

I've decided to take the leap and wire up some electronic components that will apparantly provide 5 to 8 decent sparks per second. Bruce Simpson provides the attached cicruit diagram which I guess would be effective (although - please forgive my ignorance- is the C1 capacitor at the bottom right in the correct location? looks to me like it would be permanently connected to the coil).

Shall I go for this, or is there another cicuit people would recommend?

Thanks for your help!

Dj Nafets · Post by **Dj Nafets** » Mon May 21, 2007 5:28 pm

After a few disappointments, I hate ignition systems ;)

The picture you posted is a simple circuit wich creates a square wave signal for the ignition coil. Yes, the capacitor ist on the right place. It absorbs the very high voltage when the magnetic field of the coil collapse.

But don´t try to use this system in combination with RC equipment. The servos will dance into their maximums because of the massive electromagnetic interference.

I´m just developing a system wich is strong enough to ingnit a pulsejet, but it shouldn´t disturb the RC equipment.

Here is a nice page with instructions. The HSG1 and HSG2 work very good.

loco · Post by **loco** » Mon May 21, 2007 6:31 pm

Thanks for the reply!

One last question: when looking for components, I need to know what voltage of components I'm looking for, such as the capacitors. I presume I'm looking for 20V dc, but would like to be sure so I don't get some magic smoke released from the circuit when I plug it into the car battery!

Could you not fashion some kind of metal box to store your ignition circuit in, thus making a faraday cage?

Thanks again.

larry cottrill · Post by **larry cottrill** » Mon May 21, 2007 7:13 pm

Dj Nafets wrote:I´m just developing a system which is strong enough to ingnite a pulsejet, but it shouldn´t disturb the RC equipment.

Dj -

What do you do to keep the ignition wire itself from acting as a transmitting antenna?

L Cottrill

Dj Nafets · Post by **Dj Nafets** » Mon May 21, 2007 8:17 pm

You have to use 630V capacitors. The voltage of a colapsing magnetic field in a coil is awesome.

Faradayc cage don´t work. I used metal boxes and 2 coaxial cable ( antenacable ) but it didn´t work.

loco · Post by **loco** » Mon May 21, 2007 9:28 pm

just the C1 capacitor in the diagram, right? surely the other capacitors to control the 555 timer should be 10 or 20V? I think the 555 can take something like 15V tops.

Would a higher capacitance offer a stronger spark, such as going for a 0.68uf cpacitor instead of a 0.47uf 630V capacitor?

Sorry, I really am quite clueless in this field.

Edit: I also need to know the wattage of the resistors I require. If anyone could help I would be most grateful!

Mark 42 · Post by **Mark 42** » Tue May 29, 2007 7:10 pm

Have a look at these URLs:
(BTW, does anyone here know the value & type capacitor equivalent to
a condenser in an old points type car ignition system?)

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1405

http://www.geocities.com/amptramp2002/amptramp002.htm

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=3239

http://www.pulse-jets.com/phpbb2/viewto ... c&start=30