My little high voltage project is having a snag.

[andynerd]

So I'm generally creating an ignition coil driver circuit with a 555 timer. Now here is a link to the schematic I'm using: **broken link removed**

The problem I'm having is that there is a steady 12v DC going into the coil but it's not alternating. On the meter there was a slight hair of a movement that could have been my breath for all I know. If it was a square wave I would expect to see some drastic needle movement. So I'm asking for a second opinion. I'm sure the 555 died when soldering it on. (Couldn't find my heat sink, the 30W is a killer). Or the switching regulator is dead. Thinking about it though if the regulator is allowing the full 12v to pass through with practically no voltage going to the gate (less then a volt) it is probably fried. i'm also using the 2sk3568 because that's what I had in the parts box.

 

[crutschow]

For any frequency above a 100Hz or so, the meter will just measure the average value, so you won't see an meter movement. Measure the voltage at the collector of the 2N3055 to ground. It should be well above 12V if the device is operating due to the inductive spikes from the ignition.

Of course with no zener diode protection for the transistor, those inductive spikes may very well have blown it.

The average DC output voltage at pin 3 on the 555 should be about 6V when the 555 is oscillating.


The base of a bipolar transistor is normally only about 0.7V when on.

 

[andynerd]

I'm fairly sure it doesn't run off the inductive spikes but the frequency generated by the 555 timer. And the set frequency flips the transistor on and off.

 

[crutschow]

I'm fairly sure it doesn't run off the inductive spikes but the frequency generated by the 555 timer. And the set frequency flips the transistor on and off.

I agree. No one said otherwise. Is there a question there?

 

[andynerd]

No i was just making sure because you implied it ran off of the inductive spikes.

 

[BrownOut]

I've found the 3055 is pretty good at taking the inductive spikes and surviving. The timer and any voltage regulator will get fried very quickly however. Don't use a regulated power supply with this circuit, it will fry ( ask me how I know that )

 

[Reloadron]

You may want to give this link a read. Years ago I used the lamp dimmer method to fire an ignition coil, however, if you read down they get into your circuit and a mention that the 555 may not be able to really adequately drive the 2N3055. Anyway, the lamp dimmer approach works real well.

Something I did was took an old clear glass light bulb and made an aluminum foil cap for it. Connected the coil HV to the cap using ignition wire and the negative to the base (filament) of the bulb. Pretty cool show in the glass envelop. Should you ever try the lamp dimmer method, just be careful working with mains voltage.

Also, and I may be wrong, the diagram looks like the coil is backwards (polarity)?

Ron

 

[crutschow]

No i was just making sure because you implied it ran off of the inductive spikes.

When I said "due to the inductive spikes" I meant that the spikes would cause a high measured voltage at the transistor collector if the circuit were operating normally.

 

[andynerd]

Actually I don't know if it is. When I hook it up in the correct polarity there is nothing at all happening. When I hook it up in the reverse polarity it get's mildly warm (10 degrees higher maybe not even) and it swear I hear humming. As for the wiki page I'll have to read through that thanks! And I'm actually powering it with an old computer power supply at 12v 18A. Also I'll bite brownout how do you know that?

 

[crutschow]

Actually I don't know if it is.

That's the point of making the measurements. To determine if it's working.

I believe we have a failure to communicate.

 

[andynerd]

When the polarity is matching there is 0V going through the coil so that's right on the schematic

 

[Jaguarjoe]

Here is how Motorola and GM didit years ago:

MC3334 datasheet and Application Note, Data Sheet, Circuit, PDF, Pinout | Datasheet Archive

This is commonly known as a "4 pin HEI module" readily available for $15 at any auto parts store, or for $2 at any junk yard. GM used this in millions of cars in the late 70's/early 80's. It is easy to hook up and is bulletproof. Use your 555 instead of using the reluctor to drive it. Aussie supplier Jaycar used to have a kit to roll your own.

 

[blueroomelectronics]

Might need a flyback diode across the coil.

 

[BrownOut]

Actually Also I'll bite brownout how do you know that?

Obviously, I fried my fancy, high dollar regulated power supply with the same circuit. I'd advise you to use an unregulated PS that can deliver 12V and 3-5 amps.

 

[BrownOut]

Might need a flyback diode across the coil.

That kills the spark. It allows the current to blead slowly. You want a very fast current dropoff. You just have to use a switch that can handle the spikes, or else clamp them at several hundred volts. The 3055 isn't spec'd at that voltage, but somehow survives the spikes ( at least the one I used, not all 3055's are created equal ) However, I would advise suppression on the +12V side to protect the IC.

 

[crutschow]

Might need a flyback diode across the coil.

The would kill the high voltage output. It's the inductive kick voltage of a couple hundred volts on the primary that is transferred by the typical 100:1 winding ratio of the secondary to generate the output high voltage.

 

[audioguru]

Why did you connect the power supply with reverse polarity? For sure, that has caused the 555 and the Japanese Mosfet to be destroyed.

 

[andynerd]

Well on a good note I got a spark I just had to manually tap the switch on an off. It seems like the Mosfet I was using has burned out. I'm fairly sure it burned when I desoldered it. I don't have any places near by to buy parts so I had to scrap what I could! Anyone know of some old technology I could scrap a decent Mosfet from while I wait for my online order?

 

[andynerd]

I did it because a computer psu is in reverse polarity and so is the diagram and ignition coils!

 

[audioguru]

Why do most people who read this thread miss your statement that you used a high voltage Toshiba Mosfet instead of a 2N3055?
Maybe you should have corrected your schematic before posting it.