discharging

The 555 works to a power supply of 16 volts absolute maximum and outputs 200 ma max and can dissipate 600 milliwatts max before it overheats.

That 50 ohm resistor the picture shows going to the base of the transistor (assuming too it really is the base) has to be larger - use a 100 ohm and not lower than 75 ohms, or the 555 will die a hot death. A 100 ohm should have enough current drive to turn on the 3055 with a 10 ohm load.

I'm assuming the emitter of the 3055 is going to ground - right?

75 ohms should work up to absolute maximum of a 15 volt supply - a lead acid battery puts out about 12.5 unless it is being charged then it can go as high as 14 volts or so.

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Hi

Look at the message 4 from Jamie, he said that I should have about 0.5 v to the base of the 3055. the output of the 555 is about 7v, so from this is why I tried the voltage division thing you mentioned earlier

yes I saw 18v max , I did not change anything in this circuit, it was working fine before.

yes it is.

yes its about 12.6v now

I still need to get some 555, I'll continue later tonight on it or tomorrow at the latest thanks for all the help.

ken

He is correct it should be .5 to .7 if everything is working - what is not correct is that you have to provide the .5 to .7 the transistor will do that.

You provide current, but the transistor determines the voltage. You limit the current you provide with a resistor (sized high enough to keep the 555 from burning up and low enough to push enough current into the 3055 to turn it on).

~100 ohms by my estimate, but as low as 75 should still work - lower than that, and the 555 smokes. (will be too close or above the design maximum for current)

One side of the resistor will have pretty close to the supply voltage on it (when the 555 is outputting a high signal) the other side will have .5 to .7 - that the transistor limits the voltage to.

You can check your transistor/coil drive simply by taking the side of the resistor that goes to the 555 and connecting it to +12 - that should turn on the transistor and energize the coil - disconnect it and the coil should de energize.

That tells you that the resistor is low enough to turn on the 3055 and it is hooked up correctly, and the 3055 is OK -

if it won't turn on and off as the resistor is connected to the +12 it won't work with a 555 either.

Just a simple and easy way to check that part of the circuit separately. "If'n that don' work ain't nothin' goin' ta work"

(that is disconnect the resistor from the 555 and connect it to the

+12 temporarily to check to see that the transistor turns on when it should. DO NOT connect it AND pin 3 of the 555 to +12 - bad things will happen.)

If your 555 still refuses to work on 12 volts you must be doing something else wrong - for instance:

Pin 7 the discharge pin is the collector of a transistor inside the

555. In an astable multivibrator (the oscillator connection) it discharges the capacitor that sets the timing. If the cap size is very large or the resistor charging the cap is very small, that poor little transistor gets hot and dies - and that symptom will be exacerbated by raising the supply voltage. Exactly when the little bugger is pushed close to its limit is also determined by frequency and/or pulse width. (read the application notes - from national semiconductor - on the 555 they should mention this)

All design is a balancing act and series of compromises. Until you learn the basics, you'll be having trouble. You are learning . . . that much already.

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HI all folks,

it now working, i was pretty sure I made the same setup yesterday.. Ithink a day break helped. I like to thanks every one who helped me, default, jamie, jasen and the other. turns out I had three 2N3055 in bad condition and one of the wire was also out Just one more thing. I put the output in this page.

There is a huge peak at the beginning, i was expecting a peak from an inductor but that was more then expected. so I guess this is normal ?

Ken

It just occurred to me, I have no idea where either the 7400 series came from, or where the 700 series of analog numbers came from, but here is a better history of TTL logic than I gave, if you are interested.

Some of the scope settings aren't too readable to me. What I would expect to see is some ringing on the waveform - that looks relatively clean.

When the transistor initially turns on (pulls to ground) the collector should stay at +12 for a short time then decay exponentially (close to ground on the collector) as the inductor charges eventually flattening out if the transistor stays on long enough. When the transistor switches off there should be some under shoot and ringing (but a lot will depend on the scope's high frequency response)

That looks like a digital sampling scope (?) it may be giving a distorted picture of what is actually happening. Even with a damping diode there's usually some ringing because diodes don't switch instantaneously.

High voltage spikes and ringing are common in switched inductors - even the inductance in short pieces of wire will show up if the test equipment is good enough to see them.

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Analog scopes are better than digital in this case ??

Ok so you are saying its normal

There are 200v peak in the wave form with 50v increments

ken

In my opinion analog scopes are better than digital period - if the wave form is important to you.

A digital scope really shines where it is handy to freeze several traces and compare them.

A 200 volt peak would be normal.

The way it works - voltage output (spike) is a function of how fast the magnetic field collapses, the number of turns of wire, the amount of stored energy.

How fast the field collapses is dependant on the type of core, conductive material in and around the core (eddy currents).

Even the inter winding capacity (small distributed capacitances due to one wire being close to another), and dielectric characteristics of the insulation on the wire, how close the wires are to one another.

Eddy currents are currents of electricity induced in a material when a magnetic field is changing - they oppose the change. Some eddy currents are present in your core material (steel rods or wires?), your core may have a conductive bobbin - done in solenoids to increase the eddy current effects.

In a transformer or inductor eddy current are generally treated as wasted energy. The core material behaves like shorted turns of wire - to get around that, the core is broken up by using thin wires or laminations or even powdered metal bits that are insulated from one another

You can see the effects of eddy currents by dropping a very strong magnet between two aluminum sheets - it will fall slowly. (assuming it stays oriented as it falls) An easier example is to just put an aluminum baking sheet at a steep angle but something other than 90 degrees and let the magnet slide down the surface.

Same principle used in old automobile speedometers and tachometers - rotating magnet tries to drag an aluminum disk or ring with it. The disk is working against a spring and has a pointer on it.

They deliberately increase the eddy currents in AC solenoids so they don't buzz. The eddy current is giving up some of its energy in the form of a magnetic field while the AC sine wave is at zero.

Anyhow - eddy current is the largest single factor on how fast a field collapses.

My induction coil has a core of 2" of bundled steel wires about 20" long. Basically I duplicated something I saw in an 1800's manual on electricity. There's 1200 turns of wire in four primary windings and

86,000 turns of wire in the four secondary bobbins. It will make a spark three and a half inches long. It weighs about 60 pounds - not the typical auto ignition coil.

When the electrodes are separated by a few inches the spark is a relatively thin bright line and makes a cracking sound. when the electrodes are only a 1/4" apart, the spark is very thick (obviously has some vaporized electrode in it). The interesting thing is the spark makes a hissing sound and lasts lots longer - I attribute that to the fact that the secondary behaves like a shorted turn when it is asked to carry more current, the shorted turn acts to slow the discharge. (slower changing field = lower voltage, but the same stored energy so it lasts longer)

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i find using a 10x probe removes most of the ringing.

--
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5