Need TTL Cookbook page 171 & 172. 555 timer 2N3055 vintage Electric Fence Charger

[gary350]

After thinking about this circuit for a while I decided PS should not have unlimited amps maybe that is why mosfets will not turn off. I also took a lesson I learn from induction heaters use the heat sink tap for mosfet output and cut pin 2 off. I tested all the mosfets I already used they all test good. I put a 1 ohm resistor on B+ and the circuit works the light bulb flashes on/off. I connected the ignition coil and it makes a 1/16" spark. Next I tried a 2 ohm resistor now coil makes a 1/32" spark. I tried a 3 ohm resistor the coil makes high voltage but not enough to make a spark. The little 2 watt resistor get hot enough to cook an egg in 10 seconds it had to be changed to 50 watt 2 ohms. I changed the 555 timer adjustment so it is OFF for 2 seconds then flashes ON for .1 seconds the LED is flashing the correct speed but the ignition coil seems to be pulling too many amps. How can it be pulling so many amps to need a 50W resistor when the circuit is off 99% of the time?

 

[crutschow]

Shorten the ON time to <0.1s.
That will reduce the peak current.
Edit: For a typical ignition coil you likely need no more than 10-20ms of ON time to reach several amps of primary current.
Keep reducing the ON time until the heating drops to a reasonable level.

 

[crutschow]

How can it be pulling so many amps to need a 50W resistor when the circuit is off 99% of the time?

A 2 ohm resistor dissipates 18W with 6V across it.
If it's on 1% of the time, that's 1.8W average.

 

[shortbus=]

My 1967 Chevy is 12V with a 12V coil factory original it says 12V on the side of the coil and there is no resistor.

That is because the wire from the ignition switch to the coil is made of stainless steel not copper. the stainless lead acts like a ballast resistor, it is also folded back on its self to make it longer to give enough resistance. GM was the only one to use the stainless wire and remove the ballast. Before electronic ignitions they all had a ballast of some sort that dropped the run voltage to the coil.

"
Ballast resistor
To wire the system, the ballast resistor unit (early vehicles) or ballast resistor wire feeding the points-type coil needs to be bypassed with regular copper wire. This is because the points system used this resistor to reduce the voltage to the coil to around 9 volts while the ignition switch is in the "run" position to prevent overheating the points. The points system has a "bypass" wire from the ignition switch or the starter solenoid to deliver full battery voltage to the coil during cranking. The HEI system needs the full battery voltage at all times to work its best. One common hookup method is to replace the ballast resistor or wire with a normal copper wire and attach both wires to the HEI's power input terminal. This ensures the HEI receives full power while running."
from https://en.wikipedia.org/wiki/High_energy_ignition

 

[gary350]

Best and final circuit..........maybe. I have several PC board relays from parting out old TVs, I picked out 1 that is 12vdc SPST rated 10a. Who said old TV parts are a waste of time. I replaced the mosfet with the relay now the circuit works like points on a car engine. Ignition points have a capacitor that give the spark an extra punch, I have not added the cap, not sure the relay can handle the extra punch. It makes a nice HV spark 3/32" long enough for a mild shock I touched it to make sure. That will sure wake a person up, not enough amps to be dangerous.

 

[crutschow]

A possible problem, of course, is the limited life of the relay and contacts.

 

[gary350]

A possible problem, of course, is the limited life of the relay and contacts.

YES you are right. I just wanted to build it because I can. The relay actually works a bit better than the mosfet. After I play with it a while I will put the mosfet on it again. I might try the circuit with a 2N3055 transistor before the mosfet. This was another interesting learning project.

 

[rjenkinsgb]

There is no resistor on 12V ignition coils.

A lot of vehicles use a resistance wire built in to the wiring harness, rather that a separate resistor block.

Despite any voltage markings, your '67 will have a ballast resistor - likely matching the details here:
http://67-72chevytrucks.com/vboard/showthread.php?t=548011

This is a generic 12V ignition circuit, there are minor variations:
http://www.erareplicas.com/427man/wiring/ignition.htm

 

[gary350]

My $25 Chinese scope arrived. Does anyone understand this?

Top picture is before I pushed the Hold button.

Bottom picture is after pushing the Hold button.

My digital meter reads 10v to 12v volt so I assume Vmax 10.79v is the square wave pulse that I am reading with the meter. I don't know why numbers are different after pushing hold button. I have not used a scope in 40 years. I had scope set on DC is that correct or should it be set on AC.

 

[crutschow]

I don't know why numbers are different after pushing hold button.

Neither do I.
What "hold button"?

I had scope set on DC is that correct or should it be set on AC.

DC is correct.
AC setting places a capacitor in series with the input to block DC.
It's usually only used when you want to see a small AC voltage riding on a large DC offset (such as in an AC amplifier stage).

 

[audioguru]

Your circuit with the relay will destoy the output of the 555 and destroy your 'scope if it looks at it.
The inductance of the relay coil stores a charge when the output pin 3 of the 555 goes high and releases the charge as a fairly high voltage negative spike when the output of the 555 goes low. The output of the 555 is never supposed to be negative so it gets zapped.
Here is 'ow too doo eat:

 

[AnalogKid]

Not trying to be picky, but there is no Hold button on your last schematic. Also, you don't say what the displayed signals are. and if they are repetitive, can we see a shot that shows more than 1/2 of a cycle?

ak

 

[AnalogKid]

Your circuit with the relay will destoy the output of the 555 and destroy your 'scope if it looks at it.
The inductance of the relay coil stores a charge when the output pin 3 of the 555 goes high and releases the charge as a fairly high voltage negative spike when the output of the 555 goes low.

Not automatically. The bipolar 555 is notorious for output stage cross-conduction, which is bad. However, it means that the output impedance never goes to a high value, which is good. Depending on the output slew rate, it might dissipate the coil's stored energy without the terminal voltage exceeding the power rails.

ak

 

[gary350]

Not trying to be picky, but there is no Hold button on your last schematic. Also, you don't say what the displayed signals are. and if they are repetitive, can we see a shot that shows more than 1/2 of a cycle?

ak

Hold button is on the scope.

 

[crutschow]

Hold button is on the scope.

I assume it just freezes the display(?).

 

[Mickster]

The build/user manual is here:
https://www.elecrow.com/download/UserManual_138_new.pdf

The "OK" button is used for Run/Hold and in the 2nd image that Gary posted, the display is still running. If it were actually holding the display, "HOLD" would be displayed in red, instead of "Running" in green.
The settings were changed between shots too, since the vertical resolution is 2V per div for the first image, and 0.2V per div on the second.
Difficult to read the switch position for SW3 in the first image....looks to be set to X1?

 

[shortbus=]

The build/user manual is here:
https://www.elecrow.com/download/UserManual_138_new.pdf

Thank you for that link Mick! I have one of those and the one I bought didn't have even one bit of documentation, so maybe I can start using it now, thanks again.

 

[crutschow]

If that's the 555 output pulse, try reducing the pulse-width from the 50ms shown, to 10-20ms, when connected to either transistor to see if that reduces the dissipation problem.

 

[gary350]

If that's the 555 output pulse, try reducing the pulse-width from the 50ms shown, to 10-20ms, when connected to either transistor to see if that reduces the dissipation problem.

I can adjust the pulse from 50ms to 161ms. If I change the fixed resistor it might go to 20ms.

Look at thead #105 I put a 1000uf cap between the relay and the 2 wire connection on pin 3 it makes the relay click harder. Instead of sounding like, click, click, click now it sounds like, clunk, clunk, clunk. With a .1uf cap the relay does not close. As the cap gets larger the relay starts closing & bigger the cap gets the harder the relay closes. I understand why .1uf does not close but don't understand why 1000uf closes harder.

 

[crutschow]

I can adjust the pulse from 50ms to 161ms. If I change the fixed resistor it might go to 20ms.

Yes,a smaller R3 resistor will shorten the ON pulse.

I put a 1000uf cap between the relay and the 2 wire connection on pin 3

Why.?
You appear to be making random changes to the circuit for no particular reason.