# I tried building an induction coil

## Main Question or Discussion Point

i tried to build an induction coil. the input voltage is 12.1 volts. the output voltage is 16.5 millivolts maximum. so the voltage in the primary coil is 12.1 volts. the
voltage in the secondary coil is 16.5 millivolts maximum. the induction coil consist of a nail. thicker coils form the primary. thinner coil forms the secondary. the
primary consist of 213 turns. the secondary consist of 1,266 turns.

i connect the induction coil to a transistor rated at 1 amp. the collector pin is connected to a 6 ohm resistor. the 6 ohm resistor is connected to the induction coil. so current flows into the emitter pin and out the collector pin and then to the induction coil. if i alternately connect and disconnect the base, i get random values. sometimes as low as 200 microvolts. sometimes
as high as 16.5 millivolts.

if i connect the transistor to a 555 timer, i get 2.9 millivolts. if i use shorter pulses i get 100 microvolts. usually there are
gaps between the turns in the secondary. if i use a wider core will that get me a higher voltage?
if i eliminate the gaps between the turns in the
secondary, will that get me a higher voltage?

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Baluncore
We need a circuit diagram of your circuit, including the 555 timer and transistor.
Do you use an AC or DC range to measure the output voltage from your circuit ?

this is a schematic of the circuit

i posted a schematic. i am using dc current. now a answer my questions.

Baluncore
Take a look at your post. That schematic blur is unviewable.

Tom.G
if i use a wider core will that get me a higher voltage?
No.
if i eliminate the gaps between the turns in the
secondary, will that get me a higher voltage?
No.

If you want detailed assistance you will need to supply detailed information.
For instance:
• A readable schematic, with values for all parts.
• A description of the nail you are using. The one you are using may be small enough to fit on your finger nail, or maybe it is 8 inches long.
• The approximate diameter of the nail.
• The size of the wire you are using, both primary and secondary.
(If you don't know, you can count the number of turns that will fit on one layer in 1 inch, or in 2cm.)
• What power source you are using. (batteries, what size, how many? power supply, make, model, and rating)
• What make and model meter you are using to measure the voltage and current.
That will give us a starting point. Otherwise we will have to ask these questions one at a time, making this a very long and tiresome thread.

Thanks!

i think this schematic is more readable.

the first resistor has 3000 ohms. the second resistor has 1000 ohms. the nail is approximately 9.5 centimeters
long. the diameter of the nail is approximately 4 millimeters. i think the secondary uses 28 gauge wire. i think the
primary is roughly half a millimeter. not sure what gauge that is. i use 3 18650 lithium ion cells to provide roughly 12.2 volts. i think i am using a dt850l digital multimeter.

berkeman
Mentor
You show your input and output coils shorted to themselves. If that's how it's wired, it's no wonder it isn't working. You need to be pulling down on the bottom of the primary coil with your transistor's collector, and the top of the primary coil needs to be connected to the postive power supply. Then the bottom of the output coil needs to be grounded, and the top of the output coil needs to go through a diode to a storage capacitor.

Like this:

the bottom of the primary coil is connect to the transistor's collector. the top of the primary coil is connected to the
positive power supply. so current flows out of the transistor's collector, through the primary coil, and into the
positive power supply. the secondary coil is not connected to the power supply. the secondary is connect to the
multimeter, but not the power supply.

berkeman
Mentor
Can you please update your schematic to make it accurately reflect what you just said? Thanks.

i think this reflects what i said accurately.

berkeman
Mentor
Okay, that's better, thanks. But you should still take out the lines that appear to be shorting the primary and secondary coils just to be more clear and standard for drawing schematics.

If you don't use a rectifying diode in the output and want to measure it with an AC measurement, you need to be sure that the AC measuring device can keep up with the switching frequency. Maybe start with a diode there anyway just to make it so that you can measure the output with your DMM on DC input mode.

With those changes, what do you measure for your output DC voltage?

i have not made those changes i think. but should the secondary be connected to the power supply in any way?

berkeman
Mentor
i have not made those changes i think. but should the secondary be connected to the power supply in any way?
No, it doesn't need to be. Your goal is to rectify the output pulses from the switching action of your transistor on the primary side.

is it possible the induction coil damaged the transistors? i use to read the full 12.2 volts from the collector. now i
read a fraction of a volt from the transitor. one time i measured the voltage at the collector it was .8 volts. then i
measured the voltage at the collector of a different transistor it was the full 12.2 volts. i think all of the transistors
are broken now. i will have to buy new ones next week.

Baluncore
is it possible the induction coil damaged the transistors?
Yes it is. You have no flyback diode or output load to prevent voltage breakdown of the transistor.

Tom.G
1. There is about 2 Amps flowing thru the transistor when it is On and you stated it was rated at 1 Amp.
• Use Ohms Law to calculate the Collector current based on the battery voltage and the resistance in series with the collector; then select a resistor to limit the current to about 1/2 Amp.
2. The transistor Emitter appears connected to the wrong place, or the 555 chip is wired wrong, or the schematic is wrong. Please correct and let us know.
3. Please show on the schematic:
• The 555 pin numbers (and their names if you can)
• All parts values (transistor, resistors, capacitors, battery)

Since the transistors seem to be shorted, the batteries may be dead. Check their voltage, both when they are not connected to anything and when they are supplying the circuit.

The 555 is running at a frequency about 2.4Hz (2.4 pulses per second) which is much too slow for the small induction coil you are using. You are wasting at least 90% of the battery energy by converting it to heat in the 6 Ohm resistor and the coil.

I suggest changing the 120 microfarad capacitor to 5 microfarads. You won't be draining the batteries so fast, and it will get you a frequency about 58Hz, which would be within the AC measurement range of you meter. This can be changed later if you need a different frequency.

the transistor's emitter is connected to the negative power supply.

should i connect the flyback diode to the transistor's collector?

sophiecentaur
Gold Member
If you like. Get it the right way round though.

would using thicker wires for the primary coil and keeping the secondary at gauge 28 increase the voltage in the secondary coil?

i was using the induction coil, then i heard a popping sound. i measured the voltage of the lithium ion cell. before the popping sound the lithium ion cell had a voltage of 4.01 volts. after the popping sound, the lithium ion cell has a voltage of 1.01 volts. is it possible the induction coil damage the lithium ion cell? the lithium ion cell was connected to a 6 ohm resistor.

sophiecentaur