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Having issues with my Tesla coil

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IRISHLUCK

Tue Sept 08 2015, 06:12AM

Registered Member #5555 Joined: Mon Jul 02 2012, 02:18PM
Location:
Posts: 61

So I found these plans online and build my coil but basically nothing is happening. Just isn't working.

I have a feeling that I didn't hook something up right.
Whats a little odd is that I have a switch that is wired up to it to turn it on/off when plugged in. It has a led on the light and when flipped on the LED flicks on but then right back off.

Also I measured voltage at automobile coil and im getting mV reading.

Attached are a couple pics of the tesla coil and the diagram I found.
I can take closer pictures if needed

dexter

Tue Sept 08 2015, 07:23AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

IRISHLUCK wrote ...

Whats a little odd is that I have a switch that is wired up to it to turn it on/off when plugged in. It has a led on the light and when flipped on the LED flicks on but then right back off.

Also I measured voltage at automobile coil and im getting mV reading.

1. check the oscillator section without the ignition coil and final stage transistors connected, you should see a square wave signal
2. check the final stage transistors
3. if all is ok but when the ignition coil is connected nothing happen either the coil is busted or the power supply is not capable to deliver the required power
4. measure the rail voltage when all is connected - if the voltage sags you'll need a higher watts transformer

Sulaiman

Tue Sept 08 2015, 07:29AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

there are a few things that I would look at;

1) your 18V transformer looks a little small for the job,
measure the voltage across C1, 18 Vac should give about 24 Vdc

2) it is possible that one or both of your 2N3055s is dead due to over-voltage
check for collector-emitter short circuit
if failed please do not replace with more 2N3055s as their voltage rating is too low for this application
I would replace the 2N3055s with an igbt,
if you find a dead 2N3055 report back and someone here (or I) will give suggestions

3) does the spark gap 'fire'?
if yes then increase the gap until operation becomes erratic, report gap length
if no then decrease the gap until it operates, report gap length

The 555 is wired in an unusual way, especially pin1, I will have a think about it.

EDIT: dexter beat me to it!

dexter

Tue Sept 08 2015, 09:00AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

Sulaiman wrote ...

The 555 is wired in an unusual way, especially pin1, I will have a think about it.

EDIT: dexter beat me to it!

pin 1 issue
first let assume the voltage doesn't sag
the 555 isn't referenced to ground, pin 1 is at about +8V (R1 R2 voltage divider) but the output is referenced to ground which mean it has a 8V offset which might result in a always on state of the transistors

i think the divider is used to lower the voltage across the 555 but is done wrong
either use the divider on pin 8 or use a 12-15V regulator

i'll breadboard this when i'll be back home to see how it behaves...

Sulaiman

Tue Sept 08 2015, 12:28PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

dexter, looking at it, the circuit as shown should work,
as you said, pin1 is not at 0 V,
it is also not at Vcc x 470/(470 + 1000)
due to (pin8 supply current) + (pin7 current = c50% duty Vcc via R3) + (pin3 current via R5 and Q1 + Q2 bases)
so pin1 will be at a higher than earlier calculated voltage, but it should work.
When pin3 is high there is effectively no load on it.
Why deliberately add ripple to pin1 ?, because 555 abs. max Vcc = 18V.

dexter

Tue Sept 08 2015, 03:25PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

i slapped together on a bread board the 555 side of the circuit (with the unusual pin 1 connection) used 24V supply and nothing happen on pin 3 beside a continuous logic HIGH

but if i connect pin 1 to ground the 555 starts osculating

IRISHLUCK also check pin 3 of 555 to see if its osculating

IRISHLUCK

Tue Sept 08 2015, 04:32PM

Registered Member #5555 Joined: Mon Jul 02 2012, 02:18PM
Location:
Posts: 61

I will check the 555 timer as you guys have suggested. Thanks for the tips! Trying to finish this for my classmates at school.

Also the spark gap did not fire at all.

The transformer is putting out 21.1 Vac. But this is a 18Vac transformer?

Benjamin

Tue Sept 08 2015, 10:07PM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

Imho a dc flyback with a zvs driver will work nicely with a coil that size. I built one powered by a 18 volt battery and it will make very nice 6 inch sparks. Also It is important that it is rectified because when it runs at high frequency there isn't enough time to fully charge the tank capacitor before the power supply changes polarity.

Sulaiman

Wed Sept 09 2015, 08:16AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

all transformers have winding resistance so when current is drawn the voltage drops,
the regulation of your transformer is
(21.1 - 18)/21.1 x 100 % = 14.7%
or more commonly
(21.1 - 18)/18 x 100 % = 17.22%
which is how I calculate it.

For a transformer of this size, that is about right.

IRISHLUCK

Wed Sept 09 2015, 11:04PM

Registered Member #5555 Joined: Mon Jul 02 2012, 02:18PM
Location:
Posts: 61

What frequency should pin 3 be?

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