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Building first HV source - Ignition coil or Flyback?

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Dax

Fri Nov 07 2008, 06:19AM

Registered Member #1802 Joined: Fri Nov 07 2008, 05:34AM
Location: Vancouver BC Canada
Posts: 1

Hey guys. I'm Dax. First Post

:waves:

I'm looking to build a HV source for some basic HV experiments such as a "Lifter", small Jacobs ladder and general burnanation of electronic parts that piss me off. Design considerations are: Cost, ease/speed of construction, duty cycle, peak voltage, amperage/power output, and coolness. In that order.

I did some poking around on the internet and some likely candidates are an ignition coil or flyback transformer. I am thinking of building a basic 555 timer and mosfett driver circuit to KISS, but I am open to other suggestions. I don't have a ignition coil, flyback or 555 timer chip yet, so my options are still open...

What are the advantages of ign coil vs. a flyback? I seem to remember reading the flyback will give higher voltage and frequency, but the ign coil will put out more power. Is that right? Which one would be better for the above stated experiments?

PS: If I decided to build a small tesla coil at some point would one of these supplies work better than the other one?

Any other pointers (other than don't electrocute myself) would be appreciated. Thanks in advance guys.

uzzors2k

Fri Nov 07 2008, 09:22AM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Welcome to the forum! Most of the projects you're thinking of require DC, so a flyback would be your best bet. Personally I prefer flybacks over iggie coils because the core can scavenged, output voltage is often higher, and more drivers can be used with them. I think ignition coils and flybacks are roughly equal in power handling capability.

jovica

Fri Nov 07 2008, 09:49AM

Registered Member #1790 Joined: Fri Oct 31 2008, 10:10AM
Location: Sydney, Australia
Posts: 40

Hi Dax,

I will have to agree with uzzors , a flyback will be the best for your needs.

Having said that i will give you a few suggestions to help you out picking a driver.

A quasi resonant driver circuit will be the best thing for voltage control and power consmptiom.

Here is a schematic

you can use a 555 instead of the SG3525 you make sure you use the output stage though. this driver can create enormous voltages and i have makde and arc jump 10cm or so, and by adjusting the duty cycle you have lots of control on voltage out put so you can control the thrust the lifter creates.

A zvs driver is GREAT for brute power and semi high voltage output you can push several hndred watts of power trough a decent sized flyback and create 20-30 Inch discharges if used as a HV transformer in a Tesla coil. Infact you can use it as a SSTC driver too as this video demonstrates

just use a smaller tank cap, ohh and if you want to try induction heaters you can use it there too you make a work coil with 4+4 turns as this video also demonstarates

schematic here

along with info =)

--Tekken_LordS--

Sulaiman

Sat Nov 08 2008, 03:21PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

You will probably make a few mistakes on the first attempt at a hv supply,
I've made many eht supplies and I still forget little details.
So, I suggest you start with what you can get easily and cheaply;
For most of my designs I use a 555 directly driving either a mosfet or an igbt
you can use avalanche rated transistors without a 'snubber' but I always add a 'snubber'
a (suitably rated) diode into a capacitor with either a resistor (OK) or zener/tvs (best) string.
The maximum power throughput for any particular core will always be in a non-resonant circuit.

If you can get any automotive ignition coil use it.
For Jacobs-Ladder it will be ok (higher power is always better)
For others you will need eht diodes, which do not like accidental high current...
Somewhere around 30 to 50 Vdc and c1kHz will be a good start.
Or for first experiments just use 12V for 555 and coil supply.

Flyback transformers from crt tv or monitor are great for eht dc as they have inbuilt diodes
(if there's an anode cap at the end of the eht wire) ideal for lifters etc.
If you want to use the original primary (I do) then 100 to 150 Vdc at 10 to 30 kHz is a good start.
The hv dc supply is an obvious hazard.

Whichever you go for I suggest spare transistor and coil/transformer are bought immediately ;)
Then you can push to the limit - and beyond!

To me, the main disadvantage of an ignition coil is that they work best right in the middle of my hearing bandwidth .. annoying.
My 'rough and ready' ignition coil eht supply is just that
- roughly built and always ready.. very reliable .. takes a lot of torture :)
I like operating flyback transformers above my hearing range for comfort,
so fairly high dc voltages are required for best performance.
I use flyback transformers for eht supplies when I have a specific purpose, not for general purpose use.

Other opinions may be different!

P.S. for many experiments you will want to charge up capacitors to eht.
To the power supply a discharged capacitor 'looks' like a short-circuit.

Dr. Dark Current

Sat Nov 08 2008, 03:25PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Sulaiman wrote ...

The maximum power throughput for any particular core will always be in a non-resonant circuit.

no.

uzzors2k

Sat Nov 08 2008, 04:19PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Uh-oh, two unsubstantiated claims.

Sulaiman wrote ...

To me, the main disadvantage of an ignition coil is that they work best right in the middle of my hearing bandwidth .. annoying.
....
I like operating flyback transformers above my hearing range for comfort,

Very important points. You'd be surprised how loud spark discharges can be, I have to use hearing protection while running my ignition coil.

Dr. Dark Current

Sat Nov 08 2008, 05:04PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Dr. Kilovolt wrote ...

Sulaiman wrote ...

The maximum power throughput for any particular core will always be in a non-resonant circuit.

no.

Uzzors wrote ...

Uh-oh, two unsubstantiated claims.

Take any current limited transformer (lets say a flyback) and draw arcs from it. The maximum power output happens at (short circuit current)/2 and (maximum output voltage)/2, so it equals 1/4 the reactive power present with short-circuited output.

Now put a resonant capacitor in parallel with the output of the transformer, so that it forms a resonant circuit with the limiting inductance at the driving frequency.
Now, there will still be the same reactive power with short-circuited output, but as you start drawing an arc, the driver will only supply additional real power. At the maximum output voltage, you still have the same arc current as in the short-circuit condition, so real power in this case equals reactive power with short-circuited output. Surely, the transistors will need to switch more current, but this additional current gets always transfered to real power only.
Of course you need to limit the open-circuit voltage in some way, this can be easily done with a safety spark gap, or with PWM feedback to the driver, or design the transformer in a way so it limits the voltage to a safe level by itself by means of core saturation (this is how I plan to design my monster inverter).

Sulaiman

Sat Nov 08 2008, 06:25PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

The maximum output of a transformer using a given core is determined by heating of the core and the wire,
typically (but not always)
the maximum power throughput will be when core heating and wire heating are approximately equal.

Flyback transformers actually deliver constant POWER
(not voltage or current) at any given frequency and peak current (or ON time) (Ipk = Vpri.Ton/Lpri),
so Power = energy x frequency = 1/2 x L x I x I x F

I doubt that using core saturation will work for anything other than small (say <=5W) inverters,
a large core continuously driven to saturation will rapidly overheat.
This is because core volume (heat generation) increases faster than surface area (cooling)
(unless you're in the audio range of frequencies)

Show me a design that can continuously push more power through a given core/winding than a simple hard-switched full-bridge
and I'll be very surprised.

None of this will help our new member however, so I'll get back on topic;

For later use with a TC neither the ignition coil nor the flyback are ideal as the output rectifier diodes are prone to damage
though I have used both to operate a low power sgtc..
If you can get a Neon Sign Transformer or an Oil Burner Ignition Transformer (lower power but a little more rugged)
that's definately the way to go.

Dr. Dark Current

Sat Nov 08 2008, 07:39PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Sulaiman wrote ...

Flyback transformers actually deliver constant POWER

depends on the driver

Sulaiman wrote ...

Show me a design that can continuously push more power through a given core/winding than a simple hard-switched full-bridge

I will when I finish it, I'm not claiming it will work as I think, but from mistakes we learn or not?

Sorry for OT.

Cheers

Antonio

Sat Nov 08 2008, 09:51PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

A flyback can be driven in resonant mode in a bridge configuration, and generate more power than if directly powered by the bridge. ItÂ´s enough to add a suitable capacitor in series with the primary winding, making it resonant at the driving frequency. This puts more voltage over the primary winding that the bridge can produce, and drains correspondingly more current from the driver.
But the usual flyback configuration is probably the best way to use flyback transformers. All the required parts, including the DC power supply, can be obtained from a discarded CRT monitor.

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