Can you stack, or daisy chain many transformers for high voltage?

[carl1864]

Tried searching before posting, but didn't find much on this issue.  Just wondering if you can stack or daisy chain transformers to achieve high voltage?

I'm guessing there is some sort of limiting factor, because I don't see it done much.  And I often see people pay good money for transformers to use on jacobs ladders, or tesla coils, or other very high voltage applications.

Couldn't someone just buy 3 or 4 of the cheapest transformers they could find, and chain them, causing the voltage to exponentially increase each time, to deliver similar results?  Perhaps even chaining 10 or so to get up to multiple millions of volts?

And in the same sense, its my understanding that a tesla coil is basically 2 transformers, usually one in the base which steps the initial voltage up quite high for the primary coil, and then the primary and secondary coils are the second transformer.  Well, why not add another a 10:1 ratio transformer somewhere in the chain to make the tesla coil 10 times as strong?  I'm guessing there is some limiting factor, since I don't ever see small tesla coils making 10 foot sparks.

[nilton61]

It is possible to series connect the secondary windings in order to get a higher voltage. Take care to get phasing right though.

It is NOT possible to daisy chain transformers or even switch the primary and secondary windings in order to raise the voltage. (I tried that when i was 9... lots of smoke and lots of abuse from my father..)

The reason for this that the iron in the transformer coil can only withstand a certain flow density (normally 1,2T). So even if you increase the magnetomoric force (=current or ampereturns) the flow density will not go over 1,2T(saturating the core) thus collapsing the whole inductance model. This is best described by the transformer formula:

U=4,44*Bmax*A*N*f

where

• U = RMS voltage in winding


• 4,44 = pi*sqrt(2)


• Bmax = maximum flow density in core, normally 1,2T for omnidirectional transformer steel, 1,8T for unidirectional transformer steel.


• N = Nuber of turns in winding


• f = frequency

This also explains why you can use a smaller tranformer (less iron and less copper) at higher frequencies. Thats why a switched power supply is much smaller than one with a traditional transformer. switching frequency is normally 40kHz or so

[UnoDueTre]

If you want to generate high voltages, there are several ways to do that without the need to cascade transformers:

1) Use a voltage multiplier consisting of diodes and capacitors (plenty of circuits on the net).

2) Use the magnatron's transformer from a microwave oven.

3) Transformers from neon signs give out lots of Kv's

4) Get a high voltage coil used for the spark plugs in older cars (still available from auto spares shops).

Which ever way you decide, a word of warning:
Messing about with high voltages ranges from dangerous to down right lethal depending on the available current.

[AWOL]

If you can get the right components, even a small Cockcroft-Walton generator can produce very high voltages.

[fungus]

If you can get the right components, even a small Cockcroft-Walton generator can produce very high voltages.

The problem with them is that long ones take forever to charge up and even short ones produce no current at all. Even getting a milliamp of steady output is a challenge.

[AWOL]

And yet, there's probably one in that laser printer at the end of your desk.

[fungus]

I'm guessing there is some limiting factor, since I don't ever see small tesla coils making 10 foot sparks.

It's very hard to build a high-voltage transformer. Sparks go right through insulators at high voltages and tend to set things on fire.

Winding an iron transformer for high voltage is pretty much doomed to failure.

The secondary transformer in a Tesla Coil isn't a simple transformer. It works by magnetic resonance, you have to send magnetic impulses into it at the resonant frequency of the coil and get it to oscillate (magnetically). This amplifies the magnetic fields and makes higher and higher voltages in the capacitor at the top as they collapse into it. Optimizing them is a bit of a black art

[fungus]

Cockcroft-Walton generator

I saw that one in London two weeks ago...

[fungus]

And yet, there's probably one in that laser printer at the end of your desk.

True, but that one only has to charge up some dust, not produce big sparks.

You're going to be disappointed if you think you can connect 20 capacitors/diodes in a chain and produce an electricity show to impress girls with.

(I know I was... ;-)

PS: Last year I became the proud owner of one of these: https://www.youtube.com/watch?v=z4wVveOvlqs

[AWOL]

There used to be a good mechanical model of the CW in the London Science Museum, using ball-bearings and channels with one-way traps, showing the balls gaining PE as they worked up the columns.

Do they still fire-up the big one? I haven't been there for years.
The last really big CW I saw was in Paris, in the science museum in the Grand Palais.
They did a neat demo of how lightning conductors work, with a model house and some ether.

[fungus]

Do they still fire-up the big one? I haven't been there for years.

Nothing in there looked like it could be "fired up".

It wasn't the science museum I remember as a kid.

[UnoDueTre]

You're going to be disappointed if you think you can connect 20 capacitors/diodes in a chain and produce an electricity show to impress girls with.

Are girls impressed with this kind of thing? or have I just been chasing the wrong ones?   

[TomGeorge]

Hi, with respect to the diagram showing the possible and not possible configuration of transformers.
The "possible" config should be considered with some very important parameters.

As you add secondaries in series you increase not only output voltage, but voltage difference between primary and secondary windings, and secondary windings and earth.
The transformers may not have been built to these increased voltage stresses.

Tom.....

[AWOL]

A very long time ago, I visited the HT lab at Leeds University.
I can't remember what voltage the primary transformer stepped up ordinary mains to, but the 1MV output secondary stood on a three metre tall stack of ceramic insulators, the base of which stood in an oil bath.

[nilton61]

@TomGeorge: Yes, you are right. My answer just covered the basic reason why daisy chaining is imposible, not practical implications of it.
The problem you mention can be overcome by each of the transformers having a second secondary(!) with the same voltage as the primary feeding the next transformer.  

@AWOL: I have installed a number of these: http://www.tercosweden.com/wp-content/uploads/2009/07/HV-20110222-lowres.pdf