Amplifying DC voltage

[florinanghel]

I'm trying to charge a capacitor with 220V from a 12V battery in order to flash a light bulb. What exactly should I use for that? Thanks in advance!

P.S. I'm trying to work with DC current, so no inverters, please!

 

[jackorocko]

I thought the only way to increase Voltage past the max Vin was to use a step-up transformer.

 

[florinanghel]

I thought the only way to increase Voltage past the max Vin was to use a step-up transformer.

But, as far as I know, transformers only work with AC.

 

[jackorocko]

But, as far as I know, transformers only work with AC.

Thats correct. My only guess is to turn the DC to AC step it up and then rectify it back I suppose. One of the resident experts will be along to voice in. Does your project have to use a battery as the voltage source?

 

[florinanghel]

It's for a magic trick, the rig has to be as small as possible.

 

[trobbins]

You have to use an inverter or dc-dc converter or switched capacitor circuit of some kind - they all involve non-dc methods - no other way. To choose what is the better method then you will need to specify the load and time characteristic and what type of battery source, and any other size or quirky contraints.

Ciao, Tim

 

[ChosunOne]

You can boost DC voltage without going through an inverter. Google "dc voltage doubler circuit diagram" and ignore the pay-for-download sites. Hobbyists have been doing this for a long time. It's going to take some sizable capacitors to make it, though. I don't know if you'll be able to build it small enough.

 

[Resqueline]

There are two ways to do that, one involving a transistor & a transformer, the other involving some (=>20) inverter gates & capacitors.
The first method is probably the easiest & quickest way, since you may be able to use the innards of a xenon flash. They can be had quite small nowadays.
Inverters don't need to be of the big, powerful 50Hz AC mains types you know. A xenon flash is also incorporating an inverter.

 

[florinanghel]

The circuitry will be similar to the one of a coil gun (except that the coil will be replaced with a light bulb). Which method does the coil gun use (or it can use both, too)?

 

[Resqueline]

It can use both methods. I'd put my money on a transformer circuit though; it's the most efficient, it's the smallest, & it can be scrounged for free from a used camera.
What kind of a bulb are you talking about, and what's the intended flash length & repetition rate?

 

[florinanghel]

A regular light bulb of, say, 20W. It doesn't need to have a strong glow as long as it's visible and it's length should be of about half a second (just enough for people to see it).

If I had an old camera, I'd simply modify a regular bulb and put the xenon flash into it, but I don't. That's why I have to build the circuit from scratch.

 

[trobbins]

Does the bulb need to be a special shape or colour or can it be in a reflector or? Can you use a groups of LED's?

Ciao, Tim

 

[florinanghel]

It has to have the most common shape (at least here in Romania), that is the one in the picture below. It must look like a standard, not modified light bulb, as that's the whole point of the trick. The rig, though, it's separate (hidden on the sleeve or in a pocket). That's why I prefer a standard bulb with no modification, so that I can give it to the people to check it out.

Now, if this helps in any way, the presentation would be like this: the rig is hidden and masked wires go from it to the glove (simple leather glove). This way, when I hold the bulb in a certain position, the circuit will be closed and the condenser will release the energy, slightly lighting the bulb for a short period of time.

 

[(*steve*)]

Well, one trick might be to grab the innards of a disposable camera and charge up the capacitor to the RMS voltage of your local AC supply (110, 240, etc) then discharge the cap through the lightbulb. You might be surprised at how much power you can get out of a 1.5V battery

The advantage is small size. However beware that some of them (ok most of them) emit a high pitched whine when operating so you may want some magical musical backing to ensure the audience don't here the inverter.

 

[Resqueline]

Ok.. Do you think you're up to finding & getting the parts (ferrite cores, coil former, enameled wire) & winding your own transformer?
If not then a smallish mains transformer may do the trick. A 15W bulb running (by brute force for a few seconds) at half mains voltage should be visible enough.
I figure a continuous duty inverter would be more "effective" for a show. (I'd have to test how big a cap would need to be to do the job.) What are your battery options?
The inverter circuit itself could be made quite simple, a couple of transistors resistors & capacitors. Possibly an IC if you'd want to go "fancy".

 

[florinanghel]

Steve, I guess my best choice for this is indeed to use a disposable camera. The capacitor's sound is okay, a good magician can transform any flaw in a trump (not that I'm a good magician).

Resqueline, I could probably get the parts, but I'd sort of prefer to play safe and get a higher quality already built transformer. When playing with high voltage and having to keep all the stuff so close to me, taking chances is not such a good idea.

 

[(*steve*)]

A fully charged capacitor from a disposable camera stores about 11 Joules of energy. That's enough to light a 20 watt bulb for 1/2 second. The discharge won't be even, so you'll see something different from a light bulb being on for 1/2 sec though.

Carefully try it yourself to see how it looks.

But be *very* careful. 330VDC can bite quite hard. (The energy in the capacitor is enough to kill you in fact)

 

[darkman1969]

I am thinking this project is just full of danger. You need to consider the high power involved. As Steve said, there is more than enough energy in this device to KILL you.

To my thinking, you need to implement some form of current control to control the light bulb itself as well as some form of safety system o protect yourself. The whole system could be built quite small but the smaller it gets the more expensive it will be.

Regards

 

[florinanghel]

I am aware of the dangers. Hiding the wires by sticking them to my arm/forearm and applying makeup to hide them is a pretty scary thought. Well... the makeup part is not that scary.

How thick should the wires/isolation be in order to be safe? What about the leather glove?

P.S. The project itself it's delayed for the moment, as I'm kinda busy with other stuff, I'm just documenting about this right now.

 

[trobbins]

A commercial product would most likely need any conductive part to be double insulated to a level suitable to 230VAC LV with an IP4- rating, and would need to be 'tagged/inspected' regularly. Do you appreciate how to achieve that form of protection? One guide is to use the same cabling and fittings as your un-earthed mains equipment.

Ciao, Tim