# Charging a small 100uF 450V capacitor with a small battery?

How can I easily charge a 450V capacitor with a small battery such as a 1.5V or 9V while stepping the voltage up in between so as to provide a voltage near 450V for the capacitor?

I'm looking to charge this capacitor with either pieces I buy or those I build, but I want the materials not including the capacitor and battery to cost me under $20, preferably under$10. If necessary I can take parts out of other devices, but it would be most preferable just to buy them pre-built.

I've looked up what would be necessary and it looks like I'd need a step up inverter from the small DC voltage (probably around 12V) to the large AC voltage(probably around 220V) then I'd need a 2:1 step up transformer to turn the 220V into around 440V and then I'd need another inverter to turn the 440V AC current into a 440V DC current. I might also need 2 of all of these pieces if I needed to down step the Voltage to finish the circuit, but there might be a way around that. In addition to cases for the battery or batteries. The wiring for all this will be bought separately in addition to a switch if that was a question.

• Geiger counter tubes use in that vicinity of voltage and the following contains a simple power supply mightyohm.com/blog/products/geiger-counter/design-files. Be careful though, it's obviously a dangerous amount of voltage and you seem to have a few misconceptions above so I assume you've never done anything like this before? – PeterJ Oct 27 '13 at 4:29
• What is the maximum charging time? – apalopohapa Oct 27 '13 at 5:50
• You should be able to do this in a single stage with a flyback converter. Choosing the ratio of the transformer correctly will be important. Since it doesn't sound like you need isolation, you can use a autotransformer if you can find one with the right ratio. – Olin Lathrop Oct 27 '13 at 12:33
• Take a look at disposable camera flashgun circuits - that's what they do -charge a capacitor to a high voltage from a few volts. – JIm Dearden Oct 27 '13 at 18:40
• To respond to the comments in order: 1. I have worked with plenty of circuitry components before with my dad, but this is the first time I've worked with transformers and high-voltages. I plan to use safety equipment (rubber gloves and a voltage meter) actually would it be better to use rubber gloves or to simply only use one hand with the other hand as ground? And where is the best place to find the parts listed in the bill of materials? – Ethan722 Oct 27 '13 at 22:56

What you could use is a boost converter such as the LT3573: -

This will charge up a capacitor to 300V. I reckon the parts would cost less than \$20 and there are plenty of other similar chips of this type from Linear technology and TI for instance.

The circuit above produces 300Vdc and uses primary voltage sensing to determine the secondary voltage. Using what is known as a cockroft walton diode-capacitor voltage multiplier could get you much more than this quite easily. You would typically use this type of circuit directly on the transfomer secondary.

TAKE CARE - THESE VOLTAGES ARE QUITE LETHAL AND SCARY

• This sounds quite interesting, but I can't find an image like it anywhere. In fact, the closest thing to it seems to tell a different tale: linear.com/product/LT3573 In fact the only other direct duplicate of this image was also posted by you... – Ethan722 Oct 27 '13 at 23:15
• Here is the most important advice I can give you - read the data sheet (page 23 I think). I'm being serious - cut straight to the pdf and see what it says: cds.linear.com/docs/en/datasheet/3573fc.pdf - the number of times I've missed the crown jewels by not reading the data sheet I care not to remember. Always read the data sheet if you have half a belief it might have the answer. It is good advice; the chip - there are plenty that can do this so that advice isn't as useful!!! – Andy aka Oct 27 '13 at 23:19
• I understand now! So the model number is just a blanket model for a number of variations of circuits, but why would they all be the same model number if they're all for different things? I've really only worked with minor circuitry (things under transformers and high voltage circuits) before this, so I'm making sure I read into everything including safety precautions, so how do the model numbers for these circuits work? – Ethan722 Oct 27 '13 at 23:26
• I also found this online: madscientisthut.com/Shopping/…, so I'll probably just order it since it cuts out all that time I would have had to spend finding parts. – Ethan722 Oct 27 '13 at 23:29
• The "I" version is guaranteed over the full -40 to +125ºC temperature range - it's basically the same chip but some are tested more rigourously than others and are probably double the price!! I think the unit you listed will probably do the job but beware that madscientisthut has been flooded out and although I believe them to be reputable (they have some cool circuits) there may be a delay in getting the parts. – Andy aka Oct 28 '13 at 0:10

"Take a look at disposable camera flashgun circuits - that's what they do -charge a capacitor to a high voltage from a few volts." - Jim Dearden I took his advice and found this: http://www.madscientisthut.com/Shopping/agora.cgi?product=Radiation%20Detection&user4=Camera%20Flash%20PCB Which should suffice.