Roll your own capacitors – high voltage edition

[Grenadier] tipped us off about his method for building your own high-voltage capacitors. He thought the paper and foil capacitor project was a nice introduction to the concepts, but at the same time he knew he could produce a much more powerful device.

For the dielectric he is using acetate film. This is the material from which overhead transparency sheets are made. He stuck with aluminum foil for the two plates. Just roll the foil flat with a rolling-pin, use thin wire to minimize the air that will be trapped between the dielectric layers, and make sure the foil plates are at least 4cm shorter than the acetate film on each end to prevent leakage. After rolling and securing the capacitor with zip ties you’ll be ready for the 3nF worth of fun seen in the video after the break. [Grenadier] mentions that this can be improved further if you were to vacuum impregnate the device with beeswax.

Comments

  1. H3xx says:

    Any thoughts to build a coil gun with something like this? It would make it very powerful.

  2. Anonymouse says:

    If you bring the foil out the ends and make the connections there you end up with substantially less parasitic inductance and resistance.

  3. grenadier says:

    Sure you could, you’d just need a couple thousand capacitors…

  4. Nippey says:

    @H3xx: …if u can switch it… (u have to cope with some current, too) ;)

  5. dcroy says:

    i have seen people use ordinary copper clad boards stacked together to form air capacitors, works quite well for high voltage applications

  6. Tim says:

    @H3xx

    This is a 3nF capacitor according to the article. That is about 1,000,000 times smaller than the ~3mF of capacitance found in coil guns.

    You would have to charge this 3nF capacitor to around 100,000 volts to hold the same amount of charge as a 3mF capacitor at 100 volts

  7. superkuh says:

    Nice, I guess. But a more refined and useful technique is documented over at the 4HV (For High Voltage) wiki: http://wiki.4hv.org/index.php/Rolled_foil_capacitor_-_60_kV,_3.5_nF

    I posted this reference in the last comment thread too (http://hackaday.com/2011/05/09/roll-your-own-capacitors/#comment-391958) but I guess it went unnoticed.

    Also see their use in a 300kV CW multiplier: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?39162 and how to assemble the HV diodes from 1n4007 strings in pvc tubes in oil: http://wiki.4hv.org/index.php/High_voltage_diode_-_50_kV,_30_A_peak

  8. peteroptional says:

    Why not just use two metal pipes – one large enough to fit the other inside? A thousand ways to keep them in that configuration from there.

  9. Karl says:

    What is charging the capacitor? How is it coupled? Voltage, frequency, etc? Also, why not a biggish Leyden Jar? e.g. metalized styrofoam cup Leyden jar in proximity to a Wimshurst machine. Maybe I am missing the point.

    My first reaction. Intersted in the beeswax improvement scheme.

  10. Pinky says:

    Foil capacitors like this only makes sense if you need microsecond range discharges or large continuous AC currents (tesla tank circuits).

    For millisecond range discharges for coilguns you want to use electrolytic capacitors, they have hugely better energy density.

    peteroptional : the surface area of the capacitor with the rolled foil is much larger … and thus also the capacitance.

    Karl : energy per volume and weight both kinda suck … both the Leyden jar and the styrofoam cup are poor in that respect. The rolled foil capacitor is probably the best you can DIY for larger capacitances … ideally you’d use Mylar or BOPP foil though, and putting it in a sealable pipe with oil and then vacuum pumping the pipe to get the air out of the roll would increase it’s reliability.

  11. db says:

    Got a whiff of ozone watching the video. Must be a conditioned response.

  12. Vulnavia says:

    The man actually said “Positively charged electrons” — Sometimes I despair the rising generation ;-(

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 96,301 other followers