Capacitor Values / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Capacitor Values

previous 1 2 3 next

Move Thread

LAN_403

HV Enthusiast

Sun Feb 12 2006, 06:41PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

wrote ...

Try newark or mouser for caps. I got my 42L's from newark I think...

www.alliedelec.com is the best source for 42L's.

Firkragg wrote ...

My TC also uses 15kv and 30ma transformer, and capacitor used (9nf PE bottle) is far too smal to get close to resonce. Largest sparks were ~10cm..
I need a good capacitor of at least 30nF and I think you should aalso use largest possible, then use fewer primary turns to find resonance..

9nF (or 0.009uF) is more than enough for a 15kv/30mA transformer. In fact, is pretty close to the LTR size for that particular transformer. The typical capacitor size for a 15kv/30mA transformer is about 5nF (0.005uF). 30nF is WAAYY to big - you'll never be able to charge that fast enough with 30mA to get it close to fully charged before it discharges into the primary (assuming a sync rotary gap)

Dan

Marko

Sun Feb 12 2006, 07:36PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I used small asrsg and had problems (it jammed) for so low power ordynary gap is ideal.
Secondary was 5*50cm with big toroid.
I couldnt get near resonance with capacitor I used, then I just wound helical 20 turn primary and went just for biggest coupling and turn ratio for voltage gain (fought for that 10cm spark)
Losses on capacitor were huge, it was outside and linked with too thin wires, great stray inductances and high ohmic rsistances.
It was made of 6 polypropilene distilled-water bottles (I used same water with lots of refined salt :D)

Resonance yust cannot be acheived with such small capacitor, 16nF 20kV mmc I used before worked better but still underwhelming (also blew it in half an hour)
Nothing got even close to that mmc.

Except that coil was all-wrong I dont see how to get it resonating with 9nF...

HV Enthusiast

Sun Feb 12 2006, 07:56PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Firkragg wrote ...

Resonance yust cannot be acheived with such small capacitor, 16nF 20kV mmc I used before worked better but still underwhelming (also blew it in half an hour)
Nothing got even close to that mmc.

Except that coil was all-wrong I dont see how to get it resonating with 9nF...

Your system isn't designed properly then.

Typically, the first parameters to define in any tesla coil are the transformer and the primary capacitor.
You have a 15kV/30mA transformer so the primary capacitor value for 60Hz turns out to be about 5.5nF (0.0055uF)

Next, you need to decide what size secondary / toroid you are building. Once this is determine, you design your primary coil so that you have plenty of tuning range with your given primary capacitor and secondary coil / toroid.

If you can't achieve resonance with your present system, varying the primary capacitor value is the WRONG way about tuning your system.

I would recommend taking a look at both your secondary and primary coil specifications and see where the problem is.
Sounds to me like your fres of your secondary / toroid are waaayy to low. Maybe reducing your toroid size, or redesigning your secondary coil.

Keep your primary capacitor around 0.005 to 0.010uF, and tuned so that the primary is tapped with no more than 12 turns (20 is way too much)

Marko

Sun Feb 12 2006, 08:41PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I have no oscilloscope and its impossible to determine resonant frequency, I just went trial Q eror llike with small 1,5cm coils.

To prymary seems to resonate at too high frequency because of capacitor (secondary is only 5cm diameter, about 1000 turns 0,3mm and toroid ( overall diameter about 20cm, aluminium pipe)
Il try 10nF mmc now, maybe oscilloscoping secondary will help..

As I built helical primary for overcoupling now I have prblems with arcing over, even with thick primary to secondary insulation.

Coil is actually for trash, design is all wrong so it would be great to acheive few more centimeters longer spark..

I dont even want ot take pictures because of shame...

HV Enthusiast

Sun Feb 12 2006, 09:40PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

You don't need an oscilloscope for tuning.

Your first ballpark tuning should be done based on calculation - either by hand or by using some of the CAD tesla programs out there. Its very easy, it is pretty accurate.

For the CAD programs, check out my paper I wrote a few years ago. It shows exactly how *I* design my coils using two CAD programs and is very easy to follow. The links for the free software CAD programs download is in the end of the document:

http://www.easternvoltageresearch.com/oldwebsite/datasheets/howtopart01.pdf

When you have primary to secondary arcing, insulating between the two rarely helps. Although this increases the dielectric strength between the two, the stress of the E-field is still there and eventually will find a way to arc through given enough time. I'd raise your secondary to reduce coupling if you are still getting arc-overs.

Dan

Marko

Sun Feb 12 2006, 10:11PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I cannot raise secondary, but can try to decouple primary.
Insulation ofcourse doesnt help much, corona is capacitively formed and nothing can be done there.

I also did few calculations of resonance and then added few pf for interturn capacitance of secondary (this does matter here) Also for primary and realized that reality is completly different.

Also I have to replace bad rotary gap.
I wonder is there point to use rotary again (i found some comutator AC motors that could maybe rewired as synchronous) or just return to simplest, old static gap O_o?

When I think about all errors maybe is best to trash this coil and start anew...

HV Enthusiast

Sun Feb 12 2006, 10:45PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Can you post all the specs for your coil? I'm sure we can find out whats going on with it.

Marko

Mon Feb 13 2006, 12:57PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Its half-scrapped now. And I see lots of things that are not good (wrong coupling, gap,capacitor, too small secondary).
Il ask when I really need help, now some parts need to be collected, forget it for now...
Im builDRSSTC now and probably there will be topic about it soon...

Michael W.

Fri Feb 17 2006, 04:37AM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

Ok I need help. I have a 10" tall secondary winding, 3 cm diameter with 23 AWG magnetic wire, A 7 turn flat primary, made of copper tubing with a diameter of 5mm, with 5 mm spacing between turns. I'm using two salt water bottle caps (beer bottles). My power supply is about 8KV.
TeslaCoil CAD told me that I needed to tap my primary at between 1 and 2 turns....This results in nothing. Its not until I reach the very out side of the primary where I get about 1 inch arcs to a grounded wire. Do I need more Caps? more KV's? or a larger primary? Any imput would be great....

Part Scavenger

Fri Feb 17 2006, 03:28PM

Registered Member #79 Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673

Pic would probably help alot. It'd be good to see the overall setup, the bottle caps and the primary/secondary setup.

23 is HUGE for TC work and 3cm is tiny for a diameter. This makes for a really high resonant frequency(like 3.4-4Mhz off the top of my head). With this type of coil, it's going to be difficult to get good results. You may have to stray from the traditional theories a little bit to get it to do anything. I've built one alot like this, and I'm telling you the best you'll probably ever get is 1-3" Here's what you can do to get the most out of this coil:

More turns on the primary and deathly coupling. I know that the program and the flormulae say few turns, but I needed like 8-11 coiled almost 1/8" from the secondary.

High BPS. It is possible to get like 4" if you use it as one shot with much capacitance, but for a "real" TC this is what you'll need. High BPS is achieved by small spark-gap provided it doesn't power arc, or small capacitance compared to the power of the HV transformer.

Your toroid is huge compared to the size of your secondary if you're using the one in your avatar. Also, use a ball toroid. This will act to compress all the energy into one breakout. You don't have to worry about the streamers coming and hitting the secondary/primary in a coil like this, so a ball toroid will make it more efficient. Something about 4-5" diameter should be good?

Here's what I would do to avoid frustication and time wastin'

Rewind your secondary on a 3-3.5in former about 15in. Use 27-30ga wire. If you need more tips look on my site here => http://home.att.net/~gbward4/secondarydesign.htm.

Make a new primary coil, with 17 turns, tapped somewhere around 15. Make the inbetween spacing equal to the diameter of the wire, and the primary-secondary space about 1".

I have not seen you bottle caps, but bottle caps in general are ineffiecient. So, the better you build them, the better they perform. I know this from experience and have learned how to make nice ones. http://home.att.net/~gbward4/ (under "Bottle Cap design" And you need between 4-8nF worth. You'll probably wind up using 5-6nF.

You can probably use your current toroid; whatever it is, it needs to be 12-16pF or something like that.

You don't need as high a bps with the coil I just laid out. That will make it easier to tinker with and easier on the SG. I would expect between 18-25" with a well made coil to these specs and more if you had an MMC.

Cheers!

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob