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Are These Caps Good to Use?

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cduma

Mon Jul 27 2009, 08:15PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

Are the caps in the link good to use for a tesla coil? How much larger than resonance should it be?

I will use either a 12KV 60mA or a 15KV 60mA transformer(.0133uF or .0106uF)

klugesmith

Tue Jul 28 2009, 02:17AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Have you spent a few hours searching this forum and reading old threads about MMC caps,
and perhaps checked the HvWiki,
before asking the 4hv community to (collectively) spend a few hours reading your question?

HV Enthusiast

Tue Jul 28 2009, 12:10PM

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

They are okay, but you'll need quite a large number of them to get the required capacitance and voltage. Better to use the 0.15uF, 2kV CDEs or 0.33uF 42L GE's.

cduma

Tue Jul 28 2009, 05:26PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

Dr. G: By my calculations I will only need 15 of these to achieve .0132uF at 30kv. And thank you very being a nice person and aiding me in my research. You have my respect and admiration for sharing your experience.

Klugesmith: I am sorry to hear that it would take 93 people (collectively) hours to read 2 sentences. In general I would be fearful that people who lack the education necessary to read are playing with such dangerous toys like Tesla coils. It seems that I am in the wrong place. I was looking for a community of 'coilers who want to spend there free time learning about Tesla coils and helping others. Or perhaps you are in the wrong place. You should check out a place called 4chan. There are many people there just like you!

[MOD EDIT - Fixed double post]

HV Enthusiast

Tue Jul 28 2009, 06:37PM

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

Before you purchase them, i would compare the ESR (or dissipation factor) of each of the caps (use 0.15uF CDE's as reference) to see if you would get similar numbers. You want to make sure those capacitors can withstand the high ripple current and resulting dissipations.

Arcstarter

Tue Jul 28 2009, 06:40PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well, he does have a point. If you did your research, you could have found the answer in a few minutes. Read the rules again.

Don't make any enemies, i seriously doubt anyone is actually angry at you. We just try to encourage people to do their own homework. By doing that, you could learn quite a lot about capacitors that help you later on even.

There are many threads already made that talk about WIMA capacitors, and they are pretty good.

Also, you can go to deepfriedneon and type in your transformer specs, and get the resonant capacitor size. Then multiply that by (i think) 1.5 for the ltr.

For a good bank using those capacitors, 5 in each string, and 5 parallel strings for 30kv and .022uf. Or, you could use 4 paralleled strings for .017uf, which is still fine. It is above resonant, so i dont see why not :P. I would go with .017uf personally. This is for a 12/60.

klugesmith

Tue Jul 28 2009, 07:52PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Cduma: sorry, I was unusually peevish last night & could have been more tactful.

Sure, this is a place to meet & talk with fellow coilers.
But posting questions whose answers were given here previously, or can easily be found elsewhere, burdens both the daily dialog and the permanent archive with redundant stuff, to the detriment of both social users and researchers. There's a rule against it:

Part II: Posting
B. Do your own research. If you intend to ask a question, please make sure it isn't already addressed in the archives, or on the wiki. Also, be sure to perform at least a cursory Google search. Remember, nobody wants to do your homework for you. Show some effort, and the community will repay you in kind.

With due respect, your posting history includes many questions where the apparent effort is, shall we say, on the light side.
In your own words (Jan 4, 2009) "When someone tells me to research a topic on the internet that means to post your question on a forum to seek other peoples expertise." But 4hv isn't an IM chat room or your txt-message buddies. If you -did- some homework, words to that effect would go far.

Though I do sincerely applaud the helpful and anecdotal posts you have contributed here.

Hope to see updates about your new tesla coil.
Best regards,
Rich

HV Enthusiast

Wed Jul 29 2009, 11:46AM

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

Okay guys, enough with the "do your own research" bashing. We were all beginners once and instead of jumping down someone's throat every time they ask a question thats perceived as elementary, lets be a bit more friendly and helpful.

You guys seem to have a great memory when it comes to past threads, and i'm sure it would be easier to just post a quick "yeah, those caps are okay" rather than write two paragraphs on how someone broke the rules. The former is MUCH more productive. If you want to remind someone about the rules, then simply send that person a FRIENDLY and POLITE email stating the rules.

Also, let me remind BOTH of you the following rule which you both have broken by going off on your rants.

Rule IIA. Stay on topic. When posting in a thread, look at two things. The subject, and the first post. Those two give you an idea of what is and what isn't okay in the thread. It's tempting to look at the most recent few posts and make a judgement call, but don't do it! If you need to go off-topic, create a whole new thread in the appropriate board. Under no circumstances, never ever, preface a post with "I know this is off-topic, but..." or end a post with "...and now, back on topic." This does not excuse you from the rules, but it does demonstrate that you're aware you're breaking them. Such posts will be deleted mercilessly.

Thanks
Dan

cduma

Wed Jul 29 2009, 05:12PM

Registered Member #1822 Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300

Klugesmith: Sorry I told you to go to 4chan. That was uncalled for ;)

Herr Zapp

Wed Jul 29 2009, 06:15PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

All -

I think there is a middle ground somewhere here ....

cduma -

Certainly the answer to your question about capacitor value (LTR) has been provided before and could have easily been found with a just a few minutes of research.

As to your question "Are these caps good to use?", the answer is a bit more complicated. The capacitors themselves utilize film/foil construction, and are rated for high-current pulse service at high rates of voltage change. However, they can very quickly fail in Tesla coil use if they are subjected to either excessive current, or excessive voltage. The link you provided was to the Wima FKP1 capacitor, .022uF at 6KV. Is this the actual capacitor value you are considering to use? You didn't provide any details on your MMC design, other than you will use 15 capacitors. Are you thinking about arranging these in three parallel strings of 5 capacitors per string? (It really helps to be specific in your initial post so there is no guessing, etc about what you are planning.)

Long ago Terry Fritz did some actual capacitor heating tests on the Cornell-Dubilier 942 series capacitors using a high power RF generator to "simulate" the internal heating the tank capacitor will see in a Tesla coil tank circuit. The result of this testing is the MMC Capacitor Design Chart that can be found at classictesla.com (and other Hot-streamer dot com mirrors). If you will refer to this, you will see that for either 12/60 or 15/60 NSTs, 2, 3 or even 4 strings of the C-D 942C20P15K capacitors are required to keep internal heating to an acceptable value.

You need to make sure that YOUR capacitors will meet the peak voltage, peak current, and RMS current conditions they will see in your Tesla coil circuit. Remember that the peak voltage with a 12KV NST is 16,970 volts, and 21,210 volts with a 15KV NST). Conservative MMC design practice is to require a 2X or greater margin between the circuit's peak voltage and the MMC's "DC" voltage rating. Since the C-D 942 caps have some of the highest peak and RMS current ratings of any similar-sized wound film-foil capacitors, it's possible that any other type or brand of capacitor will need even more parallel strings to meet the peak or RMS current requirements.

You need to compare the peak and RMS current ratings of the C-D capacitors used to develop the MMC Design Chart to your candidate capacitors, and determine if you can use the MMC chart data for "your" caps, or if you need to de-rate it further (if your caps have lower current ratings than the C-D caps). I think you may find that you will need more caps than the 15 pieces you seem to be plannning to use.

(I was unable to find the actual current ratings of your Wima caps anywhere on the Mouser website. Finding their current ratings is essential to help you determine if they are suitable, and how many parallel strings you will need.)

Regards,
Herr Zapp

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