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Re: [TCML] Voltage - Gap



That is fantastic, 

Does anyone else run their Maxwells in this way? I would love to collect some data on the usage! 



Thanks, 
John "Jay" Howson IV 


"Why thank you, I will be happy to take those electrons off your hands." 

----- Original Message -----
From: "drieben" <drieben@xxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
Sent: Tuesday, January 31, 2012 7:48:08 PM 
Subject: Re: [TCML] Voltage - Gap 

Jay, 

I have a cat # 31885, .1 ufd, 75 kV rated Maxwell 
that I believe is also rated at a "mere" 25 amps RMS, 
but I run my Green Monster coil (10 kVA pig fed 
and overdriven up to 20 kVA) with it as the sole 
primary cap and I have never been able to notice 
any external warmth on it above ambient temp, 
even after several minutes of non-stop 15 kVA + 
running. 

David Rieben 



----- Original Message ----- 
From: <jhowson4@xxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> 
Sent: Tuesday, January 31, 2012 3:50 PM 
Subject: Re: [TCML] Voltage - Gap 


> Hmm alright, I shall poke the archives and see what useful information i 
> can obtain. =) 
> 
> what you describe is pretty much what I have been doing, playing with the 
> data for just the .15 2Kv caps in an excel spread sheet to nail all the 
> formulas down. once i am done that i will expand it to the other cases in 
> an actual programming sense. 
> 
> 
> I have made several poly caps previously, and to date none of them have 
> failed. Two open air units and one under oil. 
> I got around the need for thick Aluminium sheeting by tapping each turn of 
> the roll with a nice long strip of aluminium and tying them all together, 
> this allows many paths for the charge to escape. Minimizing the over all 
> current flowing threw any given junction.Thus minimizing heating and the 
> like. This also means for a pretty low inductance. 
> I have run these guys for very long runs, and they get only lightly warm 
> to the touch and while being over driven for what I designed them for as 
> well. Work for me. 
> Thus far solely in terms of cost analysis, the poly caps are by far the 
> cheapest route to go for me. Due to maxwells being so bloody expensive , 
> and the sheer quantity of MMC caps i need to get the RMS currents to work 
> out. That's with my RMS current equation thought, which I am trying to 
> improve upon. Best case scenario is as I make my equation more accurate, 
> the RMS current drops and I need less capacitors. or I stumble upon some 
> very useful information regarding the ratios of actual RMS current to 
> rated RMS current. Which from what I found last night, is information that 
> does exist somewhere, I just need to dig it up again. 
> 
> Speaking of maxwells, what is the rms current that these bad boys can 
> handle for short runs? I have a 0.15uf 50Kv unit I acquired at a steal 
> price. says 25A rms. 
> What do you guys run them at? 
> 
> 
> 
> Thanks, 
> John "Jay" Howson IV 
> 
> 
> "Why thank you, I will be happy to take those electrons off your hands." 
> 
> ----- Original Message ----- 
> From: "Jim Lux" <jimlux@xxxxxxxxxxxxx> 
> To: tesla@xxxxxxxxxx 
> Sent: Tuesday, January 31, 2012 9:36:42 AM 
> Subject: Re: [TCML] Voltage - Gap 
> 
> On 1/31/12 12:06 AM, jhowson4@xxxxxxxxxxx wrote: 
>> Ah yes I see the posts you are talking about back in the archives. 
>> 
>> I am going to spend a little bit of time reading threw this 
>> material! 
>> 
>> So for the 2000Vdc cap, and the heat dissipated for the standard .15 
>> 2Kv would be .9W, seems reasonable. I don't really see how this is 
>> all that useful to me yet, but i am sure after reading thew the 
>> material you helped me find, I will learn what to do with it. 
>> 
> 
> Actually, dissipating almost a watt in something made mostly of plastic 
> might be pushing a bit. I guess they're quite a bit bigger than, say, a 
> 2W resistor, but thinking in terms of stuff you have around the house 
> that dissipates a watt in a small area. 
> 
> One way to estimate the power dissipating capability of the capacitor is 
> to look and see if there is a derating curve for the case temperature. 
> 
> 
>> Going back to what you said earlier, with before you work too hard 
>> modeling fine details, do a simple subset and see if it makes a 
>> significant difference. You might find that in an RMS current, 
>> heating sense that it doesn't make much difference between one big 
>> pulse at Imax and 3 successive pulses at Imax/3, because the duty 
>> factor is lower at the former. (Yes, heating goes as the square of 
>> current, so that's clearly not true in this specific example, but 
>> it's what I was able to come up with before my coffee as a direction 
>> to look) 
>> 
>> Its definitely something I need to consider, does this really 
>> matter? Well I am having a good time learning about all this stuff in 
>> the process, so why not try and figure it all out. Plus if i do i 
>> might be able to correlate some interesting things and add to the 
>> general knowledge base for everyone to learn from. 
> 
> 
> You make a good point. However, I find that it's nice to do a couple 
> cases by hand that sort of bracket what you're interested in. Not only 
> does that make sure you have the conceptual understanding, but it also 
> lets you spend your time effectively. You might be trying to model 
> something where there isn't any good data to model from and you wind up 
> chasing what is essentially experimental uncertainty in the raw data. 
> 
> Maybe another term is to do a sensitivity analysis. 
> 
>> 
>> another interesting thing about my coil in particular, Because I am 
>> basing it on Steves DC design, but optimizing the parameters, I can 
>> pretty much assume that the tank cap will be fully charged on what 
>> ever time scale I want it to be charged on. meaning that I can pick 
>> my BPS to be what ever I want and still achieve the maximum bang 
>> energy, assuming I have the current to push the system of course. I 
>> am designing for 600bps because that's the maximum my gap will be 
>> able to push. Hence my heavy interest in the RMS current, because 
>> that means a huge difference in price of the MMC. Its will all be too 
>> expensive for me anyway and I will be making my own poly caps in the 
>> end. But its been an interesting and knowledgeable exercise thus far, 
>> so I might as well keep going. FOR SCIENCEEEEEE!! 
>> 
> 
> 
> I don't know how much you consider your time is worth, but it's unlikely 
> that making your own poly caps will work as well as either surplus pulse 
> caps or a MMC. Making the rolled poly cap isn't all that hard, it is 
> somewhat time consuming. Although, scrounging appropriate materials is 
> harder than it seems. It's not like you go down to the supermarket and 
> buy aluminum foil and cling wrap. The archives are full of stories 
> about where to get the right plastic in the right thicknesses, and where 
> to find aluminum sheet. 
> 
> And then there's the whole "how do you attach a wire to the aluminum" 
> question. After all, you don't want a nice low impedance, low ESR cap, 
> with high AC resistance wiring connecting it. 
> 
> And the oil fill and pumpout/degassing process. Did I mention the 
> inevitable leaking oil? 
> 
> This all said, making your own capacitors is a satisfying project: you 
> DO get to say "I did it myself", and some 15-20 years later you can 
> write this post<grin> 
> 
> 
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