Hey guys I am just about to run my 15,000 volt tesla coil. The total capacitance i need for this coil is 0.025 uF. I bought 13, .33 uF caps. I need bleed resistors now. I calculated that i need .6 mega ohm resistors so far. 15,000/.025 = 600,000. = .6 Megaohm resistors. I don't know how to calculate the wattage for each resistor. I look around on the internet and i see many different answers but no straight answer so before I go out shopping I really wanted to ask some pros. When i finish i Want to show of my amazing coil. Thanks for the help if any, bye.

 

Is main concern resistor arc over voltage ?

You calc R by dividing Voltage by Capacitance ? Not sure I follow this.

VeachR = 15,000 / 13 =~ 1200V

Some insight - https://highvoltageforum.net/index.php?topic=657.0


Regards, Dana.

 

Yes that post kind of makes sense but kinda is why i am lost. I see people using 1/2 watt resistors for these powerful setups. I don't know how this adds up. So is the wattage per resistor 1200*.025 uF. That would be 30. 30 watts is not 1- 1/2 watt. I have gone over this before many times in my head and can't see how people are using such a small resistor? Thanks

 

To calculate wattage you need to know either current thru resistor
or the Vdrop across it when in operation. We sorta know the latter
so P = (E x E) / R where E = 1200V and R you know.
So I get 2.4W. So either get that wattage or raise the R value. Surfing
web I see some folks using as high as 10 Meg Ohms.

Regards, Dana.

 

Thanks alot. What is the reason for using the p = e*e/r. Where is that formula on the chart you showed? Thanks.

 

That is the same as V squared / R on the chart. V & E are voltage, I should have
used V to be consistent, my error.


Regards, Dana.

 

Ok thanks alot. This is making sense now. I need to do some more research on this chart thanks.

 

Another way to make sense is if you have memorized both Ohm's and Joule's laws:
V = R × I ⇒ I = V / R
P = V × I

Combining the two above: P = V × (V / R)

Other combinations are easy to be done:
P = (R × I) × I

 

how do i know when to use thoughs ones though, why in this particular case do you combine forumlas?

 

Using I * v for watts is the only forumla i understand, why are the others there and when do you use them.

 

Using I * v for watts is the only forumla i understand, why are the others there and when do you use them.

P = I × V is a variant of the Joule's law, which was originally stated as P = R × I^2

V = R × I is the Ohm's law, another very important equation

You may benefit from reading the following article:
https://en.wikipedia.org/wiki/Joule_heating#Formulas

 

I have no recollection of ever seeing a bleeder resistor as part of a Tesla coil system. So I am really wondering about that. What part of the circuit gets a bleeder across the caps? Or are they actually equalizer resistors to keep a similar voltage across each cap in a series string?

 

15,000/.025 = 600,000

How did you arrive at that ".025" figure? It seems entirely arbitrary.

 

What a mess.

Bleeder resistors basically discharge the capacitors in a reasonable amount of time. A figure of merti is 5*RC where the circuit would be about 98-99% discharged.

You pick a t Say 120s for 5*RCl t=5*R*C
You know C
Pick an R that doesn't break your power supply. Say 5-10% of the total current capacity. Using R=V/(1*0.01)

So, R (ohms) * C (Farads) = seconds. RC is known as the time constant.

Find power disipated by resistor. Make wattage larger.

See: http://www3.ncc.edu/Faculty/ENS/schoenf/ELT115/UCC.html

 

Tesla coil systems do not need bleeder resistors!

 

The total capacitance i need for this coil is 0.025 uF. I bought 13, .33 uF caps. I need bleed resistors now.

These would not be 'bleed' resistor, but rather equalizing resistor. 0.33uF/13 = 0.025uF.

 

Sure am glad you guys all seem to know WTF you are doing. We don't want to be giving out Darwin Awards this summer.