Building Tesla coils need help calculating bleed resistors.

Thread Starter

johnboyman

Joined Jun 1, 2019
39
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.
 

Thread Starter

johnboyman

Joined Jun 1, 2019
39
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
 

danadak

Joined Mar 10, 2018
4,057
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.
 
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Thread Starter

johnboyman

Joined Jun 1, 2019
39
Thanks alot. What is the reason for using the p = e*e/r. Where is that formula on the chart you showed? Thanks.
 

danadak

Joined Mar 10, 2018
4,057
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.
 

rsjsouza

Joined Apr 21, 2014
262
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
 

MisterBill2

Joined Jan 23, 2018
7,059
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?
 
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
 
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