Re: Bleed Resistor for Homemade/Large Caps - THE FULL DESIGN NOTE S

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jeremy Scott by way of Terry Fritz <twftesla-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>

Okay,

I've had one person say that stringing
10Mohm 1/2 Watt resistors would work...
and another saying that they all have
to be 5 Watts ...

So which is it?

As I understand it a resistor dissipates
energy as heat. The larger the resistor,
the more heat it can dissipate due to
increased contact with the air. Thus, a
resistor's length and cross section has
a direct effect on how much power it can
handle.

So stringing together 15 10Mohm 1/2 Watt
resistors *should* give 15 times more
surface area than a single 1/2 Watt resistor.
This *should* then be able to handle 7.5 watts,
providing all of the resistors are the same value.

Calculations based on 21000V, 15 1/2 Watt
10Mohm resistors.

I = V / R
I = 21000V / 150 000 000 Ohms
I = .00014A

W = I * R
W = 21000V * .00014A
W = 2.94

Voltage across each resistor in this string
of 15 is going to be about 1400V

Ir = Vr * R
Ir = 1400 / 10 000 000
Ir = .00014

Wr = 1400 * .00014
Wr = .196 W

W * 15 = 2.94















--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "by way of Terry Fritz
 > <twftesla-at-qwest-dot-net>" <Mddeming-at-aol-dot-com>
 >
 > In a message dated 10/29/02 2:50:00 PM Eastern
 > Standard Time,
 > tesla-at-pupman-dot-com writes:
 >
 >
 >
 > >Original poster: "Jonathan Peakall by way of Terry
 > Fritz
 > ><twftesla-at-qwest-dot-net>" <jpeakall-at-madlabs.info>
 > >
 > >In series, the resistors current rating will be the
 > value of the lowest
 > >resistor in the series and the resistance values
 > add up. In parallel, the
 > >current rating is added, and the resistance value
 > added. So in this case,
 > >each resistor must be rated for 5 watts.
 > >
 > >Regards,
 > >
 > >Jonathan Peakall
 >
 >
 > Hi Jonathan,
 > Let's go back to Ohm's Law 101
 > I = E / R and W=ExI
 > If there are 10 equal resistors in series, each one
 > passes current of I and
 > has a voltage drop across it of E/10. Therefore the
 > power dissipated by
 > each resistor will be I x E/10= W/10, not W. Ten
 > equal 1/2 watt resistors
 > can dissipate 5 watts total. Current passing through
 > each resistor is I,
 > total voltage drop across the string is E, total
 > power is E x I.
 >         I made this same mistake last month while
 > trying to think at 3AM. ;-)
 > Matt D.
 >
 >


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