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RE: RE: Bleeder Resistors



Original poster: "Leigh Copp" <Leigh.Copp@xxxxxxxxxxx>

Good morning,

Scott Hanson pointed out an error in my earlier comment "the capacitors
have no direct discharge path except for their own internal leakage"

The original post of course was in reference to a Maxwell cap in
-parallel- with a NST secondary, which would be a -parallel- resonant
circuit, as opposed to a series tank which is what I had on the brain.
There is by definition therefore a DC discharge path (unless as was
suggested, something else creates an open circuit condition).

All nitpicking aside, I am in total agreement with the group here;
safety first. Never mind bleeder resistors, whether you have them or not
rule #1 is assume all circuits are live until proven otherwise. In the
case of high voltages you can't measure directly, my money is on a hot
stick to ground to touch off everything before you touch it. In the RF
induction heating / radio transmitter world, we have plate supplies
operating at 20 kV DC and 10+ amps DC. Lots of big, (0.006 uF, 15 kV,
450 kHz) high current, water cooled capacitors around and smaller DC
ones too. The rule is that you touch off on everything with the hot
stick before you put your body anywhere near it. (and all of that after
you lock it out first!) Tesla coiling is of course complicated by the
fact that one side of the system is not tied to ground, so your
procedure has to be to short all energy storage components in some form
or another. (2 sticks with a resistor between them?)


Now that those important safety messages are out of the way, here is
another question regarding the MMC strings (or any series capacitor
string in parallel with a bleed path for that matter)

If we have any number of capacitors in series, the charge by definition
should be distributed over the capacitors, proportionately to their
individual capacitance value. If we short the string, we effectively
short them all. The DC discharge path is only relevant when we have
steady state, and if the charge is not evenly distributed, we have not
by definition, reached steady state. So in the case of the series
capacitor array without sharing/bleed resistors the NST secondary should
take the whole string and each of its components to zero. This would be
theory of course, and is not to be taken as a safety procedure.

Leigh



-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: January 3, 2006 12:42 AM
To: tesla@xxxxxxxxxx
Subject: Re: RE: Bleeder Resistors

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

In my case, caps laying around the office, may or may not be
charged.  Either inadvertently - or heavily charged by my
"friends"  >>:o)))  It does not help when they are sizzling from corona
%:o))))

The bleed resistors add like 50 cents to the cost, which it trivial
compared to the potential "payback"...  But fact is, adding 50 cents
worth of resistors is such an easy bet, it is stupid not too....

Digikey # 10MH-ND, and the closer values, are well tested and highly
recommended, in series, as required...

When you spend all day(s) sticking your hands in HV circuits, you get
real friendly with every cap being bleed down in a hurry ;-)))

They only have to save your life once....

Cheers,

         Terry





At 06:21 PM 1/2/2006, you wrote:
>Hi all,
>
>In a way, I agree with both sides of this argument ;^)
>If you are using a single unit commercial pulse capa-
>citor in a typical AC powered Tesla coil (except for
>an equa-drive configuration), then the primary coil
>and secondary winding of the power transformer will
>quickly bleed off the residual charge of the capacitor
>after the power is shut down.
>With multiple seriesed capacitors, like MMCs,  each
>individual capacitor in the string can indeed hold some
>residual charge and I would agree that each of the indi-
>vidual caps need to have their own bleeder resistor in this
>configuration. However, Gary also brings up a good point that
>I had not originally considered with the "worst case scenario"
>-like the transformer's secondary winding fails open
>circuit or the primary tap happens to come loose while
>the coil is powered up. Of course, the latter primary
>tap scenario would be almost impossible in my big coil
>setup as I have the tap clamped and bolted into the tap
>position on the primary coil. Also, I would say that the
>chances of my 15 kVA pole pig's high voltage winding
>failing open circuit during coil operation are rather
>slim. However, just in case the "impossible" does happen,
>bleeder resistors are the best insurance policy. I suppose
>it's a matter of how much of a risk factor that you're
>willing to accept. Every coiler accepts a certain degree
>of risk by the mere fact that they decide to build and
>operate  Tesla coils, which are inherently dangerous, in
>the first place. "I" personally don't use bleeders on my
>coil setup and like Dr. R, I've never gotten a nasty sur-
>prise from the primary capacitor after shutting down the
>power to the coil in my AC powered system. Now with a DC
>or equa-drive system, that's a very differnet story indeed
>and the risk of a dangerous shock would be VERY HIGH if
>the primary circuit components are handled after power-down
>without employing definite measures to insure that the
>capacitor(s) is/are fully discharged first!
>
>David Rieben
>
>----- Original Message -----
>From: Tesla list <tesla@xxxxxxxxxx>
>Date: Monday, January 2, 2006 6:13 pm
>Subject: RE: Bleeder Resistors
>
> > Original poster: "Lau, Gary" <Gary.Lau@xxxxxx>
> >
> > With spark gap coils, with the coil off and the gap being an open
> > circuit, the tank cap, primary coil, and NST secondary form a
> > loop, and
> > any charge in the cap is discharged essentially immediately
> > through the
> > primary and NST.  But I disagree with the good Dr about a bleeder
> > beingunnecessary.  They're unnecessary the same way seat belts are
> > unnecessary.  Should the primary tap connection or NST secondary
> > connection come loose, the discharge path is lost.  In my early
> > coilingdays I once tried to determine the best primary tap point
> > by dragging
> > the tap connection across the primary turns, while it was operating.
> > The arcing between the tap wire and the primary was fierce and I
> > abandoned that idea immediately.  But I quit with the tap
> > disconnected.When I shut off the power and attempted to make the
> > tap connection, I
> > got a very stiff ZAP, and I was lucky that the cap didn't carry a
> > largercharge.
> >
> > In short, "stuff" happens, and having a backup discharge path
> > (bleeder)in place is cheap insurance.  You won't be able to find a
> > singleoff-the-shelf resistor at a reasonable price capable of the
> > job, but one
> > can easily build a series array that will withstand the voltage.
The
> > resistance value is not critical; probably anything between 50-100
>Meg
> > is OK.  I made an array of 39 2Meg 1/4W resistors, 'cause that's
> > what I
> > had available.  See photo about half way down on my RSG page:
> > http://www.laushaus.com/tesla/sync_gap.htm
> >
> > Regards, Gary Lau
> > MA, USA
> >
> >
> > Original poster: Just Justin <rocketfuel@xxxxxxxxxxxxx>
> >
> > Can someone explain to me why this is not necessary?
> >
> > I don't see why the tank cap seems to always be 'empty' (haven't
> > actually
> > measured voltage for fear of zapping another meter) after a run.
> > If the
> > car was raised to almost-breakdown in the spark gap, shouldn't it
>stay
> > charged some of the times?
> >
> > Justin
> >
> >
> >  > Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
> >  >
> >  >
> >  >
> >  >
> >  > Bleeder resistor is not necessary unless you are running DC on
> > thiscap.
> >  >
> >  > Dr. Resonance