RE: Bleeder Resistors

["Tesla list" <tesla@xxxxxxxxxx>]

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

1k ohm will give you a very fast bleed off rate! (short discharge time)

At only 10 kV (for example) however the dissipation will be

(10000 volts)^2 / 1000 ohms = 100,000 W, or 2000 times the rating of
your resistor.

Put another way; 10000 V / 1000 ohms = 10 amps, which is probably more
than your available secondary current by a fair bit, so while you won't
hurt your 50W resistors, you won't see a lot of action off the coil :)

Pick an amount of time that seems reasonable for the capacitors to self
discharge; let's say 5 seconds for discussion purposes.

At 10,000 V (again for the sake of example), and 0.03 uF if we want to
discharge 90+ % of the cap in 5 sec, we set 5 x R x C = 5 sec.

R = 1/C = 1 / 0.03 x 10^-6 = 33.3 M ohms.

(10,000 volts)^2 / 33.3 M ohms = 3.003 watts continuous dissipation.

A 5W (minimum - I would consider 10W since we are only buying a few of
these things, and it is at least sort of a safety item after all) 33 M
ohm resistor will be fine.

With respect to 2 and 3:

Grounding out to verify zero energy state is just good practice on HV
apparatus. A few other poster covered this with the "risk versus cost"
comments. Check out your local utility at work on distribution lines the
next time you see them. Everything they use is insulated - even when the
line is dead. The sum of their personal protective equipment (gloves
etc.), tool, and aerial truck insulation ratings is far greater than the
typical working voltage of the system they are servicing. Over and above
this, when not working on a "Live Line", they ground all three phases
together and to a local ground with 1/0 or larger wire before they start
work. All of this occurs after they check voltage with a "Hot Stick"
mounted meter. We are talking in this group about using pole pigs, so we
are talking about the same voltages that these guys deal with (albeit at
less current usually, but more than lethal nonetheless).

Your wire method should be just fine to answer your question.

"Locking it out" is commonly used terminology in industry for turning
off the source of power and ensuring that only the person working on the
equipment can return it to service. Many deaths occur every day because
somebody flipped on the wrong breaker/switch etc. Every person working
on a piece of equipment must place their own lock, identified with their
name, and for which only they have the key, on each and every source of
energy for the machine. (not just electrical - pneumatic, hydraulic -
any source of energy)

Obviously this is all a bit extreme for what we talk about in this list
- but the intent is the same. (hey, you asked :) )

The obvious procedure for the average Tesla tweaker is to unplug the
darn thing -then- verify it's dead, before touching it.

The local safety trainers here like to tell you not to put your finger
anywhere you wouldn't put anything nearer and dearer to you (or your
wife!).


-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: January 3, 2006 10:39 PM
To: tesla@xxxxxxxxxx
Subject: Bleeder Resistors

Original poster: otmaskin5@xxxxxxx

My wife said don't worry, I don't need bleeder resistors.  But having
read all your advice on this topic, now I'm a little suspicious of
her motives.  Thanks for your help.  I do have a couple of other
questions...

1.  I have two wire wound power resistors (50W, 1KOhms) not being
used.  Would one or both of these make a suitable bleeder resistor
for my .03uF 35,000v Maxwell cap?

2. I'm hearing, even with bleeder resistors, hot sticking to
discharge the cap is still adviseable.  I have been holding a stiff
wire (taped to a length of PVC) accross the Maxwell's 2 terminals for
5 or 6 seconds.  Is that sufficient discharge procedure?

3. One of the responses also recommended "locking it out."  Can
someone explain what this means?

4. I also have PFC caps on my coil.  I assume these also need to be
discharged?  Same procedure as with tank caps, right?  Would you use
bleeder resistors on PFC (motor run) caps?

Thx, Dennis Hopkinton, MA