[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Resistor sizing for primary capacitors
- To: tesla@xxxxxxxxxx
- Subject: Re: Resistor sizing for primary capacitors
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Tue, 25 Oct 2005 23:05:44 -0600
- Delivered-to: testla@pupman.com
- Delivered-to: tesla@pupman.com
- Old-return-path: <vardin@twfpowerelectronics.com>
- Resent-date: Tue, 25 Oct 2005 23:06:23 -0600 (MDT)
- Resent-from: tesla@xxxxxxxxxx
- Resent-message-id: <A1256B.A.dUB.M7wXDB@poodle>
- Resent-sender: tesla-request@xxxxxxxxxx
Original poster: Ray von Postel <vonpostel@xxxxxxxxxxx>
On Oct 24, 2005, at 17:23, Tesla list wrote:
Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
At 09:35 AM 10/24/2005, Tesla list wrote:
Original poster: "Dirk Stubbs" <dirk@xxxxxxxxxxxxxx>
I have a question regarding the use of resistors to bleed
capacitors. How do you do about mathematically figuring the size of
resistor needed? What I am trying to do is bleed my primary
capacitors (doorknob style).
The basic question is how long do you want to wait to get to a "safe" voltage.
Please, unless your life insurance is paid up, do not consider
resistors across capacitors a "safety" device. Resistors open up and
the charge remains on the capacitor. This can and does happen even
with high wattage wire wound ceramic coated resistors.
"Bleeder" resistors are placed across the output of high voltage
power supplies for the purpose of improving the filtering and the
regulation of the d.c. output voltage. They are there as part of the
"filter" circuit.
Resistors are sometimes used across the capacitors in a series string
of capacitors so as to "equalize" the voltage cross each capacitor.
This usually done when capacitors are connected in series to increase
the breakdown voltage or to obtain a particular capacitance. Either
reason is not the bestpractice. Best practice is to use the correct
capacitor for the job. Yes, I realize it is not always financially
possible to follow best practice and we use what we have on hand
rather than spend hard earned money.
Always, always short the capacitors in a circuit before even
considering putting your hands into equipment. High voltage
capacitors are often stored on the shelf with a jumper between their
terminals.
They can even become charged just sitting.
I have worked with this stuff for 65 years and seen two people killed
by open "bleeder" resistors I have seen several instances where 1/4
" brass "shorting rods" have been burnt in half by supposedly dead capacitors.
Ray