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Re: (Fwd) bleeder resistors used with MMC
Original poster: "huil888" <huil888@xxxxxxxxxxxx>
DC -
Not sure exactly what specific resistors you are talking about, but
the Vishay VR37
series of glazed metal film resistors (1/2 watt) are rated at 3500 VDC, and
will actually withstand several times this voltage safely. These are only
$0.08 each, even in small quantities, and have been used successfully
for years as MMC
bleeder resistors. They are available in values from 100K to 33M
Ohms, and are described in the product literature as "high ohmic,
high voltage, pulse rated" resistors.
Allied Electronics usually has the 10M value in stock. Before Vishay
took over the product line, these were marketed by Phillips. I think
Our Moderator may have performed some voltage breakdown tests on
these resistors way back in the dawn of MMC technology, but I
couldn't find the report at Hot-Streamer dot com.
http://www.pupman.com/listarchives/2000/November/msg00073.html
Regards,
Scott Hanson
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Thursday, November 02, 2006 8:06 PM
Subject: Re: (Fwd) bleeder resistors used with MMC
Original poster: "resonance" <resonance@xxxxxxxxxxxx>
Better to use Allied Electronics pulse rated resistors --- 3.5 kV working
voltage. Only 55 cents each.
Although, I have never used any bleeder resistors in my AC NST powered
coils --- and have not found any holding a charge --- at least not in the
past 6 years!
Dr. Resonance
My first thought was : What is Bill doing making such a small coil? Is it
a toy one for Xmas. Perhaps the Griffith Observatory (which you are doing
if I recall) needs one for a small room like a toilet or broom cupboard?
Resistors for MMC have been debated many times. Some people don't use any.
Most use a single 1/2 watt 10M resistor per cap. This has always worried
me as it is way overvolting the resistors rating of perhaps 500 - 800 V
but in this pulse application they don't seem to fail. Terry uses 4.7M x
2 per cap. I use 3.3M x 3 per cap. I don't think it has been proven who
is right. My guess is it depends on the application. For home use they
are probably not required for a small coil. For a reliable larger museum
coil you need to minimise failure modes, so use 3 or more.
Peter
http://tesladownunder.com