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Re: Off Line - DRSSTC (OL-DRSSTC) Concept....
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- Subject: Re: Off Line - DRSSTC (OL-DRSSTC) Concept....
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- Date: Sat, 24 Sep 2005 11:56:19 -0600
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Original poster: "colin heath" <colin.heath4@xxxxxxxxxxxxx>
wow i like the idea of this and am thinking of building a
concept model with smaller cresonant cap so i can use irfp460 just to
try as i have bucket loads of them them!
this has got me really thinking now as i love a challenge( i built my
first drsstc just as dan m was building his first) i had nil
electronics experiance then and its a steep learning curve.
this could be fun to try
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
Sent: Saturday, September 24, 2005 6:10 AM
Subject: Off Line - DRSSTC (OL-DRSSTC) Concept....
Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
The OLTC is very simple and tough, the DRSSTC is fairly complex and
not quite as tough... I think there is a system (concept only!)
that might marry the two in a very simple, cheap, and hardy
configuration that any coiler should be able to put together...
I direct you attention to this schematic:
Allow me to explain...
From the top right, the AC line voltage (probably from a variac) is
rectified and charges a capacitor (Cresonant) through a blocking
inductor to say 300VDC. This capacitor is similar to the ~3000uF
buss caps we use in the DRSSTC. However, this capacitor is
significantly smaller in value since it is limiting system power in
this "fixed" 120 BPS coil. For a 1000W 120 BPS coil:
1000W = 120BPS x Ecap Ecap = 8.33Joules 8.33 = 1/2 x C x
300^2 C = 185uF
Note that with the proper selection of blocking inductor, the
capacitor voltage can be "resonantly doubled" off the 60Hz AC
line. I think "my" OLTC is the only one that ever used that proven concept...
Note that if the IGBTs obnoxiously decide to cross conduct, the 8.33
joules could be absorbed directly by the thermal mass of the IGBTs
and the blocking inductor would provide time for them to correct. -
It should never blow up...
So every 120th of a second, the system is provided with a say 185uF
cap charged to 300VDC to "run the thing"... The duration of the
cycle will be determined by how long it takes to use up the 185uF cap's energy.
Lprimary and Cprimary are typical per DRSSTC standards as is the
secondary coil and all...
The H-bridge has four typical IGBTs with anti-parallel diodes.
The gate drive to the IGBTS is derived directly from the primary
current now! There are four current transformers that provide
isolated gate drive directly to each of the IGBTS from the primary
current loop. Back to back Zener and Schottky diodes provide
voltage control and very fast switching control of the current from
the CTs to control the IGBTs. Of course, the "phasing" needs to be correct...
So the 185uF cap will discharge thought the IGBT H-Bridge and drive
the coil. The direct connected, but voltage limited, CTs will
feedback the primary current to the IGBTs providing synchronized
The firing MOVs "start" the cycle. Once the voltage reaches their
level, they will conduct and "turn on" the system so the CT and IGBT
system will start running.
As the 185uF cap drains, the system will fall out of
conduction. When the primary current and drive signals collapse,
the system's power will be almost all drained, so no harm should come...
This is all purely untested "pie in the sky stuff"... But if the
concept is valid, it would bring together the best of the OLTC and
DRSSTC together in a very simple, cheap, and robust system.
You can hold the AC line - to primary tank drive system in the palm
of your hand!!!
If the concept holds, everything just changed... Again ;-)))