Re: [TCML] SISG Repaired / Question about timing resistors

[Finn Hammer <f-h@xxxx>]

----- Original meddelelse -----

> Fra: caspina <caspina@xxxxxxxxx>
> Til: TCML pupman <tesla@xxxxxxxxxx>
> Dato: Søn, 17. jul 2011 13:51
> Emne: [TCML] SISG Repaired / Question about timing resistors
> 
> Hello,
> 
> My SISG is repaired.


Great

> Fact is that for my last runs I changed tank cap from 100nF to 125nF.
> Maybe this was too much for the IGBT's... Resonant frequentie is 125
> kHz.
> 
> So for the moment I use only tank cap=100nF and a big toroid
> (Fres=104kHz
> now),

100nF resonating at 104kHz requires 23.42uH of primary inductance
resulting in an impedance of 15.3ohms.
You will soon approach max. Ipri:

@Vpri: 10000V -> iPri ->653A
@Vpri: 11000V -> iPri ->718A
@Vpri: 12000V -> iPri ->784A
@Vpri: 13000V -> iPri ->849A
@Vpri: 14000V -> iPri ->914A
@Vpri: 15000V -> iPri ->980A

So increasing Lpri seems like a very good idea.

> I have a question concerning the timing resistor of the SISG (the
> famous
> R4).
> Most use 4K7 like in the schematic of Terry Fritz.
> I've been experimenting with it and use now 'only' 220 ohm for R4, in
> my
> opinion the IGBT's don't need to be 'ON' longer than a few cycles
> (4-5).
> I'm I doing wrong using such a small value?
> Could it be bad for the SISG if there is no break-out and IGBT's are
> shut
> off this early? (It happens occasionally).
> I would think the energy is trapped in the secondary system and does
> not
> harm the primary system...

My work quickly evolved into the BRISG, with only a single CM600 module,
up to 30uF of Cpri and single turn primaries with up to 6500A Ipri =:-) .
Early on I replaced the R4 with a pot, to monitor the effects of early
turn off on the scope. I seem to recall that 470 ohms became my favourite
value. 4K7 is definately on the safe side. -finn

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