Re: DC Tesla Coil FW Bridge and DQ diode string RFC

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "S&JY" <youngsters@xxxxxxxxxxxxxxx>

Jim,

The 1N5408 diodes are 3 amps, not 1.  Also, they can withstand peak currents
many times as high.  I would not recommend paralleling diodes, because the
diode drops will not be exactly the same, and currents therefore will not
divide evenly.  I think you will end up with very little additional current
handling capability as compared to a single diode string.  The only way to
share current more evenly as to add a few ohms of resistance in series with
each diode, but that is a lot of labor.  I think one string of 40 will be
all you need.  And I don't recommend adding caps and/or resistors across
either your rectifier or deQing diodes.  Most recently manufactured diode's
characteristics are uniform enough that Rs and Cs across them are not
needed.

You should consider adding a few hundred ohms worth of power resistors
between your bridge rectifiers and your filter caps to limit the peak
current through your rectifier strings in case something happens besides a
slow controlled ramp-up via your variac power into your pole pig.
--Steve Y.

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Sunday, May 15, 2005 11:09 AM
Subject: DC Tesla Coil FW Bridge and DQ diode string RFC


> Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>
>
> Hello All,
>
> Spec 15KV, 8-10KVA DC, Filtered, 500 BPSmax
>
> I am beginning construction of my rectification (FW bridge) and DQ string.
> The aforementioned charging inductor is going the experimentation route.
The
> bridge will be made of (4) strings of (6) studded 7500 volt 4amp diodes
> (HVCA HDB7.5) (looks like a HV insulator string:-)). For the DQ string I
> have (100) 1N5408 (1000v,1 amp) of which I was planning 40 - 50 paired or
> would separate strings be more advantageous?. Clearly this would double
the
> forward current rating but what other ramifications would you expect in
> either configuration?
>
> Clearly given that I am NOT a design engineer; but, I can make stuff:
>
> 1. I seem to remember snubbers and bleeders enter the picture in previous
> threads but I couldn't find reference to the DQ successful setup. I was
> thinking 1nF and 1Mohm 1/2w across each pair or signal diode given 2
> strings. Does that seem reasonable or needed?
>
> 2. I don't have a clue what do with the largish bridge diodes or if they
> need protection at all?
>
> Thanks Much for you input,
> Jim Mora
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