Re: Off-Line Tesla coils (OLTC)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jim,

At 05:20 PM 7/22/2002 -0700, you wrote:
>
>
>Tesla list wrote:
>> 
>> Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
>> 
>> Hi All,
>> 
>> Today I substantially rethought the front end of my off-line Tesla coil.
>> The schematic is at:
>> 
>> http://hot-streamer-dot-com/temp/Image1-1.gif
>>
>> 3.      The BPS rate can arbitrarily be anything the rest of the circuit 
>could
>> support.  Since it is now a true DC charger, there is no need to worry with
>> 60 or 120Hz BPS rates.  It is far simpler theoretically now that the old
>> way which was tuned to the line frequency.
>
>Don't you need a diode in series with L35 and L34, as in a typical resonant 
>charging circuit..

Do you mean have a inductor in series (sort of) with the primary cap (or
buffer cap) and drive the voltages up by resonating the thing at 60Hz off
the Ac line?  I never considered that but I guess you could run up some
darn high voltages that way...  Hehehe

But don't you need several cycle before the voltage starts to get really
high?  I guess I don't quite understand how you mean for it to work?

>
>There's also no need for both L35 and L34 (since they are in series.. and 
>the same goes for R63 and R64)  just one 20 mH choke and 1 40 ohm resistor 
>should do it.

I do that so the voltages and such in the model stay balanced.  It just
makes the computer models a little easier to work with. 

>
>OTOH maybe you've got the components sitting around...
>
>
>> 
>> 6.      The IGBT really does not care if you increase the BPS rate, so 
>nothing
>> else really changes.  You may be able to go to a smaller primary cap to
>> increase the Fo frequency.  Its value no longer depends on the input
circuit.
>> 
>> 7.      The primary tank circuit is no longer loaded by the charging
circuit.
>> That allows more and cleaner energy and more power throughput.
>> 
>> The only real disadvantage is that the two large 5600uF caps (250 joules
>> each) need a lot of care.  Fusing, soft start, safety discharging, etc. is
>> needed (don't wire them backwards ;-)).  The large caps values are really
>> not necessary and are arbitrary, but we need HIGH ripple currents.  That
>> naturally calls for thousands of uF of capacitance in common big caps.
>> Ripple current is their key specification here.
>
>The series resistors in the charging might give you soft start.... The 2 ohm 
>ones you've got will limit the current to around 100A, and the caps will 
>charge quickly.  Granted the little 1Amp 1N400x rectifiers might pop, but an 
>off the shelf 25-40Amp 600PIV bridge (use only half) probably has a healthy 
>enough Isurge that it would work.  Or, a couple of stud mount diodes.  
>
>Another trick is the "100W light bulb in series" one (probably about 10 
>ohms, cold), or a relay/resistor soft start.

The 1N4002 is the only diode supplied in the "free version" of MicroSim.  I
modified the spice internal model so it acts like a big high power diode.
A little modeling kludge...  I think DigiKey has some 1200V 100 amp high
speed puppies ;-)

I think for a lower powered coil you could get away with resistors.
However, I think I will use a lot of relays and switched resistors.  I am
sure it will work and I don't want to have too many things to "fiddle" with
in the "first" one.  Having worked with a bunch of prototype high power
stuff in my day, I like the thought of a bunch of big contactors slamming
home when I hit the "STOP!!" switch ;-))  I'll probably over design and
spend a lot more money just to make things more R&D safe and friendly since
I really don't know what I am doing ;-))  If it all works, then we can
worry about subtle stuff ;-)  However, I do want to get the circuits
basically realistic and practical so anyone can do it.

Cheers,

	Terry