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Re: xray xfrmr powered coils

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi DC and Justin,
Certainly a 60kV transformer will be difficult to deal with because of corona losses. If it wasn't for that problem, I believe one could get comparable sparks from a 60KV 300ma tranny as from a 30KV 600ma tranny both being 18KVA. 

30KV 600ma case:
You use an optimum Cp value of 2C, a primary inductance of L/2, and you run the system at 120 BPS. (why 2C and L/2 will become apparent) 

60KV 300ma case:
Since one has twice the voltage to charge to and half the current to do it with, the optimum C has to be 1/4 that used for the 30KV case, a primary inductance has to be 4X that used in the 30KV case to keep in tune, and you still use 120 BPS. 
(Cp = C/2 and Lp = 2L)
Say we make two strings of caps each with a capacitance of C and each rated for 30KV. For the 30KV case, we put both strings in parallel to get the 2C. For the 60KV case, we put the two strings in series to double the voltage rating and get a total capacitance of C/2. 

The total power processed by the 30KV case will be:
120 * 0.5 * 2C * 30000^2 or 1.08E11*C

The total power processed by the 60KV case will be:
120 * 0.5 * 0.5C * 60000^2 or 1.08E11*C

Peak current during a bang  for the 30KV case is:
30000 / sqrt [(L/2) / 2C] = 60000 / sqrt(L/C)

Peak current during a bang for the 60KV case is:
60000 / sqrt [2L / (C/2)] = 30000 / sqrt(L/C)
The power processed is the same in both cases and the cost of the caps is the same in both cases. The only differences are the power loss due to corona and the peak current. The 60KV case has half the peak current as the 30KV case so the SG losses should favor the 60KV case: 

Which one wins???  Depends on how the corona losses compare to the SG losses.

Gerry R.





Original poster: "resonance" <resonance@xxxxxxxxxxxx>
X-ray xmfr is probably not the best way to go for big sparks. It has almost too much potential and not enough current.
A standard 14.4 kV or a pair of 14.4 kV, 10 kVA pole xmfrs with sec series connected for 28.8 kV, will give you all the punch you need up to 30 ft long sparks. We run our Big Bruiser at 26 kVA on a single 14.4 kV pole xmfr and it produces 26-27 ft long sparks.
If you run at 60 kV you don't gain much because the current is much lower, and TCs just love current. A higher current can recharge the cap bank faster so you can run 550-585 pulse/sec with full charge in each pulse. A standard 14.4 kV, 10 kVA pole xmfr can be operated up to 20-25 kVA for short duty cycles --- that's 1,750 mA at 25 kVA and it will produce huge sparks.
Also, the pulse duty caps at 60 kV Erms would have to be rated almost 150 kV DC and they would be very very expensive.
The X-ray xmfr you have would be great with a full-wave doubler circuit to charge large energy discharge caps to around 100 kV using a variac on the xmfr's primary. These make an impressive blast thru a 28 AWG copper or steel wire approx 8 feet long! Not the best for Tesla coil duty without enduring a lot of headaches. It can be done but the cap cost will be prohibitive.
Be careful with older X-ray xmfrs before the 1950s and many of them contain a lot of PCBs. Not too dangerous unless you ingest them and then carcinogenic. 


Dr. Resonance