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Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
if you look at pic, i have drawn up a few schematics of my proposed SGTC circuit. i have gathered these schematics from various websites and i need help with which grounding method is correct/best. i plan on using some RF chokes to protect the transformer. im a little confused because different websites show different grounding methods. please review my schematics and post some feedback on which to use or any changes i need. also, where does the strike ring get grounded to? thank you in advance!
Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
i found this schematic.
ive seen some others online as well. is it supposed to have a capacitor and bleeder resistor for each MOV? or is it 12 caps and bleeders for any amount of MOVs?
also the digikey part no for the capacitors are DC rated. if there is supossed to be 12 caps that only adds up to 19200v. my 15 kv transformer is 21210v peak
Registered Member #133
Joined: Fri Feb 10 2006, 10:27PM
Location: Pensacola, Florida
Posts: 47
Each set of 6 capacitors is used in series to produce an equivalent 550 pF @ 9600 Vpk. The resistors are used for equalizing the voltage across each of the capacitors so that no individual capacitor will experience overvoltage. If you have a 15 kV neon sign transformer, then half of the output voltage is present from each high voltage output terminal to ground (i.e. 7.5 kVrms from each terminal to ground). I would add one more capacitor to each set in order to make two sets of seven capacitors. Each set of seven capacitors will handle 11.2 kVpk. All 14 capacitors will hold off 22.4 kVpk between the two output terminals of the transformer. Use one equalizing resistor across each capacitor.
The number of MOVs and the number of capacitors used are unrelated. The MOVs permit clamping at a voltage level that is equivalent to the sum of the MOV voltages from one of the transformer high voltage terminals to ground. For a 15 kVrms neon sign transformer, use 8 of the 1800 V MOVs per side to ground.
Registered Member #2553
Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97
im having a tough time finding 1k 100watt ceramic resistors on digikeys site. will these work? the schematic(from a different site) says ceramic, but the part no given here says wirewound, thus inductive.
also, the transformer is AC, the part no given on the schematic gives a digikey capacitor rated for 1600VDC. i cant find ac rated caps at this voltage either.
The inductance is not stated on the data sheet, but it is likely to be in the neighborhood of 100 to 200 uH, thus the inductive reactance (2Ï€fL) will be a small fraction of the 1000 Ohm stated resistance at the frequency of operation. The L100J1K0E resistors should work well.
The 1600 V (P10501-ND) capacitors will work for AC operation as long as the 1600 Vpk rating is not exceeded.
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help with correct grounding
