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I have 2 grounding rods hammered into the ground, I think there 5' rods. the wire is maybe 6ft in length but the coil is only like 4 ft away from the grounding rods. The NST is connected to one ground, the 2nd ground connects the strike rail, the terry filter, the secondary coil are grounded to the 2nd ground rod.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
IR -
Unfortunately the shaky video clip doesn't provide any useful info.
Let's try to find the root cause of your failed bypass caps; we can look at tuning and performance later.
Here's what we think we know:
1. You're using a 12Kv NST, so assuming that you're powering it with no more than 120 volts, the peak output voltage will be around 17Kv (12,000 VRMS * 1.414).
2. You are using a total of 12 series-connected Panasonic ECWH capacitors rated at 1,600 VDC. 12 * 1,600 gives a "DC" voltage rating of 19,200 volts. Technically the AC voltage rating is much lower, and 19.2 Kv does not provide much safety margin relative to the 17 KvAC peak NST output, but Terry filters built using these parts have been used for years without this type of cap failure, so something else must be going on here.
3. You are using 14 series-connected Pasonic ERZV10D182 MOVs, with a clamping voltage of ~2970 volts. Those should limit maximum voltage to around 41.6Kv (14 * 2970), so they probably won't do much to protect your caps. (Now these MOVs may actually begin to conduct at something less than 2970 volts, so they may provide more protection than the numbers indicate. Let's assume that they don't.)
4. Steve's question about copper on the bottom of the PCBA triggers other questions. Let's assume that: a) your NST output voltage is NOT exceeding 17Kv, b) that your caps are truly rated at 1600V, c) your bypass caps are failing because of overvoltage. d) The MOVs are not doing anything to prevent overvoltage across a SINGLE CAP.
The only factor that comes to mind is that some of the caps are seeing more than their proportional share of the voltage across the string.
So, check the following: 1. Check that ALL your bleeder resistors are actuallly 10 meg ohms, and that you don't have some 1 meg or 100k ohm resistors mixed in.
2.Check that none of your caps are shorted (should be extremely unlikely, but should be checked).
3. Check that there is no evidence that your resistors are arcing from lead-to-lead, either across the body, or across your circuit board. If you used standard carbon film or metal oxide resistors, they are severely overvolted in this application, and any flux residue, sweaty-hand residue, or other contamination on the resistor bodies or on the PCBA can cause surface tracking. (Ideally, you should have used Vishay VR-37 series resistors, which are rated for much higher voltage than "standard" resistors, but they still need to be surgically clean.)
4. Check the bottom of the PCBA for any evidence of arcing, especially between the cut ends of the resistor and capacitor leads. If you bent these over, and cut the leads so they had sharp points on them, and left the leads "pointing" at each other, the sharp points will generate corona and facilitate breakdown of your air insulation, or facilitate surface tracking. If one or more resistors are low resistance value, or "short out" due to arcing, the remaining caps will see greatly increased voltage stress.
Look at all your resistors and the circuit board underneath them; surface tracking on the circuit board or across the resistor bodies will l leave some evidence, but you may need to look very closely.
Post a nice clear photo of the BOTTOM of your filter circuit board, with a close-up showing the solder joints between one resistor and one capacitor.
Also, use your multimeter to MEASURE the actual input voltage to your NST when the dial is set to "100".
hm, you make some very good points of the solder ends. My soldering joints prolly aren't the best cause when I first soldered them together I had soldered them wrong. and they were already cut, So I had to take some extra wire and solder them in between.
If you think that may be the cause I think Ill redo my terry filter. Ive posted some pics below.
What kind of caps do you recommend and where can I get them?
Is there anything better to mount the terry filter too than a perf board?
Also you mentioned that the voltage my NST is putting out is 17kv and my caps are rated at 19,200. Should i put more caps in there or what?
Im going to try edit that video to do a freeze frame and see If I can get a frame of the actual arc happening.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
IR -
Well, you didn't post a close-up photo of the connections at one capacitor/resistor pair as requested, but it sure looks like you've wired up the filter incorrectly. It's only the "end" caps in each string that failed, right?
Look carefully. You've hard-wired a direct short across all four of the "center" capacitors in each string, so it's only the outermost two capacitors that are even in the circuit. That means the NST's entire 17 Kv peak output voltage is being impressed across only 4 capacitors, which collectively are rated at only 6400 volts. No wonder they failed immediately!
Wire up the filter correctly, and see what happens.
The Panasonic capacitors you originally used are fine, just replace the damaged one with identical new parts.
Well, you didn't post a close-up photo of the connections at one capacitor/resistor pair as requested, but it sure looks like you've wired up the filter incorrectly. It's only the "end" caps in each string that failed, right?
Look carefully. You've hard-wired a direct short across all four of the "center" capacitors in each string, so it's only the outermost two capacitors that are even in the circuit. That means the NST's entire 17 Kv peak output voltage is being impressed across only 4 capacitors, which collectively are rated at only 6400 volts. No wonder they failed immediately!
Wire up the filter correctly, and see what happens.
The Panasonic capacitors you originally used are fine, just replace the damaged one with identical new parts.
Herr Zapp
Sorry about that. If you look at the last image and see the green wires. How the leads go up and look like a "U" shape, those are the resistors, they are soldered together with the 1600 caps. And then the green wires connect all the caps together. The MOV's are just connected to each other and them there all soldered together at the very ends.
Yes you are correct, it is just the end caps popping.
Your prolly right as that I did connect them wrong, and I'm not doubting you at all. I guess I'm just lost on how its done right?
Cause the terry fritz diagram it shows that the 1600v caps must be soldered together correct? and then the bleed resistors must be soldered basically in the dead center of each cap. Thats what Ive done, but how you explained it that only the end caps are blowing, and they are, makes it seem that I did wire this up wrong. =/
Do you maybe have a picture of yours or does anyone have a good picture of the underside of there terry filter so I can see how this is done right?
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
IR -
I don't know what schematic you used to build your Terry filter, but here's a link to Terry's original design:
Each capacitor is connected in PARALLEL with its bleeder resistor, and then each cap/resistor "module" is connected in SERIES with all the other cap/resistor "modules".
I think you just somehow misunderstood the schematic and for some reason added wires (the insulated green wires) on the underside of the board that completely shorted out the center four cap/resistor modules.
Look at the schematic in the link, and re-wire your filter accordingly. Replace ALL FOUR caps that were at the ends of your strings.
I made a picture below to see if this is how its suppose to be ran. Its only one side.
Cause I think i see what your saying, I took those green wires and connected both terminals of one cap together! Which from what your saying would short them out..... Do I need to replace all of those caps then? Or just the 4 like you just mentioned?
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First time Tesla builder, Terry Filter caps popping?
