Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Tue Jul 07 2015, 02:35AMI just finished my TC. I have a 240W OBIT, according to the JavaTC simulator I should be getting 24" sparcs, but instead it doesn't even break out at the strongest tuning point, and I get about 4" sparks using the ground wire. I am using body builder whey bottles for my salt water caps. The SG arc is about the loudest I have heard, so plenty of energy there. This is my first TC, but I have helped a couple of students tune their TC's and get them working. I had a student with a smallish NST get his to break out with salt water caps. Is the efficiency loss with salt water caps so bad that it would shrink them all the way down to wimpy 4" sparks that don't even break out with a 240VA xformer?
update: it is breaking out, but I had to wait until it was very dark to see it -- little 1.5" streamers.
Thanks,
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Part Scavenger, Wed Jul 08 2015, 07:58PM
I see a lot of things going on here, maybe I can help. First off, the JavaTC simulator assumes you are using manufactured capacitors in an MMC. You won't get that out of saltwater caps. I'd be pretty happy with 10-12" sparks with saltwater caps.
POWER SUPPLY:
1. Knowing the output voltage of the OBIT would be helpful.
2. OBIT transformers usually have low voltage output. Anything under 8kV I wouldn't even bother with. Invest in a MOT stack or a 12kV or higher NST. I won't go into all the reasons, just trust me it will make your life easier in so many ways.
CAPACITORS:
1. Your caps will be pretty inefficient built that way. First, they're too big physically. Imagine the energy having to propagate through all that saltwater and surface area, and think of ways to improve that. Also, that black plastic needs to get away from everything tesla. It's slightly conductive at high voltages and it traps a lot of RF energy.
The way you're using capacitors, it's much better to have many smaller ones in parallel, than two large ones. Remember putting capacitors in parallel maximizes their value, but inductance and resistances in parallel are minimized! This is exactly what we want.
If I were designing the capacitor, I'd first determine how much capacitor I needed. Test the resistance of the secondary of the transformer, and then C = .0833 / 4R should get you pretty close. JavaTC should have a capacitor matching tool also.
Then I would make the salt water caps out of beer bottles, 20-30Oz and put them in parallel until I got the capacitor bank size I need. Brown glass is better than clear, green, and blue in my experience - I have tested brown 20Oz and 40Oz budweizer glass to 40kV+. If you don't have a way to test the capacitance (an LCR meter or Oscilloscope), Radioshack has their DMM's on sale for $35 right now, and the Harbor Freight http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html works surprisingly well. If you're just wanting to guess, I would start with 6 20oz beer bottles and add subtract from there.
Watch for electrode corrosion inside the beer bottles. Once they get dirty you lose performance. Make the electrodes as wide as they will fit in the mouth of the bottle, and 1.5" from the bottom of the glass.
Make sure your salt water is saturated by mixing until it starts to fall out, then discarding the fall out. Then put 1/2" oil over the top of the salt water. This will keep the water from evaporating.
When putting aluminum foil on the outside, use spray contact cement and a wallpaper roller.
Cover the top edge of the foil with electrical tape to minimize corona loss.
Bottom line, think about ways to decrease resistance and inductance.
WIRING:
Shorten EVERYTHING!!!! Nice and neat is imperative when it comes to performance. Alligator clips are the devil.
Run the coil, shut it off, and check for hot spots. These are areas you need to improve.
Use multi stranded wire for everything in the tank circuit, preferably 12AWG or greater.
SPARK GAP:
Try cooling your spark gap. Start with a muffin fan or something. If the air in the spark gap is too hot, the gap will stay on too long, and transfer energy back into the primary circuit instead of trapping it in the secondary circuit. This is the primary reason I won't use a transformer under 8kV.
TOPLOAD:
Try using a smaller topload, or rather one with equal volume but smaller cross-section. This is why the toroid is so popular. Alternatively use a breakout point, but that's no fun.. :)
Also, it could be argued you could increase your coupling by taking out the first coil of the primary, and dropping the secondary down into the primary, but I would definitely do the other things first.
Give that a try. Start with the wiring and capacitors and I'll bet you have much better success in no time.
Part Scavenger, Wed Jul 08 2015, 07:58PM
I see a lot of things going on here, maybe I can help. First off, the JavaTC simulator assumes you are using manufactured capacitors in an MMC. You won't get that out of saltwater caps. I'd be pretty happy with 10-12" sparks with saltwater caps.
POWER SUPPLY:
1. Knowing the output voltage of the OBIT would be helpful.
2. OBIT transformers usually have low voltage output. Anything under 8kV I wouldn't even bother with. Invest in a MOT stack or a 12kV or higher NST. I won't go into all the reasons, just trust me it will make your life easier in so many ways.
CAPACITORS:
1. Your caps will be pretty inefficient built that way. First, they're too big physically. Imagine the energy having to propagate through all that saltwater and surface area, and think of ways to improve that. Also, that black plastic needs to get away from everything tesla. It's slightly conductive at high voltages and it traps a lot of RF energy.
The way you're using capacitors, it's much better to have many smaller ones in parallel, than two large ones. Remember putting capacitors in parallel maximizes their value, but inductance and resistances in parallel are minimized! This is exactly what we want.
If I were designing the capacitor, I'd first determine how much capacitor I needed. Test the resistance of the secondary of the transformer, and then C = .0833 / 4R should get you pretty close. JavaTC should have a capacitor matching tool also.
Then I would make the salt water caps out of beer bottles, 20-30Oz and put them in parallel until I got the capacitor bank size I need. Brown glass is better than clear, green, and blue in my experience - I have tested brown 20Oz and 40Oz budweizer glass to 40kV+. If you don't have a way to test the capacitance (an LCR meter or Oscilloscope), Radioshack has their DMM's on sale for $35 right now, and the Harbor Freight http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html works surprisingly well. If you're just wanting to guess, I would start with 6 20oz beer bottles and add subtract from there.
Watch for electrode corrosion inside the beer bottles. Once they get dirty you lose performance. Make the electrodes as wide as they will fit in the mouth of the bottle, and 1.5" from the bottom of the glass.
Make sure your salt water is saturated by mixing until it starts to fall out, then discarding the fall out. Then put 1/2" oil over the top of the salt water. This will keep the water from evaporating.
When putting aluminum foil on the outside, use spray contact cement and a wallpaper roller.
Cover the top edge of the foil with electrical tape to minimize corona loss.
Bottom line, think about ways to decrease resistance and inductance.
WIRING:
Shorten EVERYTHING!!!! Nice and neat is imperative when it comes to performance. Alligator clips are the devil.
Run the coil, shut it off, and check for hot spots. These are areas you need to improve.
Use multi stranded wire for everything in the tank circuit, preferably 12AWG or greater.
SPARK GAP:
Try cooling your spark gap. Start with a muffin fan or something. If the air in the spark gap is too hot, the gap will stay on too long, and transfer energy back into the primary circuit instead of trapping it in the secondary circuit. This is the primary reason I won't use a transformer under 8kV.
TOPLOAD:
Try using a smaller topload, or rather one with equal volume but smaller cross-section. This is why the toroid is so popular. Alternatively use a breakout point, but that's no fun.. :)
Also, it could be argued you could increase your coupling by taking out the first coil of the primary, and dropping the secondary down into the primary, but I would definitely do the other things first.
Give that a try. Start with the wiring and capacitors and I'll bet you have much better success in no time.
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Fri Jul 10 2015, 06:51PM
Thanks, Part scavenger. I have some 40kV caps coming from China that total the 6nF that the JavaTC spec calls for. It would be nice to play with some better caps in the mean time, so I will Freecycle for some beer bottles. It did cross my mind that the large volume bottles would cause an issue. I will work on it, as I am not getting anywhere near 10" sparks. Also, my OBIT is as beefy as they come. 10kV at 23mA, yes not huge, but it is not that big of a coil, but that is big for an OBIT.
Also, my tank circuit is with heavy #10 and no gator clips accept for the tap on the primary. The two gator clips coming off the transformer are there because that is not where the high current is present. If you still think this is an issue for another reason unknown to me, let me know. I am now running pretty low on cash from the project.
For the torroid, do you think I should use 3" ducting, or purchase one of these when I get the funds:
Thanks,
Chris Maness
Chris Maness, Fri Jul 10 2015, 06:51PM
Thanks, Part scavenger. I have some 40kV caps coming from China that total the 6nF that the JavaTC spec calls for. It would be nice to play with some better caps in the mean time, so I will Freecycle for some beer bottles. It did cross my mind that the large volume bottles would cause an issue. I will work on it, as I am not getting anywhere near 10" sparks. Also, my OBIT is as beefy as they come. 10kV at 23mA, yes not huge, but it is not that big of a coil, but that is big for an OBIT.
Also, my tank circuit is with heavy #10 and no gator clips accept for the tap on the primary. The two gator clips coming off the transformer are there because that is not where the high current is present. If you still think this is an issue for another reason unknown to me, let me know. I am now running pretty low on cash from the project.
For the torroid, do you think I should use 3" ducting, or purchase one of these when I get the funds:
Thanks,
Chris Maness
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Part Scavenger, Sun Jul 12 2015, 12:43PM
That OBIT should work fine. I would definitely get rid of the clips coming off the transformer and shorten all wires. No professional torpid necessary, I would use a ducting diameter about the size of the toroid. If possible. I still think your biggest problems are the caps and a hot spark gap.
Part Scavenger, Sun Jul 12 2015, 12:43PM
That OBIT should work fine. I would definitely get rid of the clips coming off the transformer and shorten all wires. No professional torpid necessary, I would use a ducting diameter about the size of the toroid. If possible. I still think your biggest problems are the caps and a hot spark gap.
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Sun Jul 12 2015, 02:07PM
Yep, I agree. According to the tracking on the package, my caps are in LA right now, so any day.
Thanks,
Chris
Chris Maness, Sun Jul 12 2015, 02:07PM
Yep, I agree. According to the tracking on the package, my caps are in LA right now, so any day.
Thanks,
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Mon Jul 13 2015, 06:28AM
Ok, I out of shear curiosity. I tried the beer bottle caps even though I have some commercial caps on the way. It improved the coil a tiny bit. I am getting about a 15% improvement on spark length. Still pretty feeble break out without bringing the ground wire near the top load. I am getting a solid 4" from it to the gnd. Should be better tho.
Chris
Chris Maness, Mon Jul 13 2015, 06:28AM
Ok, I out of shear curiosity. I tried the beer bottle caps even though I have some commercial caps on the way. It improved the coil a tiny bit. I am getting about a 15% improvement on spark length. Still pretty feeble break out without bringing the ground wire near the top load. I am getting a solid 4" from it to the gnd. Should be better tho.
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Part Scavenger, Mon Jul 13 2015, 09:55PM
Pics?
Part Scavenger, Mon Jul 13 2015, 09:55PM
Pics?
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Tue Jul 14 2015, 12:51AM
Point is moot now. My commercial caps are now in place. I got about a 20% boost from the commercial caps. I will post pics later.
Chris
Chris Maness, Tue Jul 14 2015, 12:51AM
Point is moot now. My commercial caps are now in place. I got about a 20% boost from the commercial caps. I will post pics later.
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Tue Jul 14 2015, 04:58AM
It really lit up when I spaced the gap just a hair wider. My new cap bank died. I need to use different caps. 40kV my butt. I put the beer bottles back on for now, not too bad. Have a look:
What is a really reliable and efficient MMC capacitor to use?
Chris
Chris Maness, Tue Jul 14 2015, 04:58AM
It really lit up when I spaced the gap just a hair wider. My new cap bank died. I need to use different caps. 40kV my butt. I put the beer bottles back on for now, not too bad. Have a look:
What is a really reliable and efficient MMC capacitor to use?
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
GrantX, Tue Jul 14 2015, 05:18AM
Everybody's favourite capacitors for spark gap coils are the Cornel Dubilier 942C. Unfortunately, they are rather expensive and you'll need at least 20 of them!
GrantX, Tue Jul 14 2015, 05:18AM
Chris Maness wrote ...
It really lit up when I spaced the gap just a hair wider. My new cap bank died. I need to use different caps. 40kV my butt. I put the beer bottles back on for now, not too bad. Have a look:
What is a really reliable and efficient MMC capacitor to use?
Chris
What commercial capacitors did you use (pics or part number and manufacturer) and how was the bank connected (how many in series or parallel)?It really lit up when I spaced the gap just a hair wider. My new cap bank died. I need to use different caps. 40kV my butt. I put the beer bottles back on for now, not too bad. Have a look:
What is a really reliable and efficient MMC capacitor to use?
Chris
Everybody's favourite capacitors for spark gap coils are the Cornel Dubilier 942C. Unfortunately, they are rather expensive and you'll need at least 20 of them!
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Tue Jul 14 2015, 06:45AM
Here they are:
I used 5 in parallel.
Thanks,
Chris
Chris Maness, Tue Jul 14 2015, 06:45AM
Here they are:
I used 5 in parallel.
Thanks,
Chris
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
GrantX, Tue Jul 14 2015, 12:45PM
Polypropylene film/foil capacitors, like the CD 942C are one of the best choices. The thick foil and low loss dielectric help keep the capacitors from overheating under the large RF currents, and lots of small PP caps are usually cheaper than a couple of giant high voltage RF ceramic/mica capacitors.
GrantX, Tue Jul 14 2015, 12:45PM
Chris Maness wrote ...
Here they are:
I used 5 in parallel.
Thanks,
Chris
Ahhhh, there's your problem. Those polystyrene capacitors aren't really suitable as SGTC tank capacitors. After a brief search I saw a few reports on Instructables stating that the cheap polystyrene capacitors from Chinese ebay stores are hopeless and die quickly. I purchased a couple of them years ago, one has lasted (while being operated at only 10% it's max voltage rating), but the other died within minutes and wasn't even used for pulsed power stuff like a tank capacitor.Here they are:
I used 5 in parallel.
Thanks,
Chris
Polypropylene film/foil capacitors, like the CD 942C are one of the best choices. The thick foil and low loss dielectric help keep the capacitors from overheating under the large RF currents, and lots of small PP caps are usually cheaper than a couple of giant high voltage RF ceramic/mica capacitors.
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Mads Barnkob, Tue Jul 14 2015, 01:03PM
You should use a MMC calculator and here is a list of proven capacitors:
Mads Barnkob, Tue Jul 14 2015, 01:03PM
You should use a MMC calculator
and here is a list of proven capacitors: Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Wed Jul 15 2015, 05:32PM
Back to the beer bottles, and yes the hair dryer in cold air mode through the spark gap makes for a much steadier discharge on top. Man is she loud. I made the mistake of playing with it the first night without hearing protection, and I had tinnitus that night.
I am going to wait on the expensive caps, the bottles will have to do for now as I am already in this thing for a fairly hefty sum. I am brainstorming to figure out a way to make my beer bottles road worthy to take to summer camp. The rangers are going to love me :D
Here is the set up now after the polystyrene caps failed:
Regards,
Chris KQ6UP
Chris Maness, Wed Jul 15 2015, 05:32PM
Back to the beer bottles, and yes the hair dryer in cold air mode through the spark gap makes for a much steadier discharge on top. Man is she loud. I made the mistake of playing with it the first night without hearing protection, and I had tinnitus that night.
I am going to wait on the expensive caps, the bottles will have to do for now as I am already in this thing for a fairly hefty sum. I am brainstorming to figure out a way to make my beer bottles road worthy to take to summer camp. The rangers are going to love me :D
Here is the set up now after the polystyrene caps failed:
Regards,
Chris KQ6UP
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Part Scavenger, Sat Jul 18 2015, 04:12PM
Cool! Glad to hear it's working better! I used to keep my bottle caps in something like a coca-cola box, and I would just pull the electrodes out and cap them when they traveled.
Part Scavenger, Sat Jul 18 2015, 04:12PM
Cool! Glad to hear it's working better! I used to keep my bottle caps in something like a coca-cola box, and I would just pull the electrodes out and cap them when they traveled.
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Sat Jul 18 2015, 04:41PM
I am going to change over to a Torroid with a break out on top. I get a lot of leaky corona out of the rims of the two bowls. Although it looks cool in the dark, I think I would rather have longer streamers.
Chris Maness, Sat Jul 18 2015, 04:41PM
I am going to change over to a Torroid with a break out on top. I get a lot of leaky corona out of the rims of the two bowls. Although it looks cool in the dark, I think I would rather have longer streamers.
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Mon Jul 27 2015, 10:17PM
I just added the toroid to my bowls, and I am now getting really nice 8-10" streamers. It is working pretty good now. I just need to get a fan that shoots as much air as my cold blast hairdryer that I have rigged up. I am still stuck on salt water caps as I am very much over budget for the month. I will be going to camp with the salt water bottles.
Here is the pic:
Thanks for the help guys,
Chris M. GTHS Physics/Chemistry
Chris Maness, Mon Jul 27 2015, 10:17PM
I just added the toroid to my bowls, and I am now getting really nice 8-10" streamers. It is working pretty good now. I just need to get a fan that shoots as much air as my cold blast hairdryer that I have rigged up. I am still stuck on salt water caps as I am very much over budget for the month. I will be going to camp with the salt water bottles.
Here is the pic:
Thanks for the help guys,
Chris M. GTHS Physics/Chemistry
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Ash Small, Tue Jul 28 2015, 01:17AM
It's good to see an SGTC with saltwater caps for a change.
Please post more details of your capacitors, detailed description of manufacture, etc. When done properly these things rock, and they cost next to nothing
Ash Small, Tue Jul 28 2015, 01:17AM
It's good to see an SGTC with saltwater caps for a change.
Please post more details of your capacitors, detailed description of manufacture, etc. When done properly these things rock, and they cost next to nothing
Re: Spark Length with Salt Water Caps vs. Factory Made Caps?
Chris Maness, Tue Jul 28 2015, 02:44AM
I just used regular brown beer bottles. I Elmer glued the tin foil to the outside, and wrapped gaffer's tape around the top to prevent corona. They have a about 3' of #12 solid wire coiled in the bottle. The water is saturated and then some. It topped off with cooking oil.
Here is the video of my new toroid in action:
Regards,
Chris KQ6UP
Chris Maness, Tue Jul 28 2015, 02:44AM
I just used regular brown beer bottles. I Elmer glued the tin foil to the outside, and wrapped gaffer's tape around the top to prevent corona. They have a about 3' of #12 solid wire coiled in the bottle. The water is saturated and then some. It topped off with cooking oil.
Here is the video of my new toroid in action:
Regards,
Chris KQ6UP
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