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Registered Member #2038
Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60
My progress was not as good today as i had hoped, i set out this morning in the hope of getting the NST, some formers, end caps, materials for the top load and some magnet wire for the secondary. But when i got to the sign shop i was told that the guy i needed to see had the day off. i looked in several hardware stores for some tubing for the secondary former, there was plenty avaliable but i had to buy 6x3m lengths! not worth it when you only need a few feet of the stuff. at the electronics store the magnet wire was not in stock.
But i did manage to get my hands on some 50mm and 75mm PVC tube from a local plastic fabrications shop, they looked wuite busy at the time and i didnt want to push my luck so i didnt ask them for end caps, but the guy did say if i popped back any other time he could help with other bits of plastic. They have full CNC machining there so i might get them to make a base & primary holder if i make a MKII coil.
I decided to have a go winding the salvaged 29AWG wire on to the 50mm tube, but i couldnt find the bits i needed to make a winding table driven with power drill.
Whilst looking for parts to rotate the tube i found some aluminim tape and an unused ball stop for a water cylinder.
So i did manage to make the top load, the ball is about 4.6" dia and the tape was 50mm wide, so it was a bit tricky wrapping the ball without making small creases in the tape, it wasnt until i was applying the last strip of tape i thought of cutting the tape in half to make it 25mm and much easier to apply. But i didnt realy want to rip it all off so i'm going to see how it performs before i think about re foiling the ball.
I'm trying to figure out how to mount my top load to the top of the secondary, how solidly does it need to be atached? can anyone describe how they have done theirs?
Registered Member #1772
Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71
For my first setup, I just took a short piece of bare ground wire, put a hole in the tube near the top, and looped the ground wire through the hole and through the top of the tube to make a ring. I then soldered the magnet wire to the ring and just sat the topload on it. It was very simple and worked fine.
Registered Member #2038
Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60
Thanks oucivileng, I have spoken to a friend who has a lathe, and some bits of acrylic, he has offered to machine me a couple end caps which i intend to drill and tap so i can insert a length of threaded bar, i'll route the wire from the top of the coil round the outside.
i tried a different electronics store today and managed to get some 28AWG wire, they had 30AWG but the reel was too short for me to wind my 50mm coil so i'm now going to use the 75mm one, i also had a look for polyurethane laquer but could not find any, they did have acrlyic pcb laquer but i didnt buy any as i wasn't sure it was suitable.
Is the type of laquer used important? I've got loads of acrylic automotive laquer, would that do the job?
I spent a couple of hours winding my secondary coil this afternoon, i decided to hand wind it as i couldn't find a simple way of turning the former. i actually found hand winding the coil fairly easy, although my hands ached after a while.
I've decided not to use the 14AWG enameled copper for the primary, instead i am going to use some 5/16" copper tube, this way i can make a tap at any point along the coil for more accuracy when tuning and i think it will look less messy.
Does the primary coil get very hot? i'm thinking of mounting it on wooden struts is it likeley to be a fire hazard?
Registered Member #1083
Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256
Try to find some polyurethane varnish, oil based would be the best, but I've gotten away with using water base. You should be able to find it at your hardware store next to the wood varnishes and stains.
If you want, you can buy some 2 part epoxy, commonly used to coat furniture and tabletops. It would be in the same section. The epoxy coating is better in the sense that it only takes 1 coat, however it is a bit more tricky to apply, and if you mess up you have to sand it down and apply another coat of the expensive stuff. Polyurethane varnish is more forgiving, because if you mess up, just sand the layer off and continue adding coats. Plus it's a bit cheaper.
Registered Member #2038
Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60
Cool i'll have a look for some polyurethane varnish tomorrow.
I've been thinking about my tank capacitor, i'd rather not mess around rolling my own or making a SWC so i think i will go with the MMC option.
WinTesla says the value should be 0.0227uf for a 7kv 50ma NST, i have read that it is wise to use a larger than resonance capacitor, about twice the value of the suggested capacitor.
I've assumed that the peak voltage is about twice the rated voltage is this correct? if so i've come up with the following configurations
A single string of 8x 2kv 47nf = 16kv 47nf or two parallel strings of 8x 2kv 22nf = 16kv 44nf does this seem right?
Is there any advantage of using smaller value caps in parallel to get the same final capacitance?
Registered Member #1904
Joined: Sat Jan 03 2009, 02:40AM
Location: Pittsburgh
Posts: 14
As for the primary coil, it doesn't get terribly warm, so you can definitely use wood on it. Make sure you coat it and dry it well, though, to prevent any problems with accidental grounding. That could be a fire hazard. For creating primary coils, high-density polyethylene (HDPE) works very well: it cuts easily, doesn't conduct, and is easy to find. Cheapo plastic cutting boards served me well for my primary. As for the caps, I made the same mistake as you by going with metal film capacitors. The film inside them typically doesn't hold up under high voltages, and other members of the site have found that out the hard (and expensive) way already. Instead, try the Cornell Dublier 940c series. It's metallized, and is very reliable. I used the .15 nf capacitors rated at 2kv, ten in a series. Your transformer (7500 volts @ 50 mA) will require around 0.029 - 0.030 uf if you're running at 50 hz, or 0.025 uf if running at 60 hz. Not too sure about normal wiring in the UK.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
Ryan Parle wrote ...
Cool i'll have a look for some polyurethane varnish tomorrow.
I've been thinking about my tank capacitor, i'd rather not mess around rolling my own or making a SWC so i think i will go with the MMC option.
WinTesla says the value should be 0.0227uf for a 7kv 50ma NST, i have read that it is wise to use a larger than resonance capacitor, about twice the value of the suggested capacitor.
I've assumed that the peak voltage is about twice the rated voltage is this correct? if so i've come up with the following configurations
A single string of 8x 2kv 47nf = 16kv 47nf or two parallel strings of 8x 2kv 22nf = 16kv 44nf does this seem right?
Is there any advantage of using smaller value caps in parallel to get the same final capacitance?
The 47nf caps are Vishay MKP1841-347/205-J
The 22nf caps are Epcos B32654A2223K
If I Recall Correctly, the peak voltage is not double the voltage in sine wave AC applications, as the voltage given is RMS, or Root mean Square - so check to see if that is what is listed, and if it is you can find the peak voltage by multiplying the RMS voltage by the Square Root of Two, or (RMS*1.414) - this gives you the peak voltage, and which is doubled if you are looking for peak to Peak, but I'm pretty sure you just need the peak voltage
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Actually, the 940C series is vulnerable to failing at the leads. The 942C series is what should be used. Though Anon01 had good results with the 940C and his 10kw pig coil. I would still go with the 942C series though, they are the proven tesla coil capacitors.
Registered Member #2038
Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60
Thanks for the advice on the capacitors, i'll see if i can find a suplier with stock in the UK. my initial search found that Farnell sell the Cornell Dublier brand capacitors, but they are US stock and there is a failry hefty charge to buy them here.
EDIT: I've had a good look around for the Cornell Dublier caps and haven't had a lot of luck, digikey have a minimum order of 50 units and i cant really afford that right now.
Diarrg: I just had another look at the datasheets for the caps i was thinking of trying, they are both described as metalized film and not metal film. are you sure they wont be any good?
The coil is progressing quite nicely, i've spent the last couple of days making the base for the primary, i found some nice oak for the primary suports but had to use MDF for the base as i didnt have enough oak to make a big enough sheet.
I had a quick go at forming the primary coil last night but i found it very tricky getting the copper to stay in place, and also found it tricky to get a nice smooth curve, anyone got any hints on how to wind the primary? some of the pictures of peoples coils have some very nice looking primary coils, i just cant figure out how you've managed such smooth bends!
EDIT: I've now almost finished the primary coil, its not as neat as i had hoped for but it looks ok, for a while i struggled forming the coil as i had no way of clamping it to the primary supports. then i spotted a roll of high breaking strain fishing line, i drilled a load of holes in the primary supports and used the fishing line to tie the copper tube to the support. I also got two coats of Polyeurethane varnish on my secondary, i might give it a third coat tomorrow if it needs it.
I noticed that the remaining core left when using a 76mm hole cutter is a perfect fit inside my secondary former, so it should be easier to make end caps now.
Registered Member #2038
Joined: Fri Mar 20 2009, 03:39PM
Location: Bristol Uk
Posts: 60
Sorry for the double post, my intention is not to bump my thread, i just wanted to update my progress with the coil and to show you all some pictures of it all.
The secondary coil is now complete with end caps and the top load fitted, it can be seen here just wedged in place in the primary/base
The primary and top of the base are also complete although i need to chop off the end of the coil, tidy up the fishing line that i have used to secure the coil to the supports and chop the excess mdf off the end of the sheet
I also met up with the chap from the sign shop and picked up 2 NST's.
I got a 10kv 50ma unit made by Tunewell Transformers, here are a few images; With lid: Under the lid: Ratings plate:
And a 10kv 37ma resinblock unit: With lid: Lid removed:http://www.ryan-
parle.pwp.blueyonder.co.uk/tesla/
IMAG0065.jpg Earth leakage switch: Ratings plate:
I am not sure about the Resinblock unit, it looks a bit modern although the guy said he doesnt think it is of the solid state high frequency type, it feels pretty heavy too, it also has a few safety systems on it, such as a "switch bar" mounted on the lid that disconnects the 240vac supply when the lid is removed and the earth leakage switch. any of you seen one of these before?
I've been trying to work out if either of the NST's are center earth tapped on the secondarys with my multimeter, The tunewell unit seems to be open circuit although i'm not sure if my multimeter is capable of such high resitances?
The Resinblock seems to be center earth tapped and has 2 earth terminals, although the terminal that i would have thought to be the 240v earth seems to be the center tapped terminal.
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First Tesla Coil
