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Any advice with this schematic

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Neukyhm

Sun Jul 17 2016, 05:50PM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
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Posts: 15

Hi, I'm new here, I'm looking for advice with a tesla coil. Here is the schematic.

I will use two MOTs, expecting to achieve the same performance as redruM69 with his TC

Note: My secondary and toroid are much bigger. I will use AWG27. How many turns, 1200? would 1800 be better? The tube's diameter of the secondary is 11 cm.

I'm not sure if the spark gap will be static (w/ fan) or rotatory, tell me what's better. Also, I don't know the specs of the capacitor bank. I already have these
Can I make the capacitor bank with those capacitors? What would be the total microfarads needed?
And about the design, I have some questions: is it better to have the spark gap and capacitor bank that way or switched? Does the end of the secondary go to the same earth as the mains? because I think It's not a good idea to connect a high voltage transformer to the same earth where you have an expensive PC. You know, RAMs don't like high voltage.

Thank you in advance.

Neukyhm

Tue Jul 26 2016, 05:11PM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
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Posts: 15

I will begin to build it soon, please 4hv users say something. I have used JavaTC and it says I sould use a 20nf capacitor with the primary, so I have planned to use two of these:

Benjamin

Tue Jul 26 2016, 07:13PM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

You should match the capacitor size to the power supply first, 20 nf is way too small for 2 mots without a doubler. You would need more like 100-200 nf to achieve 5 foot sparks. However, my rotary spark gap dual mot coil uses a simple half wave voltage doubler made from 4 microwave diodes and 2 microwave capacitors feeding into a 50 nf cap bank and it has achieved a 5 foot strike from only a 3.5 by 20 inch coil! I suggest that you look through this site

and use this design

It works very well! Also, the ceramic capacitors Cf are unnecessary but use four diodes.

Neukyhm

Tue Jul 26 2016, 08:05PM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
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Posts: 15

Benjamin wrote ...

You should match the capacitor size to the power supply first, 20 nf is way too small for 2 mots without a doubler. You would need more like 100-200 nf to achieve 5 foot sparks.

So can I use a voltage doubler and two or three of these as main capacitor?

I'm asking this because I see people building big and complex MMC with a big number of capacitors to achieve for example 40nf when they could be using a capacitor like that one.

Benjamin

Tue Jul 26 2016, 10:01PM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

First off, I'm no expert in making MMC's so hopefully someone else will chime in, but I'm not sure if those capacitors are good for a tesla coil. good caps have a metallized polypropylene dielectric and a very high pulse current rating like the CDE 942C20P15K caps that everyone uses which are 0.15uf and 2000V. If you can get those ones you're in good shape but they're pretty pricey. I use 2 strings of 6 of them which is pushing it a little (not enough strings in parallel to handle the current and they get warm after a while) so I'm probably going to upgrade to 3 strings of 8 soon. Anyways there's not much information about those capacitors and just because they say tesla coil does not mean that they are good for a coil. maybe someone else knows more about those caps but if it where me I would save up and get the good ones.

Neukyhm

Thu Aug 11 2016, 06:41AM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
Location:
Posts: 15

Thanks Benjamin, finally I will use two strings of 6x 942C20P15K-F caps, for a total 50nf at 12 KV, working with two MOTs in stack. Maybe one day I will upgrade it with a voltage doubler but for now just the MOTs.

Note: Benjamin, what about using a heatsink with the caps?

Benjamin

Tue Aug 16 2016, 03:42AM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

Using a heat sink will do absolutely nothing, the best thing that you can do is have lots of airflow (but you don't need a fan, I don't have one) and keep the runtime down to less than a few minutes and it will be perfectly fine. Lastly you don't seem understand how much of a difference the doubler will make, it is nothing vs everything. The only way that the one in that video works without a doubler is with a massive (read expensive) capacitor bank and a very heavy duty high speed rotary gap. with a doubler you can get good performance with just a sucker gap and all you need to make it is two microwave caps (witch you should have already) and some diodes.

Neukyhm

Sat Aug 20 2016, 01:43AM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
Location:
Posts: 15

But Benjamin, I thought that the primary was supposed to work with as low voltage but as high intensity you can get from the MOTs, mostly because of Faraday's law.

Benjamin

Mon Aug 22 2016, 05:14PM

Registered Member #54655 Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82

Yes, but to get a tesla coil to work properly with low voltage and high current you need a very beefy rotary spark gap to quench the spark. It can work but it is very hard to do. What are you using for a spark gap?

Neukyhm

Mon Aug 22 2016, 07:13PM

Registered Member #57520 Joined: Thu Oct 15 2015, 11:21PM
Location:
Posts: 15

I'm planning to use this:

I will need some tungsten electrodes, and maybe a variac to change the speed. I'm still looking for other motors. I have a big one I disassembled from a shredder:

It says AC230V/50Hz=>DC. I disassembled it too and I found that it has brushes, so it must be a DC motor. I still could not find a rectifier circuit inside the shredder.

Edit: can it be an AC motor with brushes? Now I'm not so sure since I have seen that the other one from ebay has brushes too, and it is AC. I'm not an expert on motors.

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