Any advice with this schematic
Neukyhm, Sun Jul 17 2016, 05:50PMHi, 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.
Re: Any advice with this schematic
Neukyhm, Tue Jul 26 2016, 05:11PM
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:
Neukyhm, Tue Jul 26 2016, 05:11PM
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:
Re: Any advice with this schematic
Benjamin, Tue Jul 26 2016, 07:13PM
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.
Benjamin, Tue Jul 26 2016, 07:13PM
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.Re: Any advice with this schematic
Neukyhm, Tue Jul 26 2016, 08:05PM
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.
Neukyhm, Tue Jul 26 2016, 08:05PM
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? 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.
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.
Re: Any advice with this schematic
Benjamin, Tue Jul 26 2016, 10:01PM
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.
Benjamin, Tue Jul 26 2016, 10:01PM
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.
Re: Any advice with this schematic
Neukyhm, Thu Aug 11 2016, 06:41AM
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?
Neukyhm, Thu Aug 11 2016, 06:41AM
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?
Re: Any advice with this schematic
Benjamin, Tue Aug 16 2016, 03:42AM
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.
Benjamin, Tue Aug 16 2016, 03:42AM
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.
Re: Any advice with this schematic
Neukyhm, Sat Aug 20 2016, 01:43AM
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.
Neukyhm, Sat Aug 20 2016, 01:43AM
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.
Re: Any advice with this schematic
Benjamin, Mon Aug 22 2016, 05:14PM
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?
Benjamin, Mon Aug 22 2016, 05:14PM
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?
Re: Any advice with this schematic
Neukyhm, Mon Aug 22 2016, 07:13PM
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.
Neukyhm, Mon Aug 22 2016, 07:13PM
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.
Re: Any advice with this schematic
Benjamin, Tue Aug 23 2016, 12:02AM
You could try a propeller gap design where the the tungsten rod is pressed into a polyethylene rotor on the motor shaft and multiple stationary electrodes like this It is quite easy to build compared to other designs. Also you will want to aim for at least 300-400 BPS (breaks per second) for the gap. I don't see why you don't want to use the doubler, it will improve output and reduce spark gap heating, and I've never had any problems with it.
Benjamin, Tue Aug 23 2016, 12:02AM
You could try a propeller gap design where the the tungsten rod is pressed into a polyethylene rotor on the motor shaft and multiple stationary electrodes like this
It is quite easy to build compared to other designs. Also you will want to aim for at least 300-400 BPS (breaks per second) for the gap. I don't see why you don't want to use the doubler, it will improve output and reduce spark gap heating, and I've never had any problems with it.Re: Any advice with this schematic
Neukyhm, Tue Aug 23 2016, 12:39AM
I agree, that's a very simple design, I will go for it. And Benjamin, I don't like the idea of a doubler because of the diodes. I have read that they become hot and they can explode, and I don't like silicon for high power things lol. Also, using a doubler will turn the coil to DC.
Neukyhm, Tue Aug 23 2016, 12:39AM
I agree, that's a very simple design, I will go for it. And Benjamin, I don't like the idea of a doubler because of the diodes. I have read that they become hot and they can explode, and I don't like silicon for high power things lol. Also, using a doubler will turn the coil to DC.
Re: Any advice with this schematic
Benjamin, Tue Aug 23 2016, 01:35AM
I have also read that they can become hot and unreliable but this has not been the case in my experience. The trick is to make sure that the diode string is rated for at least double the peak supply voltage because of high voltage spikes coming from the tank circuit. These are what cause the diode heating. I use four microwave diodes in the string and it barely gets warm at all. With your rotary gap, DC will be fine and because it is a half wave rectified instead of full wave rectified power supply, no charging reactor is needed. All you have to do is add the diode string and 2 caps and you're done!
Benjamin, Tue Aug 23 2016, 01:35AM
I have also read that they can become hot and unreliable but this has not been the case in my experience. The trick is to make sure that the diode string is rated for at least double the peak supply voltage because of high voltage spikes coming from the tank circuit. These are what cause the diode heating. I use four microwave diodes in the string and it barely gets warm at all. With your rotary gap, DC will be fine and because it is a half wave rectified instead of full wave rectified power supply, no charging reactor is needed. All you have to do is add the diode string and 2 caps and you're done!
Re: Any advice with this schematic
Neukyhm, Tue Aug 23 2016, 02:05AM
Ok Benjamin, I will do this: I will build the coil without doubler, then see how it works, and try the doubler later. I still have some questions about the mots. They seem to have the secondary welded to the core so, should I remove it and weld it to a cable? or is it better to have it welded to the core and then weld a cable to it?
And another question, I have seen many people welding a ground to the middle connection of the MOTs, and that's something I don't understand. I'm a physics student, not an electric engineering one, so I don't know the reason for that. (is that ground the same ground as the mains?)
I have been reading tesla coil stuff for two years, I wanted to have as much information I could before starting to build one, but I still have a few questions without answer like that one haha.
PS: thank you very much Benjamin, without you, this thread would be empty like my wallet.
Neukyhm, Tue Aug 23 2016, 02:05AM
Ok Benjamin, I will do this: I will build the coil without doubler, then see how it works, and try the doubler later. I still have some questions about the mots. They seem to have the secondary welded to the core so, should I remove it and weld it to a cable? or is it better to have it welded to the core and then weld a cable to it?
And another question, I have seen many people welding a ground to the middle connection of the MOTs, and that's something I don't understand. I'm a physics student, not an electric engineering one, so I don't know the reason for that. (is that ground the same ground as the mains?)
I have been reading tesla coil stuff for two years, I wanted to have as much information I could before starting to build one, but I still have a few questions without answer like that one haha.
PS: thank you very much Benjamin, without you, this thread would be empty like my wallet.
Re: Any advice with this schematic
Benjamin, Tue Aug 23 2016, 03:50AM
Don't remove the middle core connection, that's only necessary when you have more than four mots in series which you don't have. Connect the cores together and make sure the mots are in phase by flipping on of the primaries if you don't get any output. Also put one capacitor on each hv terminal when using a doubler. You don't have to ground the cores but I do just to be safe. In the microwave one side of the secondary is grounded to the core and the mains ground, you are just adding a second transformer to effectively make a center tapped one. I just bolt the mains ground to both cores. Also how big are your secondary and topload going to be?
Benjamin, Tue Aug 23 2016, 03:50AM
Don't remove the middle core connection, that's only necessary when you have more than four mots in series which you don't have. Connect the cores together and make sure the mots are in phase by flipping on of the primaries if you don't get any output. Also put one capacitor on each hv terminal when using a doubler. You don't have to ground the cores but I do just to be safe. In the microwave one side of the secondary is grounded to the core and the mains ground, you are just adding a second transformer to effectively make a center tapped one. I just bolt the mains ground to both cores. Also how big are your secondary and topload going to be?
Re: Any advice with this schematic
Neukyhm, Tue Aug 23 2016, 03:00PM
The secondary is big, like 60cm of PVC, diameter is 11cm. I'm using AWG27, wich is very very thin, I expect my secondary to have a lot of turns because of that. The topload is a thoroid and it is already built. It's big, 45/75 cm of inner/outer diameter.
Neukyhm, Tue Aug 23 2016, 03:00PM
The secondary is big, like 60cm of PVC, diameter is 11cm. I'm using AWG27, wich is very very thin, I expect my secondary to have a lot of turns because of that. The topload is a thoroid and it is already built. It's big, 45/75 cm of inner/outer diameter.
Re: Any advice with this schematic
Benjamin, Tue Aug 23 2016, 04:07PM
That should work, although the high number of turns means that you will need a large number of turns for the primary to tune it. If you already have the wire, use it but if you don't I would use 24 gauge instead. my coil uses an 8.9 cm by 50 cm form with 24 gauge wire and it has put out sparks three times it's length. The key to getting large sparks out of small coils is a high break rate spark gap and a very large toroid (mine is 8 by 36 inches, 20 by 91 cm). Also you don't have to use copper tube for the primary coil, I used 10 gauge stranded insulated wire and just stripped out tap points and it gets a little warm but it seems to work fine.
Edit: Just saw your question back there. Yes AC motors can have brushes, they are called universal motors and can run on AC or DC. They are usually high speed (which is good for a rotary gap) and found in things like blenders and vacuum cleaners.
Benjamin, Tue Aug 23 2016, 04:07PM
That should work, although the high number of turns means that you will need a large number of turns for the primary to tune it. If you already have the wire, use it but if you don't I would use 24 gauge instead. my coil uses an 8.9 cm by 50 cm form with 24 gauge wire and it has put out sparks three times it's length. The key to getting large sparks out of small coils is a high break rate spark gap and a very large toroid (mine is 8 by 36 inches, 20 by 91 cm). Also you don't have to use copper tube for the primary coil, I used 10 gauge stranded insulated wire and just stripped out tap points and it gets a little warm but it seems to work fine.
Edit: Just saw your question back there. Yes AC motors can have brushes, they are called universal motors and can run on AC or DC. They are usually high speed (which is good for a rotary gap) and found in things like blenders and vacuum cleaners.
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