Low frequency tesla coils?
Artlav, Wed Apr 09 2014, 12:34PMWere there any tesla coils that ran at low resonant frequencies, like 5-10kHz?
I've only heard of and seen ones running at 100s of kHz.
For typical designs that would mean huge topload and/or huge coil, but are these the only problems?
Would there be any advantages to low frequency?
Re: Low frequency tesla coils?
Steve Conner, Wed Apr 09 2014, 01:09PM
As far as I know, the optimum characteristic impedance for a Tesla coil is about 50k ohms. That establishes a relationship between the size of the coil and the operating frequency. So, low frequencies are only usable for really large coils.
Below a certain frequency (which due to the above relationship, also implies above a certain power level) GTO thyristors will become more cost-effective than IGBTs in solid-state coils. I estimate this happens around 10kHz and 100kW average power.
Steve Conner, Wed Apr 09 2014, 01:09PM
As far as I know, the optimum characteristic impedance for a Tesla coil is about 50k ohms. That establishes a relationship between the size of the coil and the operating frequency. So, low frequencies are only usable for really large coils.
Below a certain frequency (which due to the above relationship, also implies above a certain power level) GTO thyristors will become more cost-effective than IGBTs in solid-state coils. I estimate this happens around 10kHz and 100kW average power.
Re: Low frequency tesla coils?
Uspring, Wed Apr 09 2014, 04:14PM
Artlav wrote:
Whether a match between the arc load and the bridges voltage and current capabilities can be obtained, depends mostly on the secondary to primary inductance ratio. A large secondary inductance would require a correspondingly larger primary inductance, careful tuning and as much coupling as possible. Arc impedance is probably higher at low frequencies, so the match is probably simplified somewhat. My guess is, that a low frequency, moderate power coil can be made to work.
Uspring, Wed Apr 09 2014, 04:14PM
Artlav wrote:
Would there be any advantages to low frequency?From a theoretical point of view, a lower frequency allows for more arc length for a given power. This is due to the effect, that arc lengthwise resistance can be higher since the capacitive load due to the arc capacitance is lower. Arcs can therefore be less conductive for a given arc length and thus require less heat.
Whether a match between the arc load and the bridges voltage and current capabilities can be obtained, depends mostly on the secondary to primary inductance ratio. A large secondary inductance would require a correspondingly larger primary inductance, careful tuning and as much coupling as possible. Arc impedance is probably higher at low frequencies, so the match is probably simplified somewhat. My guess is, that a low frequency, moderate power coil can be made to work.
Re: Low frequency tesla coils?
Dr. Slack, Wed Apr 09 2014, 04:21PM
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
Dr. Slack, Wed Apr 09 2014, 04:21PM
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
Re: Low frequency tesla coils?
Ash Small, Wed Apr 09 2014, 05:14PM
It's one stage from a pulse generator, it consists of a toroidal core with a one turn primary. The secondary is a shaft which fits through the hole in the centre. These stages are then stacked.
There is a description of one of these here:
(it's the link in the second post on that page)
Ash Small, Wed Apr 09 2014, 05:14PM
Dr. Slack wrote ...
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
It's one stage from a pulse generator, it consists of a toroidal core with a one turn primary. The secondary is a shaft which fits through the hole in the centre. These stages are then stacked.
There is a description of one of these here:
(it's the link in the second post on that page)Re: Low frequency tesla coils?
Artlav, Wed Apr 09 2014, 05:32PM
Now i seem to remember reading about a lighthouse-sized tesla coil (modern days one), that ran at something in the low 10s of kHz, but Google failed me here.
Anyone heard about it?
I was under impression that SCRs don't work well or at all above a few hundred hertz, which is a couple orders of magnitude too low.
Artlav, Wed Apr 09 2014, 05:32PM
Now i seem to remember reading about a lighthouse-sized tesla coil (modern days one), that ran at something in the low 10s of kHz, but Google failed me here.
Anyone heard about it?
Dr. Slack wrote ...
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
That looks like a part from a locomotive drive.OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
Steve Conner wrote ...
Below a certain frequency (which due to the above relationship, also implies above a certain power level) GTO thyristors will become more cost-effective than IGBTs in solid-state coils. I estimate this happens around 10kHz and 100kW average power.
Hm?Below a certain frequency (which due to the above relationship, also implies above a certain power level) GTO thyristors will become more cost-effective than IGBTs in solid-state coils. I estimate this happens around 10kHz and 100kW average power.
I was under impression that SCRs don't work well or at all above a few hundred hertz, which is a couple orders of magnitude too low.
Re: Low frequency tesla coils?
Uspring, Wed Apr 09 2014, 05:51PM
Uspring, Wed Apr 09 2014, 05:51PM
Anyone heard about it?
Re: Low frequency tesla coils?
Artlav, Wed Apr 09 2014, 06:05PM
Artlav, Wed Apr 09 2014, 06:05PM
Uspring wrote ...
, that's it.
38kHz as i remembered.
Not DRSSTC as i thought, but a spark gap one.
And it looks a lot smaller in the video - than on the pictures.
So, with a big enough coil low frequencies are possible.
Anyone heard about it?
, that's it.38kHz as i remembered.
Not DRSSTC as i thought, but a spark gap one.
And it looks a lot smaller in the video -
than on the pictures.So, with a big enough coil low frequencies are possible.
Re: Low frequency tesla coils?
Hydron, Wed Apr 09 2014, 07:30PM
It is indeed 38kHz, specs are here:
I've actually been to the sculpture farm it's located on, sadly it's only visible in the distance as it's in a private area, so I can't comment on what it looks like in person. It's a shame it's one of the few sculptures (most of which are extremely impressive) that aren't able to be experienced by the public on an open day.
Hydron, Wed Apr 09 2014, 07:30PM
It is indeed 38kHz, specs are here:
I've actually been to the sculpture farm it's located on, sadly it's only visible in the distance as it's in a private area, so I can't comment on what it looks like in person. It's a shame it's one of the few sculptures (most of which are extremely impressive) that aren't able to be experienced by the public on an open day.
Re: Low frequency tesla coils?
Steve Conner, Thu Apr 10 2014, 10:33AM
It's a GTO thyristor assembly from an electric locomotive. I don't know the exact spec, but it will be thousands of amps at a good few kV. The large round object is the thyristor in a hockey puck package, and the smaller semiconductors clustered around it are the gate drive. A GTO is easy enough to turn on, but needs a huge pulse of current to turn it off.
GTOs switch somewhat slower than even the slowest IGBTs, but they're still a lot faster than 50Hz. In a DRSSTC application, the resonant load would help a lot with turn-off.
I will get my hands on an H-bridge of these one day. >:)
Steve Conner, Thu Apr 10 2014, 10:33AM
Dr. Slack wrote ...
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
It's a GTO thyristor assembly from an electric locomotive. I don't know the exact spec, but it will be thousands of amps at a good few kV. The large round object is the thyristor in a hockey puck package, and the smaller semiconductors clustered around it are the gate drive. A GTO is easy enough to turn on, but needs a huge pulse of current to turn it off.
GTOs switch somewhat slower than even the slowest IGBTs, but they're still a lot faster than 50Hz. In a DRSSTC application, the resonant load would help a lot with turn-off.
I will get my hands on an H-bridge of these one day. >:)
Re: Low frequency tesla coils?
Ash Small, Thu Apr 10 2014, 12:04PM
Ok, I was wrong. I did wonder what relevance pulse generators had to this thread, although there are obviously similarities (lots of parallel semiconductors for switching it)
Ash Small, Thu Apr 10 2014, 12:04PM
Steve Conner wrote ...
It's a GTO thyristor assembly from an electric locomotive. I don't know the exact spec, but it will be thousands of amps at a good few kV. The large round object is the thyristor in a hockey puck package, and the smaller semiconductors clustered around it are the gate drive. A GTO is easy enough to turn on, but needs a huge pulse of current to turn it off.
GTOs switch somewhat slower than even the slowest IGBTs, but they're still a lot faster than 50Hz. In a DRSSTC application, the resonant load would help a lot with turn-off.
I will get my hands on an H-bridge of these one day. >:)
Dr. Slack wrote ...
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
OK Steve, tease/troll successful. What is that bit of power pron from, and what are its specs?
It's a GTO thyristor assembly from an electric locomotive. I don't know the exact spec, but it will be thousands of amps at a good few kV. The large round object is the thyristor in a hockey puck package, and the smaller semiconductors clustered around it are the gate drive. A GTO is easy enough to turn on, but needs a huge pulse of current to turn it off.
GTOs switch somewhat slower than even the slowest IGBTs, but they're still a lot faster than 50Hz. In a DRSSTC application, the resonant load would help a lot with turn-off.
I will get my hands on an H-bridge of these one day. >:)
Ok, I was wrong. I did wonder what relevance pulse generators had to this thread, although there are obviously similarities (lots of parallel semiconductors for switching it)
Re: Low frequency tesla coils?
Artlav, Thu Apr 10 2014, 04:02PM
Or the thyristors themselves?
What is between you and getting them?
Artlav, Thu Apr 10 2014, 04:02PM
Steve Conner wrote ...
I will get my hands on an H-bridge of these one day. >:)
The drivers?I will get my hands on an H-bridge of these one day. >:)
Or the thyristors themselves?
What is between you and getting them?
Re: Low frequency tesla coils?
Steve Conner, Thu Apr 10 2014, 09:20PM
The thyristor and driver come together as a unit.
The main problem is money. Not so much for the devices themselves, as the gigantic Tesla coil I would hook them up to.
It would need its own substation and a clearance zone the size of a football field.
Steve Conner, Thu Apr 10 2014, 09:20PM
The thyristor and driver come together as a unit.
The main problem is money. Not so much for the devices themselves, as the gigantic Tesla coil I would hook them up to.
It would need its own substation and a clearance zone the size of a football field.Re: Low frequency tesla coils?
Uspring, Fri Apr 11 2014, 09:54AM
These things really spoil the fun. My biggest coil occasionally trips my households 16A circuit breakers and I also can't run it in my garage when weather is bad since it'll likely burn it down.
Uspring, Fri Apr 11 2014, 09:54AM
These things really spoil the fun. My biggest coil occasionally trips my households 16A circuit breakers and I also can't run it in my garage when weather is bad since it'll likely burn it down.
Re: Low frequency tesla coils?
Artlav, Fri Apr 11 2014, 05:09PM
I was wondering if maybe i could have been able to trade some soviet vintage hockey puck SCRs for some induction heating grade capacitors.
But unfortunately i don't have any nuclear reactors on hands. :(
Artlav, Fri Apr 11 2014, 05:09PM
Steve Conner wrote ...
It would need its own substation and a clearance zone the size of a football field.
Ah. :)It would need its own substation and a clearance zone the size of a football field.
I was wondering if maybe i could have been able to trade some soviet vintage hockey puck SCRs for some induction heating grade capacitors.
But unfortunately i don't have any nuclear reactors on hands. :(
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