High Voltage Forum

Tesla coils => Dual Resonant Solid State Tesla coils => Topic started by: Vaclav on May 20, 2019, 06:38:54 PM

Title: DRSSTC design questions + project progress
Post by: Vaclav on May 20, 2019, 06:38:54 PM
Hi I’m new here,

I want to build a DRSSTC for my state-certified technician final project.
I have from now on roundabout 38 weeks.
I’ve already started.

In the past I've already tried to build a DRSSTC. I got about 10cm arc from this coil:

Primary: 5 Turns 6mm²
Secondary:
110mm Diameter
370mm length
0,1mm enameled copper wire diameter (I think this is far to low)
100x280mm topload
72kHz resonant secondary resonant frequency
fixed coupling

I think it's better when I make a complete new coil.
Is this coil good?
* final.txt


I already built:
H-Bridge
Interrupter (Steve Ward)
Control circuit
Gate driver (I don’t use GDT)
Galvanic isolated power supplies for the gate driver

I’ve tested all and it works as it should. (At least I think so)
I don't have tested the feedbackfunktion I just used my funtiongenerator.

I made some H-Bridge tests with a 75W Alight bulb.

Voltage at bulb:


When the interrupter stops the H-Bridge the last falling edge is not straight, it’s more like an e-function.
I don't have a picture of this because I killed yesterday one of my IGBTs....
I Switched the 5V off while the H-Bridge was oscillating.
Both IGBT switched on I think, because of a wrong signal and the short-circuit current killed them -.-
So I made this highly professional paint picture:


Is this curve ok?? or really bad??? Idk...

Which ferrite core is good for the feedback is this one here ok (I have some of them here from my first coil):
https://www.reichelt.de/ferritring-59770027-ft-140-77-p7921.html?

I've added the circuit diagram
I uploaded some pics as a zip file to my dropbox (can't attach them here cause they are to big):
https://www.dropbox.com/s/jcgcy6su8wmc3cz/Tesla.zip?dl=0

Greatings from Germany

Vaclav
Title: Re: DRSSTC design questions + project progress
Post by: profdc9 on May 21, 2019, 02:32:59 PM
Does your controller have undervoltage protection and is it set up correctly?

If the gate drivers on the controller are nor forced off as the voltage falls when power is removed then you may get shoot through blowing the IGBTs.

Dan

Hi I’m new here,

I want to build a DRSSTC for my state-certified technician final project.
I have from now on roundabout 38 weeks.
I’ve already started.

In the past I've already tried to build a DRSSTC. I got about 10cm arc from this coil:

Primary: 5 Turns 6mm²
Secondary:
110mm Diameter
370mm length
0,1mm enameled copper wire diameter (I think this is far to low)
100x280mm topload
72kHz resonant secondary resonant frequency
fixed coupling

I think it's better when I make a complete new coil.
Is this coil good?
* final.txt


I already built:
H-Bridge
Interrupter (Steve Ward)
Control circuit
Gate driver (I don’t use GDT)
Galvanic isolated power supplies for the gate driver

I’ve tested all and it works as it should. (At least I think so)
I don't have tested the feedbackfunktion I just used my funtiongenerator.

I made some H-Bridge tests with a 75W Alight bulb.

Voltage at bulb:


When the interrupter stops the H-Bridge the last falling edge is not straight, it’s more like an e-function.
I don't have a picture of this because I killed yesterday one of my IGBTs....
I Switched the 5V off while the H-Bridge was oscillating.
Both IGBT switched on I think, because of a wrong signal and the short-circuit current killed them -.-
So I made this highly professional paint picture:


Is this curve ok?? or really bad??? Idk...

Which ferrite core is good for the feedback is this one here ok (I have some of them here from my first coil):
https://www.reichelt.de/ferritring-59770027-ft-140-77-p7921.html?

I've added the circuit diagram
I uploaded some pics as a zip file to my dropbox (can't attach them here cause they are to big):
https://www.dropbox.com/s/jcgcy6su8wmc3cz/Tesla.zip?dl=0

Greatings from Germany

Vaclav
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 21, 2019, 03:46:56 PM
Does your controller have undervoltage protection and is it set up correctly?

I don't have any undervoltage protection.

I have 2 ideas:

1. Switch the IGBTs instantly off if there is undervoltage.
Worst case: I switch them off while peak current.


2. I switch the IGBTs off when there's 0 current.
Worstcase: needs longer (worst 1 complete cycle time at 82kHz --> 12,2µS) maybe Voltage drops in this time to far and I can't switch them of in time.
Solution would be to add more capacity on my power supplies.


In both cases I have to add a diode in series to my power supply.
For the Undervoltage detection I would use one relay for each supply because I need galvanic isolation.

Vaclav
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 21, 2019, 03:56:56 PM
I think it's better when I make a complete new coil.
Is this coil good?
* final.txt

 [ Invalid Attachment ]
Title: Re: DRSSTC design questions + project progress
Post by: profdc9 on May 21, 2019, 04:06:38 PM
A relay might work, but it is slow and requires a lot of coil current to operate.

Perhaps use an optoisolator such as the 4N28/4N35 to pull the signal to ground if there is undervoltage.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 21, 2019, 06:21:37 PM
A relay might work, but it is slow and requires a lot of coil current to operate.

Perhaps use an optoisolator such as the 4N28/4N35 to pull the signal to ground if there is undervoltage.

I will use the 2. idear because the caps are big enouth.

I have ~1A Driver current.
At least 220µF on the driver.
84KHz^-1 = 12µs --> 15µs for safety.

I think the effective current is quite constant.
So I use this equation.

U = I/C * t --> (1A/220µF) * 15µs  ~ 68mV

68mV  voltage drop is realy good.

This is the schematic for the undervoltage detection.

I could use op amps but there is not enough space in the case.
Detecting 0V is ok for me.

Can some one have a look on my Coil design?
I wanna buy some parts for it this week :)

Vaclav
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on May 21, 2019, 08:28:43 PM
Which ferrite core is good for the feedback is this one here ok (I have some of them here from my first coil):
https://www.reichelt.de/ferritring-59770027-ft-140-77-p7921.html?

It might work, despite it is only a 2000 permeability core, it is advised to use around 5000 or higher for CTs in a DRSSTC.

Can some one have a look on my Coil design?
I wanna buy some parts for it this week :)

Vaclav

You are within all the best-practise limits of designing a good run of the mill DRSSTC, I see no short comings in your JavaTC design.

Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 21, 2019, 08:59:57 PM
It might work, despite it is only a 2000 permeability core, it is advised to use around 5000 or higher for CTs in a DRSSTC.

Just to be sure this one here, T38 material would be much better?
http://www.farnell.com/datasheets/2168097.pdf
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on May 22, 2019, 08:31:55 PM
I have used N30 material plenty of times, T65 and T37 is also good choices, too high and the 50% frequency roll-off might get into your resonant frequency region, check the datasheets.

Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 24, 2019, 09:36:15 PM
When the interrupter stops the H-Bridge the last falling edge is not straight, it’s more like an e-function.
I don't have a picture of this because I killed yesterday one of my IGBTs....
I Switched the 5V off while the H-Bridge was oscillating.
Both IGBT switched on I think, because of a wrong signal and the short-circuit current killed them -.-
So I made this highly professional paint picture:


Is this curve ok?? or really bad??? Idk...

The new IGBT is here.
This is the actual voltage curve with a 75W light bulb as load.
I don't know is that good or bad?
 [ Invalid Attachment ]
 [ Invalid Attachment ]
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on May 26, 2019, 08:43:45 PM
The switching transient spikes are within reason, very low energy and short lived, could be better, depends what DC bus voltage you did this test on?

The trailing edge with its RC characteristic also puzzles me, I doubt it would be able to damage a IGBT brick, there is simply not enough energy in it for that, they are after all rated for high short circuit currents for 1ms.

It could be busbar inductance and snubber caps RC time constant? Try to calculate it from your values. Or change the snubber caps to higher or lower values and see if the slope changes.

You have built a very neat looking bridge, clean layout and no mess of wires, so I really doubt that is the source of your problem.

On a little side-note, how satisfied are you with the EEVBlog diff. probe? If you want to, please do write a review in the electronics subforum.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 26, 2019, 11:13:45 PM
The switching transient spikes are within reason, very low energy and short lived, could be better, depends what DC bus voltage you did this test on?
Test was with 230V DC

I used this connectors for my snubber caps and my TVS diodes.
https://de.farnell.com/amp-te-connectivity/1-5380758-1/mini-spring-buchse-tht-20-16awg/dp/2310196?ost=2310196&ddkey=https%3Ade-DE%2FElement14_Germany%2Fsearch
https://de.farnell.com/amp-te-connectivity/5050864-1/terminal-discrete-socket-6-53mm/dp/2452556?ost=2452556&ddkey=https%3Ade-DE%2FElement14_Germany%2Fsearch
Maybe the resistance is to high?
I will make a test without the snubbers tomorrow.
 [ Invalid Attachment ]

On a little side-note, how satisfied are you with the EEVBlog diff. probe? If you want to, please do write a review in the electronics subforum.
I can't say much about it its my only diff. probe and this was literally my first measurement with it.
Title: Re: DRSSTC design questions + project progress
Post by: Netzpfuscher on May 27, 2019, 07:55:56 AM
I think there is problem with your driver. On the inverter output is no component which can cause this. Please measure your gate drive if there is also such a signal.

The P-Channel FETs in your driver are AC coupled and you have a pair of UCC27321 and UCC27322. If you disable the the drive signal at the ADUM1200 with a zero, this zero gets to the UCC pair. The upper part gets inverted and the N-Channel conducts which is fine. But the lower UCC is not inverted and with a zero on the input the P-Channel conducts, but after a short time the coupling capacitor is full and the P-Channel goes to non conducting and the IGBT gate gets a floating input on one side.

With such a uncontrolled decay of the drive signal it's possible that you get massive shot troughs which can kill the IGBT easily. 

You should change you gate drive that it is capable to transfer DC. One option is to toss the P/N-channel fets and use only the UCCs which should be strong enough for the small bricks. I have driven a CM300 directly with a UCC pair.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 27, 2019, 07:19:49 PM
It could be busbar inductance and snubber caps RC time constant? Try to calculate it from your values. Or change the snubber caps to higher or lower values and see if the slope changes.
I made measurements with one and with no snubber cap.
The measurement didn't changed.
And I don't understand why this should make any difference.

I think there is problem with your driver. On the inverter output is no component which can cause this. Please measure your gate drive if there is also such a signal.

Yellow = Gate
Blue = Interrupter signal
Gate1:

Gate:2

Gate3:

Gate4:


I think the bad spikes are due to this:

In the final assembly I will use shielded cables.

The P-Channel FETs in your driver are AC coupled and you have a pair of UCC27321 and UCC27322. If you disable the the drive signal at the ADUM1200 with a zero, this zero gets to the UCC pair. The upper part gets inverted and the N-Channel conducts which is fine. But the lower UCC is not inverted and with a zero on the input the P-Channel conducts, but after a short time the coupling capacitor is full and the P-Channel goes to non conducting and the IGBT gate gets a floating input on one side.

With such a uncontrolled decay of the drive signal it's possible that you get massive shot troughs which can kill the IGBT easily. 
I think adding a resistor is not a bad idea.


You should change you gate drive that it is capable to transfer DC. One option is to toss the P/N-channel fets and use only the UCCs which should be strong enough for the small bricks. I have driven a CM300 directly with a UCC pair.
I realy want to keep my driver design.
Adding the resistor for safety is probably not a bad idea.

I noticed if there is no load at the bridge the bridge voltage stays high when the Interrupter turns it off.


When I add the 75W bulb I geht this:



I think I have some parasitic capacity at the bridge output.

Time from Hight to 0V is ~8µs --> Tau = 1,6µs
cold bulb resistance = ~59R
hot bulb resistance = ~770R (I measured the current at 230V AC and calculate it)
1,6µs/59R = ~27nF
1,6µs/770R = ~2nF

When I change the duty cycle of the interrupter.
The bulb temp change --> bulb resistance change--> ramp change.

I think there must be some capacity between 2nF-27nF.
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on May 27, 2019, 10:09:10 PM
Try to add a 10K resistor across the inverter output, I use this on my large DRSSTC. It has to do with the UD2.1b driver with phase lead has issues with residual MMC charge and it can act up weird and trigger randomly.

Not that you have this jittering issue here, but if you got residual charge on your bridge when the power is off, bleed it away.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 28, 2019, 09:48:59 PM
Try to add a 10K resistor across the inverter output, I use this on my large DRSSTC. It has to do with the UD2.1b driver with phase lead has issues with residual MMC charge and it can act up weird and trigger randomly.

Not that you have this jittering issue here, but if you got residual charge on your bridge when the power is off, bleed it away.
Do you know where the residual charge came from?

By the way I really want to say thank you for the nice help I get here.

Next step will be building a bigger winding rig.
The old one is just too small.
Title: Re: DRSSTC design questions + project progress
Post by: Teravolt on May 29, 2019, 07:19:09 PM
hi there Vaclave, I like your design however I am with Netzpfuscher. dump the mosfet driver fets and the bootstrapping unless you can make it work. the UCC's will drive each igbt directly for short periods. I am not completely clear on your circuit because it is kind of broken up and hard to get a clear picture. I am assuming that the ADuM1200 are for galvanic isolation and they are driving the UCC's? (That would be my choice.) I have tried this with the

https://www.nve.com/Downloads/il710.pdf

and using them to drive

https://www.digikey.com/product-detail/en/ixys-integrated-circuits-division/IXDD614CI/CLA356-ND/2424696

with isolated supplies

https://www.digikey.com/product-detail/en/murata-power-solutions-inc/MGJ6D051505SC/811-3229-ND/6202202

later I ended up using

https://www.infineon.com/dgdl/Infineon-1EDI60N12AF-DS-v02_00-EN.pdf?fileId=db3a3043427ac3e201428e5da08f372a

to me I see a lot of shoot through at your driver scope shots. make your leads to the gates as short as possible and add dead time at u3c and u3d

 http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridge-control/

I hope that I have not overstepped on your thread. I am interested in what you are doing do you have a topside picture of your driver box
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 29, 2019, 08:18:16 PM
hi there Vaclave, I like your design however I am with Netzpfuscher. dump the mosfet driver fets and the bootstrapping unless you can make it work.
To me it looks like it is working I don't can see any problem.

This is the schematic with the pullups
* Driver.pdf


the UCC's will drive each igbt directly for short periods. I am not completely clear on your circuit because it is kind of broken up and hard to get a clear picture.
I know the schematic is confusing...

I am assuming that the ADuM1200 are for galvanic isolation and they are driving the UCC's? (That would be my choice.)
That's right.

to me I see a lot of shoot through at your driver scope shots. make your leads to the gates as short as possible and add dead time at u3c and u3d
How can you see shoot through??
Can u explain that to me??

In theory I can adjust the dead time with P8 and P9 on the control board.
But I don't see any difference on my inverter ouput voltage and the current consumption (according to my power supply) of the inverter don't change when I adjust the trimpots.
* Control.pdf

The connection to the gate can't be shorter.


I hope that I have not overstepped on your thread. I am interested in what you are doing do you have a topside picture of your driver box


Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on May 29, 2019, 08:52:05 PM
Short explanation of my construction:
I have on box with 2x 230V AC inputs. On input is only for the inverter so I can use my variac to change the inverter voltage. The other is for the control voltage power supply.
Inside the box: Resistor for inverter cap charging. Relay to short out this resistor. Rectifier for the inverter voltage. Some Fuses + connectors for 230V Output (to the control voltage power supply).

There is a self-build power supply with 2 Transformer (each 2*18VAC output):
The power supply outputs are:
-4x 18DC each for on driver (galvanically isolated)
-12V for the fans. I get the 12V DC from an AC/DC power supply. This is a workaround. At first I wanted to supply my drivers with 3x 18V because I thought the 2 driver to the negative rail are at the same potential... that was a mistake and I had to get one galvanically isolated supply more.
-5V for the control board (with a regulator from the 12V)

Control board:
-feedback with adjustable phase lead. Signal via current transformer.
-over temperature detection of the inverter via NTC
-overcurrent detection via a current transformer
-under voltage detection
-optical fiber input for the interrupter
-some type of interrupter signal monitoring (if the on time is to long the interrupter signal is forced low)
-dead time adjustment to avoid shot through (independent adjustment for positive and negative edge feedback signals)
-4x adum for isolation between low voltage and inverter
-4x outputs to the 4 drivers

2x complete identical driver boards (each for one brick / two IGBTs):
Each driver board hast 2 identical drivers on it.
Every driver has one 5V regulator for the HV side of the adum.
Title: Re: DRSSTC design questions + project progress
Post by: Teravolt on May 31, 2019, 07:43:11 PM
Hi Vaclav, the picture, gate 4, has a lot of noise I think remove the 2k's that you have added and add 2k from IGBT gate and emitter and see if that helps. to my knowledge not many people hear have tried to do direct drive and usually uses transformers. I have seen this before. also try adding incrementally resistance say 2k 2w temporarily across 1/2 of the bridge output to the center tap of mains multiplier capacitors. The idea is to add a mild resistive loading to your bridge output to the center tap of the capacitors to damp transient noise generated by emi. If you look at your blue gate signal the transients are synchronized with your transitions if the IGBTs. this also can be caused by not enough dead time. I have tried what your doing with good results but I wanted to reduce the complications of lots of circuitry so it can easily be reproduced I have outlined this in my thread

https://highvoltageforum.net/index.php?topic=632.0

Using direct drive I think IGBT transition times small enough to use bricks up to 100khz out side normal operating frequency, also phase manipulation or PWM is more possible
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on June 01, 2019, 12:56:34 AM
Hi Vaclav, the picture, gate 4, has a lot of noise I think remove the 2k's that you have added and add 2k from IGBT gate and emitter and see if that helps.
I added 2k across gate and emitter. --> signal didn't change
I even go down to 1K --> nothing changed
Removing the 2K to gnd. --> no change

I make this test only with on driver. Should I do this with all 4 at the same time?

also try adding incrementally resistance say 2k 2w temporarily across 1/2 of the bridge output to the center tap of mains multiplier capacitors. The idea is to add a mild resistive loading to your bridge output to the center tap of the capacitors to damp transient noise generated by emi.
I don't understand you completely. What do you mean with "center tap of mains multiplier capacitors" I have 2x 3.3mF in parallel to smooth the rectified sine.
I tried adding 2,5K from one inverter output to the negative rail. do you mean that?? --> nothing changed with this resistor.

I turned up the dead time to get this signals:




When I rise the dead time the noisy part goes more to the right and gets smaller.

I think the new dead time is much too high about 1,5-1,7µs (frequency is 82KHz):


The inverter output looks now like this (with the 75W bulb as load):
The edges are far too bad I think.

Without the bulb the inverter signal looks like this:


rising/falling edge (without bulb):



rising/falling edge (with bulb):



Could it be a problem that I use tow slightly different IGBT bricks?
FF400R12KT3: https://www.infineon.com/dgdl/Infineon-FF400R12KT3-DS-v03_00-EN.pdf?fileId=db3a304412b407950112b4345f49601d
FF400R12KE3: https://www.galco.com/techdoc/eupc/ff400r12ke3_dat.pdf
The FF400R12KT3 is a lite bit faster.

I really have no clue how to make the signal better or what the exact problem is.
Title: Re: DRSSTC design questions + project progress
Post by: Teravolt on June 01, 2019, 08:19:52 PM
it looks good. I agree 1.5uS is a little to much, how about 1uS, is it adjustable? hear in the US we or I have 220vac with a center taped ground and typically builders use a full wave capacitive doubler to boost the voltage but I'm looking at your setup closer and I am assuming you have 220Vac with no center tap and you are running rectified mains and the big caps are your filtering and energy storage. have you tried firing up the bridge with a isolation transformer and variac? in a answer to your question about adding some dampening resistance at the output to a center taped junction ignore that. I was able to reduce the over shot on my bridge by adding non inductive resistance to a stiff reference. In your case I am not shure where to do that or even if it is necessary. have you tried adding the primary circuit and using the feed back yet? when you do start at a low mains voltage and monitor as raising the voltage watch for to much overshoot and cross conduction

In a note for your future builds I would have put the ADuM1200CR next to the UCC ic instead of separating them with a twisted pair and use a TTL A-drive and B-drive signals in coax, ie BNC. About using 2 different half bridges as long as your dead time covers the slow brick I think you will be ok. keep the pictures coming if you have questions. just remember that you are doing something that tesla enthusiasts don't usually do but because of its complications is done in the commercial arena all the time.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on June 02, 2019, 12:25:42 PM
I made some further test and went down with the dead time to 1µS.

I added 2k across gate and emitter. --> signal didn't change
I even go down to 1K --> nothing changed
I noticed that adding the resistor damps the spike. But not that much
IDK why I didn't see this last time...

I make this test only with on driver. Should I do this with all 4 at the same time?
I made the test with all 4 at the same time and noticed that the spikes on the gate signal for the high side IGBTs are much worse.
Than the spike on the gate of the low side IGBTs.
White high side gate (White is stored in the oscilloscope normally they are 180° phase shifted)
Yellow low side gate


I tried adding a resistor in series to the gate. At first I thought I don’t need them… now I think that was pretty naive.
I only have enough resistors to do this with 2 gates at the same time.
Each gate has 2,5Ohm in series.


These is the new voltage directly at the gats:
High side IGBT:




Low side IGBT:

Ignore the straight line at ~-18V I forgot the stop the oscilloscope.



Inverter output has now some flat part at 0V:




I will buy some smaller resistors 0,5Ohm and 1Ohm and redo the test with all 4 IGBTs.
Title: Re: DRSSTC design questions + project progress
Post by: Teravolt on June 03, 2019, 09:04:29 PM
If you want to try more dampening going from each half bridge to ground say 1000 to 220 you will have try it your self. the last wave form is much better and when you get the spikes and overshoot under controle you might slowly decrease your dead time to something less to close the time at zero volts. you should be able to see on the scope as you are addjusting. Things may change when you add your resonant primary and feed back so go slow and monitor safely if you can whyle you see what happens when you turn up the voltage to see if the spikes get bigger.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on June 06, 2019, 08:36:58 PM
I added now 2,2Ohm in series to my gate
New signals looking like this:

"Worst" gate signal of all 4 signals:

Edges:

Edges in detail:


Inverter output:
The slope at the end is still there I think it's ok.

Edges:

I can't do anything against the sinusoidal part in the rising edge.

All my test until now were made with my "high voltage" DC power supply (max. 600V,6A,1000W)
I made all test with up to 325V.
I made the first test run with main power via isolation transformer.
One driver has failed and cause short circuit on one 18V rail.
I switched off the supply to all the control voltages (5V and 4x18V).
And it happened the way it had to... I blow another IGBT brick... (I can get a used on for 50€ at eBay, so it’s not that much of a problem)
I started digging around and noticed that the problem does not came from the driver and not from the controller.
The problem are the ADUMs the make a spike at the output if the low voltage supply is off before the high voltage side does.
This spike will occur at all 4 ADUMs at once and the drivers short the complete inverter.
As a workaround I will ad 0,5F at my 5V supply rail. I tried all my available big capacitors and measured that ~30mF are enough.
0,5F is the next bigger cap I find at the shop I'm used to buy from.


I've already finished winding my current transformers.
I will mount them on a brass rod.


I'm on holiday now. I' ll be back in about 3 weeks.
Title: Re: DRSSTC design questions + project progress
Post by: Teravolt on June 07, 2019, 06:14:45 PM
you might be able to find where the spikes are comming from by finding out what edge or operation they are synced to. you also may have stray inductance in your connections that are feading into the driver
Title: Re: DRSSTC design questions + project progress
Post by: Netzpfuscher on June 07, 2019, 08:04:57 PM
It's more simple the datasheet has a table. It's normal that you get a high signal, if you switch off the Vcc.

 [ Invalid Attachment ]
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on July 25, 2019, 10:10:49 PM
Finally, I'm back with some progress.

It's more simple the datasheet has a table. It's normal that you get a high signal, if you switch off the Vcc.

Wow I feel like a huge idiot because I don't have seen this...
I chanced the ADuMs to this one ADuM1285BRZ.
After that I had a similar problem but it came from the fiber optic receiver.
I solved the problem with adding a 0,5F cap across the 5V supply and a better under voltage detection for the 5V supply (with OPV).
New under voltage detection:


Old one:

Vaclav

The problem is now completely gone.
And the the Inverter with function generator as feedback signal and lightbulb as load is running perfectly.


I build the primary coil, I made the high of the coil adjustable so I can change the coupling between primary and secondary.


I also finished the current transformer assembly.


The secondary and the topload is completed.

Secondary was planned with 1800 windings, I got about ~1616
I got some small bubbles in the varnish of the secondary.
I used this varnish: https://www.ebay.de/itm/Wilckens-Yachtline-DD-Hartlack-750-ml-Farbauswahl-2-K-Polyurethan-Bootslack/321632791504?ssPageName=STRK%3AMEBIDX%3AIT&var=510526219327&_trksid=p2057872.m2749.l2649
I measured the resonant frequency of the secondary coil. ~86.75kHz

My IGBTs support a maximum current of 800A peak.
So I designed my MMC for max 800A peak.
I used Mads MMC calculator (http://kaizerpowerelectronics.dk/calculators/mmc-calculator/)
Idk which value I should use for the on time and the BPS.
I even don’t know if I have understood BPS and on time right.
BPS = Basically the Interrupter frequency??
On time = time the coil is on --> on time of the Interrupter signal??
I want to use a Musical interrupter later.
To play different sounds the musical Interrupter changes the frequency of the Interrupter signal? --> different BPS
With the given 200µS on time and 200BPS get these two MMCs.
I think that I will use these capacitor: https://www.mouser.de/ProductDetail/Cornell-Dubilier-CDE/940C20P1K-F?qs=KAyk88b%2FVhdRi0pubeTg4g==
Which one is better?
0.4µF capacity (results in ~5 windings Primary)
0.5µF capacity (results in ~4 windings Primary)
My primary has only 5 windings so I think the 0.5µF would be better because I have more adjustability. And the 0.5µF Is cheaper.

0.4µF:

0.5µF:


Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on August 01, 2019, 10:40:41 PM
I think my question went down in my long post.
BPS = Basically the Interrupter frequency??
On time = time the coil is on --> on time of the Interrupter signal??
I want to use a Musical interrupter later.
To play different sounds the musical Interrupter changes the frequency of the Interrupter signal? --> different BPS
I have really been looking for an answer for a long time but found nothing that makes me really 100% sure.

Which of the two options is better?
0.4µF capacity (results in ~5 windings Primary)
0.5µF capacity (results in ~4 windings Primary)
My primary has only 5 windings so I think the 0.5µF would be better because I have more adjustability. And the 0.5µF Is cheaper.

Thanks for all the help, I certainly couldn't do this project without some help.
Title: Re: DRSSTC design questions + project progress
Post by: dexter on August 02, 2019, 10:01:27 AM

BPS = Basically the Interrupter frequency??
On time = time the coil is on --> on time of the Interrupter signal??
I want to use a Musical interrupter later.
To play different sounds the musical Interrupter changes the frequency of the Interrupter signal? --> different BPS

Yes for all

For your MMC the.0.5 one might suffer when playing music as higher BPS translate to higher rms current. Increase tbe BPS in the MMC calculator and see how much the Temperature rise per cap increases. If you plan to use the coil for sort-ish periods of times (giving the MMC time to cool) it will work fine.

Another thing to consider is impedance matching of the primary and secondary... The primary capacitor plays a role in that and there is a formula but i can't find it right now (on the phone)
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on August 02, 2019, 01:56:19 PM
Thanks for the quick answer.

For your MMC the.0.5 one might suffer when playing music as higher BPS translate to higher rms current. Increase tbe BPS in the MMC calculator and see how much the Temperature rise per cap increases. If you plan to use the coil for sort-ish periods of times (giving the MMC time to cool) it will work fine.

What is a good max BPS for music? I think 1500BPS should be enought. Or should I go for more BPS?
I will recalculate the MMC in relation to the new BPS.

Another thing to consider is impedance matching of the primary and secondary... The primary capacitor plays a role in that and there is a formula but i can't find it right now (on the phone)
The primary side should have approximately the same resonance frequency as the secondary side.
As far as I know, the primary circuit should have a little more inductivity than it must have in the resonance case.
So if I use a bigger MMC the inductivity will be smaller. For the same resonance frequency.

Is it now better to have more or less turns on the primary side, or is that completely irrelevant in the case of one turn more or less?
Because I would then choose the MMC accordingly.
Title: Re: DRSSTC design questions + project progress
Post by: dexter on August 02, 2019, 08:57:31 PM
What is a good max BPS for music? I think 1500BPS should be enought. Or should I go for more BPS?
I will recalculate the MMC in relation to the new BPS.
depends on the music...
Keep in mind there are pauses and the BPS is not constant so the RMS current will vary quite substantially.
I wouldn't go as far to overdesign the MMC for 1500 BPS but i'd go ~10-20% over the minimum values for normal operation.

Is it now better to have more or less turns on the primary side, or is that completely irrelevant in the case of one turn more or less?
Because I would then choose the MMC accordingly.

read this
https://highvoltageforum.net/index.php?topic=113.0
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on August 04, 2019, 01:15:29 AM
thx for the tips!

I think I will go with the 0.4µF MMC.
If I want higher current, I can change it later to 0.5µ or higher.

I made some simulations (primary oscillating circuit coupled with secondary oscillating circuit).
I got ~80µS to transmit all energy to the secondary side. Therefore I will go for ~80µ on time

I chose 1000BPS. Probably my rectifier will not be able to provide enough energy, but I can change that later on.

I think I will go with this MMC, I don't want to increase the RMS current of the MMC, maybe I will cool the caps active or go with a little bit less BPS.
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on August 05, 2019, 08:46:58 AM
Designed for 1000 BPS, with only RMS current being higher than MMC specifications, it is all fine! You are not going to push it that hard continuously anyway, not even with MIDI if its edited correct.

The simulated 80us transfer-time does not mean that you can not run longer on-times, longer on-time will still produce longer sparks as you keep pumping energy into the grown spark channel.
Title: Re: DRSSTC design questions + project progress
Post by: Uspring on August 05, 2019, 12:15:44 PM
Vaclav wrote:
Quote
I made some simulations (primary oscillating circuit coupled with secondary oscillating circuit).
I got ~80µS to transmit all energy to the secondary side. Therefore I will go for ~80µ on time
That holds true for a perfectly tuned SGTC. In a DRSSTC you keep supplying energy to the primary coil. Since that is not immediately transferred to the secondary, there will always be some energy in the primary. Have a look at Mads docs on his TCs. He shows primary current scope shots and all show some primary current, i.e. energy in the primary tank as long as the burst persists. Once you stop the burst, most of the primary energy returns to the bus caps via the IGBTs reverse diodes. Actually a sad side effect of stopping the burst.
Title: Re: DRSSTC design questions + project progress
Post by: Mads Barnkob on August 05, 2019, 12:31:53 PM
Vaclav wrote:
Quote
I made some simulations (primary oscillating circuit coupled with secondary oscillating circuit).
I got ~80µS to transmit all energy to the secondary side. Therefore I will go for ~80µ on time
That holds true for a perfectly tuned SGTC. In a DRSSTC you keep supplying energy to the primary coil. Since that is not immediately transferred to the secondary, there will always be some energy in the primary. Have a look at Mads docs on his TCs. He shows primary current scope shots and all show some primary current, i.e. energy in the primary tank as long as the burst persists. Once you stop the burst, most of the primary energy returns to the bus caps via the IGBTs reverse diodes. Actually a sad side effect of stopping the burst.

I got the best oscilloscope shots showing this from my small DRSSTC, as a very long on-times is less and less "necessary" on a large coil with higher peak currents, there you get the spark length more in a manner comparable to a SGTC, but for low peak currents, longer on-time gives better reults.

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-drsstc-ii/
Title: Re: DRSSTC design questions + project progress
Post by: Netzpfuscher on August 05, 2019, 12:48:57 PM
A long ontime is better for MIDI modulation. It gives you more resolution for the MIDI volume. Lets say you have only 4 full cycles in a interrupter period, you can only get 3 different volumes on the midi voices.

A good midi interrupter should always have a duty cycle limiter. It should lower the ontime for high pitched notes or transpose them down.
Title: Re: DRSSTC design questions + project progress
Post by: Vaclav on August 06, 2019, 02:12:17 AM
Thanks for the informative posts.

I bought the caps for the MMC.
36 of this one: https://www.mouser.de/ProductDetail/Cornell-Dubilier-CDE/940C20P1K-F?qs=KAyk88b%2FVhdRi0pubeTg4g==

Vaclav wrote:
Quote
I made some simulations (primary oscillating circuit coupled with secondary oscillating circuit).
I got ~80µS to transmit all energy to the secondary side. Therefore I will go for ~80µ on time
That holds true for a perfectly tuned SGTC. In a DRSSTC you keep supplying energy to the primary coil. Since that is not immediately transferred to the secondary, there will always be some energy in the primary. Have a look at Mads docs on his TCs. He shows primary current scope shots and all show some primary current, i.e. energy in the primary tank as long as the burst persists. Once you stop the burst, most of the primary energy returns to the bus caps via the IGBTs reverse diodes. Actually a sad side effect of stopping the burst.

I got the best oscilloscope shots showing this from my small DRSSTC, as a very long on-times is less and less "necessary" on a large coil with higher peak currents, there you get the spark length more in a manner comparable to a SGTC, but for low peak currents, longer on-time gives better reults.

http://kaizerpowerelectronics.dk/tesla-coils/kaizer-drsstc-ii/

Good to know, untill now I thought you can't pump more energy in the secondary after the 80µS.

A long ontime is better for MIDI modulation. It gives you more resolution for the MIDI volume. Lets say you have only 4 full cycles in a interrupter period, you can only get 3 different volumes on the midi voices.

A good midi interrupter should always have a duty cycle limiter. It should lower the ontime for high pitched notes or transpose them down.
I will pay attention when I designe/select the MIDI interupter.
But first, the coil has to work. :)