DRSSTC Tuning, UD2.7C
orac12, Mon Apr 18 2016, 10:12AMThis is the first tesla coil I've built, taken a few ideas from others seen around here :)
It's basically completed and time for tuning, not sure what to expect or what is acceptable so some pointers in the right direction would be great.
CM600 Full bridge
680VDC ~ Bus
0.6uF MMC
10 turn primary, tapped at approx turn 6 for now
1100~ turn 24AWG secondry
Ring style toriod
Automatic precharge + discharge
JavaTC calculates the primary at approx 40kHz, and the secondry a little higher. (Don't have all the JavaTC stuff with me atm to post right now)
At the moment we are running a lower bus voltage, 360~VDC while testing.
A few questions for people with more experience than me that could point me in the right direction:
What sort of on time and BPS should we be expecting before getting any breakout?
When tuning the phase lead, what would be an acceptable voltage spike? When tuning phase lead, we arent really seeing any improvements.
What sort of primary currents do we want to be tuning phase lead at? At the moment I believe we are at 3-500 amps primary.
We havent yet had any breakout, but it is certainly buzzing quite loud and if I bring a earthed wire up to the toroid it will strike an arc from around 1ft away.
Here are some scope shots. Current transducer is 1V : 100amps
There is approx a 100v spike on the bridge output and cannot seem to get it any smaller, is that acceptable? Some of these shots have different bus voltages as we were experimenting.
Re: DRSSTC Tuning, UD2.7C
Blackcurrant, Mon Apr 18 2016, 07:41PM
Hi Orac, A few things I would do first before putting any real power in.
Tune your coils first with a signal generator and scope.
I would start by finding the secondary frequency, quite easy and should peak quite sharply on the scope. The scope will pick it up meters away just with a probe with a small wire attached. Also a fluorescent tube will light quite easy just leave it on top.
Then work out your needed tap point on the spiral coil and check this frequency to.
When your happy that it's more or less in tune, add a sharp breakout point on top then power it up slowly. you can always remove this later it just gives an easy way for testing.
Also in the dark you may see were this buzzing is coming from.
Above all keep your distance!
PS from your picture I would say it may flash over near the bottom part, remember to keep everything smooth. My first coil was rather crude and had all sorts of things (small fires/flash-overs) happen.
Blackcurrant, Mon Apr 18 2016, 07:41PM
Hi Orac, A few things I would do first before putting any real power in.
Tune your coils first with a signal generator and scope.
I would start by finding the secondary frequency, quite easy and should peak quite sharply on the scope. The scope will pick it up meters away just with a probe with a small wire attached. Also a fluorescent tube will light quite easy just leave it on top.
Then work out your needed tap point on the spiral coil and check this frequency to.
When your happy that it's more or less in tune, add a sharp breakout point on top then power it up slowly. you can always remove this later it just gives an easy way for testing.
Also in the dark you may see were this buzzing is coming from.
Above all keep your distance!
PS from your picture I would say it may flash over near the bottom part, remember to keep everything smooth. My first coil was rather crude and had all sorts of things (small fires/flash-overs) happen.
Re: DRSSTC Tuning, UD2.7C
Uspring, Tue Apr 19 2016, 08:16AM
You should definitely add a breakout point to the top. It helps tuning especially if you're still much out of tune. Then play around with your primary tap, adding or subtracting quarter turns.
The breakout point is essential also for another reason: For best performance, the secondary must be tuned somewhat higher than the primary. When the arc begins to grow it will then add capacitance to the top and pull the coil into tune. That means also, that the coil will be initially somewhat out of tune, providing not very much voltage. A breakout point will help to start the arc in this condition.
Uspring, Tue Apr 19 2016, 08:16AM
You should definitely add a breakout point to the top. It helps tuning especially if you're still much out of tune. Then play around with your primary tap, adding or subtracting quarter turns.
The breakout point is essential also for another reason: For best performance, the secondary must be tuned somewhat higher than the primary. When the arc begins to grow it will then add capacitance to the top and pull the coil into tune. That means also, that the coil will be initially somewhat out of tune, providing not very much voltage. A breakout point will help to start the arc in this condition.
Re: DRSSTC Tuning, UD2.7C
orac12, Tue Apr 19 2016, 08:54AM
I did have a small breakout point, but that was just a piece of solder wrapped around and sticking out. I have completed a proper breakout point tonight and will check secondary frequency in the next few days.
Blackcurrant: What part are you referring to at the bottom that you suspect may flash over?
orac12, Tue Apr 19 2016, 08:54AM
I did have a small breakout point, but that was just a piece of solder wrapped around and sticking out. I have completed a proper breakout point tonight and will check secondary frequency in the next few days.
Blackcurrant: What part are you referring to at the bottom that you suspect may flash over?
Re: DRSSTC Tuning, UD2.7C
Blackcurrant, Tue Apr 19 2016, 12:52PM
The closest part between the two coils, although I had this happening on a spark gap based coil. It might not be quite the same with a transistor driven one.
Blackcurrant, Tue Apr 19 2016, 12:52PM
The closest part between the two coils, although I had this happening on a spark gap based coil. It might not be quite the same with a transistor driven one.
Re: DRSSTC Tuning, UD2.7C
Graham Armitage, Tue Apr 19 2016, 03:40PM
I had the same ringing/spikes with my UD2.7 driver, but the phase shifting helped. It does not remove the spikes, but I could shift the peak spikes within the beat envelope. LoneOceans suggestion was to adjust the phase so that the high spike occurred at the beginning of the pulse and and was smallest just before the end of the pulse. That way you don't get the spike on top of the peak of the envelope. Running like this I never had any problem and the IGBT ran very cool.
I did my testing at around 30-40 amps and it seemed ok for low power testing.
Graham Armitage, Tue Apr 19 2016, 03:40PM
I had the same ringing/spikes with my UD2.7 driver, but the phase shifting helped. It does not remove the spikes, but I could shift the peak spikes within the beat envelope. LoneOceans suggestion was to adjust the phase so that the high spike occurred at the beginning of the pulse and and was smallest just before the end of the pulse. That way you don't get the spike on top of the peak of the envelope. Running like this I never had any problem and the IGBT ran very cool.
I did my testing at around 30-40 amps and it seemed ok for low power testing.
Re: DRSSTC Tuning, UD2.7C
orac12, Wed Apr 20 2016, 02:48AM
Closer up picture of between the primary and secondary. There is no real sharp edges, but we will see what happens.
Measured the secondary frequency at 35.71 khz.
Just replacing a precharge resistor, then will check freq of primary and adjust.
orac12, Wed Apr 20 2016, 02:48AM
Closer up picture of between the primary and secondary. There is no real sharp edges, but we will see what happens.
Measured the secondary frequency at 35.71 khz.
Just replacing a precharge resistor, then will check freq of primary and adjust.
Re: DRSSTC Tuning, UD2.7C
orac12, Fri Apr 22 2016, 11:45PM
Ok, so started having some flash over between primary and secondary.
Whats the best way of stopping this?
Options I see are:
Take some inner turns out of the primary to give more space between the two.
Lift the secondary higher so its further away.
What are other people doing to try and prevent flash over?
orac12, Fri Apr 22 2016, 11:45PM
Ok, so started having some flash over between primary and secondary.
Whats the best way of stopping this?
Options I see are:
Take some inner turns out of the primary to give more space between the two.
Lift the secondary higher so its further away.
What are other people doing to try and prevent flash over?
Re: DRSSTC Tuning, UD2.7C
Antonio, Sat Apr 23 2016, 01:40AM
You can keep the inner end of the primary coil grounded. Note that the currect tune of a DRSSTC is not with the primary and secondary exactly resonating at the same frequency, even ideally. The difference is small if the coupling coefficient is not too high, however. The waveforms show significant voltage drop at the driver, and strange spikes in the middle of the half cycles that should not be there. Verify if the connections used in the measurements are correct, with the oscilloscope correctly grounded.
Antonio, Sat Apr 23 2016, 01:40AM
You can keep the inner end of the primary coil grounded. Note that the currect tune of a DRSSTC is not with the primary and secondary exactly resonating at the same frequency, even ideally. The difference is small if the coupling coefficient is not too high, however. The waveforms show significant voltage drop at the driver, and strange spikes in the middle of the half cycles that should not be there. Verify if the connections used in the measurements are correct, with the oscilloscope correctly grounded.
Re: DRSSTC Tuning, UD2.7C
Blackcurrant, Sat Apr 23 2016, 09:24PM
I see you can easily put more space between pri and sec coils by just starting the pri coil further out, also you could put some insulating tubing on the first pri turn if needed after.
I would run the thing with a current limited power supply, say 30v on the Bus until you figure out whats happening with the wave forms etc this way even if somethings not quite right you will save things melting.
Blackcurrant, Sat Apr 23 2016, 09:24PM
I see you can easily put more space between pri and sec coils by just starting the pri coil further out, also you could put some insulating tubing on the first pri turn if needed after.
I would run the thing with a current limited power supply, say 30v on the Bus until you figure out whats happening with the wave forms etc this way even if somethings not quite right you will save things melting.
Re: DRSSTC Tuning, UD2.7C
Hydron, Sun Apr 24 2016, 09:57AM
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Hydron, Sun Apr 24 2016, 09:57AM
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sun Apr 24 2016, 11:19AM
Yes good question!
I was going to ask the same thing.
Im in Tauranga Orac12, send me a PM if you like to get in contact.
I am working on my first DRSSTC and i have no idea what problems i will encounter, i may come across the same issues no doubt, but we can at least exchange some information on what we both learn with our coils.
nzoomed, Sun Apr 24 2016, 11:19AM
Hydron wrote ...
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Insulation can actually make the problem worse - the E-field gets concentrated in the airgap (due to the dielectric constant of the insulation being significantly higher than air's 1) and the air gap is now smaller due to the insulation you just put there. My vote would be to start the primary a little further away.
Another thing to check, is the inner of the primary connected to one bridge output? The end of the primary with the capacitor connection has significantly higher voltages present on it.
Edit: forgot to ask, where about in NZ is this coil? Good to see a few more NZ coilers on here - I'm living in the UK right now but the stuff I built is still in Auckland; am looking forward to having a go at getting my QCW working when I'm back in August.
Yes good question!
I was going to ask the same thing.
Im in Tauranga Orac12, send me a PM if you like to get in contact.
I am working on my first DRSSTC and i have no idea what problems i will encounter, i may come across the same issues no doubt, but we can at least exchange some information on what we both learn with our coils.
Re: DRSSTC Tuning, UD2.7C
orac12, Mon Apr 25 2016, 09:54PM
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
I'm in Hamilton.
orac12, Mon Apr 25 2016, 09:54PM
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
I'm in Hamilton.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Mon Apr 25 2016, 11:10PM
OK, thats pretty handy to me.
I have had no experience in tuning them either so i dont know what i will encounter when i fire mine up first go.
nzoomed, Mon Apr 25 2016, 11:10PM
orac12 wrote ...
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
I'm in Hamilton.
The inner of the primary is connected to the MMC, so thats a good point. I will take some turns off the inner to give a bigger gap and connect it to the bridge output at the same time. Hopefully that should solve that problem.
I'm in Hamilton.
OK, thats pretty handy to me.
I have had no experience in tuning them either so i dont know what i will encounter when i fire mine up first go.
Re: DRSSTC Tuning, UD2.7C
Goodchild, Tue Apr 26 2016, 01:54PM
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
Goodchild, Tue Apr 26 2016, 01:54PM
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
Re: DRSSTC Tuning, UD2.7C
loneoceans, Tue Apr 26 2016, 04:46PM
That's right; also another point - it's hard to see from the current shots you have - could you zoom in into one of the transition points? You're having some quick transitions on the gate drive at each turn on. Initial guess could be that your IGBTs are turning on too slowly - what gate resistor are you using and which specific IGBTs? Otherwise the driver looks like it's doing just fine.
loneoceans, Tue Apr 26 2016, 04:46PM
Goodchild wrote ...
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
You need to do a serious double check of your bridge. The fact that you have a negative going spike during the rectification period (when the IGBTs are not driven) means that it has nothing to do with your controller.
I would recommend posting a photo of the bridge. Folks here will be able to tell very quickly if you have something out of place.
That's right; also another point - it's hard to see from the current shots you have - could you zoom in into one of the transition points? You're having some quick transitions on the gate drive at each turn on. Initial guess could be that your IGBTs are turning on too slowly - what gate resistor are you using and which specific IGBTs? Otherwise the driver looks like it's doing just fine.
Re: DRSSTC Tuning, UD2.7C
orac12, Tue Apr 26 2016, 08:52PM
Ok, I'm going to change the polarity of the primary and get some new scope shots. Those ones in the first post are a bit old now.
Just to be sure I'm doing the right thing ( and not getting different waveforms because I've done something different), how is everyone scoping their bridges? I have a x10 probe on the output of the bridge and a CT on the output connected to the primary coil.
The IGBT's are CM600HA-24H and using 4.7 ohm gate resistors.
orac12, Tue Apr 26 2016, 08:52PM
Ok, I'm going to change the polarity of the primary and get some new scope shots. Those ones in the first post are a bit old now.
Just to be sure I'm doing the right thing ( and not getting different waveforms because I've done something different), how is everyone scoping their bridges? I have a x10 probe on the output of the bridge and a CT on the output connected to the primary coil.
The IGBT's are CM600HA-24H and using 4.7 ohm gate resistors.
Re: DRSSTC Tuning, UD2.7C
meawoppl, Tue Apr 26 2016, 09:59PM
Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
meawoppl, Tue Apr 26 2016, 09:59PM
Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
- CM600's get pretty hot during operation. I would make sure your drive wires aren't sandwitched b/t them
- It is also common to add a bias to the charge/discharge cycle on these to minimize shoot-through.
- I have a CM600 face-mounting board that incorporates these (and nice connectors), our coil became more reliable when we replaced the deadbugs in that segment of our design.
- Make sure you have read the application notes for the UD27, there are a couple components to adjust for the big brick IGBT's
Re: DRSSTC Tuning, UD2.7C
orac12, Tue Apr 26 2016, 10:52PM
The drive wires do go between them, but there is room and are not sandwiched tightly. Will keep an eye on it and make sure they don't get hot though.
What do you mean by bias on the charge / discharge cycle?
I have changed C33 to 2.2nF on the UD. Is there anything else that needs adjusting? I have gone over the notes multiple times, but its a lot to learn all at once and I may have missed something.
orac12, Tue Apr 26 2016, 10:52PM
meawoppl wrote ...
Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
Where it has the gap / dropped half cycle, I believe that is where the drive has stopped / IGBT's are off and current is ringing back and forth? Thats why current is out of phase at that point?Big thing: It looks like you drop a half cycle in the control somehow. Your LC and drive seem out of phase, which will damp the oscillation...
A couple little things:
- CM600's get pretty hot during operation. I would make sure your drive wires aren't sandwitched b/t them
- It is also common to add a bias to the charge/discharge cycle on these to minimize shoot-through.
- I have a CM600 face-mounting board that incorporates these (and nice connectors), our coil became more reliable when we replaced the deadbugs in that segment of our design.
- Make sure you have read the application notes for the UD27, there are a couple components to adjust for the big brick IGBT's
The drive wires do go between them, but there is room and are not sandwiched tightly. Will keep an eye on it and make sure they don't get hot though.
What do you mean by bias on the charge / discharge cycle?
I have changed C33 to 2.2nF on the UD. Is there anything else that needs adjusting? I have gone over the notes multiple times, but its a lot to learn all at once and I may have missed something.
Re: DRSSTC Tuning, UD2.7C
orac12, Thu Apr 28 2016, 08:17AM
OK, I have changed the polarity of the primary so that the MMC is connected to the outside of the primary and the bridge output connected to the inside, I also removed two turns from the side to give more room. I then retuned the primary to about 35kHz (slightly lower than secondary).
These scope shots were taken at 90VDC bus, 100uS on time. Scope probe connected across bridge output, current transformer on the bridge output to the outside of the primary.
Still seem to be having large spikes, have tried a whole range of inductors and only seem to make it worse by winding the inductor all the way to the bottom and bottoming it out. Other than that, cannot seem to make it any better.
Maybe a snubber problem??
orac12, Thu Apr 28 2016, 08:17AM
OK, I have changed the polarity of the primary so that the MMC is connected to the outside of the primary and the bridge output connected to the inside, I also removed two turns from the side to give more room. I then retuned the primary to about 35kHz (slightly lower than secondary).
These scope shots were taken at 90VDC bus, 100uS on time. Scope probe connected across bridge output, current transformer on the bridge output to the outside of the primary.
Still seem to be having large spikes, have tried a whole range of inductors and only seem to make it worse by winding the inductor all the way to the bottom and bottoming it out. Other than that, cannot seem to make it any better.
Maybe a snubber problem??
Re: DRSSTC Tuning, UD2.7C
orac12, Thu Apr 28 2016, 08:20AM
Kepp forgetting to convert images from .bmp ....
Closer up shot.. I tuned the inductor so current crossed as close to zero as possible, this minimised spikes in the current and you can hear a noticeable increase in noise from the breakout point (gets louder)
orac12, Thu Apr 28 2016, 08:20AM
Kepp forgetting to convert images from .bmp ....
Closer up shot.. I tuned the inductor so current crossed as close to zero as possible, this minimised spikes in the current and you can hear a noticeable increase in noise from the breakout point (gets louder)
Re: DRSSTC Tuning, UD2.7C
Blackcurrant, Thu Apr 28 2016, 10:06PM
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Blackcurrant, Thu Apr 28 2016, 10:06PM
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Re: DRSSTC Tuning, UD2.7C
orac12, Thu Apr 28 2016, 10:25PM
Where should the snubber caps be across? I have seen schematics that show them across the DC bus, and then pictures and other information showing them across collector and emitter.
Will check gate signals.
orac12, Thu Apr 28 2016, 10:25PM
Blackcurrant wrote ...
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Where should the snubber caps be across? I have seen schematics that show them across the DC bus, and then pictures and other information showing them across collector and emitter.
Will check gate signals.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Thu Apr 28 2016, 10:36PM
AFAIK, they go across the DC bus, but thats essentially the same thing as collector and emitter anyway.
The negative rail connects the emitters from both IGBT's together and same with the collectors to the positive rail respectively.
Most people bolt them to the collector and emitter terminals such as this:
nzoomed, Thu Apr 28 2016, 10:36PM
orac12 wrote ...
Where should the snubber caps be across? I have seen schematics that show them across the DC bus, and then pictures and other information showing them across collector and emitter.
Will check gate signals.
Blackcurrant wrote ...
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Have you had a look at the gate drive waveform? (careful with the scope ground lead)
It took me some time to optimize the GDT
A small gate resister may drive it too fast and ring
maybe try an ohm or two more see if the ringing goes down
also keep the GDT twisted wires all the way up, minimize leakage inductance.
I take it those black things are snubber caps across the bridge
One thing I would tune the coils at the same frequency to start with, then fine tune (shift pri res lower) after it was running ok
Where should the snubber caps be across? I have seen schematics that show them across the DC bus, and then pictures and other information showing them across collector and emitter.
Will check gate signals.
AFAIK, they go across the DC bus, but thats essentially the same thing as collector and emitter anyway.
The negative rail connects the emitters from both IGBT's together and same with the collectors to the positive rail respectively.
Most people bolt them to the collector and emitter terminals such as this:
Re: DRSSTC Tuning, UD2.7C
orac12, Fri Apr 29 2016, 02:58AM
Have done some experimenting with different snubbers etc and taken shots of gate signal.
Gate signal
Gate signal close up
10uF snubber across collector emitter
10uF snubber across collector emitter close up
20uF across collector emitter:
With no snubber
With no snubber close up
orac12, Fri Apr 29 2016, 02:58AM
Have done some experimenting with different snubbers etc and taken shots of gate signal.
Gate signal
Gate signal close up
10uF snubber across collector emitter
10uF snubber across collector emitter close up
20uF across collector emitter:
With no snubber
With no snubber close up
Re: DRSSTC Tuning, UD2.7C
Kizmo, Fri Apr 29 2016, 06:47AM
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Kizmo, Fri Apr 29 2016, 06:47AM
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Re: DRSSTC Tuning, UD2.7C
orac12, Fri Apr 29 2016, 07:18AM
Ok, thanks for the clarification. I have tryed all sorts of things (but at low power, and lucky the cm600's are resistant to abuse) and haven't damaged anything catastrophically yet.
It was just pictures and caps recommended for CM600's stated they bolted across the IGBT, but they may have been dual IGBT modules.
orac12, Fri Apr 29 2016, 07:18AM
Kizmo wrote ...
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Ok, thanks for the clarification. I have tryed all sorts of things (but at low power, and lucky the cm600's are resistant to abuse) and haven't damaged anything catastrophically yet.
It was just pictures and caps recommended for CM600's stated they bolted across the IGBT, but they may have been dual IGBT modules.
Re: DRSSTC Tuning, UD2.7C
Kizmo, Fri Apr 29 2016, 08:05AM
I cleaned up your double post mistake :)
But yeah, regarding your switching spikes, dont be too worried about them. There is a interesting physics thing going on in your bridge which is causing most of these spikes. And they are much more visible large bridges like yours.
Have a look at CM600 datasheet:
We are now interested in the "Coes" value
As you can see the IGBT open state capacitance is largely depending on the voltage that is applied over Collector-emitter! And imagine what happens at your bridge when for example high side transistor turns on and low side transistor turns off. The emitter of the low side brick is tied to negative bus rail, and collector is quickly whacked to the full bus voltage which means the parasitic capacitance inside of the brick will be charged to your dc bus voltage at very high voltage rise time. And that charge current must travel through all parasitic inductances that your bridge has.
As you increase your bus voltage, your parasitic capacitance will decrease and amplitude of these transients related to the bus voltage will go down. My big coil does that too, at 100V bus the transients are almost 200% above bus voltage. But at 650V they are only maybe 20% over.
I would tune the phase lead for switching ever so slightly before zero crossings and leave it there.
Kizmo, Fri Apr 29 2016, 08:05AM
I cleaned up your double post mistake :)
But yeah, regarding your switching spikes, dont be too worried about them. There is a interesting physics thing going on in your bridge which is causing most of these spikes. And they are much more visible large bridges like yours.
Have a look at CM600 datasheet:
We are now interested in the "Coes" value
prx app note wrote ...
Coes – Output Capacitance
This is the output capacitance measured between the
collector and emitter terminals with the gate shorted to
the emitter for AC voltages. Coes is made up of the
collector to emitter capacitance (CCE) in parallel with
the gate to collector capacitance (CGC), or
Coes = Cce + Cgc
For soft switching applications, Coes is important
because it can affect the resonance of the circuit.
Coes – Output Capacitance
This is the output capacitance measured between the
collector and emitter terminals with the gate shorted to
the emitter for AC voltages. Coes is made up of the
collector to emitter capacitance (CCE) in parallel with
the gate to collector capacitance (CGC), or
Coes = Cce + Cgc
For soft switching applications, Coes is important
because it can affect the resonance of the circuit.
As you can see the IGBT open state capacitance is largely depending on the voltage that is applied over Collector-emitter! And imagine what happens at your bridge when for example high side transistor turns on and low side transistor turns off. The emitter of the low side brick is tied to negative bus rail, and collector is quickly whacked to the full bus voltage which means the parasitic capacitance inside of the brick will be charged to your dc bus voltage at very high voltage rise time. And that charge current must travel through all parasitic inductances that your bridge has.
As you increase your bus voltage, your parasitic capacitance will decrease and amplitude of these transients related to the bus voltage will go down. My big coil does that too, at 100V bus the transients are almost 200% above bus voltage. But at 650V they are only maybe 20% over.
I would tune the phase lead for switching ever so slightly before zero crossings and leave it there.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Fri Apr 29 2016, 11:53AM
Dont think this is even possible since both are connected internally and there is no connection possible.
nzoomed, Fri Apr 29 2016, 11:53AM
Kizmo wrote ...
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Dont think this is even possible since both are connected internally and there is no connection possible.
Re: DRSSTC Tuning, UD2.7C
Hydron, Fri Apr 29 2016, 09:19PM
edit: second set of scope shots look OK, I had similar questions when first starting to use CM300s:
Hydron, Fri Apr 29 2016, 09:19PM
nzoomed wrote ...
Dont think this is even possible since both are connected internally and there is no connection possible.
Kizmo is 100% correct. On dual-IGBT bricks capacitor goes between C1 and E2, across the DC bus (skip the C2E1 connection that is one leg of the bridge output). On single IGBT bricks you need to connect the cap between the two bricks, across the DC bus connections (it ALWAYS goes across the DC bus).Kizmo wrote ...
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Dont think this is even possible since both are connected internally and there is no connection possible.
edit: second set of scope shots look OK, I had similar questions when first starting to use CM300s:
Re: DRSSTC Tuning, UD2.7C
Blackcurrant, Fri Apr 29 2016, 11:13PM
I can't see the under side of those caps but maybe
Solder a copper strip on to them so it goes out towards the bus, then fold it 90Deg and use the bus bolt holes already there. So the caps will be in the same place but sit higher up.
just for info
Fig2 near bottom
Blackcurrant, Fri Apr 29 2016, 11:13PM
I can't see the under side of those caps but maybe
Solder a copper strip on to them so it goes out towards the bus, then fold it 90Deg and use the bus bolt holes already there. So the caps will be in the same place but sit higher up.
just for info
Fig2 near bottom
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sat Apr 30 2016, 08:41AM
Yes he is correct, i was on a different wavelength sorry.
Here is a photo of my inverter ive just completed assembly of.
Orac12, you can see how the snubbers should be fitted to a Dual IGBT module.
I see yours are single modules?
.
nzoomed, Sat Apr 30 2016, 08:41AM
Hydron wrote ...
edit: second set of scope shots look OK, I had similar questions when first starting to use CM300s:
nzoomed wrote ...
Dont think this is even possible since both are connected internally and there is no connection possible.
Kizmo is 100% correct. On dual-IGBT bricks capacitor goes between C1 and E2, across the DC bus (skip the C2E1 connection that is one leg of the bridge output). On single IGBT bricks you need to connect the cap between the two bricks, across the DC bus connections (it ALWAYS goes across the DC bus).Kizmo wrote ...
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Yes the snubber/decoupling capacitors should be between low side side transistor emitter and high side transistor collector.
If you place your capacitors between collector and emitter of same transistor very bad things will happen
Dont think this is even possible since both are connected internally and there is no connection possible.
edit: second set of scope shots look OK, I had similar questions when first starting to use CM300s:
Yes he is correct, i was on a different wavelength sorry.
Here is a photo of my inverter ive just completed assembly of.
Orac12, you can see how the snubbers should be fitted to a Dual IGBT module.
I see yours are single modules?
.
Re: DRSSTC Tuning, UD2.7C
orac12, Sat Apr 30 2016, 09:41PM
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
orac12, Sat Apr 30 2016, 09:41PM
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sun May 01 2016, 10:44AM
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
nzoomed, Sun May 01 2016, 10:44AM
orac12 wrote ...
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
Re: DRSSTC Tuning, UD2.7C
orac12, Sun May 01 2016, 08:52PM
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
orac12, Sun May 01 2016, 08:52PM
nzoomed wrote ...
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
orac12 wrote ...
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sun May 01 2016, 10:06PM
OK, you may need more then possibly, i can see some 4uf on ebay but are only rated around 630v.
You could put 2x 2uf in parallel each side of the bus and you would get 4UF, which should do the trick for you.
nzoomed, Sun May 01 2016, 10:06PM
orac12 wrote ...
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
nzoomed wrote ...
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
orac12 wrote ...
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
Yeah mine are single. Next one will use dual igbt module.
After re-reading the replies this morning it all makes a lot more sense and my original configuration was correct.
Now the snubber caps I have, I've made up of a series parallel string of 3x2 20uF 350VDC which gives 13.2 uF at 1050V.
Im not sure how having them in series will affect their performance but I suspect it will..
Should I be looking for something more suitable?
I would recommend the Aerovox RGPB series 2uf 1000v, thats what ive got on mine and they seem to be very popular amongst coil builders.
More reliable to have a single cap rates at a higher voltage than stringing several together, however if they are good quality caps it should be OK.
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
OK, you may need more then possibly, i can see some 4uf on ebay but are only rated around 630v.
You could put 2x 2uf in parallel each side of the bus and you would get 4UF, which should do the trick for you.
Re: DRSSTC Tuning, UD2.7C
meawoppl, Mon May 02 2016, 04:44AM
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase.
It seemed strange to me, and possibly indicated some sort of control issue...
meawoppl, Mon May 02 2016, 04:44AM
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase.
It seemed strange to me, and possibly indicated some sort of control issue...
Re: DRSSTC Tuning, UD2.7C
orac12, Mon May 02 2016, 05:35AM
I believe that is where the IGBT's are turned off, and the residual voltage in the MMC and such things rings back and forth through the free wheel diodes, hence it shows out of phase.
Thats how I believe it works, if anyone can explain it better than me then I'd be learning something.
orac12, Mon May 02 2016, 05:35AM
meawoppl wrote ...
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase.
It seemed strange to me, and possibly indicated some sort of control issue...
In this link:
There is a weird "skip" where the 5th drive wave seems twice as long, then the whole thing is 1/2 cycle out of phase.
It seemed strange to me, and possibly indicated some sort of control issue...
I believe that is where the IGBT's are turned off, and the residual voltage in the MMC and such things rings back and forth through the free wheel diodes, hence it shows out of phase.
Thats how I believe it works, if anyone can explain it better than me then I'd be learning something.
Re: DRSSTC Tuning, UD2.7C
Hydron, Mon May 02 2016, 07:21AM
Hydron, Mon May 02 2016, 07:21AM
orac12 wrote ...
I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
I'd just go with what seems to work, if 2uF is enough to keep the ringing manageable then don't worry about stuffing more on there. Layout, inductance etc are probably far more critical than how much capacitance you have.I was going with the general rule of thumb 1uF per 100A, so that means I would need multiple anyway..
Re: DRSSTC Tuning, UD2.7C
orac12, Thu May 26 2016, 11:54PM
With some diodes across the gate resistors in anti parallel has removed all switching spikes.
orac12, Thu May 26 2016, 11:54PM
With some diodes across the gate resistors in anti parallel has removed all switching spikes.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Thu May 26 2016, 11:59PM
That's great to hear!
nzoomed, Thu May 26 2016, 11:59PM
orac12 wrote ...
With some diodes across the gate resistors in anti parallel has removed all switching spikes.
With some diodes across the gate resistors in anti parallel has removed all switching spikes.
That's great to hear!
Re: DRSSTC Tuning, UD2.7C
orac12, Fri Jun 17 2016, 10:36PM
Quick video.
Need to build a new mmc
orac12, Fri Jun 17 2016, 10:36PM
Quick video.
Need to build a new mmc
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sat Jun 18 2016, 05:25AM
nzoomed, Sat Jun 18 2016, 05:25AM
orac12 wrote ...
Need to build a new mmc
Are you wanting to raise its capacity or current/voltage rating?Need to build a new mmc
Re: DRSSTC Tuning, UD2.7C
orac12, Sat Jun 18 2016, 07:06AM
It's lacking in current rating.
orac12, Sat Jun 18 2016, 07:06AM
nzoomed wrote ...
orac12 wrote ...
Need to build a new mmc
Are you wanting to raise its capacity or current/voltage rating?Need to build a new mmc
It's lacking in current rating.
Re: DRSSTC Tuning, UD2.7C
nzoomed, Sat Jun 18 2016, 07:23AM
Im wondering if i need to raise mine more, although with OCD cutting at 600A, im getting streamers about 1.5M long! So i should hit the 2M mark easily at 700A.
Im concerned that i should have cooling added to mine, how hot do these typically get? I do feel some warmth on it if i put my hand up to it after use.
The IGBT's on the other hand, well the heatsink still feels cold, so i guess thats a good sign that the IGBT's are handling it fine?
nzoomed, Sat Jun 18 2016, 07:23AM
Im wondering if i need to raise mine more, although with OCD cutting at 600A, im getting streamers about 1.5M long! So i should hit the 2M mark easily at 700A.
Im concerned that i should have cooling added to mine, how hot do these typically get? I do feel some warmth on it if i put my hand up to it after use.
The IGBT's on the other hand, well the heatsink still feels cold, so i guess thats a good sign that the IGBT's are handling it fine?
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