First SSTC's first light! What tweaks/refinements are possible?
aonomus, Sun Sept 28 2008, 03:50AMFor the last 3 weeks I've been on and off building Steve Ward's Mini SSTC5
Right, so after a frustrating day of accidentally blowing my halfbridge mosfets, I fixed the problem (one loose wire from the GDT = avalanching power through one mosfet that fails as a short, avalanching through the other mosfet), and ran my SSTC from 30VDC off of a benchtop power supply.
Anyways, my questions are how to give this project its finishing touches, more specifically a good breakout point ontop (apparently galvanized screws and solder do not work), and also if there is a way to prevent corrona from forming on the feedback antenna? Any other finishing touches that would either improve performance or just make it look cooler? I'll take more photos tomorrow when there is decent lighting, but the body of the SSTC is made from MDF and dimensional lumber.
From the pictures below, you can see that:
1. I do get breakout, however I am also loosing a crapton of energy through the little bend where the wire goes onto the plexi, I will varnish that several times to fix that problem.
2. You can see just *slightly* some corrona forming on the feedback antenna, its some scrap enameled magnet wire from a unwound torroid, will extra varnish/insulation fix this? What happens if I get a full fledged strike to the antenna?
(Click the photo, you won't be able to see the feedback antenna's corrona at this size)
Re: First SSTC's first light! What tweaks/refinements are possible?
MRacerxdl, Sun Sept 28 2008, 05:37PM
If you use the Clamp diodes, its not a problem the corona at Antenna, once, when I was testing it opened an arc between the top of load and the antenna, nothing happens, only the wire gets burned.
The better thing to stop corona from other points is getting a topload with a breakpoint, not direct a breakpoint. Also topload increase sparks.
MRacerxdl, Sun Sept 28 2008, 05:37PM
If you use the Clamp diodes, its not a problem the corona at Antenna, once, when I was testing it opened an arc between the top of load and the antenna, nothing happens, only the wire gets burned.
The better thing to stop corona from other points is getting a topload with a breakpoint, not direct a breakpoint. Also topload increase sparks.
Re: First SSTC's first light! What tweaks/refinements are possible?
uzzors2k, Sun Sept 28 2008, 07:05PM
Making a little loop on the end of the antenna and moving it further away should decrease the amount of corona. For your next coil bring the secondary wire in through the side of the former, and cover the bend with lots of epoxy.
uzzors2k, Sun Sept 28 2008, 07:05PM
Making a little loop on the end of the antenna and moving it further away should decrease the amount of corona. For your next coil bring the secondary wire in through the side of the former, and cover the bend with lots of epoxy.
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Mon Sept 29 2008, 12:00PM
Topload and breakout point blew another set of MOSFETs + fuse. I think I'll have to adjust the primary to have a longer off time and shorter on time....
aonomus, Mon Sept 29 2008, 12:00PM
Topload and breakout point blew another set of MOSFETs + fuse. I think I'll have to adjust the primary to have a longer off time and shorter on time....
Re: First SSTC's first light! What tweaks/refinements are possible?
MRacerxdl, Mon Sept 29 2008, 10:50PM
That can be much current consuming, how much turns have your primary?
I forgot to mention, that topload also increases the current.
MRacerxdl, Mon Sept 29 2008, 10:50PM
That can be much current consuming, how much turns have your primary?
I forgot to mention, that topload also increases the current.
Re: First SSTC's first light! What tweaks/refinements are possible?
uzzors2k, Tue Sept 30 2008, 12:25PM
? Do you mean the interrupter or actual primary? By tuning the primary you can set the coil to draw pretty much any current at any voltage.
uzzors2k, Tue Sept 30 2008, 12:25PM
aonomus wrote ...
I think I'll have to adjust the primary to have a longer off time and shorter on time....
I think I'll have to adjust the primary to have a longer off time and shorter on time....
? Do you mean the interrupter or actual primary? By tuning the primary you can set the coil to draw pretty much any current at any voltage.
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Tue Sept 30 2008, 08:07PM
Following some discussion on IRC about what things I could do to reduce the coronna on the wire leading up to the breakout point, Steve McConner suggested I use a open ring of copper pipe (ie: a circle with a small gap) and place it just above the offending point where more breakout likes to occur. Anyone have any thoughts on this? My only fear is that adding the copper pipe (in theory the copper pipe is smooth enough to prevent breakout, so all the energy continues onto the breakout point at the top) will act like a topload itself, and then cause another halfbridge failure.
Also, a more powerful example of the broken insulation is seen here:
Pushing the SSTC to higher levels with a breakout point works, I only need to be conservative as to how high a voltage I can apply to the primary (before MOSFET breakdown). What I've noticed is that running off a benchtop power supply that can only produce 30VDC, the energy gets recycled back into the smoothing cap where I've seen it run up to 40VDC, and theoretically with my variac's range of 135V max, I might exceed the 200VDC rating of the MOSFETs (which might have been the cause of some failure early on).
aonomus, Tue Sept 30 2008, 08:07PM
Following some discussion on IRC about what things I could do to reduce the coronna on the wire leading up to the breakout point, Steve McConner suggested I use a open ring of copper pipe (ie: a circle with a small gap) and place it just above the offending point where more breakout likes to occur. Anyone have any thoughts on this? My only fear is that adding the copper pipe (in theory the copper pipe is smooth enough to prevent breakout, so all the energy continues onto the breakout point at the top) will act like a topload itself, and then cause another halfbridge failure.
Also, a more powerful example of the broken insulation is seen here:
Pushing the SSTC to higher levels with a breakout point works, I only need to be conservative as to how high a voltage I can apply to the primary (before MOSFET breakdown). What I've noticed is that running off a benchtop power supply that can only produce 30VDC, the energy gets recycled back into the smoothing cap where I've seen it run up to 40VDC, and theoretically with my variac's range of 135V max, I might exceed the 200VDC rating of the MOSFETs (which might have been the cause of some failure early on).
Re: First SSTC's first light! What tweaks/refinements are possible?
CT2, Tue Sept 30 2008, 09:24PM
I would suggest the copper ring, I did the exact same thing for my coil and it worked perfectly. It will have some "topload" like behavior but it shouldn't destroy your bridge. If you are getting too much current try adding more turns to your primary, this will lower the current, as you increase the voltage you will most likely HAVE to do this. I would recomend not running it without that copper ring steve suggested, the breakout at the point where the wire bends is hot stuff, it will either burn your wire or melt your coil form... bad stuff.
EDIT
This is how I did my ring
or . The first one is just 14 AWG wire bent into a ring, the second one uses copper pipe.
CT2, Tue Sept 30 2008, 09:24PM
I would suggest the copper ring, I did the exact same thing for my coil and it worked perfectly. It will have some "topload" like behavior but it shouldn't destroy your bridge. If you are getting too much current try adding more turns to your primary, this will lower the current, as you increase the voltage you will most likely HAVE to do this. I would recomend not running it without that copper ring steve suggested, the breakout at the point where the wire bends is hot stuff, it will either burn your wire or melt your coil form... bad stuff.
EDIT
This is how I did my ring
or 
. The first one is just 14 AWG wire bent into a ring, the second one uses copper pipe.Re: First SSTC's first light! What tweaks/refinements are possible?
MRacerxdl, Tue Sept 30 2008, 10:21PM
If your mosfets are for 200V, you can run perfectly a 127 Mains retified, I was runned IRFP250 direct from mains, at Full Wave Smoothed Supply (150-170VDC) it doesnt make anything to the mosfets.
MRacerxdl, Tue Sept 30 2008, 10:21PM
If your mosfets are for 200V, you can run perfectly a 127 Mains retified, I was runned IRFP250 direct from mains, at Full Wave Smoothed Supply (150-170VDC) it doesnt make anything to the mosfets.
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Wed Oct 01 2008, 05:34AM
So after blowing a total of 10 (!!!) IRFP250N's, I tried replacing them with the MTW32N20E (more current, slightly slower) and changing the 555 to give a 10 uS on time, 20 uS off time pulse. With the slower pulse and slightly better MOSFET I've gotten some more power out of the SSTC (read: I can run a topload with enough power to cause the TV nearby to turn itself on) without blowing anything up (yet).
The one major recommendation I can give to anyone making their first SSTC: use panelmount breakers! (not the pushbutton type, actual toggle type which have both the bimetallic strip for slight overcurrent, and magnetic trip for spike/short overcurrent). While I am doing bad things by bypassing the fuse in my variac (fast blow is too fast for the breaker to trip), the time delay between fuse and breaker is negligible so long as I don't trip it too often.
Major variations from Steve Ward's design:
Secondary: 4" diam (instead of 4.5")
MOSFETs: MTW32N20E currently
Tank caps: 2x 1uF 1000V caps ($2 electronics goldmine) instead of 0.68uF
Edit: Note that most of the spark photos are taken at low power (20-30%) because it was about 1AM and I'm assuming people mind the noise, as well as the fact that TV's turn themseves on in this things presence...
Edit 2: I totally used seconds instead of microseconds.... a 10second pulse would fry any mosfets and blow the breaker yet again.
Photos:
Burning steel wool
Photoflash tube from a camera, overheats somewhat quickly so not recommended for prolonged usage
Aluminum foil wrapped over the breakout point, as it melts the point becomes rounded and breakout becomes harder. This eventually burned out (yet another) set of MOSFETs
aonomus, Wed Oct 01 2008, 05:34AM
So after blowing a total of 10 (!!!) IRFP250N's, I tried replacing them with the MTW32N20E (more current, slightly slower) and changing the 555 to give a 10 uS on time, 20 uS off time pulse. With the slower pulse and slightly better MOSFET I've gotten some more power out of the SSTC (read: I can run a topload with enough power to cause the TV nearby to turn itself on) without blowing anything up (yet).
The one major recommendation I can give to anyone making their first SSTC: use panelmount breakers! (not the pushbutton type, actual toggle type which have both the bimetallic strip for slight overcurrent, and magnetic trip for spike/short overcurrent). While I am doing bad things by bypassing the fuse in my variac (fast blow is too fast for the breaker to trip), the time delay between fuse and breaker is negligible so long as I don't trip it too often.
Major variations from Steve Ward's design:
Secondary: 4" diam (instead of 4.5")
MOSFETs: MTW32N20E currently
Tank caps: 2x 1uF 1000V caps ($2 electronics goldmine) instead of 0.68uF
Edit: Note that most of the spark photos are taken at low power (20-30%) because it was about 1AM and I'm assuming people mind the noise, as well as the fact that TV's turn themseves on in this things presence...
Edit 2: I totally used seconds instead of microseconds.... a 10second pulse would fry any mosfets and blow the breaker yet again.
Photos:
Burning steel wool
Photoflash tube from a camera, overheats somewhat quickly so not recommended for prolonged usage
Aluminum foil wrapped over the breakout point, as it melts the point becomes rounded and breakout becomes harder. This eventually burned out (yet another) set of MOSFETs
Re: First SSTC's first light! What tweaks/refinements are possible?
Coronafix, Wed Oct 01 2008, 11:54AM
Nice work! You got to try and fix that corona leak at the bend in the wire though, at higher power it will
eventually burn it out. I space wind the last 5 or so turns of the secondary to encourage this, but
you could try curving the last turn on more of an angle towards the top and try and take the bend out.
Epoxy or varnish will really help it. Cutting a curving channel in the side of the end cap where the leak is
and filling it with epoxy would really help.
The further away from 90 degree bends the better.
Love your layout, it shows a lot of thought.
Coronafix, Wed Oct 01 2008, 11:54AM
Nice work! You got to try and fix that corona leak at the bend in the wire though, at higher power it will
eventually burn it out. I space wind the last 5 or so turns of the secondary to encourage this, but
you could try curving the last turn on more of an angle towards the top and try and take the bend out.
Epoxy or varnish will really help it. Cutting a curving channel in the side of the end cap where the leak is
and filling it with epoxy would really help.
The further away from 90 degree bends the better.
Love your layout, it shows a lot of thought.
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Wed Oct 01 2008, 12:00PM
Yea, unfortunately since I didn't think that far ahead in terms of the secondary I'll be a bit of a loss but I'll just get the copper pipe sometime this week and try to fix it. In terms of the layout, I found myself backpedaling because the rubber feet on the bottom took up too much space in the end which could have given me more stability (ie: mount the GDT somewhere so it doesn't break wires so often).
I will definitely re-engineer the secondary for my next SSTC (likely a musical SSTC) to get around these problems, cutting a groove in the acrylic and filling in with some kind of epoxy sounds like a very good idea. The first piece of my SSTC built was the secondary, and I hadn't done as much research until now. Since I live in a small apartment I won't build beefy DRSSTCs till I have more space, and most importantly money (I have the parts for another SSTC lying around, but not for a DRSSTC).
aonomus, Wed Oct 01 2008, 12:00PM
Yea, unfortunately since I didn't think that far ahead in terms of the secondary I'll be a bit of a loss but I'll just get the copper pipe sometime this week and try to fix it. In terms of the layout, I found myself backpedaling because the rubber feet on the bottom took up too much space in the end which could have given me more stability (ie: mount the GDT somewhere so it doesn't break wires so often).
I will definitely re-engineer the secondary for my next SSTC (likely a musical SSTC) to get around these problems, cutting a groove in the acrylic and filling in with some kind of epoxy sounds like a very good idea. The first piece of my SSTC built was the secondary, and I hadn't done as much research until now. Since I live in a small apartment I won't build beefy DRSSTCs till I have more space, and most importantly money (I have the parts for another SSTC lying around, but not for a DRSSTC).
Re: First SSTC's first light! What tweaks/refinements are possible?
uzzors2k, Wed Oct 01 2008, 09:06PM
You still haven't provided any details on the primary winding. Given that the coil actually dies from low voltage tests unless interrupted, I assume you're using way too few turns. Beef it up man! Your coil should do CW from 40V without the mosfets so much as breaking a sweat. Toploads increase current by lowering fres (and other effects I'm not sure of) so you'll need more primary turns to keep the impedance the same. All of your problems are a matter of tuning! You can always remove turns once you have the coil under control.
uzzors2k, Wed Oct 01 2008, 09:06PM
You still haven't provided any details on the primary winding. Given that the coil actually dies from low voltage tests unless interrupted, I assume you're using way too few turns. Beef it up man! Your coil should do CW from 40V without the mosfets so much as breaking a sweat. Toploads increase current by lowering fres (and other effects I'm not sure of) so you'll need more primary turns to keep the impedance the same. All of your problems are a matter of tuning! You can always remove turns once you have the coil under control.
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Wed Oct 01 2008, 09:51PM
Well, details:
Currently 4.5 primary turns of 16AWG, the coil doesn't fail with low voltage tests, however they fail cold. I'm trying to find a suitable primary form to lower the coupling (and add more windings).
I'm still stumped overall as to why it fails with the topload. Since the coil runs off its own feedback via a 74HC14 it should stay in tune correct?
aonomus, Wed Oct 01 2008, 09:51PM
Well, details:
Currently 4.5 primary turns of 16AWG, the coil doesn't fail with low voltage tests, however they fail cold. I'm trying to find a suitable primary form to lower the coupling (and add more windings).
I'm still stumped overall as to why it fails with the topload. Since the coil runs off its own feedback via a 74HC14 it should stay in tune correct?
Re: First SSTC's first light! What tweaks/refinements are possible?
MRacerxdl, Wed Oct 01 2008, 10:20PM
4.5 Primary turns? I was used for my IRFP250 coil 7 Turns for a Half Bridge, and I get 20cm sparks :D
It can fail with topload because low turns, and the antenna can get massive signal and stops to work for a few nS, that can kill the mosfets.
Try to increase the turns to 10, and test it, if runs ok with no heat at mosfets (not on the heatsink, some times the mosfets heat in the front of it, but not on the heatsink) reduce the turns by 1, and try again.
MRacerxdl, Wed Oct 01 2008, 10:20PM
4.5 Primary turns? I was used for my IRFP250 coil 7 Turns for a Half Bridge, and I get 20cm sparks :D
It can fail with topload because low turns, and the antenna can get massive signal and stops to work for a few nS, that can kill the mosfets.
Try to increase the turns to 10, and test it, if runs ok with no heat at mosfets (not on the heatsink, some times the mosfets heat in the front of it, but not on the heatsink) reduce the turns by 1, and try again.
Re: First SSTC's first light! What tweaks/refinements are possible?
Coronafix, Wed Oct 01 2008, 10:45PM
4.5 turns is way too few turns, that explains why they are blowing.
Do about 20 and as Uzzors said, you can always remove some later. The impedance of the secondary wants to suck amps into it, if the primary impedance isn't enough to supply it, then the pump is going to blow (mosfets).
I'm sure there are better analogies but that's mine on the run this morning. :)
Coronafix, Wed Oct 01 2008, 10:45PM
4.5 turns is way too few turns, that explains why they are blowing.
Do about 20 and as Uzzors said, you can always remove some later. The impedance of the secondary wants to suck amps into it, if the primary impedance isn't enough to supply it, then the pump is going to blow (mosfets).
I'm sure there are better analogies but that's mine on the run this morning. :)
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Thu Oct 02 2008, 12:37AM
I just followed the schematic :/
With 20 turns should I have a low BPS or higher BPS?
I'm trying 10 turns now and I can support a topload at low BPS with easy breakout, and hard breakout at high BPS (near CW).
Yet another edit:
With primary at 10 turns with about 5 BPS and topload w/ breakout point I get nice 7" sparks
Overall, about 7-8" sparks
Full power, 1/5th second shutter speed
Full power, 1/50th second shutter speed
And video:
aonomus, Thu Oct 02 2008, 12:37AM
I just followed the schematic :/
With 20 turns should I have a low BPS or higher BPS?
I'm trying 10 turns now and I can support a topload at low BPS with easy breakout, and hard breakout at high BPS (near CW).
Yet another edit:
With primary at 10 turns with about 5 BPS and topload w/ breakout point I get nice 7" sparks
Overall, about 7-8" sparks
Full power, 1/5th second shutter speed
Full power, 1/50th second shutter speed
And video:
Re: First SSTC's first light! What tweaks/refinements are possible?
uzzors2k, Fri Oct 03 2008, 03:36PM
Haha, nice. First light with power always rocks. More turns will decrease the current draw, allowing you to use a higher duty cycle on your coil. I would find the interrupter setting which gives the best sparks, and then remove as many turns as you're comfortable with from there.
uzzors2k, Fri Oct 03 2008, 03:36PM
Haha, nice. First light with power always rocks. More turns will decrease the current draw, allowing you to use a higher duty cycle on your coil. I would find the interrupter setting which gives the best sparks, and then remove as many turns as you're comfortable with from there.
Re: First SSTC's first light! What tweaks/refinements are possible?
Ken M., Fri Oct 03 2008, 03:42PM
Very nice, you got it running and its looks similar to steves arcs and mine (I'm still dicking around fixing mine ><). Congradulations again!
Ken M., Fri Oct 03 2008, 03:42PM
Very nice, you got it running and its looks similar to steves arcs and mine (I'm still dicking around fixing mine ><). Congradulations again!
Re: First SSTC's first light! What tweaks/refinements are possible?
MRacerxdl, Fri Oct 03 2008, 09:56PM
You can try to use HalfWave retified mains. That will make the sparks grow a little and current gets down.
Now the arcs are looking good :D
MRacerxdl, Fri Oct 03 2008, 09:56PM
You can try to use HalfWave retified mains. That will make the sparks grow a little and current gets down.
Now the arcs are looking good :D
Re: First SSTC's first light! What tweaks/refinements are possible?
CT2, Sat Oct 04 2008, 12:53AM
Hey sweet sparks! Glad it's working, one thing though, your primary coil is wound directly over the secondary. If there is any sort of insulation failuer (say you added a topload, and it didn't want to break out, so all the voltage has to go somewhere) then you risk blowing your bridge, I think the same thing was happening to me befor. That may have been why that was happening, with the MOSFETs dieing cold. I'd say add something between them, and also try spacing the primary turns and/or raising the primary, that will change the length of the sparks dramatically (from experience).
CT2, Sat Oct 04 2008, 12:53AM
Hey sweet sparks! Glad it's working, one thing though, your primary coil is wound directly over the secondary. If there is any sort of insulation failuer (say you added a topload, and it didn't want to break out, so all the voltage has to go somewhere) then you risk blowing your bridge, I think the same thing was happening to me befor. That may have been why that was happening, with the MOSFETs dieing cold. I'd say add something between them, and also try spacing the primary turns and/or raising the primary, that will change the length of the sparks dramatically (from experience).
Re: First SSTC's first light! What tweaks/refinements are possible?
aonomus, Sat Oct 04 2008, 01:18AM
What makes a suitable primary coil form that is not PVC pipe? I don't feel like buying another 10ft of material that I won't use for a long time, perhaps some sort of tupperware container?
aonomus, Sat Oct 04 2008, 01:18AM
What makes a suitable primary coil form that is not PVC pipe? I don't feel like buying another 10ft of material that I won't use for a long time, perhaps some sort of tupperware container?
Re: First SSTC's first light! What tweaks/refinements are possible?
Coronafix, Sat Oct 04 2008, 03:25AM
You can use cardboard, but to be safe I would dry it in the oven and then coat it with enamel.
Nice work, looks good. You should give half wave a try, I reckon the sparks look good, less hot too.
Coronafix, Sat Oct 04 2008, 03:25AM
You can use cardboard, but to be safe I would dry it in the oven and then coat it with enamel.
Nice work, looks good. You should give half wave a try, I reckon the sparks look good, less hot too.
Re: First SSTC's first light! What tweaks/refinements are possible?
Ken M., Sat Oct 04 2008, 04:51AM
I used a peice of 6in dia 6in long peice of rubber attachement, the kind youd use to connect 2 6in dia pipes and just tightend down with hose clamps. Just remove the hose clamps and trim the rubber to fit snuggly over your secondary, and then ust aplly a crap load of electrical tape or some other kind of insulation material to cover up the joint. It works great, in my case I would get corona to build up on the out side of the insulated 10awg wire but never arc over since I had .5in of rubber between the pri and secondary, a well as aa good 2in of air\rubber from the top turn to the secondry.
Ken M., Sat Oct 04 2008, 04:51AM
I used a peice of 6in dia 6in long peice of rubber attachement, the kind youd use to connect 2 6in dia pipes and just tightend down with hose clamps. Just remove the hose clamps and trim the rubber to fit snuggly over your secondary, and then ust aplly a crap load of electrical tape or some other kind of insulation material to cover up the joint. It works great, in my case I would get corona to build up on the out side of the insulated 10awg wire but never arc over since I had .5in of rubber between the pri and secondary, a well as aa good 2in of air\rubber from the top turn to the secondry.
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