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Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Benjamin wrote ...
Hi, nzoomed, I just have a quick question. Where are you getting your ud 2.7 driver? Or are you building your own? Because if I ever build a big drsstc that's probably what I would want to use.
I got mine from loneoceans, he has got a thread here on getting the boards, he has plenty available too :)
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
nzoomed wrote ...
Im also unsure about the data provided in wintesla, everyone talks about JavaTC, but i cant get it to work because the values H1 and H2 for the secondary dont seem to be accepted, so i must be doing something wrong.
JavaTC should work fine - was invaluable while designing my coil, here are the inputs I used for my secondary (metric mode, note use of cm rather than mm as a unit, and the inconsistent use of diameter vs radius) 8 = Radius 1 8 = Radius 2 50 = Height 1 120 = Height 2 1920 = Turns 0.0315 = Wire Diameter
Also if the MMC cost looks too high, be aware that there are alternative to the 942C caps, especially for DRSSTCs with their lower peak currents than spark gap coils.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
nzoomed wrote ...
Im also unsure about the data provided in wintesla, everyone talks about JavaTC, but i cant get it to work because the values H1 and H2 for the secondary dont seem to be accepted, so i must be doing something wrong.
JavaTC should work fine - was invaluable while designing my coil, here are the inputs I used for my secondary (metric mode, note use of cm rather than mm as a unit, and the inconsistent use of diameter vs radius) 8 = Radius 1 8 = Radius 2 50 = Height 1 120 = Height 2 1920 = Turns 0.0315 = Wire Diameter
Also if the MMC cost looks too high, be aware that there are alternative to the 942C caps, especially for DRSSTCs with their lower peak currents than spark gap coils.
Yes i since found out i was using mm in JavaTC and thats where i went wrong! lol If you can suggest any other caps for the MMC that are cheaper, that would be good, i did think they were alot higher spec, but your right, alot of these are higher grade for use in a SGTC.
I was trying to find some eurofarad caps, but they are probably very high spec also.
Ive been going through reworking the secondary specs and now im going with a slightly heavier wire, i will use 30 AWG and now the coil will be having a H/D aspect of 4.51 which i believe is a desired coil ratio. The coil will now be 28.53 inches long with 2621 turns approx and an operating of 97.91 KHZ without toroid.
I should be able to keep the same sized toroid with this coil and hopefully this will significantly reduce the amount of flashover to the strike ring.
Here is the screenshot in JavaTC, if anything ive probably got alot better specs now.
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
That's more like the numbers I had, which worked (in my opinion) rather well. Your DC resistance is about double what I had, which will increase the secondary losses a bit, but the increased turns will lower the IGBT switching speed requirements, so it's a tradeoff.
You'll probably want to raise the toroid position a bit in JavaTC too, which will probably pull the frequency down a little bit as well.
One other thing - try not to post twice in a row. It's frowned upon in this forum, so better to edit the earlier post to add stuff.
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Here are some of the latest construction photos.
The "misti" fan grills were 3D printed and are an obvious tribute to the manufacturer of the IGBTs that will power this coil! They have LED backlit fans to light them up as shown in my avatar photo.
I added the primary coil last weekend and am still in the process of assembling the toroid, i still have to wire up everything to the UD board etc, but its almost done. Cant wait to try it for the first time.
Couple of questions, ive been reading a bit on setting the phase lead, and it seems you dont need to run the coil at full bus voltage when scoping the bridge output.
Is this correct? If so, this will make tuning my coil much simpler and safer and i wont need to worry about getting an expensive differential probe if i can just test it with an isolated 50VDC power supply.
I thought that the behaviour of the IGBT's may be different at higher voltages , but if this is not the case, thats good news. :)
Another question is on power connectors. Im using an IEC C19 / C20 connector for the HT supply. These are rated at 15A, so i though it should be sweet, however i see people using far more heavy duty power connectors on their coils of similar power to mine, so was wondering if i should use something a bit more beefy?
Thanks for your help, and please keep an eye on this thread, as i will have more questions to come thats for sure :)
Registered Member #30656
Joined: Tue Jul 30 2013, 02:40AM
Location: UK
Posts: 208
IEC plug should be fine.
As for scoping the output you can just grab a cheap 100x probe - they should be rated at least 1kV and are handy to have anyway (they normally have low input capacitance, so are also useful for probing sensitive circuits). Scope from earth to one bridge output, the waveform will be centered around 0V, but you should still be able to see what you need without investing in a differential probe, and you'll be able to run the coil up to realistic voltages as you do so. For reference see this waveform, captured as I described:
Registered Member #54503
Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288
Hydron wrote ...
IEC plug should be fine.
As for scoping the output you can just grab a cheap 100x probe - they should be rated at least 1kV and are handy to have anyway (they normally have low input capacitance, so are also useful for probing sensitive circuits). Scope from earth to one bridge output, the waveform will be centered around 0V, but you should still be able to see what you need without investing in a differential probe, and you'll be able to run the coil up to realistic voltages as you do so. For reference see this waveform, captured as I described:
OK ill look into getting one. I take it these are safe enough to protect the scope from high voltages? Do i still need an isolation transformer? I would need a fairly high wattage unit if im tuning it at full power.
Ive been working on the coil again this weekend and things are coming together nicely.
One question is regarding TVS Diodes.
Its supposed to be a good idea to put a TVS Clamp across each GDT output to protect the gates from any voltage spikes.
Im trying to find a suitable TVS diode on RS and the selection is huge.
What confuses me is that they say you need 30V TVS clamps, but i didnt think the gates of a CM300 could take much more than 20V?
I believe the voltage from the GDT is close to 19V so there is not much room for error.
When they say a 30V TVS clamp, is that supposed to be the minimum breakdown voltage or maximum breakdown voltage?
I would assume it would be the minimum. Is bi-directional the same as bipolar? Its important that they are bipolar i believe.
TIA :)
The gates of IGBTs used in coils are typically driven +15V. Datasheet maximums are +-20V, but coilers often overdrive the IGBTs. Having a greater gate voltage (e.g. +-24V) helps in a variety of ways such as forcing the IGBT into greater saturation, however at the risk of blowing out the gate, so YMMV.
If you're driving your IGBT at 19V, try the 1.5KE20CA or 22CA with a 20 or 22V clamp. These are bidirectional TVS diodes. Alternatively you can put back to back zener diodes of your desired voltage. The 1.5KE series come in 1.5KE_breakdownvolts_A/CA with the CA line being bidirectional (no polarity so they look like a diode with no white line). The breakdown voltage is the one you should be looking at. The clamping voltage is when the TVS becomes very conductive at its ~I_FSM rating (typically 00s of A), but typically just look at the breakdown voltage.
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Building my first DRSSTC - Updated thread...
