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4hv.org :: Forums :: Tesla Coils
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DC Resonant charging

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LD LANGER19
Mon Apr 11 2011, 03:18AM Print
LD LANGER19 Registered Member #3825 Joined: Sun Apr 10 2011, 08:50PM
Location:
Posts: 4
Hello, I am in the early stages of building my first DC Resonant TC and I am just curious about my charger and tank design and I'm wondering if anyone can throw in their two cents.

Charging:
MOT with voltage quadrupler (0.1 uF at 200% rated voltage for the doubler caps (string of 10uF) and string of 1000V diodes rated at 200%)

*Is the capacitance of the quadrupler too small to provide ample current?

Inductor:
8 MOT secondaries in series

*Should I be altering the cores ie. taking the primary off and introducing an air gap between the E and I? If I end up not grinding off the welds should I be shorting or opening the primary?

Tank Cap:

2 strings of 20: 940 series CDE caps 1200VDC at 0.1uF for a total of 24000VDC at 0.1uF

*I already bought the caps and the 942s were far to expensive but is this capacitance too small and will these caps survive the 16kV that the inductor will charge the cap?

Spark Gap:

3600rpm rotary with 10 electrodes for 600BPS.




Thanks for your time,

Daniel Lang


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ScotchTapeLord
Mon Apr 11 2011, 03:35AM
ScotchTapeLord Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
LD LANGER19 wrote ...

Hello, I am in the early stages of building my first DC Resonant TC and I am just curious about my charger and tank design and I'm wondering if anyone can throw in their two cents.

Charging:
MOT with voltage quadrupler (0.1 uF at 200% rated voltage for the doubler caps (string of 10uF) and string of 1000V diodes rated at 200%)

*Is the capacitance of the quadrupler too small to provide ample current?


Probably, but it depends on your definition of "ample" I suppose.

LD LANGER19 wrote ...

Inductor:
8 MOT secondaries in series

*Should I be altering the cores ie. taking the primary off and introducing an air gap between the E and I? If I end up not grinding off the welds should I be shorting or opening the primary?

You won't really know if that's necessary for sure until later on when you are tweaking. Probably best not to mess around with this yet.

LD LANGER19 wrote ...

Tank Cap:

2 strings of 20: 940 series CDE caps 1200VDC at 0.1uF for a total of 24000VDC at 0.1uF

*I already bought the caps and the 942s were far to expensive but is this capacitance too small and will these caps survive the 16kV that the inductor will charge the cap?


Your MOT will put out around 2kVAC. This peaks at 2000V*1.41 = 2820V. Quadrupled, this becomes 11280V, which when doubled by the choke, becomes 22560V peak. Cutting it a bit close there, eh? (It won't last long)


My advice would be to use two MOTs in series as your supply so that they are balanced about a common GND and ditch any kind of multiplier (use those in your tank if they are suitable).
If you do that, then you won't need as many MOTs in your choke and your tank capacitor bank will be suitable.
And once you get it working you can scale it up from there.

Just my opinion, though.
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LD LANGER19
Mon Apr 11 2011, 01:21PM
LD LANGER19 Registered Member #3825 Joined: Sun Apr 10 2011, 08:50PM
Location:
Posts: 4
That seems like a good idea. Would I also then need any caps to reduce the large ripple?

Thanks,
Daniel
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ScotchTapeLord
Mon Apr 11 2011, 03:40PM
ScotchTapeLord Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I recommend reading Richie Burnett's documentation on the matter.
Link2

As it says there, you do need a smoothing supply, but you can use a bank of electrolytic capacitors for that (though they need high ripple current ratings).
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haikara
Mon Apr 11 2011, 05:52PM
haikara Registered Member #3599 Joined: Mon Jan 10 2011, 05:50PM
Location:
Posts: 15
as you stated above,

your mmc should only get a total of 10nf.
2 strings of 20 .1uF
i suggest you need a really high bps there to compensate cuz ur tank cap is too small, u need atleast 30nf? i think

for your supply, 1 mot is good but 2 in series is better and more power. use voltage doubler too, serves as a ballast somewhat

in tesla coil duty, i think u dont need to filter the dc output of your supply but if u have the caps already just use it though
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ScotchTapeLord
Mon Apr 11 2011, 06:23PM
ScotchTapeLord Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
If you don't use filtering then it will need to be tuned to the incoming line frequency and you will be running AC resonant, so you wouldn't even need rectifiers, but you would be limited to 2x line frequency for your BPS.

If you want DC charging then you need the capacitor as a reservoir.

You can read more about different modes of operation on the site I linked.
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LD LANGER19
Tue Apr 12 2011, 08:52PM
LD LANGER19 Registered Member #3825 Joined: Sun Apr 10 2011, 08:50PM
Location:
Posts: 4
Thanks everyone for the info, very helpful in finalising my design. I just have one thing I'm not quite sure of:

I'm going to use two MOT's in series balanced about a common ground for ~4kV --> then full wave rectified for +2kV and -2kV respective to ground --> Then put a large electrolytic (polarized) capacitor in parallel across the +2kV and -2kV terminals to reduce the ripple significantly.

Now, will this cap in parallel double the voltage seen at the charging inductor?

Thanks,
Daniel
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ScotchTapeLord
Tue Apr 12 2011, 11:57PM
ScotchTapeLord Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
The capacitor will be charged to the peak voltage, which is the AC voltage multiplied by the square root of 2.
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LD LANGER
Wed Apr 13 2011, 07:23PM
LD LANGER Registered Member #3824 Joined: Sun Apr 10 2011, 08:29PM
Location: Edmonton, Alberta, Canada
Posts: 54
Again thanks for all the help. I have the schematic of what I am to build, if someone could quickly glance over this and point out any obvious errors that would be much appreciated!


*As well the rectifier diodes are backwards, I fixed that not to worry.

Thank you,

Daniel
]dc_reso_charging_tc1.pdf[/file]
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ScotchTapeLord
Wed Apr 13 2011, 10:15PM
ScotchTapeLord Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
I don't think you'll need that many MOTs for the choke.
As for the diodes in series, you should use ones that are avalanche rated..
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