Author Topic: What's the best way to trigger these things?  (Read 331 times)

Offline John123

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What's the best way to trigger these things?
« on: March 05, 2020, 09:37:59 PM »
When trying to discharge a big capacitor bank into a load using a chicken stick it wastes a lot of energy in sparking, energy which doesn't get dissipated in the load.

Is there some kind of go-to SCR or contactor to reduce wasted switching energy? Assume the load in series is very low impedance, wouldn't it just destroy the switching device too?

Offline Mads Barnkob

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Re: What's the best way to trigger these things?
« Reply #1 on: March 05, 2020, 10:23:44 PM »
SCRs or Thyratrons would be the way to go, albeit they can be costly and hard to source where a spark gap can be anything that can conduct a current :)

The spark losses are determined by the charge in coulomb and thus the lower voltages, the higher spark gap losses/wear. So good and effective spark gaps uses higher voltages. Which is suitable with lower voltage SCRs being more accessible.

I got a paper on spark gap material wear, form, function and losses etc. on my website, download the "Erosion in High Current Discharges" PDF here: http://kaizerpowerelectronics.dk/tools/file-archive/?drawer=application_notes*pulse_power

If you use my capacitor energy calculator, lets take an example of a 50 kJ bank: http://kaizerpowerelectronics.dk/calculators/capacitor-energy-calculator/

Electrolytic capacitor bank at 1000V / 100000uF would hold a charge of 100 Coulombs

Film discharge capacitor at 100kV / 10uF would only hold a charge of 1 Coulombs

So spark gaps do actually become efficient at higher voltages. Downside to SCRs is an uneven hole distribution when it turns on and it can result in hotspots and exploding silicon   :'(
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline John123

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Re: What's the best way to trigger these things?
« Reply #2 on: March 07, 2020, 04:53:32 PM »
I noticed on your website you've come up with a spring loaded contactor, was there a noticable difference in energy transferred to the load when you switched over to this?

Offline klugesmith

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Re: What's the best way to trigger these things?
« Reply #3 on: March 16, 2020, 04:09:30 AM »
Question in OP gives no hint about the "large" capacitor banks and the loads.

That covers spaces several orders of magnitude wide
in voltage, capacitance, energy, load impedance, and pulse timing & damping.
Do we all agree that an ideal short-circuit "load" can never receive any power?
That to receive more than half the total energy, load resistance needs to be higher than the resistance of capacitor + switch + interconnection?

No switch type is optimal, or even usable, for all variations.
There are places for SCRs, IGBTs, ignitrons, spark gaps (fixed or electrically or mechanically triggered), and contactors.
« Last Edit: March 16, 2020, 04:14:06 AM by klugesmith »

Offline John123

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Re: What's the best way to trigger these things?
« Reply #4 on: March 16, 2020, 04:18:04 AM »
It's 330v at around 2200uF, so actually not that large compared to the multi-kilovolt monsters on here.

The load could be a coil for launching things or something that's about to get its end blown out.

Offline ritaismyconscience

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Re: What's the best way to trigger these things?
« Reply #5 on: March 16, 2020, 04:32:45 AM »
Definitely go with SCR for that one.

Offline Mads Barnkob

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Re: What's the best way to trigger these things?
« Reply #6 on: March 16, 2020, 07:43:33 AM »
It's 330v at around 2200uF, so actually not that large compared to the multi-kilovolt monsters on here.

The load could be a coil for launching things or something that's about to get its end blown out.

I agree on SCRs for this voltage. Thyratrons are still for higher voltages and a spark gap would just weld itself shut very fast.

I noticed on your website you've come up with a spring loaded contactor, was there a noticable difference in energy transferred to the load when you switched over to this?

Despite being closed with a 50Hz solenoid, I still think this method is too slow and I would like to make some more designs (some day) from that PDF about erosion I linked earlier.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

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Re: What's the best way to trigger these things?
« Reply #6 on: March 16, 2020, 07:43:33 AM »

 


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