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Thread: Power supply interrupter

  1. #11
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    I was thinking about your circuit earlier while eating lunch. Using the variac to adjust the voltage during steady state operation sounds fine. My concern would be the initial cap voltage before your first trigger pulse. Its possible the caps could be charged several percent more than during steady state operation. This could give a huge first pulse.

    Edit: I guess you are probably starting the trigger pulses then slowly turning up the variac voltage. This would solve the possible big first pulse issue.
    Actually, I just planned to begin triggering without regard to the charging state. My thought is that at such a low rep rate the caps will reach their maximum charge (determined by the variac) long before, as in many cycles, a pulse is sent to the lamps.

    The collapsing field should cause a spike in the secondary as well. I am not sure how to calculate that.
    Isn't the field collapsing because it is being drained by the secondary? With the primary isolated from input current or from reverse current through the open relay, why would this cause spikes? Now, I am the first to admit that I do not understand this process well enough (that's why this thread), but if the relay is opened then the primary is isolated from the line and so it seems that the only effect at the secondary would be a collapsing field that would have a delta V/T no greater than when the field is driven by the line voltage.

    Its hard to say how low the cap voltage will be after each discharge
    Based on the papers I have looked at and more so on my single pulse experiments the caps will probably be around 1,000 V immediately after a discharge and will require something like 10 full cycles to reach the pre-discharge state

  2. #12
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    After wasting some time trying to help a young enthusiast and seeing the completely inappropriate, unappreciative, arrogant and aggressive and push back, I realize what an opportunity he squandered trying to protect his naive ego. Serves him right!

    Thanks for all the help in my quest to build "The Beast"

  3. #13
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    Quote Originally Posted by planters View Post
    After wasting some time trying to help a young enthusiast and seeing the completely inappropriate, unappreciative, arrogant and aggressive and push back, I realize what an opportunity he squandered trying to protect his naive ego. Serves him right!

    Thanks for all the help in my quest to build "The Beast"
    Um... is this directed at me, or someone else participating in this thread? If so... super confused. Just trying to offer ideas; no offense intended.

  4. #14
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    No! NO! NO! Sorry about the confusion. I was referring to "Solidude" from the degenerated thread:

    http://www.photonlexicon.com/forums/...058#post299058

    The help I have received here has bee fantastic and absolutely spot on. I Just ordered the very part you linked to and in the normally closed mode...perfect and with a momentary rating of 600A it is likely to survive whatever energy the coil in the variac can spit out after it closes. Thanks again.

  5. #15
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    Ah, ok! Yes, I stopped reading that thread after the first page. I really hope that SSR works out for you or I'm going to feel bad. Please keep us posted.

  6. #16
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    Disclaimer: I am working off of what i remember from school 20 years ago. Just trying to put out some things to think about/ prepare for....

    Actually, I just planned to begin triggering without regard to the charging state. My thought is that at such a low rep rate the caps will reach their maximum charge (determined by the variac) long before, as in many cycles, a pulse is sent to the lamps.
    At 6hz rep rate you only have 10 full cycles to recharge. So, 20 chances to recharge the caps with a bridge rectifier. The caps can only be charged when the voltage of the sine wave is higher than the voltage of the caps plus the diodes forward voltage.

    Isn't the field collapsing because it is being drained by the secondary? With the primary isolated from input current or from reverse current through the open relay, why would this cause spikes? Now, I am the first to admit that I do not understand this process well enough (that's why this thread), but if the relay is opened then the primary is isolated from the line and so it seems that the only effect at the secondary would be a collapsing field that would have a delta V/T no greater than when the field is driven by the line voltage.
    In your circuit a spike in the secondary shouldn't happen when its under load. Even when the caps are charged a spike shouldn't cause you too much grief mainly because the caps are a low Z load that can't change voltage really fast. So, no real worries there.

    The spike on the primary is because the collapsing field in the transformer core has to affect both the primary and the secondary. The induced secondary current will go into the load. Current or flux can't instantly change in an inductive circuit (unlike voltage which can). So the primary which is now open has to react to the collapsing field causing the pressure (voltage) to shoot up.

    Like I said i'm only an EET not an EE. So, what I normally do is some rough 1st aprox. calcs then build the thing and see what happens (this is where the fun is anyway). Which is is where you are at. I look forward to seeing your results. I am sure it will blow my socks off. Just don't blow your socks off. Seriously, one hand behind your back!

  7. #17
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    Got ya. I am thinking along the same approximate lines. I agree that an MOV to dampen a voltage spike can't hurt (can it?). So, whats your guess on the cut off and Joules?

    Seriously, one hand behind your back!
    Oh.....yes! Actually stage three is destined for a bunker outdoors with bleed resistors across the caps, always.

  8. #18
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    Looks good. The power supply is finished. The solid state relay works well and although I haven't had the system over 1,000V yet (tomorrow) there are no surprises so far. I went with a large MOV rated to begin conducting @ 300V and to be fully closed at around 500V which is below the SSR's 600V rating. These MOT's are a good deal. They are nice and bulky, very cheap and they self limit at around 3,000 VA in a dead short, but as a capacitor charging source this just means that they will need a circuit that will tolerate their peak draw. The pulse repetition frequency will determine their average output. Four of these transformers in a 2+2 parallel/series arrangement should accommodate 4-5kW of average power and such a power supply can be constructed for about $200 ($350 with a variac).

  9. #19
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    Sweet! Thanks for the update.

    I hope whenever you're finished you'll make another one of your videos.

  10. #20
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    That's what I'm debating. The final stage (of three) is scarey ambitious, but the first stage which involves converting and improving a small medical dye laser is less exciting. I wouldn't be surprised if the entire project took over a year. So, a rolling saga or a single blast?

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