Voltage sensing cut-off or throttle back

Discussion in 'The Projects Forum' started by will1234, Nov 23, 2007.

  1. will1234

    Thread Starter New Member

    Nov 10, 2007
    8
    0
    I have a YAG laser that is flash tube pumped from a 1000 VDC UL30 capacitor. I have a new 5kv 30mA neon transformer that I have rectified and want to charge the UL30 with. I want to charge the cap with as much of the 5kv as I can so it will charge quicker but as it nears or just tops 1000v either cut the power supply off or otherwise throttle it back so I can leave it on after the desired charge is reached without overvolting it. Clamping is an option but as mentioned earlier I want as much ot the 5kv as I can get for the initial charge. Could I use a 1000v zener (how much watts for zener) that would break down and somehow trigger a relay to shut off the transformer power or clamp if to an extremely low voltage until the zener want back below its breakdown voltage? Wouldn't clamping 5kv 30mA to 24v (just picked a number for this value) build up a lot of hear and potentially damage the transformer? Is there an easier (or proper) way to accomplish this? I'm new to the electronics world and am finding that the accidental misuse of a single word can be the difference between success or failure or burned up components. If anything above doesn't 'sound right' please let me know and I'll try to re-word it correctly.

    Thanks in advance......
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I'd be afraid to be in the same room with a 1000 volt zener. Seriously, zeners don't come in such large ratings.

    The fun with the 5 KV is that it likes to reach out and touch other components. If you can find a relay rated to interrupt that much voltage, it would be simple to arrange a divider and let a comparator control the relay to feed the cap.

    It is a bit uncomfortable, though, thinking of arranging things to be fail safe, so the cap doesn't get toasted. It would be so much more comfortable to feed the cap with a 950 volt source.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The universe doesn't work that way. Charge time is independent of voltage. I strongly suggest you do a lot more studying before you play with your very dangerous new toys.
     
  4. will1234

    Thread Starter New Member

    Nov 10, 2007
    8
    0
    Hearing that charge time and voltage aren't related would I be none the worse if I just clamped the power supply at 950 to 1000 volts? I do have a few 200v zeners.. I have clamped similarly by connecting 5 of them in series for a 1000v clamp.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    I am no expert on neon transformers, but this article (near the end) suggests that the optimum load voltage is about half of the open circuit voltage, and that excessive loading for an extended period of time may damage the transformer.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    It is worth noting that most designers use a cap who's voltage rating is at least twice what said cap will see in service.
     
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