LF 330uF 600V pulse capacitor

[MorneDJ]

Been spending time on mantech's website and also tried electronics123, yet I cannot find this capacitor. Anyone knows something of such a cap or where I can find it (or something similar)

[LAV]

Where is it used?

[tangmonster]

I would use two of these in series

http://za.rs-online.com/web/p/aluminium/0575444/

But you have to add equal size resistors across them to make sure they share the potential difference equally.

[LAV]

I also browsed RS, seems like the highest rated ones are 450V. They had 500V but it's been discontinued. The series plan sounds like a good one.

[MorneDJ]

It is used in a fish shocker/stunner. For those days that dynamite just won't do ... or could wake the neighbors....

The plan indicates 4x 330 600V in series. The transformer that I got wound have a 500VAC output, and after the diode bridge I expect it would be a bit higher (707VDC ...). Would using these in series allow me to cater for the higher voltage

Thanks for the help, spend some time on the net yesterday but just could not find it. Electronics is not my strongest suit.

[tangmonster]

Do those capacitors have resistors across them?

[Ampdog]

Morné,

600V electrolytics are not at all common - cant recall I have ever seen one. But first I need to ask; you mention 'pulse capacitor', and from your description it appears that you are talking of a quick-discharge action here, rather similar to that in an electronic camera flash?

If so you cannot use capacitors in series at all. A rapid discharge involves high currents, and if there is any difference in the capacity (as there are likely to be with electrolytics), the lowest value one will discharge more quickly and runs the danger of being reverse-polarised severely while the other is discharging. (This is irrespective of whether each will have half the voltage across it as determined by a resistor voltage divider chain.) Draw the equivalent diagram: Two series capacitors with a short across them at the moment of discharge. You then have two charged capacitors in parallel, reversely connected! (It is like two batteries in parallel but one connected with opposite polarity.)

Thus the exact use must first be clear before you proceed. If the above is true you will have no option but to use a single capacitor and adapt your circuit to the lower available voltage. The circuit of what you are using will reveal what action you can take. 

[MorneDJ]

The circuit is actually quite easy. Is a basic oscillator (about 46Hz the one I have) that feeds a 2N3055 that in turn feeds a step-up transformer, taking 12V to about 500VAC. There is a 1 K resistor before the 2N3055 to limit current (I think). After the transistor there is a diode bridge to make it DC, then  a 40 ohm resistor (10watt - I do not know the purpose, current limiting again ?), then 4x 330 uF, 600V caps in series (between positive and negative). These 4x caps are in paralleled with 2x 1M resistors ... why they use 2 I do not know. They are in series, again between positive and negative. After this is another 40 ohm resistor (in positive) before a triac. They made use of a relay, but I have removed the relay and use a triac. Whether that will work I do not know else I will get the relay.

The triac is triggered via another circuit that can generate a variable oscillation (5 - 22Hz) ... I have to build this still.

[NoSnipeLimit]

So you need something like this:

[LAV]

Post the diagram.

[MorneDJ]

Please note, if you build this and get caught using it in South Africa, you will be in a world of trouble unless you have some sort of permission ...

[LAV]

Aha, quite interesting. There are two oscillators here, one would be a low frequency one (the one at the bottom of the diagram) that pulses the relay. The other part is an oscillator on the transformer primary, this is effectively a step-up / inverter circuit to generate the HT.

I see your caps and I raise you...oops, sorry, wrong thread 

I am assuming the series caps C5 to C8 are the ones you're referring to in the original post? They do not have any resistors in parallel in this circuit. Which 1 Meg resistors are you referring to? If these are R11 and R12, they are series resistors for the neon lamp NE1.

You could add more caps in series to get to the desired max rating, but you might want to observe the precautions mentioned by others...or you could just go to your nearest Ocean Basket 

[Ampdog]

OK ....

The direct 'load' is water - which can have a quite low resistance. Not my field of experience, but I still have reservations about dumping the charge of series capacitors into that (possibly?) low a load. Might one suppose the designer is knowledgable enough to have checked that? How long is the piuse before the load is turned off - how far do the capacitors discharge?

Sorry, Morné, only adding to your problems. I must stop there, but if this was me I would certainly check first - unless someone else has experience. (A check could be difficult; rather quickly registering hold measurements required, perhaps by a dvm connected across each cap. Perhaps switch the power supply off just before the pulse to stop to rapid recharge before reading the meters - blah blah blah. Waiting for others' wisdom.

[MorneDJ]

Ahh, I forgot that I did change the design slightly.

First. The guys at Peter Souris () wound the transformer incorrect, even after I send them two pages of instructions (as per the document where I got this plan from). So the transformer is wrong and is just a plain  12VAC in, 300, 400 and 500VAC out taps.

So I got a circuit from Wikipedia (Basic BJT astable multivibrator - http://en.wikipedia.org/wiki/Multivibrator), calculated the required values and got a circuit that gives me a 46-47Hz AC voltage. Because I use BC237 transistor, I decided to put the output through a pwr transistor (2N3055). From another circuit I saw that I should have a resistor in front of the 2N3055 (do not know the purpose), and since they used a 1K resistor, I used the same. But now the AC output from the 2N3055 is 5 VAC. So I think I should reduce the value of this resistor ...

With regards to the output capacitors, I do not want something that big. I think it is only there to filter the output a bit. I still require a low current (less than 50 mA for safety and to ensure it does not kill the fish). However, I do not want these capacitors to blow up in my face.

Regards

Morne