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Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
I suggested to Andyman that i saw picture of a 4 mot system that i have seen one of those caps used. I am prety shure that they have a low ESR. those kind of caps are used in pulse forming lines and marxes and are pulse rated. at 35kv rating i think they could handle a cuple NST and MOTs for shure. but they are right, it is oil filled. at richarson electronics you can get 50 942c20p15k-f 2kv .15uf mmc caps for 136$ and you can use them for a DRSSTC or induction heater later. maby thease guys have a cheaper alterinitives that have a low ESR and hi di/dt. it will take, i think, around 100$ in caps to duplicate Tesla Down Under's expieriment. good luck
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Marko wrote ...
Can someone explain me rightly what voltage reversal really is?
I thought is was the maximum percentage the voltage can ring under zero after cap was charged to it's rated voltage?
I still don't understand what significance this has, how in a world can this cause the cap to fail.
Only explanation I got is that high voltage reversal would cause high mechanical stresses to dielectric. (how can that be a problem?)
What does this have to do with the AC voltage rating of the cap? Why are AC ratings always so much lower than DC ratings?
Marko
I'm not sure whether this is an explanation, but here are et least my speculations:
The dielectric stress is about pulling electrons from the dielectricum. Let say, that pulling these electrons too far or rather too many from the material leads to its destruction. In case the DC is applied the electrons are pulled only one way. After the discharge the electrons tends to go back (to zero). This “going back drive†gives the electrons certain amount of energy (ideally the same like when they were pulled but with the oposite vector). It is the same like with flip-flap. So, in case of an AC or capacitive load, the tension pulling the electrons oscillates. So when the electrons are going back to the zero position suddenly the reverse pulling is added to this force. This effect is so stronger how higher is the ocilation frequency. The final energy (the speed) of the electrons in AC mode is now a result of energy they already had on their way back plus new energy created by the tension which pulls in the same direction. In other words, the electrons are accelerated in the dielectric layer in case the AC is applied which make much more easy to pull too many of them from the material and destroy its molecular construction...
It is just my unadept opinion about the whole thing which gives me sense. Maybe reality is pretty different
Registered Member #341
Joined: Thu Mar 23 2006, 07:41PM
Location: Northern Illinois, USA
Posts: 69
Richardson Electronics is just down the road from me. I have purchased CDE caps from them in the past and after visiting their facility my feeling is that like any well run business they don't carry any more inventory than they have to.
For CDE caps. they wait until they have enough orders to get the best price from the manufacturer and then place an order. If your order to them is first and/or too small, it may take some time. If your order fills out a bulk order, it will probably be filled quite soon.
Nothing sinister, just good inventory control to keep prices down.
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MMC versus a single Maxwell
