Re: Another MMC cap candidate (UK)
Alan, and all,
When I built my MMC I simply stacked the capacitors in an
8 by 8 block shape, (kind of like a hexagon pattern.) I
then twisted the leads together at the ends and soldered
the twisted ends with a generous amount of solder.
___ ___ This shows the stack of capacitors
/ \___/ \___ from one side. The + and - connections
\_!_/ \_!_/ \ are bussed along the top and bottom
/ ! \_!_/ ! \_!_/ at the other side. I used thick Cu bar.
\___/ ! \___/ ! \
/ \___/ \___/ I think this method minimises effort
\_!_/ \_!_/ \ and also minimises L & R by keeping
/ ! \_!_/ ! \_!_/ those thin leads as short as possible.
\___/ ! \___/ ! \ You can also easily interconnect strings
\___/ \___/ if you want to. I wouldn't etch a PCB.
My boxed 8x8 MMC measures 125x110x42mm,
(Not bad for 47nF -at- 12kv.)
If you use seperate equalizing resistors for each string,
you may want to use more than 10M to keep overall leakage and
dissipation low. If you interconnect strings then one string
of 10M resistors works just fine.
I plan to buy another 130 of these 47nF/1500V units from RS.
I can't find a cheaper supply. However there is a significant
reduction in unit cost for a bulk order, if any UK people are
100 off -at- 0.348 500 off -at- 0.32 1000 off -at- 0.254
I guess the jury is still out until they are thoroughly tested.
- In sunny Newcastle.
On Mon, 21 Jun 1999, Tesla List wrote:
> Original Poster: Alan Sharp <AlanSharp-at-compuserve-dot-com>
> Greetings all,
> I just tried out a string of the 0.047uF 1500V DC caps
> in parellel with my existing 0.067uF cap.
> The transformer is 8KV DC, 250mA
> The coil frequency is 200kHZ.
> I started with 8 in series no problem, went down to
> 6 and ran for over a minute with no apparent heating.
> I then tried 5 but I stopped the run when I thought I
> saw a flash from one of the caps - no apparent damage though.
> The caps are film and foil polypropylene, axial construction.
> pulse rated at 2000 V/uS.
> Made by LCR, available from Farnell (code 106-372)
> 5+ 46p (70cents) 25+ 40p, 100+ 35p, 500+ 32p
> I'm also using 10M equalising resistors, rated for 2500VAC (.5W)
> metal glazed. 10+ 16p, 300+ 11p,
> Farnell code (341-850)
> I'm probably going to use 8 in series for safety, and build 2, 8 by 8 caps
> I'll put off purchasing these in case any one has ideas on
> how to get them cheaper.
> I've got some large single sided copper clad board, is it a good idea to
> build the cap on a PCB, I can have a one inch gap for each capacitor,
> and give an inch and a half width of copper for the buses at each end.
> I'ld also give it a couple of coats of varnish to discourage ionisation
> on the edges of the copper tracks.
> Alan Sharp (UK)