Re: Further MMC woes.

[Terry Fritz <twftesla-at-xxxxxxxxxx>]

Hi Garry,

At 08:33 PM 11/23/2000 -0800, you wrote: 
>Well, after trying to replace the blown caps with all the spares I had I 
>have a worthless $84 MMC.
> 
>I built an MMC out of 3 strings of .033 uF caps at 2kv part number 940C 
>20S33K from Mouser electronics. 15 caps per string.
> 
>I placed short pieces of thick plastic tubing around every other cap by 
>slitting the tubing length wise and slipping it over every other cap. This 
>effectively insulated every cap from its neighbor. Then I place poly 
>sheeting between the caps and the resisters and put generous amounts of 
>silicone seal around the ends to make sure there was no possibility of 
>arching between the solder joints. I used heat sinks to protect the caps 
>from heat when I was soldering the joints as well. Within 3-10 seconds after 
>I hooked it up to my tank circuit of a static air-cooled gap and a 12/30 
>tranny, a cap would blow, throwing carbon all over the place. 
> 
>Also, I noted that resisters would BLOW as well, arching accross the body of 
>the resister as if it were a spark gap.

Sounds like the resistors were acting as little gaps themselves.  Something
must be terribly wrong.

> 
>I know I got the correct type of resisters for I got the resister part 
>number from Terry and they looked identical.
> 
>I noted that the resisters would blow, and then when I snipped out the 
>resister the cap accompanying that resister blew.
> 
>All in all about 10 caps were destroyed as I jumpered caps and tried 
>everything I could possibly do to make this thing work.
> 
>As far as I am concerned, these caps are NOT suitable for MMCs and should be 
>avoided like the plague! If the caps were good, there should have been 
>plenty of other caps to take up the slack of the jumpered out bad ones to 
>handle the voltage easily but they blew and blew and blew. Many of them look 
>like they have been nuked. I watched one cap light up with dozens of 
>sparkles as the dialectric was machine gunned clear through.

A 3 x 15 array of caps should have been able to take anything.

> 
>By contrast, the EMMC cap that Terry Fritz sent had not blown but it does 
>seem to have quite a drift after a minute of operation, the coil seems to 
>reduce in power output.

Interesting.  If the caps are heating, the value may be drifting.  or the
spark gaps or something else is doing that.

> 
>The part number for the caps is a part number for caps that have worked in 
>MMC's but I got a note in the packing slip that the caps had been replaced 
>with equivalent caps instead of the original brown broad teardrop caps I was 
>expecting with these white tubular caps. So, it's the replacements they sent 
>me that are defective. I think that if they had sent me the caps I 
>originally ordered instead of these substitutes, I would have a good MMC.

If the caps are not the equivalent and far from it.  That would be "bad".
But best to figure out what exactly went wrong before jumping to conclusions.

> 
>To say I am disgusted is an understatement and if it weren't for a kind soul 
>here that offered to put together and test a multiple string MMC, I would be 
>quitting the tesla hobby. I do not think I will be ever attempting to make 
>another MMC myself. I do not think it would be smart of me to try this again 
>as apparrently, I am either doing something horribly wrong (I am pretty 
>certain I am not) or I have the worst luck in the world and am doomed to 
>failure with making MMC's. I will not invite the thief of bad luck to have a 
>heyday with my wallet again.
> 
>I feel like a fool, I feel like an idiot that doesn't know when to quit. 
>This in fact feels like what I imagine being hooked on gambling (Something I 
>do not do), as I hope the next near $100 bucks gets me something that 
>doesn't go up in smoke.

This is probably not your fault.

> 
>My only consolation is that maybe my extreme misfortune will save someone 
>else the loss.
> 
>I won't risk mucking up the market for all of you by mentioning a thing to 
>Mouser about this desasterous loss so I will keep my mouth shut. I will 
>forever wonder if I had at least called and asked nicely if they were aware 
>of any problems with the replacement caps that they might have replaced them 
>or given me at least a partial refund. I do suggest that when ordering caps, 
>to specify that no substitutions are to be made. I feel THIS was the cause 
>of my failure of this MMC.

If Mouser did substitute the wrong type of capacitor, They can maybe they
can be nicely requested to send the correct ones or credit you.  However,
that all may be a bigger mess than it is worth especially when you can't
return the bad ones.  Best to find the exact problem first before getting
into anything like that IMHO. 

> 
>Terry Fritz, Would you like me to send this MMC to you so you can look at it 
>and perhaps find out what the big problem with this cap is?
> 

Yes!  Definitely.  This is by far the worst MMC event I have heard of and
we need to find the exact problem.  I would be happy to pay postage both
ways and all that.  You know where to find me.  Hopefully it will be
something fixable.

Sorry all this happened Garry.  It really should have worked perfectly.  I
guess I am the type who takes much more interest in why things don't work
like they should rather than why they do work...  Finding the cause of this
dramatic problem will help us all.

Cheers,

	Terry