[Prev][Next][Index][Thread]

Re: MMC question

Hi Terry, Michael,

Terry has answered most of your questions, so Iīll just add my comments

> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
> At 04:13 PM 6/7/99 +1000, you wrote:
> >My name is michael and I am new(ish) tp this list.
> >
> >I would like to know if standard metallised polyester greencaps will
> >work at all in a coil. I was recently given a few hundred (like 500)
> >these each rated at 100Vdc and 0.49uF.

TF:
> I don't know what cap value you want but these caps look like they
>would be very difficult to use.  You need a lot in a string to get to a
>reasonable voltage but then the capacitance is pretty high.
>Polyester will heat quickly and you will only be able to use one or
> two strings which means they will see very high current. For
> example: 250 caps in two string gives a 25kV 4nF cap. The
> current will really be too high for just two strings.  I fear you
> would wire up 500 caps and it would fail quickly.  I don't know all
> the variables but I would really be careful...

Agreed. Forget about using polyester caps. They will die VERY
quickly in TC usage. Polyester has a tan alpha loss factor of 0.02,
whereas PP has only <5*10^-4. So, polyester is ~100 times more
lossy. More loss means more heat and that is something you DONīT
want in a cap. Also, usually, these caps are not designed to handle
the high peak amps, which they will exprience in TC usage.

> >I would also like to know if  "Plastic film Boxed casing MKT 250V"
> >will work. I have made a few bricks (5" X .5") of 360 each, but am
> >worried about blowing them when they have other uses. They are each
> >rated 250V and 0.022uF.

TF:
> The key is if they are polypropylene or not.  If so they have a good
>chance of working.  Just don't let them heat up.

MKT is the abreviation for metallized polyester foil caps (see
abreviations below). So these caps have two disadvantages. One
being the dielectric material (polyester) and the other being, they
use metallized plastic foil.

Now you are sort of in a dilema, because you have already built them.
Were they expensive? If not (i.e: = free), then I would go ahead and use
them, but keep run times very low and donīt expect them to last very
long. On the other hand, if you shelled out a load of dough, I wouldnīt
ruin them in TC usage. 22nF-at-250V is a handy cap for various (non
high voltage, non tc) experiments.

MKT = Metallisierter Kunststoff (polyester) = metallized polyester foil
MP = Metal/Papier = metal foil/paper
MKP = Metal Kunststoff (polyprop) = metallized or metal foil and PP
MKC = Metallisierter Kunststoff (polycarbonate) = metallized PC foil
MKT = Metallisierter Kunststoff (PET) = metallized PET foil
ALE = Aluminium Elektrolyt = polarized (DC) electrolytic cap
TAP = Tantal = polarized tantalum caps
(the ones that go boom right away, if connected backwards ;o])
FKC= see MKC, except they use metal foil.
FKP= see MKP, except they are definately built with metal foil.
FKT (rare)= MKT except they are made with metal foil.
MKH = MKS= MKT (no difference)
KP = MKP, except the tolerance class is very low (~2.5-3%)
MKI =  Metallisierter Kunststoff (polyphenylensulfid) = metallized PPS
MKK/MKV = Compensation caps made from different materials for
HV AC usage (too expensive for our purposes, tho)

That pretty much sums up the capacitor abreviations used (aside from
SMD and spedcial purposes caps, but who wants to use SMD caps on
a TC ;ö))


Coiler greets from germany,
Reinhard