I donno. The GFI kicks into action not because too much current is being
drawn but because mains current in is not equal to mains current out, i.e.
mains current must be leaking, or something else is happening that looks
like that. Too much secondary current cannot be drawn because of the
built-in current limiting of the NST shunts.
30 mA flowing through a 1K resistor only drops the voltage by I*R=30 volts,
not a significant loss out of 6000V. That said, resistors in protection
networks do get quite warm, so it's possible more current than
faceplate-rating is flowing due to core saturation. But resistors are made
to get hot. Putting an aluminum heat sink on it is probably not necessary
and if the R is part of an R-C low-pass filter, could compromise the
high-voltage stand-off rating of the resistor.
All I know is that it works. Take the resisters out, and GF pops.
I can't argue with success. Thank you for reporting this! After all this
blathering on my part, I don't have an alternate explanation for why the
presence of the two resistors allows the GF NST to work.
Regards,, Gary Lau
MA, USA
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On Fri, Nov 30, 2018 at 9:16 PM Matthew Deming <mddeming44@xxxxxxxxx> wrote:
I think that I have figured out why your GF NST is working. With a standard
SGTC the start of the discharge looks like a dead short across the NST
secondary. (Pop!) The resistors dissipate enough power to keep it from
looking like a short to the NST. The only drawback is the power eaten by
the resistors is not available to the TC.
On Fri, Nov 30, 2018, 11:39 AM Douglas Johnson <doug379306@xxxxxxxxx>
wrote:
Hi Ed. Standard TC setup, except the {1K 25 Watt power resisters} are
connected between the NST HV leads and safety gap lugs on the coil.
Please understand, I have little technical knowledge here I was just
playing around and it worked! I would hope some of the more technical
minded members on the list would do a little trial and error with this,
it
could possibly open a new source of usable NST's, ie [GF NST's] for small
and moderate coils.
These power resisters are inexpensive as are aluminum heat-sinks if
needed.
I wish I had a 12 or 15K GF NST to test out but I do not.
Thanks for your reply.
Doug
On Fri, Nov 30, 2018 at 9:05 AM Ed <evp@xxxxxxxxxxx> wrote:
What's your circuit?
Ed
On 11/29/2018 6:53 PM, Douglas Johnson wrote:
Gary, I am far from technical when it comes to this stuff as I am
sure
you
can see by a lot of my questions! It was just a fluke that I tried
this
out
of boredom. All I know is that it works. Take the resisters out, and
GF
pops.
The resisters are similar in appearance to these >
https://www.ebay.com/itm/2Pcs-Wirewound-Ceramic-Cement-Resistor-0-5-1K-Ohm-5-25W-Watt/352350026175?hash=item5209b2b9bf:m:mowqAUe59odwZoiyCa7jxDg:rk:38:pf:0
Maybe it works because, in my ignorance, I didn't know it wouldn't😉
Doug
On Thu, Nov 29, 2018 at 9:20 PM Gary Lau <glau1024@xxxxxxxxx> wrote:
I can't comment on your GF working in a TC. I've not personally
tried
it,
but the prevailing wisdom is that it typically doesn't work in a TC
application. I wonder if higher voltage GF NST's are more affected
than
lower voltage ones?
The resistors - 1KOhm, 25Watt, 210-what? What are these for? It
sounds
like they're intended to be part of a protection network, except
that
resistors must be used with capacitors to form a low-pass filter
network.
By themselves or with safety gaps, resistors serve no protective
purpose.
Regards, Gary Lau
MA, USA
On Thu, Nov 29, 2018 at 6:22 PM Douglas Johnson <
doug379306@xxxxxxxxx
wrote:
I had a 6K GF NST laying around and decided to see if I could use
it
on a
small TC. I ran a 1K 25w210 wire wound resistor between each leg of
the
NST
and the safety gap, it worked just fine. I switched the GF 6kv NST
with a
non GF 6kv nst and the coil output was identical.
I was always told that a GF NST would not work for a TC??
Resistors are holding up ok.
Comments please
Doug
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