[Amps] HF2500 Power Supply Caps

Mon Apr 7 09:35:24 EDT 2014

I'm using microwave oven fuses, rated at 5kV and available in various
current ratings, up to 900 mA. They can be paralleled for higher currents.
They look like elongated 3AG fuses, and fit in 3AG fuse clips. I had one
blow recently at 2700V, because of a tube short, and it worked well,
although the glass body exploded into tiny pieces.  They're available on
eBay, cost about a dollar in quantities of 20, including shipping from
China.

I have no data on the fuses. In my experience a fuse will last for minutes
at its rated current, with the interrupt time growing shorter as the current
overload increases. I'm guessing these fuses blow in a couple mS when
something shorts the HV supply, but haven't tried to measure the time. Would
be hard to do without specialized equipment.
73,
Jim W8ZR

> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Thomson
> Sent: Monday, April 07, 2014 2:34 AM
> To: Paul Hewitt; amps at contesting.com
> Subject: Re: [Amps] HF2500 Power Supply Caps
> 
> ## Check out the Buss  HVU series of HV fuses...then extrapolate the
curves.
> Then test on the bench
> with a scope to verify that data.  BTW, those fuses can easily be rebuilt.
> I have also tried hb hv fuses,
> encased in either teflon spagetti tubing  or heat shrink.....suspended
> between standoffs.    Then crank up the
> screws tight, in a CW fashion, so there is lots of tension in the fuse
wire.
> 
> ##  For folks that want to use a 25 ohm glitch and say a 3 kv supply..
fault
> current is  120 A.   Stuff 120 A  through
> a 1 A rated fuse...and you will soon see it blows open pretty damn quick.
> Even with a 50 ohm glitch and same 3 kv,
> the 60A fault current will still open up a 1 A rated fuse very fast.
> 
> ##  You could put the scope across the cold end of the last resistor  in a
> HV multiplier string.
>
http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resou
rces/produc
> t-datasheets-b/Bus_Ele_DS_6003_HV_Series.pdf
> 
> You can see that with just 4A  flowing through a 1A rated HV fuse..it will
> open up in 10 msecs.   Now stuff  50-60-120 amps through the same
> 1A rated fuse..and you will measure a LOT less than 10 msecs.
> 
> Jim   VE7RF
> 
> 
> -----Original Message-----
> From: Paul Hewitt
> Sent: Sunday, April 06, 2014 2:21 PM
> To: 'Jim Thomson' ; amps at contesting.com
> Subject: RE: [Amps] HF2500 Power Supply Caps
> 
> Hi Jim
> I see your posts about high voltage fuses disrupting current in 2ms so how
> about a part number/manufacturer.  I would like to see the data sheets I2T
> curves.  Most of these fuses open times are measured in seconds and are
very
> large.
> Thanks &73,
> Paul
> 
> 
> Paul Hewitt
> WD7S Productions
> QRO Homebrew components
> http://home.earthlink.net/~wd7s/contents.htm
> 
> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Jim Thomson
> Sent: Saturday, April 05, 2014 1:29 PM
> To: amps at contesting.com
> Subject: [Amps] HF2500 Power Supply Caps
> 
> Date: Sat, 05 Apr 2014 08:41:38 -0700
> From: Bill Turner <dezrat1242 at wildblue.net>
> To: amps at contesting.com
> Subject: Re: [Amps] HF2500 Power Supply Caps
> 
> On 4/5/2014 8:06 AM, Carl wrote:
> > but more C doesnt buy anything useful.
> 
> REPLY:
> 
> More C can actually be harmful. In case of an arc, more C just dumps more
> energy into the arc with potentially more damage.
> 
> 73, Bill W6WRT
> 
> ##  With a 50 ohm glitch Resistor installed, the peak fault current
remains
> the same, regardless
> of C used.   However, the 50 ohm glitch + total C  will  form a RC  time
> constant, whose duration
> will be  longer when more C is used.   With 2500 vdc  + a 50 ohm glitch
> Resistor used, peak fault
> current is 50 Amps..... which will easily blow open a 1-2 Amp rated HV
> fuse...and under 2 msecs.
> 
> ##  The 50 ohm glitch resistor LIMITS the peak fault current.   The HV
fuse,
> just prior, and in series with the
> 50 ohm glitch resistor, INTERRUPTS the peak fault current.   You can
cro-bar
> the supply all day long if you want.
> All that happens is the HV fuse blows open.
> 
> ##  use whatever size cap you want.    The 440-600 uf types work just
fine.
> The bigger the total C used, the better the
> dynamic regulation  of the supply.   The ripple is also lower, and in
> proportion to  C used.   A 600 uf cap will have one third the
> ripple of a 200 uf cap..and way better dynamic regulation on ssb and cw.
> Your load line is not all over the map.
> Now this all works with the proviso that a 50 ohm glitch R  and HV fuse is
> used.
> 
> ## As far as regulation goes, you require a plate xfmr that doesnt sag to
> begin with....and big enough ga wire from HV supply
> back to main 200A panel.  You also  require  large enough rated relays and
> contactors.   Any Z between main panel and plate xfmr
> will create V drops..which is bad news with any high C filter.
> 
> Jim   VE7RF
> 
> 
> 
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