Re: HiPot testing my filament xformer

Howdy,

A good rule of thumb (derived from many UL specifications)
for equipment with a safety ground is use twice the operating
voltage plus 1KV AC with a test period of one minute.

For reduced test time, one second is allowed for _production_line_
testing with increased test voltage

So for equipment operating at 115VAC you'd qualifying test of
1230VAC from primary to secondary for one minute (use 1250VAC.)

Isolating components like transformers often have to meet the
requirements for double insulation so they are tested at twice
the basic test voltage which is where the 2500VAC test value
comes from.

Often the basic test voltage 1500VAC is applied from input to
ground (chassis) and the double insulation test voltage of
2500VAC is applied from input to output. Because the output
is not tied to the safety ground.

The criteria for failure is non-linear rise of applied voltage or
a sustained arc or measured current above some value. The current
limit varies but 3mA is a good value for equipment that is safety
grounded (not double insulated.)

UL also requires the hi-pot machine to be capable of 500VA output.

Double insulated transformers tested to IEC standards for the EU
with it's higher nominal line voltage may be subjected to hi-pot
voltages as high as 1500V primary to ground and 4000VAC primary
to secondary for one minute.


Caveats

Hi-pot only a test. There are are dimensional requirements
(safety from conductor spacings) and requirements for durability
of insulating materials. You could still grossly violate the
standards, producing a dangerous component, and pass hi-pot.
Two pieces of heavy build magnet wire twisted together will
usually pass 5KVAC hipot, would you trust that with your life?

A person should to follow and understand the applicable standards
under fear of fire, injury or death.


And as always, all of the above may be horribly wrong.


73,
Grumpy


raypsi <RBorowiak@xxxxxxxxx> wrote in news:57a0b89a-3205-4ca1-b5e9-
03f4796c0a16@xxxxxxxxxxxxxxxxxxxxxxxxxxx:

I built my own 7.5VACT 21amp filament xformer. I needed to supply
-500VDC screen voltage to the center tap.So a local ham tells me the
insulation better be able to withstand at least 500VDC.

I built my own hipot tester from a voltage doubler and a bank of eight
400WVDC caps. Each cap had a 330 volt charge so like 2640VDC. I
figured no problem. I looky up the specs and see if this thingy
passes.

I googled and can find no specs for hipot testing. I came across in a
usernet group: 2500VAC at 1ma for 1 minute. That didn't really tell me
much.

My results are 0,2 micro amps thru a 1 meg series resistor at 1980VDC
source voltage. This from either the core or the primary to secondary.
The current didn't change even when I went to a 10meg series resistor.

Is there nowhere that you can get specs without paying big bucks for a
UL or IEEE book on the topic?

73
n8zu

.

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