Brian, et al,
Lots of good discussion but let's focus on the basics.
Nute has pointed out that during hi-pot testing the current that
flows will be related to the increase in voltage. So, if the hi-pot voltage
is 10x the line voltage then the test current will be 10x the line current
that the product normally draws. This will charge the internal capacitance
each cycle for AC testing but only once for DC testing.
The hi-pot unit usually has a variable alarm setting that is
supposed to be set just above the current drawn during the test so that the
alarm won't sound until this value is superseded by the DUT. Is the hi-pot
di/dt sensitive in some way that is not generally recognized? That signals
an opportunity to determine why some unit 'sound' failure but other don't.
Again, if DC testing doesn't provide the same separation between
good and 'failed' units then more investigation is needed. Start with the
test procedure especially the current readings between units and then
proceed in more detail; you might have to push some of this back onto the
supplier to dig down into the innards of the power supply to determine the
differences. However, the PS mfgr has already done such a test and
proclaimed each one good before it was ever released as a product; pushing
back will cause some consternation in your supply chain.
In the end, either AC or DC tests should provide the same separation
of power supplies into good and 'failed'.
So, whoever can get to the bottom of this - test house or mfgr -
should bring the details into the sunlight for all to learn from it.
:>) br, Pete
Peter E Perkins, PE
Principal Product Safety Engineer
PO Box 23427
Tigard, ORe 97281-3427
503/452-1201 fone/fax
[email protected]
_ _ _ _ _
No. Nicht. Aon. It does NOT matter that current flows through the 'filters'
and other stuff during AC hi-pot and 'trips' the instrument. This is a good
thing - set limit levels on your test equipment to verify cap values and
leakage paths. There is no inherent current limit for this test in the
affected standards for di-electric withstand.
You do control the ramp and current levels in your factory hi-pot? No? Sit
in the corner.
Brian
-----Original Message-----
From: Brian Oconnell
Sent: Monday, June 23, 2014 5:30 PM
To: [email protected]
Subject: UL61010-1 CSDS Proposal for 6.5.2.4
This is excerpted from the latest UL61010-1 CSDS Proposal for 6.5.2.4
Impedance of PROTECTIVE BONDING of plug-connected equipment:
"It was proposed that all hi-pot tests should be permitted to be performed
with either ac or dc, particularly because OEM power supplies often fail
when tested with ac, but pass when tested with dc.
This seems to be because IEC 60601-1 3rd edition, IEC 60950, and IEC
62368-1, to which most of these power supplies are tested, permit either ac
or dc testing. The consensus of ISA 82 is that this change is appropriate.
It is also recommended that this change be re?ected in the US comments on
Part 1 by the USTAG."
Ok, why are component power supplies failing AC, but passing the equivalent
DC withstand test levels? If from reactance, just control dv/dt (many
standards provide a min rate). And what does the protective bond test have
to do with the test conditions for di-electric withstand? Or am I missing
something obvious?
Brian
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