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500VDC isolation for 500W Full Bridge SMPS?

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Advanced Member level 5
Jun 13, 2021
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We have seen a Full Bridge for 220V to 28V (back end of 115VAC, 60Hz PFC'd supply).
Its for "Airborne use"
Full Bridge transformer is RM14 with enamelled copper wire (strands) pri and sec, no margin tape, just interwinding tape.
No tubing spec'd for terminations.
1....Do you know what AC isolation voltage the 500Vdc corresponds to? It doesnt say how long the 500Vdc should be applied in isolation test, nor what leakage current is acceptable?
2....Also, do you believe you can officially pass 500Vdc isol test with enamelled copper wire as stated?
(i appreciate it wont blow up in normal use, but is it going to pass the official test?)

115VAC is spec'd to give "1kV max transient"...however , woudl think the PFC output caps would "eat" this.

If one does not have a good working knowledge of applicable safety standards for transformers, then best not to tackle such jobs. For mains to user isolation an absolute minimum of 2500 Vac ( 1 min ) is required and 6 mm creepage, and 3.5mm air clearance. 3 layers of nomex ( or other suitable material ) between pri and sec, with side extentions to give the 3 +3 = 6mm clearance, or 1mm solid insulation.

Unlikely RM14i will provide the space for required insulation systems to meet standards, unless TIW used.
Thanks, just looked in our cust spec....
The ACDC PSU will be connected to the 115V AC power supply, the minimum Creepage Distance shall be 5mm.
The ACDC PSU will be connected to the 115V AC power supply, the minimum Clearance Distance for internal wiring shall be 3mm.
..they may of course be wrong in this.

For some reason the transformer spec states "500VDC and 20Megohm", not the "2500VRMS for 1min".
Also, only "enamelled copper wire" for pri and sec (np/ns = 30:6 [15//6//15] ...and no margin tape, and no tubing.....thus creepage is sincere apologies, schem said "RM14"....its actually RM12 (full bridge at 450kHz from 275vdc to 28vdc and 500w)

I am convinced this whole thing is trash (a cust sent it to us and asked us to sort it), and im just working toward officially reasoning the trashing.
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3mm clearance is correct for internal wiring on the mains side only - actually 3.2mm for example between P or N to earth and for P to N, this is not the safety isolation clearance to output.

5mm creepage to output may indeed be the case for 130Vac mains, we always design for 265 Vac.

However RM12i will never meet this. Time for a frank chat with the customer.
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