Due to space limit I had to design the PCB in multi-level form, the top front side of the PCB is AC line and under that is DC capacitors:

Is the 3mm air gap between AC line and DC capacitors enough for isolation? if not should I place a 2mm plexiglass in between them?

Edit: considering the top capacitor pin and solder, the air gap is actually 2mm.

  • \$\begingroup\$ Please provide some more specs regarding voltages and current (iirc line voltage can range from 90Vac to 265Vac). Do you just basic insulation or reinforced? etc \$\endgroup\$ – Huisman Jan 22 '20 at 7:52
  • \$\begingroup\$ @Huisman city AC line, 220 V and maximum current is 2 A. bottom DC line is -5V. \$\endgroup\$ – ElectronSurf Jan 22 '20 at 7:54
  • \$\begingroup\$ if you fill it with a solid insulator then 3mm is probably enough. can you use shorter capacitors, or do you need 50V capacitors on the bottom deck? \$\endgroup\$ – Jasen Jan 22 '20 at 9:14
  • \$\begingroup\$ @Jasen I didn't find shorter caps (or lower voltage with same capacitance) in the local store, should look online. what kind of insulator, is plexiglass good enough? \$\endgroup\$ – ElectronSurf Jan 22 '20 at 9:17

Plexiglass is not a well defined term, 2mm of certain exactly defined and approved material such as polycarbonate is ok. I guess you mean polymethylmethacrylate (=PMMA) when you say plexiglass, not some resembling trade mark. It can be used as well in this place.


1) There should be also certain minimum route length along the surface of the insulator (=creepage). It can be for ex. 8 millimeters for 240VAC mains. The requirements vary with operating voltage, environmental conditions, mains overvoltage category level and the end application.

2) There are as well insulation requirements for the transformer.

You really should get the safety standards for mains AC operated equipment if you are building them.

BTW: is it possible to change the lengths of the spacers? Then no extra insulators would be necessary.

  • \$\begingroup\$ Thanks, no i can't increase the height. but going to order shorter caps. how much distance the caps should have with above PCB? 8mm? \$\endgroup\$ – ElectronSurf Jan 22 '20 at 11:23
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    \$\begingroup\$ Do not increase the height, shorten the lower legs as much as you make the others longer. Current 2mm gap is far too small if reinforced insulation is needed. 8 mm distance should cover all gap requirements. You can try this calculator, but you should know its terminology which is taken from standards: creepage.com Hopefully you know how much the boards can get bent when someone knocks the device or the temperature changes. It affects the gap, too. \$\endgroup\$ – user287001 Jan 22 '20 at 11:57
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    \$\begingroup\$ (continued) I guess occasional knocks are possible although your construction seems to be one which fall to pieces soon under vibrations, for ex. during repeating transports. Solder joints do not stand repeating punishment. \$\endgroup\$ – user287001 Jan 22 '20 at 12:12
  • \$\begingroup\$ About the vibration; hot gluing the components the board is enough to keep them in place? \$\endgroup\$ – ElectronSurf Jan 22 '20 at 12:19
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    \$\begingroup\$ Hot glue helps if it's used generously. You have many high parts, their mass centers are far away from the solder joints, any horizontal vibration causes substantial torque which can break the joints. The glue must be also between the parts to prevent this. \$\endgroup\$ – user287001 Jan 22 '20 at 12:58

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