[chbot] Robotics Group meeting, Monday 19 Nov 2018, 630pm, 5 Idris Road

[Trevor Wignall]

It is a common practice to route a slot in the PCB underneath the opto so
there is some air gap providing isolation between the copper pads. I have a
distant recollection that for 230V AC, you need 8mm creapage distance, not
4mm, hence the slot. However I will happily accept corrections on this. In
any case, the more separation, the safer the design.
Trevor

On Tue, Nov 20, 2018 at 12:13 AM Volker Kuhlmann <list57 at top.geek.nz> wrote:

> On Mon 19 Nov 2018 23:09:26 NZDT +1300, Mark Atherton wrote:
>
> > I have seen that schematic before, however the implementation as an
> > Arduino Nano shield looks like a death trap to me.
>
> Yes, agreed, a Very Dumb(TM) idea. But that was only for the link. Click
> on schematic and you get the hackaday article with the real dirt. Forget
> the shield rubbish.
>
> If the SMD resistors are specd for 250Vac/350Vdc in the datasheet I
> don't see a problem, the 2016 (metric) size I think isn't so one would
> have to go up in size. I just used TH parts. TE Connectivity LR1F220K.
>
> > Would like to see an opto with at least 1kV AC isolation. Also
> > enough PCB room to allow for a decent isolation gap.
>
> Vishay 4N35, 5kVrms ;-)
> I think other manufacturers' 4N35 weren't as high. I didn't use a socket
> because I wasn't sure of its isolation. The gap is prescribed by the
> DIP6 package size, pitch is 7.62mm so you get about 6mm from the edges
> of the copper, comfortably more than the 4mm required.
>
> > http://www.magazines007.com/pdf/High-Voltage-PCDesign.pdf seems to
> > be quite interesting and relevant.
>
> Well, I'm not doing 40kV and don't plan to design a PCB for it. FR-4 is
> accepted material for 240Vac.
>
> Thanks,
>
> Volker
>
> --
> Volker Kuhlmann
> http://volker.top.geek.nz/      Please do not CC list postings to me.
>
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