Dual Source Electricity!

[meow2222]

Where's the problem with using a relay?

NT

[Colin Stamp]

It's easy enough to do device by device if they have external DC power supplies. Just get the device an extra PSU and diode-or them together.

Could get expensive if you have a lot of devices though.

Cheers,

Colin.

[polygonum]

It needs to be something with relevant approvals. I certainly would not trust myself to make something that was safe enough for use in a workplace, many of which also get members of the public visiting. (And that's assuming I was able to decide which relay, how wired, to achieve what I want, reliably, and not simply knock the device into reboot.)

[polygonum]

Most of them run off kettle leads but, as mentioned earlier, they could possibly have a DC option as well - need to check.

[meow2222]

For anyone else not worried about approvals, diode ORing 2 rectified mains supplies works great with smpsus. Obviously both feeds would have to be treated as if connected.

NT

[polygonum]

You also fooled me because I need it to handle mains (at least mostly).

[Andy Burns]

I think he *does* mean feeding two mains supplies as the input to one PSU, rather than feeding the output of two separate PSUs into the equipment, e.g.

mains1-->rectifier-->diode--\ |-->SMPSU-->kit mains2-->rectifier-->diode--/

where mains2 might be the output of a UPS.

[meow2222]

Yes - though you dont need the last diode, the BRs do that.

mains1-->rectifier--\ |-->SMPSU-->kit mains2-->rectifier--/

Just dont plug an old iron cored wallwart into it, and label it suitably.

NT

[spuorgelgoog]

Can you connect up temporary switches/routers next to the ones on the UPS, and swap the users' ethernet cables from normal to temp. This would interrupt the ethernet for about 1 second per user.

VoIP might be interrupted but most networky things should just degrade gracefully and accommodate the packet loss.

Owain

[polygonum]

But that doesn't help where the equipment has only one IEC (kettle) lead input and no ELV option. :-(

[meow2222]

It is precisely for such situations. It feeds rectified mains into the mains input of the appliance. If you set the UPS to deliver a volt or 2 less than mains voltage all works very nicely.

NT

[polygonum]

Will any random device rated for normal mains be happy running off this "rectified" mains? Will both mains plugs be safe with no possibility of one having a voltage at the pins of the plug when the other plug is still connected to a live source?

Given that mains voltage varies, how do you get a UPS to continuously deliver a volt or two lower than mains?

[meow2222]

No. Some is, some isnt a bit happy. Equipment with built in smpsus run just the same, so its fine for almost all modern computer equipment - but not eg for speakers with built in transformer that may still be 50Hz iron cored.

They won't be live, but an insulation breakdown could make them so - like most things really. I'd Use 1kV rated bridge rectifiers, though you only need 500v to pass the pat test.

Depends on your UPS. 10 or 20v less would be fine too. The ups output should be synced with the mains too, otherwise it gets more complicated.

NT

[Dave Liquorice]

If the UPS is an online type. ie the kit is run from the invertor at all times, rather than the mains normally being routed through perhaps with some trim/boost and only runs from the invertor when the mains disappears.

On online UPS not in sync I'd expect to let the magic smoke out in fairly short order...

[meow2222]

Hardly. The only result of out of sync is that the load draws some of its current from the ups.

NT