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Thread: Dumb question: which PSU protection from high voltage on AC mains?

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    Quote Originally Posted by crmaris View Post
    just use a decent UPS with AVR.
    Wouldn't it suffer IF it were fed by a (to say) 400VAC?
    Best, Luca

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    When voltage goes over or under a specified threshold the battery kicks in and protects the PSU or the equipment connected to the UPS.

    I use UPS on all of my equipment and never ever faced a loss due to mains voltage overshoots (and we have a lot here, where I live). I only shut down my systems when there are thunderstorms and lightings in the area (we have those too).

    ps. Don't know if the UPS would live for a prolonged period under 400V. Never tried it and I think that it has to do with the UPS model, its quality and design. What matters though is that the equipment fed by the UPS will survive since a relay disconnects the mains and employs its battery once the incoming voltage goes out of spec.

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    People are worried about the PC, but with a 400 V input there are many other things on your house to be damaged, for sure...
    Last edited by Internet; 01-30-2017 at 04:54 PM.

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    Quote Originally Posted by Internet View Post
    People are worried about the PC, but with a 400 V input there are many other things on your house to be damaged, for sure...
    Yep. Heck, you could build something that will protect (turn off!!!) stuff from 400v with some cheap electronics that you can buy on ebay.

    @quest for silence, how are you gonna get 400v+??? 2 live 240v lines, each 180 degrees out of phase?

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    Quote Originally Posted by ridgid13579 View Post
    Yep. Heck, you could build something that will protect (turn off!!!) stuff from 400v with some cheap electronics that you can buy on ebay.
    Are you thinking to something different from that already said above?


    Quote Originally Posted by ridgid13579 View Post
    @quest for silence, how are you gonna get 400v+??? 2 live 240v lines, each 180 degrees out of phase?
    Actually I gonna get nothing, ridgid: it's a "safety measure" I'd like to implement.
    Best, Luca

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    Quote Originally Posted by crmaris View Post
    ps. Don't know if the UPS would live for a prolonged period under 400V. Never tried it and I think that it has to do with the UPS model, its quality and design. What matters though is that the equipment fed by the UPS will survive since a relay disconnects the mains and employs its battery once the incoming voltage goes out of spec.
    Thank you, Aris: if there's a chance it may go bad, I'd rather to not use an UPS like sort of a "fuse".
    Best, Luca

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    Well as internet said, there's a lot more to be worried if your main voltage suddenly jumped to 400v then your PC... Give me a bit of time and lemme think of something.

    It would be the same principle though, with a relay to cut mains
    Last edited by ridgid13579; 01-31-2017 at 09:50 AM.

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    http://imgur.com/a/Psdms

    Here's a rough flowchart to make it easier to understand, instead of a full blown schematic...

    Some notes...

    1. 2 relays, just incase your incoming voltage is live-live instead of live-neutral (which is how I get 240v 60hz in Canada)
    2. Vmonitor can be basically anything - From a simple transformer step down and a rectifier, to a cheap ebay single phase ac sensor(best way possibly!)... The only thing that changes in the schematic is how you connect it, and how you program the arduino.
    3. Small value capacitors on the relay input after the transistor may be required because of some "jitter".. You do not want to be testing the holdup time of your psu do you? :P....
    4. Uses a cheap battery pack/18650 cells with boost converter, It'll last a longgg while, but if you leave it unplugged for long enough you may need to charge the battery externally.
    5. Another advantage is that you can program it to also cut off when the voltage drops below x voltage, so not just cut off at a higher voltage.


    And the list goes on and on and on.

    Yes, I know this flowchart looks sketchy, but I did this while eating my mcD hashbrown

    Remember, this wouldn't be designed (not at all close) for some production work or anything. But if i needed to have OVP from mains because my voltage suddenly jumped to 400v then I think it's perfectly fine IMO. Build it properly, know how it works inside and out and do a little bit of testing before deploying it...

    You can program the arduino to send a low signal to the relays when the voltage goes under or over a certain range...

    Also, one may be killing to ask why there's no optoisolation,
    Add it if you wanted, else arduinos are pretty cheap (and the relay should turn off if you fry the arduino).... But that shouldn't happen..... even that ebay single phase AC thing has a transformer and an op amp.


    @Quest for silence, get what I mean? It's rather simple even with DIY stuff, you can make it much better then the sketch I made for you.
    Last edited by ridgid13579; 01-31-2017 at 05:12 PM.

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    Quote Originally Posted by quest for silence View Post
    No, I'm not talking about surge/peak: just of wrong voltage feed from mains.

    Is there something which will disconnect from mains immediately, preventing from blowing the PSU?
    Either UPS, some should be able to even keep working thanks to line-interactive (AVR) functions, or on-line models. Or some DIN-mounted protections work too. Not sure if you can buy something what is plug'n'play, these things are usually in power distributor. It is often combined with circuit-breaker in a single device. Or you have separate voltage trigger which than triggers what, according to dictionary, translates as "switch isolator". No idea if it's the right term, I only know some of the established name in czech. There are also some which are used with ordinary circuit breaker, as an add-on, it triggers the breaker mechanism.
    Last edited by Behemot; 01-31-2017 at 01:12 PM.

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    Quote Originally Posted by quest for silence View Post
    Thanks Per!

    And as an additional hypothesis (or further dumb question!), as far as you know, if it switched, to say, between 230V and 260V, it would disconnect the device (PSU) at any peak/surge or just if the AC mean value were >260V continuatively?
    Most decent power supplies will actually have a full range rating of 80v > 264v.
    You must ask yourself how this 400v will appear, because as you saw in my example linked in my previous post it's certainly possible.
    But then again how likely are you to encounter an electrical outlet where some muppet has wired it up with two live phases instead of live & neutral?

    Because if that is what you are trying to protect against then either my example or the one by ridgid13579 in post #18 will certainly work.
    Though I have my doubts about the response time of an arduino.
    We will after all want to switch off the output even before a full sine wave period has occured.
    Here is one implementation, to get rid of the voltage selector switch, it can't be used for 400v protection though but it's a good paper:

    http://www.st.com/content/ccc/resour...CD00003861.pdf

    But as others mentioned what you probably want it a whole house protector, failing that some easy to use device like this comes to mind:
    http://www.neopower.hk/Automatic-vol...cher(AVS).html
    "The one who says it cannot be done should never interrupt the one who is doing it."

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