Mains fuse indicator

Discussion in 'The Projects Forum' started by bigcatman, Nov 17, 2011.

  1. bigcatman

    Thread Starter New Member

    Nov 17, 2011
    8
    0
    Hi everyone, first time here so hopefully, you'll look after me.

    I've had a look around the site for a simple circuit that can illuminate an LED to show that there is a current flowing to a load and then for it to change colour when the fuse has blown.
    All I can find on the forum are circuits that are for 5v or 12v.
    I have seen some circuits on the web and these use 1n4007's with a 100k resistor on the Neg line of the mains.
    I'm no genius, but doing it that way would cause alot of heat from the resistor and I'm after reducing the heat as much as I can.
    Back in the good old days I used neons and resitors to do the job but what with health and safety I'd rather be safe than sorry.
    If I can get a circuit that suits me, I want to be able to transfer it on to a PCB so that it can be mounted inside a case.

    So, if anyone out there has any ideas as to a safe and stable circuit I would be grateful.
     
  2. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    Not sure what resistors and neons have to do with health and safety. Hooking something up to the AC mains has to with health and safety.
     
  3. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Circuits that hook up directly to the AC mains are not allowed here in AAC, for safety reasons. Any 220VAC talk must be held behind the safety of a 1:1 transformer and a proper fuse. Therefore, kender's post #2 was edited.

    Please confine your discussion behind a 1:1 transformer and a fuse.

    Thank you.
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Fuses are used elsewhere than on the mains, but any attempt to put indicator lamps across them must compromise their isolating function to some extent. Whether or not this could be acceptable would depend on the context, and any applicable regulations.
    Such regulations may have become more strict over the years, hence the reference to health and safety.

    Some larger fuses are equipped with physical blowing indicators, which typically cause a piece to protrude from the end of the fuse when it has blown.
     
  5. bigcatman

    Thread Starter New Member

    Nov 17, 2011
    8
    0
    Back in the old days, the cheapest way of showing that a fuse had blown was to place a neon and resistor in a certain part of the circuit so that when the fuse blew, the neon would indicate.
    If this was to be done nowadays this would be a major problem with regards H & S

    I intend to use it as part of a distro unit and will have 4 of these in parallel with each other in a case.
    If I start to use them in a 1:1 configuration, then this would make the project too big as it the whole idea is to place it high up and when the indicator goes red I know there's a fuse blown.


    I have seen those fuses that Adjuster mentioned, but they are useless to me as they will not be suitable when the distro is at height hence the idea of having LED etc so that a blown fuse can be seen from the ground.

    The reference to H & S, I want the circuit to be safe enough to use.

    Whilst I understand that as soon as someone mentions mains electric people start to shudder, but I cannot see any other way of trying to keep the circuit down to a minimum.
    The way I see it, having a 1:1 set-up would require 8 transformers (i want the indicators to be green for OK and red for blown fuse) and this would take alot of space up on a PCB which would make the project a waste of time.

    If any one has ideas to overcome this and have a circuit small enough then I'm all ears.

    If there is a problem with supplying advise on the subject of mains on the forum then is it possible to PM me with the details?
     
  6. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    The site is mainly focused to educational purposes, and for that reason has a large userbase of amateurs and hobbyists. To protect that userbase, the safety guidelines are admittedly strict but necessary.

    I 'll close the thread now and start a discussion with the other mods. If your appeal is accepted, it will be re-opened. But I don't promise anything.
     
  7. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Okay, you can post any valid and tested blown fuse detection method, but the restriction of no LEDs to mains still applies.

    Please post responsibly.
     
  8. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    Well, one way to do this that is ENTIRELY SAFE would be simply to plug a light into an outlet. When the light's on, the power is there. If off, not. The light could be a tiny night-light thing, with no intention of actually illuminating anything.

    Then I suppose you could use a battery-powered device to light a red light or sound an alarm if the power goes away (relay drops, etc). It could be run via a wall wart and have batteries that are kept recharged as long as power is on.
     
  9. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    try this circuit...........
     
  10. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    No no no. Not allowed to bypass the fuse in any way.
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    I would do it with a SPDT relay. put a relay (coil) beween L & N downsteam of the main fuse. run voltage (from upstream of the main fuse) through another smaller fuse then through the common to NO contact to green pilot light. wire the NO contact to a red pilot light. make sure, if both L & N are fused, that you wire these pilot lights to the N upstream of the main fuse or it won't work.
     
    bigcatman likes this.
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