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Discuss Need a specific relay - If exists??? in the Looking for Commercial Electricians? area at ElectrciansForums.co.uk.

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  1. 8yf13l0
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    8yf13l0 Active EF Member

    Location:
    United Kingdom
    Gents

    I am requiring a 12Vdc Relay that is normally closed, but I also require the relay to delay before returning to closed position (when de-energised).
    Are there relays on market that do all this combined or do I require a seperate time delay module of some kind?
     
  2. Richard Burns
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    Richard Burns Trusted Advisor

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    With a relay if you cut the power to the relay you cannot maintain the contacts open for a specific period of time because there is now no power to the relay.
    There are off delay relays that have a control signal in coming and when that stops (even though the power to the relay is maintained) the relay will switch after a set time. If the power to these relays is cut then the contact will switch instantly.
     
  3. Rob
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    Rob Trusted Advisor

    Location:
    North west
    You can get some that will hold open even when all the power is removed. However these are expensive and only really offer a couple of seconds worth of delay maximum. It just uses a capacitor.
     
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  4. SparkyChick
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    SparkyChick Making a banana smoothy for my fave gorilla Electrician's Arms

    Location:
    South Wales
    Business Name:
    SparkyChick
    What is it that you are trying to achieve with this relay?
     
  5. Cadgey123
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    Cadgey123 Regular EF Member

    Location:
    London

    Get a little programmable controller.
    An Omron Zen should do the function of that you request. You can programme it with the keypad buttons too. Quick and easy!!
     
  6. 8yf13l0
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    8yf13l0 Active EF Member

    Location:
    United Kingdom
    A perminant float trickle charger to install on a small 4kw diesel backup generator behind a customers house (still in design stage). But here lies 2 problems I see to over come. (1)Having a way of seperating the charger output from the battery termainals when engine running so the diodes don't get fried by the alternator on the engine or both. (2)When the power to the house and charger input is cut, I want to do the same again so charger does not risk draining battery down.
    (2) I initially thought a 230V relay normally open - solenoid feed in parallel with charger input, so charger and battery only connected when chargers 230v input is present.
    (1) A 12V relay normally closed (charger and battery connected in dormant state) then a switch feed from emergency stop button when pulled out to open relay prior to engine startup. But here I have come stuck because I realised that when you want to stop engine by pressing stop button in, the relay will close instantly but the alternator will still deliver 14v charge potential during engines gracefull shut down.
    Here its where I am exploring potencials of time delay so the relay does not close instantly, but for about 10 seconds or so.

    Any constructive suggestions appreciated.
     
  7. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Yes there are timer relays that do exactly what you want, though they do often require a permanent live supply to support the timer function.

    I use Schneider (was telemecanique) for these things, they do a multifunction timer or else dedicated units for a specific function.
     
  8. 8yf13l0
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    8yf13l0 Active EF Member

    Location:
    United Kingdom
    Sounds good. Don't suppose anyone will have a link to a preferred online supplier?

    Cheers
     
  9. sparkdog
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    sparkdog sparkdog Electrician's Arms

    Location:
    Sunny Sussex
    Business Name:
    C MacRae Electrical
    You could have a transistor driving the relay coil and have a suitable size capacitor in its base circuit, so the charge leaks away slowly before it switches. If you are into designing that sort of stuff.
     
  10. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    I usually use farnell,

    The Schneider re17 series might do what you need, I think you need a 'C' type timing function but may need to go for a multifunction unit to get the 12V operation. It would be a lot simpler if you could use 24V
     
    Last edited: Jul 25, 2017
  11. spinlondon
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    spinlondon Trusted Advisor

    Location:
    Harlow Essex
    You can purchase trickle chargers which can be left connected when the generator starts.
    No need for a relay.
     
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  12. Marvo
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    Marvo GMES....You absolute beauty. YOU ROCK DUDE!!!! Staff Member

    Location:
    South Africa
    Going back some years we also used a type that were 'slugged'. They had a thick iron sleeve over the coil that used to hold them in via residual magnetic field for a short period when power was removed. Not sure if they still make them though, last time I saw them was late 70's, early 80's.
     
  13. Lucien Nunes
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    Lucien Nunes Mercury Arc Rectifier Trusted Advisor

    Location:
    London
    Yes this sounds completely unnecessary. Unless it is of a peculiar design, there's no need to disconnect the charger when the alternator is running. The only reason you might want to disconnect it is if it has a battery status meter on the output that would discharge the batt when neither mains nor generator power are available for a day or two. Many take zero current when off and can be left permanently connected without fear of discharging the battery.

    You mention both float and trickle charging, these are opposites in that float is constant voltage and trickle is constant current. Float or multi-stage terminating in float is what you need for permanent maintenance of charge in a modern lead acid.

    FWIW on a DC relay, a suitably sized electrolytic across the coil will hold it for a few seconds, but add a series resistor to limit the inrush when the control circuit closes and charges the capacitor. The relay contacts may have to be derated when slugging because the operation is not as swift.
     
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