Any Voltage Relay?

Discussion in 'General Electronics Chat' started by Patrickbic, May 26, 2015.

  1. Patrickbic

    Thread Starter New Member

    May 26, 2015
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  2. MaxHeadRoom

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    Jul 18, 2013
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    What do you mean by 'Take a wide variety of signal voltages' ? does this apply to the input signal or the controlled side (output).?
    Max.
     
  3. Patrickbic

    Thread Starter New Member

    May 26, 2015
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    Just the input signal.
     
  4. MaxHeadRoom

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    Jul 18, 2013
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    If it is just for one permanent installation, you could tailor the input to suit, what is the application that such a large signal input swing is needed?
    Max..
     
  5. Patrickbic

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    May 26, 2015
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    I have a piece of equipment that requires a contact closure to run (low current run signal). I would like to be able to run it with a variety of input voltages depending on where I am. It seems like a relay with a wide input range would do the trick.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I am not sure what you are doing, so please be a bit clearer to describe what is the load and what is the control.

    Generally SSRs are either AC or DC on the load side as they use different elements for AC (a TRIAC) or DC (MOSFET).

    AFAIK both types want a DC control. It should be a simple matter to either limit a large DC control signal or convert an AC to a DC control.
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Anything you do using resistors, Zeners, transistors to drop a 230V signal to the max allowed voltage/current into the input of an SSR is likely to dissipate so much power as to be not practical.

    I would go get a surplus SMPS 5V cell-phone charger. Feed it 100V to 250V on the input side, and use the 5V output to tickle the SSR.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    My favourite continuity tester contains a pair of LEDs and a thin film PTC thermistor - that allows it to draw somewhere close to constant curren at anywhere between 4 - 440V. The tester is a Steinel (not sure which way round the I & E go). So far I've never seen the thermistors advertised, its a tiny ceramic tube with a thin film thermistor material coating on the outside, might be worth looking in the general direction of Polyfuses.

    Assuming such a thin film PTC can be found, one of those in series with the LED in an opto-coupler should do the trick - the optos found in some telecoms gear (modems etc) have AC input (inverse parallel pair of LEDs) Probably not worth the extra cost, but would be a little more sensitive and you don't need to add a reverse protection diode on the LED side.
     
  9. Patrickbic

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    May 26, 2015
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    Thanks Ian, I'll look into designing a PTC/optocoupled circuit that will do what I need.
     
  10. ian field

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    Oct 27, 2012
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    Don't get your hopes too high - as I said, I've never seen those thin film PTC thermistors advertised anywhere. There might be something related to the Polyfuse that will do though.

    A feature of using any PTC thermistor in this type of application is very high initial current - PTC thermistors were used to drive the degauss coil in CRT displays, the AC fed to the coil starts off from a very high peak and decays.

    You can add clamping protection for the LED, I've seen 3 series silicon rectifiers clamping a red LED current draw indicator, the LED has about 100R in series across the clamp diodes for a bit of protection. IIRC: the IRLED in an opto coupler has a slightly lower Vf, you might have to mix & match silicon and Shottky-barrier diodes to get the clamping voltage just right.
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Personally I'd just use a socketed relay, grab a handful of different coil voltages and swap to whatever you need for that location..
    Throw a diode bridge before it to allow DC relays with any AC supply..
     
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