Mains Voltage Protector

Discussion in 'General Electronics Chat' started by hazim, Jan 6, 2014.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Mains Voltage Protector

    Dear.

    I'm trying to design a simple circuit that will be used as a mains voltage protector. In my country we have a really bad electricity service. Sometimes the electricity goes OFF and ON, ON and OFF, very quickly, which may harm electronic devices.

    Also, the mains voltage here is 220V but it comes weak mostly, 180 and lower and even down to 100! due to the bad and old mains lines and network.

    A switch mode 12V or 9V adapter with 100-240V AC input will be used to power the circuit, that will turn ON a relay as the electricity ON, and turn it OFF when the electricity starts going ON and OFF quickly. The circuit will wait after the electricity being continuously ON for about a minute then switching the relay ON again.

    The appliances will be supplied from the relay.

    I thought about using 555 timer, but didn't know how to do it.

    Hope you understood me well.

    Any help is strongly appreciated.

    Best Regards,
    Hazim
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    I thought that is what a UPS (uninterruptible power supply) is supposed to do.
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    you can just use an off the shelf delay on make relay triggering another relay..
    Of course you are more than likely going to need a large relay (aka contactor) to be able to switch off ALL your power. Most relays just do a few amps.. A whole house could require much more than that..

    BUT IMO if you don't know how to do it you have no business attempting to play with mains electricity..
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Look at a watch-dog timer, detect the 50Hz from a L.V. transformer through a rectifier and reset a 555 timer that times out after 60sec if not reset by your pulses.
    You obviously will need an aux DC supply for the detector circuit.
    Max.
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
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    I use these on commercial pumping stations and refrigeration compressor loads.. Different delays for each load.
     
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  6. Gdrumm

    Distinguished Member

    Aug 29, 2008
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    Nice avitar inwo, reminds me of my childhood.
    Kinda looks like me back then too.
    But that would have been 1955, and I'm from Texas, not SE Mn.

    Come to think of it, I think I used a bobby pin....
     
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  7. inwo

    Well-Known Member

    Nov 7, 2013
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    It looks exactly like I did in the 50s.:)
     
  8. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Actually I'm using a APS (Automatic Power Supply) which is similar to the UPS but have a relay that switch between mains and inverter, the relay switches ON when the mains electricity is available and so... my main problem is that the relay contacts become bad due to sparks happen when the mains starts to go on and off quickly, I don't know the the word in English to explain it, but the relay starts to chatter which damage it and damage the inverter when happens frequently.

    There are cheap "Voltage Protectors" in the market which have a delay time before it outputs voltage, but it stops low voltage (<180V) and high voltage (>245). I don't need it to stop the voltage if it's low even at 100V because I use it to supply SMPS 100~240V power supply. I tried to make some changes with these products to adjust the low voltage cutoff down to 100 or stop this functionality but didn't succeed.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You could use a LM311 comparator to detect the 100v level from a small L.V. transformer secondary, the output could trigger a 555 monostable timer set to 1 min.
    How do you know the 1 min will be sufficient, it may start again after the 1 min period?
    Max.
     
  10. inwo

    Well-Known Member

    Nov 7, 2013
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    A harmonic neutralized transformer that I found here keeps input at 118 volts over a range of 95 t0 190.

    That would translate to 236 vac from 190vac to 380vac with properly designed model.

    That with a time cube for momentary interruptions should work if the power relay holds down to 180vac.
     
  11. MrChips

    Moderator

    Oct 2, 2009
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    We call those things constant voltage transformers.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Big power wasters though!
    Max.
     
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  13. inwo

    Well-Known Member

    Nov 7, 2013
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    How so?
    Transformers are pretty efficient.

    I'm guessing as I didn't do the research.:confused:
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    All the ones I have used run at their full rated Kva, regardless, the load reduces the CVS load to maintain its rated value.
    IOW a 5kva unit running with zero load consumes 5Kva.
    This is evident by the extreme heat they run at.
    They usually have shields to prevent burns.
    Max.
     
  15. inwo

    Well-Known Member

    Nov 7, 2013
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    Efficiency isn't great. You're right. (I checked):p

    Not ridiculous though, for what it does.
    If sized right for small loads it may make sense.

    750 va transformer consumes 105 watts with no load.

    A 300 watt bulb (250W actual) uses 372 watt input to trans. @ 118vac in.
    @ 90 volt in = 364W in
    @ 130 volt in = 387W in

    Couldn't put my hands on a 750va right now.

    ps.
    Are you sure you weren't measuring VA inputs?
    A 250va buck/boost uses only 10 watts stand no load.

    A smaller Sola, 120va, =29 watt @ no load.:eek:
    Thought it might improve @ full load and nominal line voltage.

    No dice!
    A 97 watt load uses 135 watts.:(

    ps.
    Are you sure you weren't measuring VA input?
     
  16. inwo

    Well-Known Member

    Nov 7, 2013
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    Repaired a half dozen battery chargers a few weeks ago using similar transformers.

    I think I posted.

    They act like a short when powering up slowly thru a variac.
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The vast majority I have used are around the 5Kva minimum mark.
    They make nice heaters!
    Max.
     
  18. inwo

    Well-Known Member

    Nov 7, 2013
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    The ratio of kva to no load current should be close though.

    I could see possibly drawing full load current at worst. Though unlikely.

    But not full watts.

    Oh I'm sorry, I see you did say KVA.:p

    Yet, the 120 kva draws 35kva (29W) No load.

    No where near full kva.:confused:

    Thus my big junk box..............

    ps.
    Hope I don't come off argumentative.
    I like learning by doing. :)
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The way it was explained to me by Sola, was that the transformer runs in saturation mode, any secondary load is subtractive from this saturation, the result is that the overall load current is neither increased or reduced.
    Also the supply voltage has to drop significantly before the output voltage drops from its rated output.
    (take it out of saturation).
    Max.
     
  20. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
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    I will try again to change the resistors at the LM234 comparator inputs in the voltage protectors available in the market. There should be a solution for that.
    I have one that was trying with, it have a delay for about 4min, I catched easily the resistor and capacitor responsible for this delay and made the delay shorter as I need, 1min is ok for me. For our bad electricity service here, my problem is with going fast on and of, or having the relay chatter.

    Anyway, I'm so busy these days, when I have enough time I will try to solve this problem either by editing available voltage protector or designing new one that matches my need.

    All suggestions are strongly appreciated.

    Regards,
    Hazim
     
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