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Control circuit

Discussion in 'General Electronics Discussion' started by Heeran, Dec 9, 2012.

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  1. Heeran

    Heeran

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    Nov 13, 2012
    Hi
    I could really use with some help with the circuit that I want to build but i have no clue where to start.I want to build a circuit that can basically switch off a battery charger and switch on the charger, i am using two 12volt batteries that are connected in series which is 24 volts and when the voltage drops to 13volts, I want the circuit to switch on the charger and the battery is fully charged (24V) than the ciciut must switch off the charger completly.All the circuit must do is be able to activate a relay when on and deactivate the relay when off. I would like to know how to also build a circuit with a RED/ORANGE/GREEN led bulbs to show the status of the battery. Please assist me.
    Thanks
     
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Draining them that low you will likely damage the batteries.

    Chris
     
  3. Heeran

    Heeran

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    Nov 13, 2012
    Okay, i understand what you mean, what will you recomend be the correct voltage for the circuit to switch the charger on, I know that the charger will switch of at full charge of the battery.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    To see some examples of LED indicators for battery voltage, Google battery voltage indicator LEDs lead acid

    I assume your "24V" battery is actually 27.6V. If it's a lead-acid chemistry, you should not allow its terminal voltage to drop below about 21V.

    Batteries are also sensitive to temperature, and the undervoltage cutoff and charge target voltage should be adjusted according to temperature. Find your battery manufacturer's web site and look for application notes.

    I have to ask, though... If you can charge the battery anytime, you must have mains present, so why use a battery at all?
     
  5. Heeran

    Heeran

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    Nov 13, 2012
    I am using the battery as the primary source of energy, the mains is just used to charge the battery, i am going to use a trickle charger,but i need it to switch on at the voltage that you have recomended and to switch of at full charge. The battery will be kept in a sheltered area so it will be cool, i am using two 12volt batteries and a 24 volt trickle charger.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I get what you're doing. My question is, why?
     
  7. Heeran

    Heeran

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    Nov 13, 2012
    The reason im doing this is to provide power due to the constant power cutt off in my country.
     
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK. Not enough information but it's a start.

    If you use the method you described, you are cycling the battery. If the power fails when the battery is near its low voltage cutoff point, the charger won't be able to charge it, and either (a) the load will over-discharge the battery, or (b) you will have to disconnect the load when the low voltage cutoff voltage is reached. In either case, the load will lose power.

    There is another problem with charging a battery while you're drawing current out of it. The charger has to supply both the current into the battery, AND the current you're drawing out of it. The charger can't tell how much current is going into the battery, and how much current is going into your load. So it may over-charge, or under-charge, the battery.

    The way your needs are normally met is called "float charging". The battery is kept at a fixed voltage (once its initial charge has finished), and the load is powered from a separate mains-powered power supply. When the mains fails, the battery takes over, and runs until its low voltage limit is reached. At that time, you run out of power, but that method gives you the maximum backup time, rather than a random backup time that depends on the state of charge of the battery at the time that the mains fails.

    Lead-acid batteries tend to last longer if they aren't being cycled continuously, as well.

    Tell me more about your application. What type of batteries? In other words, what chemistry? Lead-acid or something else? What's their capacity? Do you have a data sheet for them? What are you powering? Is the load continuous or intermittent?
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Curious; what will you be powering that requires 24VDC?

    Chris
     
  10. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Maybe it's hard to say your post is too short there are no periods it's hard to read you ran five sentences into one it's messy you need to give much more information.

    Edit: the post that this post was a parody of appears to have been deleted.
     
    Last edited: Dec 31, 2012
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Mobile phones have their own charge control circuit that stops charging when it decides that the battery is full. A mobile phone "charger" is just a power supply that the phone can use to charge its battery if it wants to.

    Or are you talking about charging a separate battery, not the mobile phone's internal battery?

    Have you worked out how to generate a pulse from a USB-interfaced circuit? Do you have the USB endpoint designed and programmed?

    How do you intend to control the charger? A relay in series with the mains power input to it?

    What advantage is this system meant to provide, compared to connecting the phone to the charger and letting it charge up immediately?
     
  12. Heeran

    Heeran

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    Nov 13, 2012
    Sorry for the delay, the battery im using is a lead acid . The size is a 658, 95 AH and 850 rating. I want to build a circuit that can cutt off and on the charger aswell as display the draw from the mains when the charger is switched on.
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    What does "850 rating" mean?

    Please re-read my post #8 in this thread.

    There are several problems with what you want to do.
    There are several questions in that post that you haven't answered.
     
  14. Heeran

    Heeran

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    Nov 13, 2012
    Hi
    The application of my load is a high power LED lighting circuit and it is going to be used like how the lights in a home is used.

    The charger that I intent on using is a 12/24 volt 5 amp charger that will be pluged into the mains but i want this circuit to be able to break that circuit between the mains and the charger when the battery is fully charged and reconnect when required.

    The battery is a lead acid baterry that 12 volts, 95Ah, 850Aen and they going to be conected in series to provide the 24 or 27 volts.

    I would also like to know, how can i build a display that shows the amount of Kw that the charger is drawing when is use from the mains and it must store that infomation, but must also have a calender so you can monitor draw aswell as a reset button to restart it when ever you may want to.
     
  15. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Thank you for explaining that.

    Turning the charger ON AND OFF is a BAD IDEA. Please read this quote carefully:

    Connecting the load STRAIGHT ACROSS the battery is a BAD IDEA. Please read this quote carefully.

    That is a very complicated problem. You can buy energy monitors that plug in between the mains power and the load (the charger) and can display kWh and store information from one day to the next. It is not worthwhile trying to make your own. They are complex. It is best to buy one.
     
    Last edited: Dec 11, 2012
  16. Heeran

    Heeran

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    Nov 13, 2012
    I would still like to build the intial circuit were the charger is switched off and on automaticly at 22 volts and off at full charge. I understand that it is complicated to build the display but I realy would like to build it. It is realy expensive to buy it.
     
  17. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    I think turning the charger on and off is a bad idea. Perhaps someone else on the forums will design it for you.

    The reason energy meters are expensive is that they are complex internally. They may be expensive, but they will still be cheaper than buying all the needed components yourself. They also have a lot of firmware, which takes a long time to develop and test. They are also accurately calibrated. There is NO WAY you can save money by making one yourself. Making something useful would cost a lot more and would require a LOT of software development and testing. It is NOT practical in any way.
     
  18. VAT

    VAT

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    Dec 10, 2012
    There are some IC's out there that does exactly what you want, I am not sure if they work in the scale that you want but they take care of all the under voltage, over voltage, temperature effects on batteries, and even a coulomb counter to know exactly the % of charge your battery is at which you can then use to display.(some of their outputs are I2C)
    you should check out linear IC's, if I remember correctly it shouldn't be that expensive but I may be wrong :S

    However if you wish to do things on your own then you should read about DC/DC converters and their principles on how they manage outputs that will give you an idea.

    Either way you have a lot of reading to do buddy =)
     
  19. Heeran

    Heeran

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    Nov 13, 2012
    Thanks alot. I will read up.
     
  20. willqa

    willqa

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    Dec 4, 2012
    Last edited by a moderator: Dec 30, 2012
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