Isolator for 12 or 24 volts supply.

Discussion in 'The Projects Forum' started by RodneyB, Oct 11, 2015.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I have a circuit that runs from either a a 12 or 24 volt supply. I would like to make an isolator that cuts off both positive and negative from the supply if the source is turned off.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    A double-pole toggle switch or two-pole relay?
     
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  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Thank you, It has to be automatic, I tried it with a 24 Volt relay and the first problem I faced was the coil energised at 12 Volts. I would prefer to use the relay but need to try and get the coil to energise on the 24 Volt source over 16 Volts which is not critical but cant be less.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Try a resistor in series with the relay coil to drop the volts down.
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Rodney,

    I thought we went through all of this in this previous thread. What in the previous thread didn't work so that you have to start all over again?????

    I have better things to do with my time...
     
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  6. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    The advice you gave me and the advice you give me is always 100% on the nail. Every circuit you have ever helped me with I am using. The voltage selector works perfectly you designed it.

    I think I may not be explaining myself. When the source voltage connected I only want the battery left in the circuit I want to completely Isolate any other electronics.

    Your advice and assistance is priceless and I apologise if you feel I have wasted your time
     
  7. MikeML

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    This is confusing. I'm trying to understand your request: What do you mean by supply? source? Is source different than supply?

    Is the source 12 or 24V?

    Is the supply 12 or 24V?

    Is the battery 12 or 24V? Is the battery either the source or the supply, or neither?

    Perhaps if you posted a sketch of what you are describing it would be clearer to me...
     
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  8. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Hi Mike I have attached the drawing and will try to explain.

    The supply voltage is either 12 or 24 volt. if 12 volt from the supply it goes directly to the 12 volt battery in the unit. This is why I was asking for a voltage selector circuit. If the voltage is 24 Volts the relay selects that it goes through U1 where the voltage is regulated to 14 Volts, U2 limits the charge current to 1.5 Amps.

    The first part of the circuit selects the voltage and charges a battery,

    The battery powers a 12 Volt tracking unit. This is a car vehicle tracking unit so I can tell which position the solar panel is. If the battery voltage drops to 10.6 volts the tracking unit is disconnected and the battery has no drain on it.

    Now the Isolator switch is to disconnect everything except for the battery except for the low voltage cut out and the tracking unit. I want the batteries not to drain at all when it reaches its low voltage limit therefore the isolator.

    I hope I have explained myself clearly
     
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  9. MikeML

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    Oct 2, 2009
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    How does RL1 ever get any power?

    Seems like U1 and U2 are in the wrong order. Shouldn't it be, limit current first, and then regulate voltage second?

    Can you tolerate the forward drops of D1, D3, and D4?
     
  10. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Hi Mike I have swopped U2 and U1 as you pointed out.

    I corrected my drawing by adding the supply to the relay and the negative I forgot to U1

    The voltage Drop across D3 will be o.6 Volts so I can increase the voltage output from U1.

    D1 is a reverse polarity diode so not sure what to do there, D4 is so the voltage from is not going to an output but to the battery.

    The reaon I want to have the isolator if necessary is so that only the low voltage cut out is left when the source is removed, this will yhen cut out the load when it gets to 10.6 volts
     
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