voltage controlled switch

Discussion in 'The Projects Forum' started by macmaze, Dec 30, 2009.

  1. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    I am building a battery charge that will charge a 12v-200AHr battery and I need a circuit(switch) that will cut off charging while it's fully charged. Can any one help me with a voltage controlled switch; thanks
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    A 200AH battery needs a heavy duty charger.
    First Question is do you want a SMPS charger or a linear charger
    second Q is do you have a powerful enuf transformer if you prefer a linear charger?

    Rifaa
     
  3. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    It is a linear charger and the transformer is powerful enough to give 30A
     
  4. R!f@@

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    Apr 2, 2009
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    please give me ur transformer specs

    Rifaa
     
  5. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    The specs are 220v/14v; the coils used are: for the pry (input) coil 24swg and for the sec (output)coil 18swg tri-filar
     
  6. R!f@@

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    what type of battery are you going to charge?

    Rifaa
     
    Last edited: Jan 7, 2010
  7. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    200AHr Deep cycle battery; make is su-kam.
     
  8. R!f@@

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    macmaze, are you from india?

    Rifaa
     
  9. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    No am not; Su-kam is more available in Nigeria; Plse help me with the circuit so I can build the charger.
    Thanks a lot
     
  10. R!f@@

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    Apr 2, 2009
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    I'll get back to u.
    Keep checking, quite bzy at the moment.

    Rifaa
     
  11. R!f@@

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    Apr 2, 2009
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    Do u want a heavy duty charger or a Switch ( referring to ur post).
    By the way, to build a charger for 200AH battery you will need at least a transformer that could output 20VAC at 40 Amps continuous

    Rifaa
     
  12. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    I just need a switch but why would I need a 20VAC at 40 Amps continuous that will give me a 16.4VDC output if am not wrong. Is that safe? for I have been charging with maximum 15.5VDC and it has been fairly ok except for the issue of having to switch off when fully charged, please enlighten me the more. Thanks.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    You really wouldn't want to charge it faster than 1/8 the AH rating, which is 25A. You'll be heating up the battery quite a bit charging it at a 25A rate anyway. The hotter the battery is, the greater the chemical activity, and the shorter the life of the battery.

    You should charge the battery at a constant current until it is about 90% charged, and then charge it at a constant voltage until the current drops off.
     
  14. macmaze

    Thread Starter New Member

    Nov 17, 2008
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    I thought I could achieve that using the tappings from my tri-filar transformer, that is why I needed a voltage controlled switch. So how do I achieve the kind of process you are recommending.
     
  15. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Ah! I see.
    So you do have a charger, in that case, even the charger output is enough to cutoff the battery when a predetermined voltage level is reached.
    All you need is a comparator and relay with enough contact rating.
    The comparator can monitor the battery current or voltage and cutoff the battery via the relay.

    Hey Sgt.
    You guys don't say anything twice the same way. Do you? :confused:
    What I mean is in a previous post some one replied that LSA should be charged initially at 1/5th of the AH capacity, now it is 1/8th, so which one is it.
    A 200 AH battery needs 40A initially, if it is 1/5th.
    but at 1/8th it is 25A.
    This Initial charge current of a SLA should be the same for everyone I think.

    Rifaa
     
  16. R!f@@

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    Apr 2, 2009
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    Well !
    Why doesn't any one comment.
    cat got ur tongue?
     
  17. Duane P Wetick

    Active Member

    Apr 23, 2009
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    Charging at 1/8 AH rating is probably easier and safer anyway, so proceed on that basis. Full charging is usually about 2.4 Vdc/ cell and Float charging is about 2.2 Vdc/ cell; 2.4 x 6 = 14.4 Vdc, 2.2 x 6 = 13.2 Vdc. These figures will vary according to temperature, (80 deg F base). See 4 points of gravity discussion by Intl. Harvester. You should be able to float charge continuously with no problem. The specific gravity of the electrolyte will be the final answer in checking if your battery is fully charged; 1.265 = 100% and 1.120 = 0. (Don't forget the 4 points correction)

    Cheers, DPW [ Everyone's knowledge is in-complete...Albert Einstein]

    Just thinking about your problem...you could have a switch that manually selects 1 of 2 pots that sets the rate, Full charge or Float charge for the DC rate. The other thing that you could do is monitor the temperature of the electrolyte, if you have a proportional (PID) controller.
     
    Last edited: Jan 15, 2010
  18. R!f@@

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    Probably is not good enuf?
    Every one needs a figure.
    Should the initial charging current be at 1/5th or 1/8th of the SLA AH rating?

    Moderators and Admin's have a very vast theoretical knowledge on these matters.
    Far better than me but when it comes to field work I would beg to differ.
    How many of you have actually charged a battery while monitoring it.
    I know I have, and these figures differ, that is why I am asking what is the best ratio to charge a SLA.
    I like to hear everyone's opinion on this matter.

    Rifaa
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    It really depends upon the manufacturer's recommendations for the particular battery in question.

    Some can take a higher charge rate. For example, an AGM battery can be charged at a very high rate, while a gel-cell needs a very low rate.

    If the manufacturer's recommendations are not followed, you cannot expect to have a good service life from the battery.
     
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I don't think even 25% of 'em can get there hands on the battery Spec's.
    Most of the time time we don't even buy a battery, instead you'll get it from a dead equipment or from a friend.

    It is always better to optimize a charger for the cells you currently have.
    Only then u can get the maximum life out of your battery.

    Rifaa
     
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