24 Volt Battery Charger

Discussion in 'The Projects Forum' started by RodneyB, Jul 29, 2013.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    13
    I am needing to make a battery charger for a 24 Volt deep cycle battery 250Ah

    Please could someone point me in the right direction of a suitable circuit.

    Many thanks

    Rodney
     
  2. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,021
    Definitely a buy versus make. It'll cost you more to build your own than to just buy one.
     
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    mmmm not in Zimbabwe, that's why I am asking what most of the first world can buy off the shelf we have to import at huge cost. Its better to make so that we can look after things.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,021
    Well, what do you have locally? A simple charger starts with a transformer and uses a full wave bridge rectifier to produce pulsing DC. A charge controller circuit then handles the various functions of controlling current during the charging phases, shutting down on overheat, protection against short circuit and so on. The transformer is the expensive and heavy component.

    More modern switching power supplies (SMPS) do away with the large transformer at the expense of more complicated circuitry.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
    743
    Do you have access to transformers or an old ATX psus?
     
  6. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
    633
    13
    Thanks for all the help thus far. I have access to transformers from my calculations I will need a 600Va transformer.

    a 25 Amp charger is big I know but I took your advice and went looking locally, well what a Fas there was a shop selling 24 volt 15 amp battery chargers for US$120.00 so I took a better look inside of this super fancy box was a 10 Va transformer a rectifier rated at 15 amps a massive wire wound resistor and a 15 Amp fuse. The battery clips were connected to 0.5mm flex. so its clear even if it costs more and I get what I need I am going to have to build my own.

    Would I need a 30 volt secondary as from my calculations the battery should charge at 26.4 volts.

    From here on I am a bit lost in producing a charger that has the features mentioned above

    Thanks

    Rodney
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,083
    3,021
    I think that voltage is a bit low for bulk charging, although it would be OK for a trickle.

    You have to be careful applying a number to the voltage of the secondary. If the 30V is the RMS AC voltage of the unloaded secondary, the peaks are 1.4X higher. The rectifier will produce DC pulsing 42V p-p, less a diode drop of ~1.4V. Those peaks may not matter to the battery but could affect your electronics.

    For simplicity you might want to make a constant voltage power supply. It's not a bad strategy and it's very handy in cutting itself off when charging is complete. You might use the LM317 for that. You'll need power transistors to handle the current.

    A negative feature of the constant voltage approach is no limit on current. If you also include current-limiting along with the constant voltage strategy, you'll have solved several charging problems. Adding temperature compensation would be another.

    A couple of other examples: here and here. I'm not endorsing them, just making the point that there are MANY options.
     
    Last edited: Jul 30, 2013
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