Lead-Acid Battery Charging

Discussion in 'General Electronics Chat' started by harikanaidu, Apr 27, 2016.

  1. harikanaidu

    Thread Starter Member

    Nov 28, 2014
    76
    1
    Hi, I have a sealed lead acid battery...its specifications are 12v/1.3 A...it is written on that constant voltage charge:stand by use-13.5 to 13.8V,cycle use:14.4 to 15V , initial current less than 0.39A...I want to charge this battery ....what i know is i have give a voltage of 14v .... what is current i should supply.?..i want to do this using a solar panel...What does these specifications stand by use,cycle use initial current mean??What is constant voltage charge is explaining??
     
  2. Tonyr1084

    Active Member

    Sep 24, 2015
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    Recently I've had my knowledge on batteries challenged, so I'll do my best to explain. If I'm wrong I'm sure someone will correct me.

    You ask "What is constant voltage charge?" Assuming the battery is fully charged, in order to keep it fully charged and ready (in a standby state) you'll need to keep it powered with 13.5 to 13.8 volts. With Lead Acid Sealed batteries I'd prefer to stay toward the lower side as it's been my experience that if you charge them at the higher voltage they tend to dry out quicker, and that renders the battery useless. Constant voltage is what you need to keep the battery ready to perform at it's peak.

    When the battery has been used for a while it's State Of Charge (SOC) will need to be restored. The 14.4 to 15 volts is what's needed to recharge the battery. This is different from the constant voltage. I believe it's purpose is to eliminate (or reduce) sulfates that are produced on the battery plates. The higher voltage is sort of to "clean house" if I can use that term, but the battery doesn't need to sit at that voltage very long. Exactly how long, I don't know.

    Batteries will draw whatever current they need to in order to recharge. What the battery specs are telling you is that this recharging voltage (14.4 - 15v) will draw less than 0.39 A (or 390 mA (milli Amps)). So whatever you use to charge the battery, it needs to be able to deliver 390 mA of current. Using an under rated charger will overheat the charger, possibly damaging it or causing complete failure. 390 mA is not a lot of power, but some "Wall Warts" (that's what we call those power packs that plug into the wall) may not be able to deliver that much current. I don't think I've seen one that was able to deliver less than 600 mA, but you never know.

    You mentioned you want to charge this battery using a solar battery. Here's what you'll need: A solar panel (or panels) capable of delivering as much as 15 volts and as much as 400 mA. Using a 12 volt solar panel will never produce enough voltage to charge and maintain that battery, so you'll probably need to use two panels. I suppose they come in different voltages - perhaps two 9V PV (Photo Voltaic solar battery) (if they exist) will work. But just putting a battery on a 15 volt PV will likely overcharge the battery. If overcharged then the battery life will be drastically shortened, possibly even killed.

    Charge control circuits are great for managing batteries. I remember when I was a kid I received a plug in battery powered flashlight. You plug it in overnight and the next morning it was ready - fully charged. Well, I plugged it in for a few days. When I wanted to play with it the battery was dead. It only had a transformer and rectifier circuit in the charger - that's why the battery was overcharged. My new toy was ruined because I failed to limit the charge.

    It sounds like you're new to the world of electronics. Welcome to a new and exciting field. There's a lot to be learned and even after many years I too am still learning. You mentioned your battery was rated at 12 v / 1.3 A... I'm willing to bet it says 1.3Ah - or Amp Hours. That's how many amps the battery is expected to deliver over a period of one hour. It may be capable of delivering more power for a short period of time, but if it's on the battery then you didn't include that information. Car batteries are rated in CCA or Cold Cranking Amperage. They may be 80Ah but they can deliver 450 CCA - the amount of energy they can release at any given moment. Like starting a car in cold weather.

    AllAboutCircuits has some pretty interesting and informative lessons that if you haven't begun going through yet, I'd recommend you do so. Learning the basics is important because everything else is based off of the basics. Like building blocks, you don't start at the top and work your way down, you first build the foundation then add to your knowledge.
     
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  3. harikanaidu

    Thread Starter Member

    Nov 28, 2014
    76
    1
    Thank you ..this is really help full......As you said minimum 400m amps current is required to charge the battery....what if i give 1 amp to it??will it damage my battery ...will there be any maximum current specification that i can give??I think if i give more current battery will charge more quickly am i right ???How to calculate the time reequired for charging
     
  4. Tonyr1084

    Active Member

    Sep 24, 2015
    540
    86
    Sorry, I don't know how to calculate the charge time. Likely the amount of time required will depend on how depleted the battery is (the SOC). The lower the SOC the longer it will take to recharge it.

    Batteries will draw however much current they need. Whether you have a charger capable of 400 mA or one capable of 10 amps - the battery will draw - as is on your spec sheet (or the battery itself) it will draw not more than 390 mA (0.39 A).

    Having more power available will not hurt the battery (in the case of the lead acid battery). But some batteries are designed with different chemistry and if allowed they may draw more amperage than is advisable. Some batteries - if charged improperly - can self destruct. Most may leak acid, but in some cases they can explode.

    Since we're discussing the lead acid sealed battery, having extra current available won't hurt anything. The battery will only draw as much as it can, not how much is available, unless what's available is less than it can draw. In cases like that the charger may overheat. Asking a 200 mA charger to deliver 390 mA will likely burn out components in the charger. But having 1 or 2 or even more amps available, the lead acid battery will only draw no more than 390 mA initially. That amount of current may be drawn for a short period of time (again, I don't know how long) but as the battery charges it will draw less and less current. Once fully charged it may only draw a few mA to keep itself at a standby charge (13.5V to 13.8V). Such low charge rates are called "Trickle Charge".

    Trickle chargers are designed to limit the amount of current the battery can draw. EVEN IF the battery wants more - the charger is designed to limit it to a preset level. For instance (and I'm making up these numbers) a car battery may want to draw 30 amps to recharge (after starting the car). The alternator will easily handle that requirement. But once the battery is fully charged the alternator may only supply 100 mA or less. Again, I am making up numbers but I'm doing so that you can understand what is going on.

    You can buy battery chargers for your car. They may deliver 20 amps or 10 amps or they may be trickle chargers. The 20 amp charger is designed to bring a battery up quicker than the 10 amp charger, but the trickle charger is meant to keep a battery at its peak while being stored for a long time. Like if you park the car in the garage for the winter. Cars, even when they're off still use some electrical power, so a battery can go dead over the winter. Trickle chargers prevent that. And I'm sure there are other reasons for using a trickle charger.

    I sure hope someone else will chime in here. I'm nervous that some of my information may be inaccurate. I wouldn't want to cause any damage or hurt anyone by giving bad information.

    Anyway, I hope this is all helpful information. I still suggest reading the tutorials AAC has to offer. Look under the "EDUCATION" tab and start reading.
     
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  5. recklessrog

    Member

    May 23, 2013
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  6. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Sorry, but that's not true.
    The battery charge current rating is the maximum charge current (not a minimum) that you should use (.39A in this case).
    It will indeed absorb more than that if the charger can deliver it, which can damage the battery by causing out-gassing,.
    This is why the charger needs a current-limit as well as a voltage limit.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,156
    3,063
    A missing piece here is the capacity of the panel you want to use. It's possible your panel cannot supply a damaging current to your battery, even in full sun with the battery fully charged. In that case, you're done. There are no likely conditions that can damage your battery.

    If the panel can drive more than 390mA into a load at 13-15V, then you will need to throttle it somehow. There are all sorts of ways you might do that. It could be as simple as adding an extra diode (to drop the voltage a bit) or as elaborate as a dedicated charge controller.
     
  8. Tonyr1084

    Active Member

    Sep 24, 2015
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    Isn't that what I said?
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Not as I understand it.

    You said:
    "Batteries will draw however much current they need. Whether you have a charger capable of 400 mA or one capable of 10 amps - the battery will draw - as is on your spec sheet (or the battery itself) it will draw not more than 390 mA (0.39 A)."

    To mean that means you think the battery will automatically limit the current to 390mA, but it won't.
    It will tend to draw whatever current the charger can supply.
     
  10. The Kadet

    New Member

    Apr 27, 2016
    7
    0
    I know that a led acid batery(a car batery) can only draw in amps arround 10% of what it needs to fully charge, so if it draws four amps it will take 40 amps to charge, as the batery charges this this current will drop porporcionaly, maintaining the same ratio.

    The charging of a batery is not constant at the beguining charges faster in the end it draws a constant current for a long time, this because it is fully charged, if that current is quite high compared to the capacity of the batery it is because batery is "broken"(adicteded, not working properly) this in the case of most car bateries is because there are no longuer thick metal plates inside they got corroded or bent...
     
  11. harikanaidu

    Thread Starter Member

    Nov 28, 2014
    76
    1
    i have solar panel of 17v and 5watts which means current will be 0.29 amps maximum....So my battery needs 0.39 amps..How much time will it take to charge the battery??(AS i said my battery is 12v/1.3Ah)...
    And i have another doubt that as my panel wattage is 5 watts..If i decrease the voltage to 14 volts , will my panel produce a current of 2.8 amps??If so how can i decrease the voltage by placing it in low sunlight or by other means like using some voltage regulator ???
     
  12. Tonyr1084

    Active Member

    Sep 24, 2015
    540
    86
    Reduced sunlight will mean reduced wattage.

    Your battery will still charge, just slower. Sorry, I can't answer how long it would take. It would depend on how depleted the battery is to begin with.
     
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