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  1. #1
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    Default Lead acid minimum charge current

    I hope someone has done some tests or researched the topic of minimum charge current to at least get a good life for a stand by application like loadshedding.
    A number of topics have mentioned that a minute charge does not charge enough and shortens the life.
    I would like to know if such a minimum charge is based on the Ah capacity.
    I have been using a 3A charger on a 100Ah and found it gives a long life. I just wondered if 1.25A permanently would be too low.

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    Default Re: Lead acid minimum charge current

    Did you check Battery University yet? Maybe they will have some data to that effect.
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    Default Re: Lead acid minimum charge current

    What does a solar charge controller do?

    Many systems on holiday homes/2nd homes are on 'standby'
    Gets charged to float and stays at float for prolonged periods of time. Solar controller regulates the amps going into the battery to stay at float. Same as what trickle charger would do. (the better ones?)

    Same as if would put a 10W panel, 5A PWM solar controller on a battery to keep it at float.
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  5. #4
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    Default Re: Lead acid minimum charge current

    Short answer is for maintaining a fully charged 100Ah battery it would make zero difference. Charging drained battery it will.
    I will explain more tomorrow when I can get to a keyboard that is more appropriate for my thick fingers...
    Donít blame yourself over past mistakes. Itís like driving down the N1 while looking in the rear view mirror only.

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  7. #5
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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by Prof View Post
    What does a solar charge controller do?

    Many systems on holiday homes/2nd homes are on 'standby'
    Gets charged to float and stays at float for prolonged periods of time. Solar controller regulates the amps going into the battery to stay at float. Same as what trickle charger would do. (the better ones?)

    Same as if would put a 10W panel, 5A PWM solar controller on a battery to keep it at float.
    My testing of a 10W panel with PWM controller still caused a car battery in my Freelander to discharge. This was on a well used battery about 6 months before I had to replace it.

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    Default Re: Lead acid minimum charge current

    Generally it is 1/10 so 100Ah will be 10A charge. The charging current is determined by the temperature of the battery, you don't want the electrolyte temperature getting too high.

    On non intelligent chargers do not exceed a charging current of more than 1/10th of the Ah rating.

    On decent intelligent battery chargers I would not be averse to 1/5th of the Ah rating as the charger manages the current.

    If you are able to replenish lost charge with a 3A charging current then you appear to have over specified you battery and or you have long periods between battery usage which allow the 3A charger to catchup.
    Last edited by Andrew Leigh; 2021/09/19 at 02:25 PM.

  9. #7
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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by Andrew Leigh View Post
    Generally it is 1/10 so 100Ah will be 10A charge. The charging current is determined by the temperature of the battery, you don't want the electrolyte temperature getting too high.

    On non intelligent chargers do not exceed a charging current of more than 1/10th of the Ah rating.

    On decent intelligent battery chargers I would not be averse to 1/5th of the Ah rating as the charger manages the current.

    If you are able to replenish lost charge with a 3A charging current then you appear to have over specified you battery and or you have long periods between battery usage which allow the 3A charger to catchup.
    Quite happy with the 3-6A charging rate. Battery is used for outside lights from 12V. Although far over specced the price per Ah is better than smaller batteries. Yes the 10A is fine for normal charging.
    I would like to know the minimum rate of charge to keep charged.

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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by ekkekan View Post
    Quite happy with the 3-6A charging rate. Battery is used for outside lights from 12V. Although far over specced the price per Ah is better than smaller batteries. Yes the 10A is fine for normal charging.
    I would like to know the minimum rate of charge to keep charged.
    A couple of hundred milliamps when you go into trickle charge. You are merely replacing the standby current of the inverter and internal battery losses.

    Batteries like to work, these very low discharge and charging rates cause the battery plates to sulfation and reduce battery life. I would rather allow the battery to discharge to say 50% and then give it a brisk charge.

    Google "sulfation"

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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by ekkekan View Post
    My testing of a 10W panel with PWM controller still caused a car battery in my Freelander to discharge. This was on a well used battery about 6 months before I had to replace it.
    I expect 10W for 4-5 hours per day will be too little to keep it maintained.....
    Donít blame yourself over past mistakes. Itís like driving down the N1 while looking in the rear view mirror only.

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  13. #10
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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by Andrew Leigh View Post
    A couple of hundred milliamps when you go into trickle charge. You are merely replacing the standby current of the inverter and internal battery losses.

    Batteries like to work, these very low discharge and charging rates cause the battery plates to sulfation and reduce battery life. I would rather allow the battery to discharge to say 50% and then give it a brisk charge.

    Google "sulfation"
    IIRC I have seen graphs that indicate the faster you charge/discharge the shorter the life would be. May be our fundis could comment on this as well.??
    When using a charger that de sulphates sulfation should not be a problem.
    Last edited by ekkekan; 2021/09/19 at 03:39 PM.

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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by Dungbeetle View Post
    I expect 10W for 4-5 hours per day will be too little to keep it maintained.....
    And there we live in vastly different areas of SA

    During the first lockdown I maintained vehicle batteries with a 10W as mentioned & 5W maintainer system. One was a five year old battery.

    All happy and still going strong.
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  18. #13
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    Default Re: Lead acid minimum charge current

    Quote Originally Posted by Prof View Post
    And there we live in vastly different areas of SA

    During the first lockdown I maintained vehicle batteries with a 10W as mentioned & 5W maintainer system. One was a five year old battery.

    All happy and still going strong.
    I would rather put it down to gadgets drawing power. The Freelander has a battery monitor. Long after the battery will no longer crank the engine it opens the tailgate window before the battery is totally flat. It might be these loads. At the time my battery got discharged after about 7-9 days and would no longer crank. At that point in time it would easily not move for 3 to 4 weeks.

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  20. #14
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    Default Re: Lead acid minimum charge current

    I taken a 12 adaptor unit that has variable settings from 3 to 12 volt. Hard wired it to 12 volts and to the cable with plug off. Fitted 2 screw terminals on it. When open circuit it puts out about 17 volts. Made up cable with a patch cable that is wired to battery. When car is parked I plug cable in with a one way plug. When checking voltage going to battery it sit at 13.8v and adaptor doesn't get any warmer than body temp. Draws about 60mA from mains and max going to batteries is just over 100mA. My Prado stands for long periods as its holiday vehicle and when its needed starts first turn of the key. The other vehicle is Opel Astra and it starts no problems either.
    Have another little charger with toroidal transformer etc. It has a little lm137 IC which is a full charger circuit in an IC which does duty at keeping my bikes and extra batteries charged.

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