Solar battery charger question

Discussion in 'Off Grid Living' started by kckndrgn, Jan 16, 2014.

  1. kckndrgn

    kckndrgn Monkey+++ Moderator Emeritus Founding Member

    I have, what is probably a simple question, but I just can't seem to work it out. I have the following items for a small solar setup for charging a deep cycle battery while at my off grid cabin.

    NPower Amorphous Solar panel - 20W X 2
    (Sunforce Solar Power Kit — 60 Watts, Model# 59050 | Battery Backup Packages| Northern Tool + Equipment

    NPower Solar Charger 127.5W, 8.5A
    (NPower Solar Charge Controller — 127 1/2 Watts, 8 1/2 Amps | Charge Controllers| Northern Tool + Equipment

    When charging the battery from a standard 120v battery charger I read 13.x volts on the battery, but when running from the solar panels I see the voltage stays at whatever the battery is currently at, say 12.5vdc

    I have verified that the charger is putting out 13.x volts, as the cut-in voltage is 13v. Using a small adjustable DC powersupply set to 13.5VDC I hooked up the system system and verified that the input into the charge was 13.5, output from the charger was 13.5 when not connected to the battery, but dropped to battery voltage when hookup. Is this right?
    I left the setup go for about an hour and did notice that the voltage at the battery increased by .3v So it appears to be functional.

    So am I worrying about nothing, or should I truly be seeing 13v?

    One more question. When charging the battery, and there is a load on the battery, should the charge controller be fused so that the load doesn't try to pull too much power from it? My thought is the controller can provide only so much power, and if the load requires more then it would "come from" the battery. Essentially if the charge controller was actively charging the battery with no load then all power is being put into the battery. If a small load is applied the amount of charge going into the battery is reduced and finally if a load on the system exceeds what the charge controller can output the battery will supplement it. Is this correct?

    Thanks in advance.
  2. ghrit

    ghrit Bad company Administrator Founding Member

    I think you should not worry overmuch. With the charger charging an unloaded battery, there will be a voltage showing at the charger set point. When disconnected from the battery after charging is complete, the battery should show the same voltage as the charger under no load. (Battery voltage will drop after a while due to self discharge.) When you connect the battery to a load, the voltage must drop to supply the load with power, the difference is the result of the load drawing power.

    The charge controller should have circuitry to limit amperage when running in parallel with the battery under loaded conditions. A possible alternative would be internal fuses or circuit breakers to take it off line. The O&M manual should tell about that.
  3. BTPost

    BTPost Stumpy Old Fart,Deadman Walking, Snow Monkey Moderator

    When charging any Battery, What IS important is the Current (Amps) that you are pushing thru the Battery to recharge it. If your Charger is capable of 14.4 Vdc Output, it will push the required AMPs (What ever those may be) thru the Battery, until the Battery Voltage Rises (Reversing the Discharging Chemical Reactions) to the equal the Charging Voltage. In order to push the Current (Amps) thru the Battery, the Charger Voltage MUST Be Higher, than the Battery Voltage, and as the Battery's Voltage rises, less and less Current, (Amps) will flow, until the Charging Voltage is the same as the Battery Voltage, at which point NO Current will flow thru the Battery. Different Battery types require different Charging Voltages to push current thru the Batteries.
    1. Lead Acid Wet Cells require minimum 13.6 Vdc for Full Recharge, for 12 Volt Batteries.
    2. AGM Cells require minimum 14.4 Vdc for for Full Recharge, for 12 Volt Batteries.
    3. NiCad Cells require minimum 14.0 Vdc for for Full Recharge, for 12 Volt Batteries.
    and so on....
    The last 10% of Recharging Cycle takes 75% of the Recharging Time, and if you push more Amps,
    thru faster, than that type of Battery can handle, you will boil, or burn off, the Electrolyte, which
    unless replaced, will ruin the Battery. In the case of Sealed Batteries, where the Electrolyte can NOT
    be replaced the Battery will eventually be come unusable. If you exceed the Maximum Battery Voltage
    you will also boil off, or burn off, the Electrolyte, and ruin the Battery. This is what happens when you leave an UnRegulated Battery Charger on longer, than the time it takes to reach 100% charge. Todays Modern Battery Chargers have Charge Controllers that have builtin Charge Tables for each type of Battery, and they charge, using those parameters, specific for that type of battery, as well as being Three State Chargers.
    First State is: Bulk Charge, You push the Maximum Charging Amps thru the Battery, until the Battery Voltage rises to 80% of MAXIMUM Battery Voltage.
    Second State is: Finish Charge, You push whatever Amps thru the Battery until the Maximum Charging Voltage is obtained.
    Third State is: Float Charge, you keep the Battery at it designed Maximum Float Voltage.
    Charging starts with Bulk Charging, then Finish Charging, and finally Float Charging. (Maintaining)
    Mountainman likes this.
  4. reosolar

    reosolar The Solar Guy

    Your battery charger will be going through a charging cycle that will include the raising and lowering of voltage and amperage accordingly. Both the voltage and amperage going into the battery bank are equally as important, the charger will balance these to control the wattage being absorbed. In terms of actual battery SOC it will need to rest and have all charging sources turn of to get an accurate reading via voltage. As what BTPost said, the charger will go through a bulk absorbs and float stage which will have noticeable voltage and amperage differences through out each stage.
  5. kckndrgn

    kckndrgn Monkey+++ Moderator Emeritus Founding Member

    Thanks all, I thought maybe i fried the controller but it doesn't look like it.

    Still getting a new one though, two is one and one is none.
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