Charge Controller won't go into Float.

InCogKneeToeInCogKneeToe Registered Users Posts: 34 ✭✭
edited June 29 in Solar Beginners Corner #1
Ok, so I recently returned to my Old Controller to monitor my Batteries. The C40, doesn't have the Meter.

It's a Coleman/Sunforce 30A Digital. I Hydrometer every cell, all showed "Full" 1 Battery was a little down but well into the Full.

Everything was good, showing 15-20A charging. Topped up to "Float" on my Generator before bed time. 13.8V, settled to 13.5v by 11:00pm. Controller lights off.

I woke up at 5:00AM, and it dropped to 12.8v Everything shut off? The Controller was showing "Charging" even before Sunrise, But only @ 0.1a

I watched it Everything shut off until 11:00, it eventually got to 14.7V and 5.0a, Never hit Float?

So, I don't understand Why it can't exceed 5.0a and 14.7v?

Comments

  • mcgivormcgivor Solar Expert Posts: 3,426 ✭✭✭✭✭
    How old are the batteries and what capacity are they? LA batteries need extensive absorption, once the setpoint is reached, 14.7 V in your case, the controller will be in constant voltage mode. As they near saturation the current will decrease, when the current drops to a certain level the transition float will occur, however without knowing the algorithm of the controller it's not possible to predict what that value would be. Below is an answer from Morningstar tech support when I asked the same question, which may provide some insight, though not directly related to your specific controller(s), the information is relevant as the theroy of operation will be the same.

    The duty cycle is used to determine when to transition into float.  The duty cycle is derived from a square waveform and the percentage of time - out of each complete cycle - when current is allowed to flow. Current is regulated by opening and closing the PV-battery circuit -- the essence of a series charge controller. A 50% duty cycle means that current is flowing, and interrupted for, half of the cycle. Our controllers pulse with a frequency of 300 Hz, so each cycle lasts 1/300th of a second. By varying the duty cycle, we can control the average current going into the battery so that the regulation voltage is maintained but not exceeded. As the battery reaches full charge at a particular voltage, it will require less and less current to maintain that voltage and the duty cycle will decrease. The duty cycle will approach zero %, but will never actually get there because losses and battery self-discharge require at least some current to maintain regulation voltage. A Morningstar PWM controller's float transition algorithm waits for the duty cycle to reach 30% or less before starting a one hour timer. When the timer expires, the controller moves from absorption to float voltage. A 30% duty cycle simply means that 30% of AVAILABLE charging current is allowed to pass. Duty cycle is the best measure we have to determine how deep a battery may be in regulation. Factors affecting the accuracy of this method include: 1. Reduced radiation and current. With less available charge current, the duty cycle will inevitably be higher making the transition to float more difficult; 2. Load on the battery. Loads on the battery drain current from the battery which causes a higher duty cycle. If the load is large enough (greater than the amount of solar current ) it can pull the controller into 100% duty cycle and out of absorption - into bulk charging; 3. Aging batteries. Old batteries tend to absorb more current at regulation, keeping duty cycle high. Sulfation leads to higher internal resistance, and more energy loss in the form of heat, which leads to excessive water loss.

    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • PhotowhitPhotowhit Solar Expert Posts: 5,215 ✭✭✭✭
    First, there is a difference between charging voltage and resting voltage. A Lead Acid battery should be roughly 'full' with a resting voltage of around 12.7 volts. AGMs may be slightly higher.

    The voltage when charging will be higher than resting voltage to allow the current to flow from the panels to the battery bank. Here's some info on lead acid battery charging;

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    BULK;
    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    ABSORB;
    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    FLOAT;
    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage. Voltage is a poor source to estimate a batteries state of charge. 

    Sounds like you have been using a car hydrometer, perhaps with colored beads? If you have one with a colored range, and it's in the good range (green) it doesn't necessarily fully charged. While starting Specific gravity differs between battery brands, most are 1.280-1.300. The charge controller can't 'see' the capacity of your battery bank, but it can see the amps passing through it. It can also not see the battery bank capacity. They will often switch to float when they see a minimal amount of current flowing to the battery bank.

    So what is the size of your array, size of the battery bank...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • InCogKneeToeInCogKneeToe Registered Users Posts: 34 ✭✭
    Photowhit said:
    First, there is a difference between charging voltage and resting voltage. A Lead Acid battery should be roughly 'full' with a resting voltage of around 12.7 volts. AGMs may be slightly higher.

    The voltage when charging will be higher than resting voltage to allow the current to flow from the panels to the battery bank. Here's some info on lead acid battery charging;

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    BULK;
    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    ABSORB;
    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    FLOAT;
    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level. With sealed batteries, you would want to disconnect the battery from the system and allow it to 'rest' for a while to get an accurate idea of it's SOC (State Of Charge) from the voltage. Voltage is a poor source to estimate a batteries state of charge. 

    Sounds like you have been using a car hydrometer, perhaps with colored beads? If you have one with a colored range, and it's in the good range (green) it doesn't necessarily fully charged. While starting Specific gravity differs between battery brands, most are 1.280-1.300. The charge controller can't 'see' the capacity of your battery bank, but it can see the amps passing through it. It can also not see the battery bank capacity. They will often switch to float when they see a minimal amount of current flowing to the battery bank.

    So what is the size of your array, size of the battery bank...
    Ok Thanks. 12.7v @ rest is normal, then I won't fret the drop over night. My System does basically Shut Down when not in use. So over night was a Full Rest. 

    I am only running 400w Array, Batteries Vary (I know) 2/ 105Ah 12v are 3 years old, 1/ 105Ah 2 years old, 1/ 1 year old and 2/ 230Ah 6v added this year.

    I was gifted a Xantex C40, which I hooked up and set at 13.6 Float/14.5 Bulk. It ran 2 weeks before switching back to the Coleman/Sunforce, for the Meter vs Blinking LED. The C40 would get to Solid LED @ 14.5v so that also makes sense. https://sunforceproducts.com/products/30-amp-12-volt-digital-solar-charge-controller/

    Now I know that my Array, doesn't meet my Battery Storage (weekend Usage) but I am planning adding a second Array, and building towards that. Also my Charger (just a Battery Charger that starts when Generator is running) has a Equalization Mode, but not capable for this much battery amperage. 

    So my next Steps are, Check Tuesday Night, to see if the system reached Float. Friday Night, Isolate the lowest, Hydrometer battery and run an Equalization on that one only. Saturday Equalize the second 3yo battery. and see where I stand.

    or

    Can I just run a lengthy Equalization on all of them? Or a Shock Cleaning @ 80A Engine Start feature on 1 at a time?
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