charge controller info needed

Crazy_Wolf1234Crazy_Wolf1234 Posts: 14Registered Users ✭✭
do charge controllers draw energy from the solar or  turbine like a load or is it more like a voltage regulator on a car, taking voltage from the source and dispensing it as needed.

Comments

  • BB.BB. Posts: 27,887Super Moderators, Administrators admin
    There are different controllers and different methods... But the basic solar charge controller (PWM--Pulse Wave Modulation) is a simple on/off switch between the panels and the battery bank. Cycling at hundreds (or more) times per second. So, technically, the solar charge controller controls "average current" into the battery bank. And the battery, more or less, controls the DC voltage. The charge controller monitors the battery voltage (and many also monitor time) and adjust the current flow to give you the average 14.7 volts (charging) or 13.6 volts (float). Because you can turn off the current from a typical solar electric panel, a series On/Off switch is just fine (also called a series type charge controller).

    If you disconnect the battery bank from the solar charge controller--The controller is not capable of holding 14.x volts to run the rest of the electronics--The battery bank is needed to stabilize the voltage. Which is what also happens if you disconnect the battery in your car while the engine is running--It is very possible for the alternator to reach >100 VDC and wipe out your car's electronics and lights if you do that.

    For typical wind turbines--They need constant electrical load to keep the blades/turbine from over speeding and self destructing (horizontal axis wind turbines). So for those type systems--The turbine is connected directly to the battery bank and a "charge controller" is connected to a resistor bank (electric heater)--The controller "turns on" when the battery bank is full, and turns off when the bank needs charging. This is a "dump or shunt" type charge controller (also PWM).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • jonrjonr Posts: 1,075Solar Expert ✭✭✭✭
    I wonder just how high a peak voltage the system sees.   For example, say you have 25+V, 30A coming from the panels and a 12V battery that isn't accepting much charge.  An inverter connected to the battery might see pulses more than its ~16V limit.
  • BB.BB. Posts: 27,887Super Moderators, Administrators admin
    The answer is "it's complicated"...

    A 12 volt battery bank (flooded cell lead acid) will range from 10.5 volts to 15+ volts (dead to fairly aggressive charging)... And it can get as high as 16+ volts (charging a cold battery bank, equalizing an industrial type flooded cell lead acid battery).

    The higher the rate of charge, the higher the battery voltage can be... If you have too high of charging the current, the battery can "lose control" of the bus voltage and the charging current will overwhelm the battery (>18+ volts is possible).

    We have lots of rules of thumbs, but one of them is to (roughly) not exceed 1,000 Watts of charging current per 400 AH of battery (@ 12 volt battery) capacity (20 Hour Rating):
    • Charging current from solar array ~ 1,000 Watts * 0.77 panel+controller derating * 1/14.75 volts charging = 52 amps
    • 52 Amps charging / 400 AH battery bank = 0.13 = 13.% rate of charge
    If you have more charging current and a nearly full battery bank, it is possible that you will exceed >>16+ volts.

    You can exceed 13% rate of charge--But the battery bank should be significantly discharged (less than 80% state of charge--SWAG).

    Here is a nice article that gives you charging vs voltage (and discharging vs voltage) for a typical deep cycle flooded cell battery bank:

    http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

    And this is a problem with many AC inverters--They simply set their cutoff voltage to 15.0 volts--And for many of our friends in the far north, they need to recharge their battery banks at >15.0 volts. The standard is -5 mVolts per degree C per Cell... or for a -5C battery 12 volt battery bank, the temperature corrected charging voltage for the battery bank would be:
    • (-5C - 25C standard temp) * -0.005 volts per C per cell * 6 cells (aka 12 volt battery) = +-0.9 volt charging voltage offset
    • 14.75 volts charging + 0.9 volts offset (12 volt bank at -5C) = 15.65 volts "temperature corrected" Absorb charging @ -5C
    And for those folks, finding AC Inverters with 16.5 volts (or more) maximum battery bus voltage works much better (in cold weather) than the old "standard" of 15.0 battery cutoff voltage.

    It is odd--Folks that design both Charge Controllers and AC inverters on lead acid batteries seem to have "ignored" this issue for many decades.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Posts: 4,015Solar Expert ✭✭✭✭
    I would say "some" folks who design  both Charge Controllers and AC inverters on lead acid batteries seem to have "ignored" this issue for many decades.

    Good equipment is regulated and exceeding the 1000 watts per 400 AH is often done in large systems because they are designed to charge in winter. Both Outback and Schneider and otheres can limit charge current to protect the battery from too high of a charge current.

    It was nice Bill to see the old adds in Home Power. Richard Perez is not a spring chicken these days.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • jonrjonr Posts: 1,075Solar Expert ✭✭✭✭
    edited August 2016 #6
    A graph of SOC vs voltage is for a steady state voltage.   Start pulsing (ie, PWM to control average power ) and the instantaneous peak voltage will be higher.  Perhaps high enough to either trip the inverter or do damage to the input section (if the protection circuit isn't fast enough to catch the peaks).    Sounds like the inverter max input voltage is often right on the edge even without this voltage ripple issue.

    A filter on the output of the PWM controller would help smooth off the voltage peaks.  Or maybe the battery has enough capacitance to fully filter the waveform?   Guess I'd want to see a 'scope trace.

    I suggest that most PWM controllers are 100Hz or less (which makes the issue worse).  Morningstar advertises 300hz.


  • jonrjonr Posts: 1,075Solar Expert ✭✭✭✭
    edited August 2016 #7
    One reference I found shows ripple from a PWM charge controller at > 5V PP.   So if you are charging at a nominal 15V, the inverter may see peaks > 20V.  Even more under other conditions.

    Another reference concerned with battery health suggests that voltage ripple during float charging should be < .5% RMS (< .1V).  Other sources say 5%.
  • Dave AngeliniDave Angelini Posts: 4,015Solar Expert ✭✭✭✭
    edited August 2016 #8
    This does not happen with good equipment BTW. If it did AGM's would be dropping like flies or the nasty wasps I have this year.
    Certainly the new lion batteries might be catching fire, which they are not, I just looked......
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • jonrjonr Posts: 1,075Solar Expert ✭✭✭✭
    You are using a PWM controller?  A buck converter based controller is operating at much higher frequencies (10s of Khz) and has output filters.   So far less ripple.
  • Dave AngeliniDave Angelini Posts: 4,015Solar Expert ✭✭✭✭
    My old Trace PWM from the early 90's never had any problems like you are talking about. Certainly not anywhere near 5V on a scope.
    There was some overshoot on loads cycling but pretty solid DC. 

    At this time (last week) I am cycling a 3/4 HP centrifical pump and see very little on the scope besides a solid 52.6V float voltage with a very slight drop that recovers in less than 1 second and a little mppt hash. 


    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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