charge controller function?

spockmckoyspockmckoy Registered Users Posts: 6
Hi, I already have a 1500 watt full sine wave 12 volt inverter which I don't wish to replace. I have 4 new 6 volt golf batteries, which I would combo them in series/parallel to get 12 volts out of them which I also don't wish to replace at this time. My 1st question is, will a charge controller accept 24 volts from solar panels and convert to 14.4 charging voltage automatically? To keep the wire size from the solar panels to a minimum, I could hook 2 up in series for 24 volts, but I am not sure exactly how charge controllers function. Do solar panels need to be wired to match the battery bank user voltage? I'm not sure which panels are a good fit for this system I'm currently thinking about building. I am not interested in running my house. I would be interested in powering existing 120 volt LED/CFL lights and a small appliance or 2 on a time sharing plan. I'm not interested in running luxury items such as tv's, etc. I am not opposed to the ability to add more panels/batteries in future. I understand that charge controllers can be max'd, so additional charge controllers may be needed as well. I'm not near the batteries, or I'd tell you their capacity. Thanks in advance for any opinions.

Comments

  • AguarancherAguarancher Solar Expert Posts: 313 ✭✭✭
    Re: charge controller function?

    Short answer, yes a mppt controller will down convert as you wish. Long answer, you have the cart in front of the horse. How are you keeping those new batteries charged?
  • spockmckoyspockmckoy Registered Users Posts: 6
    Re: charge controller function?

    Currently there is a battery charger keeping them topped off. A charging/desulfating type. IF my inverter takes them down to a point where the inverter shuts down [10 volts?], then I have a heavier charger and a generator which can charge them quicker. I am interested in panels, and as I asked, am open to suggestions. I saw Renogy mono's on Amazon, but are open to suggestions if Renogy are of poor quality. All except, Harbor Freight types.
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: charge controller function?

    spock
    If you take them down to 10 volts, they may only last a couple of charge discharge cycles and may be damaged the very first time you do it.

    Much to low.
    gww
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: charge controller function?

    OK... There are two major classes of series type solar charge controllers.

    The first is a simple PWM (Pulse Width Modulation solar charge controller. Basically a computer controlled On/Off switch. On, the power from the panel is flowing to the battery. Off, no power. Turn on/off 10's to 1,000's of times a second and vary the percentage of "on vs off time", you have a simple charge controller.

    This type of charge controller passes current from the solar array (solar panels are "current sources")--More or less, an 8 amp panel will output 8 amps from zero to Vmp-panel voltage.

    For an "optimum" PWM based system, the Vmp-array should be in the range of Vmp~17.5 to 19 volts or so. This allows for Vmp-array drop in hot weather and charging a "12 volt" battery at ~15 volts maximum.

    Say you have an 8 amp Imp @ 18 volt Vmp panel--~124 watt "12 volt" panel... Charging would look like:

    Power = Current * Voltage
    8 amps * zero volts (shorted panel) = zero watts
    8 amps * 10.5 volts (dead battery) = 84 watts into battery
    8 amps * 14.5 volts (near full battery) = 116 Watts into battery
    8 amps * 18 volts (over charged battery) = ??? Don't know voltage drop of wiring, how hot panel is, etc... Current falls when Vbatt is over ~15 volts on a hot day

    You can find Vmp~30 volt panels (60 cell panels) and use them on a PWM controller--However, you will lose a lot of power charging a 12 volt battery bank directly... Say 8 amps Imp and 30 Volts Vmp

    Pmp-panel = Imp * Vmp = 8 amps * 30 volts = 240 volt panel
    8 amps * zero volts (shorted panel) = zero watts
    8 amps * 10.5 volts (dead battery) = 84 watts into battery
    8 amps * 14.5 volts (near full battery) = 116 Watts into battery

    Now into a 24 volt battery with PWM controller:
    8 amps * 21 volts = 168 Watts into "dead 24 volt" battery
    8 amps * 29 volts = 232 Watts into near full "24 volt" battery

    So, yes it can be done, but it will be terribly inefficient--However solar panels are getting very cheap--It may make sense for some smaller installations with a Vmp~30 volt panel and a 12 volt battery bank with a PWM controller (sometimes Vmp~18 volt panels are 2x or more the cost of Vmp~30 volt panels of equal wattage).

    The other type of charge controller is MPPT (Maximum Power Point Tracking) solar charge controllers... The technical details are that MPPT charge controllers have switch mode (Buck type) down converting switching power supply internally. More or less, it allows them to take High voltage/low current and efficiently down convert it to low voltage/high current needed to charge the battery bank.

    In general, MPPT charge controllers are much more expensive and have more losses because of the switching power supply+electronics. But they can take the energy from a 240 Watt 30 volt Vmp panel and efficiently charge any battery from 12 to 24 volts:

    240 watts * 0.77 typical panel+controller derating = 185 Watts from panel + controller
    185 Watts / 10.5 volts charging = 17.6 amps
    185 Watts / 14.5 volts charging = 12.8 amps
    185 Watts / 21 volts charging = 8.8 amps
    185 Watts / 29 volts charging = 6.5 amps

    A lead acid battery "cares" about the number of amps flowing into the battery. So an MPPT type charge controller can match higher voltage panels/arrays efficiently to lower voltage battery banks... But they are not magic--It costs money for this function.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: charge controller function?

    Well we usually start planning a system by getting a statement of the loads in Watt hours from the initiator,you, as well as the specifics of any equipment already at hand, make model serial number , etc and ask you to show it in the signature line of your profile.
    Then we start from the beginning so please tell us what you have got, in detail...

    as to panels it pretty much comes down to price per Watt as there is little guarantee that that maker will be around in 10 years or less... just a statement of the current state of the industry, as long as you get a good brand .
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • spockmckoyspockmckoy Registered Users Posts: 6
    Re: charge controller function?

    Not positive, but I thought 10volts is what the inverter does to protect itself. Not adjustable as far as I know. What battery voltage is typical for inverters to shut down? 10 volts is what? 16.7% drop in battery voltage?
  • gww1gww1 Solar Expert Posts: 963 ✭✭
    Re: charge controller function?

    Spock
    Your question is hard. I think you want to end up a bit above 12 volts after you remove the load. I have an adjustable low voltate and I have it set at about 11.5 volts and when it disconects I can watch the battery bounce back above 12 volts almost imediatly. It your inverter can not be adjusted there are other ways depending on the cc you buy and if it has a divertion load function or aux funtion. As you have a small system, the cc you end up with may not have these funtions, I am sure there is some other voltage type relay that would work. I really don't know what they would be.

    As you have had two people that are much smarter then me who have commented on this thread and they did not highlight my concerns, maby you should wait for someone else to re affirm my assumption. I thought it was important to mention but perhaps a little more comment is in order.
    gww
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: charge controller function?

    For 12 volt inverters--The "typical" model runs from 10.5 to 15.0 volts (older, less expensive, those intended connect to a car's electrical system, etc.).

    For an off grid system, it would be better if the inverter ran from 11.5 volts (perhaps a 1-5 minute delay, shut off at 10.5 volts imedeatly) to ~16+ volts (sometimes, lead acid batteries need >16 volts during charging--many inverters will shutdown at ~15.x volts).

    You will find some inverters (more recent, really designed for off grid systems) will allow you to change the low voltage cutoff to some other value/time delays. Usually these inverters are not cheap--And many are larger (kWatts in size)--Not many small inverters have these options.

    The 10.5 cutoff is to protect the inverter from excessive current (too much current, over heats the inverter). The battery bank would be better protected if never below 20% state of charge, and it would be nice if the inverter had warning/shutdown programmable to ~50% state of charge.

    Lead acid batteries voltage varies with temperature, state of charge, and load... Using a pure voltage as the battery set point is difficult--And very difficult if the battery bank is exposed to a wide range of temperatures.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bendorfoldbendorfold Registered Users Posts: 4
    Re: charge controller function?
    spockmckoy wrote: »
    Not positive, but I thought 10volts is what the inverter does to protect itself. Not adjustable as far as I know. What battery voltage is typical for inverters to shut down? 10 volts is what? 16.7% drop in battery voltage?
    The RENOGY PWM30CC 30Amp charge controller has these specs:
    Load Disconnect_________________11.1V (12V), 22.2V (24V)
    Load Reconnect_________________12.6V (12V), 25.2V (24V)
    Equalization Voltage (30 minutes)___14.6V (12V), 29.2V (24V)
    Boost Voltage (30 minutes)________14.4V (12V), 28.8V (24V)
    Float Voltage___________________13.6V (12V), 27.2V (24V)
    Battery type____________________Sealed Lead Acid and Flooded

    http://www.batterystuff.com/kb/articles/battery-articles/battery-basics.html
    There is a State of Charge (SOC) chart on the above link that puts discharge at 11.9v (for 12v system) and 12.2v (for 12v system) for the 50% charge state. 50% is one of the 'rule of thumb' numbers I've learned from this forum. You don't want to go below 50% very often (shortens battery life).

    I think it's been mentioned, inverter shutdown protects the inverter - not the battery.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: charge controller function?

    Nota Bene:

    You do NOT run an inverter from the 'LOAD' terminals of a charge controller.
  • spockmckoyspockmckoy Registered Users Posts: 6
    Re: charge controller function?

    Well, this certainly got complicated in a hurry. Thanks to all who have voiced their ideas. For those who have solar panels on their roofs, either due to available land space/vandal protection, etc. IF you live in a cold climate, do you go up on the roof to clean off snow and change the angle every season? IF I do install panels, my roof seems to be the only option and it does face Southward. I looked at an online solar panel calculator and input my town and 12 months out of the year, it specs different angles. I can't imagine setting up a ladder and changing each panels pitch once a month.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: charge controller function?

    Look at which time of the year with the largest loads and see if you need to optimize the angle for that and can live with it the rest of the year... in my case it is winter
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • bendorfoldbendorfold Registered Users Posts: 4
    Re: charge controller function?
    spockmckoy wrote: »
    ... IF you live in a cold climate, do you go up on the roof to clean off snow and change the angle every season? ...
    Here is a web site that may help: http://pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation
    You can adjust for different time of year, different tilt angles and find approximate hours of sun with sunrise and sunset.
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