controller

91winsun91winsun Registered Users Posts: 14
what is the lowest voltage that the classic 200 controller,Midnite, can convert to 24 volt???

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: controller

    depending on the battery you will need at least 28.8 volts to charge a 24V battery, regardless of CC.
     
    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
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: controller

    As a rule an MPPT controller needs only the Vmp usually available from "standard" panels. For a 24 Volt system that would be 35 Volts. Disregarding the panel base, any amount of Voltage above the charge set point is enough to charge the batteries.

    Or in simple terms the MidNite does not require any specific Voltage above the system nominal to work, just enough to charge the battery.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: controller

    You need Vbatt-charging (~29 volts for a 24 volt bank) plus a volt or two for wiring/controller drop.

    If you have solar panels, their Vmp output voltage falls as the panels get hot (and remember, battery charging voltage rises as batteries get cold). Typically, Vmp-array minimum of ~35-36 volts is recommended for a 24 volt battery bank (same for PWM or MPPT charge controllers).

    Most solar charge controllers can only "drop" voltage--They cannot take low Vmp-array voltage and boost it for higher Vbatt-charging voltage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • arsalanarahimarsalanarahim Registered Users Posts: 1
    Re: controller

    I am Arsalan A Rahim , teaching at University of Engineering and Technology Lahore, Pakistan, Electrical Department there....I have some questions and some observation regarding the above stated facts here....

    If certainly a 24V system requires 35 to 36V Vmp, then why the big producers of solar modules like Yingli, Sharp, Trina Solar, Suntech....they are making Vmp in the range of 29 to 31V now....I remember i have Sharp modules of 175W in my array.....almost 6 to 8 years old....they had a Vmp of 35.4V but now why Sharp is producing Vmp of 31V or even 30.1V in some cases...Even Yingli one of the largest producers is also producing Mono panels in range of 29.x or 30.x range......INfact their polycrystalline is actually at 29.6V and at NOCT conditions it is at 27.6V which is well below the 28.8V cyclic use battery voltage.? Can anyone explain this.

    In this way these panels cannot be used for 24V battery system, yes certainly for grid applications it can be used.....Any suggestion on this?
    I need a technical answer because i have to make a big system at my campus upto 500KW and i have to decide on it ..

    Thanks ( by the way nice topic)
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: controller
    I am Arsalan A Rahim , teaching at University of Engineering and Technology Lahore, Pakistan, Electrical Department there....I have some questions and some observation regarding the above stated facts here....

    If certainly a 24V system requires 35 to 36V Vmp, then why the big producers of solar modules like Yingli, Sharp, Trina Solar, Suntech....they are making Vmp in the range of 29 to 31V now....I remember i have Sharp modules of 175W in my array.....almost 6 to 8 years old....they had a Vmp of 35.4V but now why Sharp is producing Vmp of 31V or even 30.1V in some cases...Even Yingli one of the largest producers is also producing Mono panels in range of 29.x or 30.x range......INfact their polycrystalline is actually at 29.6V and at NOCT conditions it is at 27.6V which is well below the 28.8V cyclic use battery voltage.? Can anyone explain this.

    In this way these panels cannot be used for 24V battery system, yes certainly for grid applications it can be used.....Any suggestion on this?
    I need a technical answer because i have to make a big system at my campus upto 500KW and i have to decide on it ..

    Thanks ( by the way nice topic)

    I think that the main answer is that the market for panels for grid tie usage is far greater than the market for off-grid battery systems.
    Since all Grid Tie Inverters (GTIs) are designed to handle a wide range of DC input voltages, up to a rather high value, the manufacturers of panels for that use can design so that they get the highest output from a given area at the lowest cost. If this results in a design with a Vmp of 30 volts, they will make it and assume that the users will put some number of these panels in series. And also that their 200 watt panel at a Vmp of 30 will be just a useful to that kind of customer as somebody else's 200 watt panel with a Vmp of 40 volts. The competition comes down directly to price per watt (and secondarily the area required per watt if space is limited.)

    For this reason, customers who want to charge batteries have to either pay more per watt for lower production volume panels made just for battery charging through a PWM charge controller or else buy the cheaper per watt GT panels and use an MPPT charge controller.
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: controller

    There may even be another reason for the difference in Vmp voltages (newer panels with lower Vmp)... Just a guess but silicon wafers are getting larger and larger in diameter (larger wafers are more cost effective vs smaller diameter wafers in many applications).

    So, the larger wafer takes up more physical space--And we may be seeing some limits in the physical size of solar panels (either because of material handling and/or physical size of glass blanks, structural limits, etc.). So, you get fewer ~0.5 volt cells in series which gives you lower operational voltage per panel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • boBboB Solar Expert Posts: 995 ✭✭✭✭
    Re: controller

    If certainly a 24V system requires 35 to 36V Vmp, then why the big producers of solar modules like Yingli, Sharp, Trina Solar, Suntech....they are making Vmp in the range of 29 to 31V now....

    I think that inetdog and BB gave the correct answer for this but it doesn't matter because MPPT controllers don't care so much these days and it is normally better to use higher input voltage rather than the lower input voltage of 34 volts or so.

    The Midnite Classic Charge controller will require some minimum Voc above battery voltage to turn on and varies with the actual battery voltage. For a 24V battery, somewhere in the 30 volt Voc range will be needed.

    Since this subject is in the wind section of this forum, if the Classic was being used for wind rather than solar then the input voltage only needs to be at or above the lowest turbine power curve voltage corresponding to the 0 amp (cut in) data point.

    boB
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