what charge controller do I need for a 250watt panel

fopoku2k2fopoku2k2 Registered Users Posts: 1
Quick question. I just bought two 250 watt solar panels rated at 8.27 amps & 37.7 volts each. Can I connect them in parallel to my existing pwn charge controller rated at 42 volts maximum solar input voltage and 30 amps rated load and charge current.

My system consist of 24 volt batteries

Thank you


  • westbranchwestbranch Solar Expert Posts: 5,182 ✭✭✭✭
    Welcome.... probably, but a few questions first, make and model of the CC will tell us the full story, and all the specs off the PV panels spec sheet , on the back, will tell us almost all we need
    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
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    When you say "rated at 8.27 amps & 37.7 volts each", can you give the full nameplate spec. We need to know the Voc, Vmp, Isc. 250W panels are normally 60 cells. If so then it can be tricky to get enough voltage out of them to fully charge a 24V lead bank. Youd also need to check the max cold weather Voc, which sounds like your getting close.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,

  • PhotowhitPhotowhit Solar Expert Posts: 5,105 ✭✭✭✭
    fopoku2k2 wrote: »
    Can I connect them in parallel to my existing pwn charge controller rated at 42 volts maximum solar input voltage and 30 amps rated load and charge current.

    Since it appears you are giving us short circuit numbers, 8.27 amps X 37.7 volts = 300+ watts, You can hook them up, but they likely will not have enough voltage in the heat of summer to work effectively and won't help with equalizing, if you have flooded batteries.

    A solar panel loses voltage as it gets hotter, VOC that you have posted isn't a very valuable number, The VMP is the voltage under load in Standard test conditions Panels at about 25 degrees centigrade, unfortunately, panels make their living in the sun, So better numbers are NOCT values(normal operating cell temperature).

    I popped up the numbers for Solar World 250 watt panels, they have a VOC of 37.6 volts so close to your panels, their VMP is 30.5 volts and their NOCT value is 27.8 volts. Charging a 24 volt battery bank you usually want the voltage in absorption mode to reach 28.8+ volts so you can see why these won't work very well for you...

    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
  • JohannJohann Solar Expert Posts: 244 ✭✭✭
    If the panel the OP has is in question for being suitable because of potential lower voltage, why not use an MPPT ( maximum power point tracking) charge controller that can handle at least 80 volts and wire the 2 panels in series and the OP still can use his 24 volt battery bank.
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