12 to 24v battery charging

I am using a 40w 12v panel to charge 2 marine batteries set up as 24v. 

This is the panel:

ALEKO 40W 40-Watt Monocrystalline... https://www.amazon.com/dp/B00XOIT6ZU?ref=ppx_pop_mob_ap_share

This is the control unit:

EPEVER 40a Solar Charge... https://www.amazon.com/dp/B07NVDJFD4?ref=ppx_pop_mob_ap_share

Here is is the issue:

It works fine as long as the batteries are set up as 12v.   When I set them up as 24v, the control unit does not allow a charge.  

Please assume my wiring is correct. Is the issue with the panel being a 12v?  If that’s the case, do I need a converter?   I’m fairly new to solar power, but I’ve checked and rechecked the system multiple times to no avail.  At this point, my only conclusion is the panel not being 24v but what do I know. 

Any advise is appreciated!

mike

Comments

  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    You are correct. A 12 volt panel cannot charge a 24 volt battery bank with 99.9% of the solar charge controllers.

    You need, at least Vmp-array of 35 volts to charge a 24 volt battery bank.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon ✭✭✭✭✭ Registered Users Posts: 4,087 ✭✭✭✭✭
    The simplest solution is probably to add a second identical panel in series with the first.  When hooking up the panels, the +ive of one plugs into the -ive of the other, leaving a single +ive and -ive from the pair to the controller.  Amperage will be the same, but voltage will be ~2x that of the single panel, and should be enough to charge your 24v battery string.

    Be sure the controller is already powered by the batteries and fully booted up before connecting the panel string to the controller.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mikeabeckmikeabeck Registered Users Posts: 2
    I don’t have room for a second panel.    So it sounds like my best option is a 24v panel.  However, I’ve seen a few 12-24v converters to install between the panel and converter.   Is this an option or a gimmick?
  • mcgivormcgivor ✭✭✭✭✭ Solar Expert Posts: 3,116 ✭✭✭✭✭
    The converter likely wouldn't work, the best method is using to correct voltage panels as described in the above comments. 
    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.
  • EstragonEstragon ✭✭✭✭✭ Registered Users Posts: 4,087 ✭✭✭✭✭
    Finding a 24v panel that will fit in the space occupied by a 40w 12v panel is likely to be a challenge.

    A DC/DC "boost" converter to up voltage from the panel might work, but it may not play well with the charge controller.  I wouldn't say it's necessarily a gimmick.  Might work.  Might not.  Lots of "it depends".  Generally speaking, a converter would be designed to use a source like a battery that can supply a fairly constant voltage with varying current.  Some are designed to provide a constant output voltage (eg 11-15v in 24v out, some are designed to output voltage proportionate to input voltage (eg 11v in = 22v out, 14v in = 28v out).  I think you'd want the latter.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • BB.BB. admin Super Moderators, Administrators Posts: 29,634 admin
    There is one solar charge controller (that I am aware of) from Genasun GVB-xx family.
    Not cheap--But should do what you ask.
    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • NANOcontrolNANOcontrol ✭✭✭ Registered Users Posts: 165 ✭✭✭
    I question if you have enough panel to even charge those batteries.  I don't know what your use is, but you have to have more room for another panel or forget this idea altogether
  • TecnodaveTecnodave ✭✭✭✭ Registered Users Posts: 415 ✭✭✭✭
    All MPPT controllers are switch mode buck converters as is a switch mode DC to DC boost converter, they will not play well togather as the switching pulses of one will interfere with the other device. It is not workable. Your solution will be to use a panel to provide at least 40 volts input to the MPPT charge controller.
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • EstragonEstragon ✭✭✭✭✭ Registered Users Posts: 4,087 ✭✭✭✭✭
    Actually, most (not all) are buck converters.  Genasun per Bill's link does make a boost.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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