PWM that can 24v(28+v) input with 12v(14+v) output

KhellSk
KhellSk Registered Users Posts: 91 ✭✭
in General Solar Power Topics #1

Is there such devices ? or do I absolutly have to go MPPT

_____________________________________________
[3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
[Victron 50/100 700wMax MPPT]







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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2

    It does depend on what your power source is (solar panel or 24 volt battery), and what the input voltage rating of the PWM charge controller is (i.e., >24 volts input rating).

    PWM controllers are, more or less, just an on/off switch. The current input to the PWM needs to be limited (solar panels are "current sources" and will only output X amps Imp under full sun). If you attached a 24 volt battery to the input, and 12 volt battery to the output, the current flow would approach being a "dead short circuit" and probably blow the "switch" in the PWM controller.

    You could, for example, put a resistor on the input for a PWM controller and size it (and the wattage rating) to limit the current (say 29 volts input, and 10.5 volts output). Obviously, the maximum current falls (with a fixed resistor) as the input voltage falls to 24 volts and the output voltage rises to 14.8 volts... So charging would "slow down".

    However, sending 24 volts in and 12 volts out, you will lose 1/2 of the energy of the input energy (Power=Voltage*Current).

    An MPPT type charge controller is a very efficient digital switching power supply whitch approaches 95% power conversion efficiency.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • KhellSk
    KhellSk Registered Users Posts: 91 ✭✭
    #3

    thanks guys

    _____________________________________________
    [3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
    [Victron 50/100 700wMax MPPT]







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  • NANOcontrol
    NANOcontrol Registered Users Posts: 273 ✭✭✭
    #4

    I've use modified $5 buck converters to keep the panels at the power point voltage and outputted 15V to one of those $5 PWM controllers. A poor boys MPPT.

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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #5

    I believe some of the robust PWM charge controllers that can be used for diversion controllers, can handle the higher voltage input.

    You still lose the wattage of the higher wattage panel (they only conserve the current/amperage)

    I believe the maximum input voltage is the same for 48 volt output as it is for 12 volt output for charge controllers like the Morningstar TS45 and TS60 and Trace/Xantrex/Schneider C40.

    These are more expensive units, so the savings over buying a MPPT wouldn't be worth it in my opinion. but if you find one used and local, it might be worth it. Please read manuals and ask questions (Morningstar is pretty good about getting back with people) This is from the feeble mind of an ever older man...

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #6

    The Trace/Xantrex/Schneider C40 will tolerate up to 125 volts.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited March 2019 #7

    Typical cheap PWM 12/24V controllers can handle 30-50V input . Figure about a 40% (not 50%) loss (as compared to MPPT) when using PWM at 2x the battery charging voltage. Partly because current rises (as you drop below Vmp) and partly due to increased losses in MPPT controllers.

    I am available for custom hardware/firmware development

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  • KhellSk
    KhellSk Registered Users Posts: 91 ✭✭
    #8

    @Photowhit

    Earlier this winter you guys suggested me yo put panels in series to make sure my batteries would get 14v min daily. 2 string of (2x 48w 16v). Im fine now coz luminosity increased. But I want to fix that for next winter.

    My chargecobtroller is pwm 12vonly. I was wondering if i could either

    Change the controller for a pwm 48vto12v Send 16vx2 to the controller to make sure i maintain that daily minimum 14.4v throughout winter

    OR

    make a 24v array plus battery bank and use 12v outnof the bank.

    Am I to understand that option 1 will not work unless using mppt and option 2 will not work without damaging batteries?

    _____________________________________________
    [3p3s 48w 15.9Vmp] [Flooded 2x 6v 150ah]
    [Victron 50/100 700wMax MPPT]







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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9

    Generally, if your panels are "12 volt" rated (Vmp~17,5-18,5) volts, that is the "accepted" standard for connecting a PWM controller to a 12 volt Lead Acid battery bank.

    Long wiring (too small of diameter), very hot weather with cool battery bank, etc. (Vmp falls as temperature rise, Lead Acid battery charging voltage rises as they get cold) and the voltage drop from hot panels / long wire run from array to cool battery bank (higher voltages needed)--You can run into reduced charging current in Hot weather.

    In cold weather, Vmp-array rises--But for a PWM controller that "extra/free" energy (power=Voltage*Current, rising V = rising available power) is lost.

    A MPPT based charge controller is like an automatic transmission between the solar array and battery bank. It can run the solar array at "optimum Vmp and Imp" and charge the battery bank at "optimum Vbatt and Ibatt".

    If, for example, you put 2x "12 volt" panels in series with an MPPT charge controller, then in Hot Weather, Vmp-array-hot is still way higher voltage than you need to charge/equalize your battery bank. And in subfreezing weather, the increase in Vmp-array (~10-20% increase in voltage), the MPPT controller can supply that "extra free power" to the battery bank charging/running your loads).

    In the old days when solar panels were over $10 a Watt and golf cart batteries--Optimizing a system to save on solar panel costs made sense.

    Today, batteries are 2x or more expensive, and solar panels (large wattage) less than $1 per Watt... So optimizing the battery charging/loading conditions for longer battery life makes sense--And throwing cheap panels at your system to keep your expensive batteries "happy" makes sense today.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • NANOcontrol
    NANOcontrol Registered Users Posts: 273 ✭✭✭
    #10

    Some controllers are positive ground and some are negative. This refers to which input and output is common and not switched. Many cheap controllers switch the negative side. I could see potential conflicts if two controllers are uses and the panels are set for 24V and a common 12V tap.

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