Is this safe?

SolaRACSolaRAC Solar Expert Posts: 52 ✭✭✭✭
I've connected my 12v power supply to the solar panel port on my charge controller and connected my single 12v battery to the battery port on the charge controller. Is this safe? Will this actually charge my battery?


  • BB.BB. Super Moderators, Administrators Posts: 33,319 admin
    Re: Is this safe?

    Possibly, battery charges tend to be rectified transformer outputs, so it will probably have enough voltage to take the additional controller drop.

    However, the charger may shutdown early because of the extra voltage drop.

    If the charger current is less than the charge controller rating, it is probably "safe".

    If you are trying to float charge your battery bank, I would use a lamp timer set to turn on one hour power day. Keeps battery charged with a cheap charger and does not over charge. Adjust on time as needed.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is this safe?

    Depending on the particular charge controller and power supply it could work.
    Sometimes power supplies don't output very "clean" power and the charge controller may not like that. An MPPT type controller would be most likely to malfunction as a result. PWM not so much so.

    Otherwise, so long as the "12 Volt" power supply is capable of putting out more than 12 Volts and sufficient current against the battery load it should charge. If it actually is regulated at 12 VDC or can cannot manage the needed Amps of current it won't.
  • bmetbmet Solar Expert Posts: 630 ✭✭
    Re: Is this safe?

    Isn't a 12V power supply supposed to output 13.8V @ 5 Amps?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Is this safe?
    bmet wrote: »
    Isn't a 12V power supply supposed to output 13.8V @ 5 Amps?

    Not necessarily. There are thousands of "12 Volt" power supplies ranging from milliamps at 12 VDC under load to lots of Amps potential with open circuit Voltages well over 12. The term "12 Volt power supply" is simply too vague.
  • john pjohn p Solar Expert Posts: 814 ✭✭✭
    Re: Is this safe?

    many 12 v supplies are exactly that
    even a supply that can output at 13.8 v is not really that good for charging batr/ies through a MPPT controller as there will be a voltage drop mabe .7v mabe even more that means the best the battery/ies could ever be charged is 13.1v but mabe less
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Is this safe?

    john has got a good point as the voltage from the supply is low already. this will not do much for the battery through a cc and many power supplies can't take being connected directly to a battery without damage to the supply. even if one got lucky and was able to put the supply straight to the battery, 13.8v is not enough to properly charge it.

    now 13.8v is not 12v, but many so called 12v supplies are actually set to 13.8v to mimic the output seen in many automotive applications. some of these are made to be able to variable in the voltage a bit to suit and the current output of a supply is not necessarily a fixed 5a as this can be made to be nearly anything, but becomes more difficult to obtain from a single supply the higher the current goes. costs go up as well with current capacity and with the quality and features one may see in a supply.
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Is this safe?

    If this "power supply" is a true regulated power supply. Most have built-in overvoltage protection. As such, this could limit the PV output voltage to the charge controller.
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