DC Load directly off charge controller

bratan
bratan Solar Expert Posts: 32 ✭
in Solar Beginners Corner #1
I have Morningstar ProStar PS-30M charge controller. It has DC Load output terminals. In my mind I expected it would regulate exactly 12Volts from that port, but after testing it with multimeter I discovered that it's actually voltage that's going to the battery (12-14+ ) :(
This means I can't just plug in 12V DC light into it? Would I need some kind of DC-DC adapter that converts voltage to 12V?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,660 admin
    #2
    Re: DC Load directly off charge controller

    LVD ports are just generally battery voltage.

    Turns out, it is more costly/less efficient to regulated from 10.5 to 15 volts to 12.0 volts regulated.

    Basically there are "buck" regulators which drop voltage. And "boost" regulators that raise voltage. And "Buck/Boost" regulators that can regulated "around" a voltage.

    But "12 volt" LED lamps should have their own "internal ballast" to regulate their input voltage--Really, they are regulating the current to the LED's themselves. If you feed a "constant voltage" to an LED, it will either not light (too low of voltage) or over current and fail (just right to too high of voltage). LED's really need "current regulators" (or ballast resistors) to limit their current to what the LED can handle.

    Do you have a specific LED lamp you are looking at?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #3
    Re: DC Load directly off charge controller
    BB. wrote: »
    If you feed a "constant voltage" to an LED, it will either not light (too low of voltage) or over current and fail (just right to too high of voltage). LED's really need "current regulators" (or ballast resistors) to limit their current to what the LED can handle.
    In the real world, individual LEDs and LED arrays typically have a high enough internal resistance to give your at least a small voltage window to work with. And the cheap LED arrays without a current driver will usually at least incorporate a series resistor.
    Depending on how much power they are willing to waste in the resistor, you might have a working range of several volts. But the current will be proportional to the difference between the applied voltage and the LED operating voltage rather than proportional to the applied voltage itself.
    SMA SB 3000, old BP panels.
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  • bratan
    bratan Solar Expert Posts: 32 ✭
    #4
    Re: DC Load directly off charge controller

    Thank you! Sounds like it should work.
    BB. wrote: »
    LVD ports are just generally battery voltage.


    Do you have a specific LED lamp you are looking at?

    -Bill
    It's this one.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,660 admin
    #5
    Re: DC Load directly off charge controller

    There is not enough information--But I would guess that you can try connecting it to 12 VDC and see what happens.

    This may actually be 12 VAC or similar lights--One of the comments on taking a failed unit apart:
    There is a circuit inside that looks like it includes 5 diodes, a capacitor and a coil. I have not drawn out the circuit,
    but I suspect that it makes up a reverse polarity diode, and a full wave bridge for rectifying 12VAC and a filter.
    I had one fail and just bypassed it to run strictly on 12Vdc and the LED array works again.
    I suggest that if you change to a 20 watt LED array, that you bypass this circuit too since it may not handle the additional current. I have used 4 of these fixtures so far and this is the only one that has failed.

    They are probably "rugged enough" to at least give it a shot and see what happens.

    A few folks are using these for video lighting (and their brighter cousins)--So, I would guess that the output Lumens is probably stable enough for off grid lighting use...

    Note that LED's are temperature senstive, and the operating "voltage" point falls as the diode gets warmer--I would guess that if you are driving a lot of current through these devices, that you would not find voltage regulation to be sufficient. Current based regulation (or using a resistor "ballast") would be needed if driven near rated power (i.e., these most likely already have some sort of ballast internal to the fixture besides the input AC to DC rectifier+filter).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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