Load terminals?

stmarstmar Solar Expert Posts: 362 ✭✭✭
I have a Morningstar Pro-Star PS-30 controller for my solar array. I am doing some remodel and had a question about the "load terminals" on this unit. I have a 24VDC Sun Frost RF-16 refrigerator freezer. Can I use those terminals for my frig/freezer? I am now going directly off the batteries and have never used the load terminals on the controller. From the documentation I cannot tell if the load terminals are integrated with the batteries or are just controlled by the solar array and I can't tell what the load limits are.

Never mind: Found that compressors/motors/inverters are not to be connected to the load terminals of the controller. Learn something new every day!!!

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Load terminals?

    Don't bother.

    LOAD terminals are for controlling loads up to the current limit which is usually the same as the controller's output (i.e. 30 Amps in this case). They run from the battery, but with a LVD setting (sometimes programmable). Some have lighting control function (turn on when PV input falls low).

    For most applications they are not used.
  • stmarstmar Solar Expert Posts: 362 ✭✭✭
    Re: Load terminals?

    I may put the RF on a breaker, it is fused at 7.5 amps per compressor (2).
  • unseenoneunseenone Solar Expert Posts: 61
    Re: Load terminals?

    Where did you find that. I would like to read about it. I thought you could use anything within the load limits of the controller.
  • BB.BB. Super Moderators, Administrators Posts: 30,488 admin
    Re: Load terminals?

    Usually it is the surge current that "kills" the LVD circuits on this smaller controllers. Inverters, DC compressors, etc. all can have 2x or higher than rated surge current.

    http://www.morningstarcorp.com/wp-content/uploads/2014/02/ALL.DIG_.TS_Load_SureSine.01.EN_.pdf
    • The Inverter cannot be connected directly to the Load +/- terminals of the TriStar Load Controller. Instead, it is connected directly to the battery bank.
    • In order to use the TriStar Load Control with the inverter connected directly to the battery bank, a Relay must be used.
    • A Relay is used as a contactor for the Remote ON/OFF terminal present on the SureSine 300. The TriStar controller when the Relay turns ON/OFF. Via the Relay connected to the Remote terminal, the SureSine AC output is turned ON/OFF.
    • For detailed installation information, please consult the respective product manuals (TriStar, SureSine).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stmarstmar Solar Expert Posts: 362 ✭✭✭
    Re: Load terminals?

    "Some loads are not suitable for direct connection to the Load terminals of a Morningstar
    controller. Heavily inductive or capacitive loads such as pumps, motors, compressors, and
    inverters should not be wired to the controller’s Load terminals."
    unseenone wrote: »
    Where did you find that. I would like to read about it. I thought you could use anything within the load limits of the controller.
    I found this at: http://www.morningstarcorp.com/wp-content/uploads/2014/02/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Load terminals?

    Another related caution about LOAD terminals: if you plan on running them anyplace near the max rated current you need really good wiring. Otherwise the Voltage sag can trigger false LVD just like the surge demands Bill mentioned would.

    Really they're meant for low current DC lighting applications. So if you fall asleep reading in bed with the light on it will shut off before the battery gets drained too far down.
  • unseenoneunseenone Solar Expert Posts: 61
    Re: Load terminals?

    Thanks for that. It looks like for normal loads, such as a 3amp DC draw fridge with virtually no surge or other minor loads would be OK or not? Just in conjunction with an inverter, this makes sense. Would that be what you would think?

    Thank you for posting that.. Great information.
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    Re: Load terminals?

    As one whom has tried to use those "load terminals" inappropriately, I would go with with Cariboocoot says: ... they're meant for low current DC lighting application.

    Connect all else to them darn batteries ... use a battery monitor's relay to disconnect the load earlier if that is your plan.
  • stmarstmar Solar Expert Posts: 362 ✭✭✭
    Re: Load terminals?

    I guess it would depend on what kind of surge you have at start up. I know that I have two compressors on my frig and the surge would probably be too much to take a chance, even though they are fused at 7.5 amps. Even at 3 amps you would have to have some surge.
    Thanks to the guys for their input, always something to learn about these systems.
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