Morningstar MPPT 15 question

W3ABC
W3ABC Registered Users Posts: 19 ✭
in Off Grid Solar & Battery Systems #1
The product page says this charge controller is rated at 15A output. Is the output considered what's going to the batteries, or what's going to the load?

http://www.morningstarcorp.com/en/sunsavermppt
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Morningstar MPPT 15 question
    W3ABC wrote: »
    The product page says this charge controller is rated at 15A output. Is the output considered what's going to the batteries, or what's going to the load?

    http://www.morningstarcorp.com/en/sunsavermppt

    Welcome to the forum.

    In this case it is either. It can handle up to 15 Amps on the load terminals (which may come from the batteries or the solar panels or a combination thereof) or 15 Amps to the batteries (power coming from panels only; no load reduction). In other words as far as it is concerned the DC output side handles 15 Amps in total. Where it comes from and where it goes to doesn't matter.

    It will not pass 15 Amps to the batteries and 15 Amps to the loads at the same time. That would be 30 Amps total on the output side: the equivalent of about 525 Watts of "12 Volt" panel. As you can see 200 Watts +/- is the recommended maximum for a 12 Volt system.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Morningstar MPPT 15 question

    The maximum charging current to the battery bank is 15 amps. The maximum output through the DC Load Terminals is also 15 amps maximum.

    http://www.morningstarcorp.com/en/support/library/SSMPPT.IOM.EN.02.pdf

    LVD (low voltage disconnect) function is always a bit of a question. At 15 amps, you should not connect any inverters >100 watts (at 12 volts). And LVD is not really designed to prevent a battery from being over discharged as battery voltage is not really a good indicator of state of charge.

    So, what it is usually good for are small loads that might be damaged by running at less than XX volts (motors, some electronics, etc.).

    Major devices, such as inverters, usually have their own LVD function to prevent them from over current during brown outs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Morningstar MPPT 15 question

    welcome to the forum.
    as coot said, it is both, but to be clear the controller will only output 15a even if the pv source would warrant higher currents as it is limited. no matter if you choose to send that power to the batteries or to a load, that is the most you will see from the cc as it is not a case of 15a to the batteries and the cc sending another 15a to the loads for a total of 30a. it would merely be diverting it's output to loads if you elect to use the cc as a go between for said loads. the battery can still be tapped for your loads, even those loads higher than 15a, but it just won't have anything to do with the cc controlling the said loads.
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  • W3ABC
    W3ABC Registered Users Posts: 19 ✭
    #5
    Re: Morningstar MPPT 15 question

    Thanks for the quick replies.

    Will the load connections pull from the batteries if the solar panels aren't producing enough current?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Morningstar MPPT 15 question

    Yes. Battery bank is the buffer. Nothing fancy going on inside the controller other than a switch with voltage and possibly current detection.

    -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 ✭✭✭✭
    #7
    Re: Morningstar MPPT 15 question
    BB. wrote: »
    Yes. Battery bank is the buffer. Nothing fancy going on inside the controller other than a switch with voltage and possibly current detection.

    -Bill
    Yes, the Load connection will definitely shut down if the battery voltage drops too low. But its LVCO voltage may actually be set too low to properly protect your batteries.
    The maximum current allowed will either be limited by the CC (in an unspecified way) or by a fuse.
    In some CCs, the Load terminal is only powered when the Charger function is in Absorb or Float.
    Depending on the CC, either the Load or the charging function will have priority for the available panel current. Not sure of the details of the Morningstar unit.
    SMA SB 3000, old BP panels.
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  • W3ABC
    W3ABC Registered Users Posts: 19 ✭
    #8
    Re: Morningstar MPPT 15 question

    Thanks so much for the help!

    One more question - if I exceed the max input rating (250w @ 12v or 500w @ 24v for example), what happens? Is it dangerous or will the energy just be lost?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: Morningstar MPPT 15 question

    With MPPT type charge controllers (as opposed to PWM), they have the ability to control/limit their output current to a safe amount.

    As long as the input voltage meets the requirements, the MPPT controller will output the available solar power up to the rated output current.

    In fact, a few of these controllers have been used to take 24/48 volt battery banks and down convert to 12 volts--Work just fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #10
    Re: Morningstar MPPT 15 question
    Will the load connections pull from the batteries if the solar panels aren't producing enough current?

    For its small size, MPPT 15 is actually very sophisticated and programmable, if you get Morningstar's meterbus adapter and download their software from the website. The meterbus adapter uses RS232, so you also either need a computer that still has that, or a USB-RS232 adapter.

    Anyway, once you're in programming it, you can set it to turn DC loads on and off according to different parameters, like daylight, battery voltage, time, etc. You can do this on two separate channels.

    By the way, the software will also let you see what the MPPT 15 is doing (input watts, amps, volts, etc.).
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  • porch13
    porch13 Registered Users Posts: 68 ✭✭✭
    #11
    Re: Morningstar MPPT 15 question
    BB. wrote: »
    voltage is not really a good indicator of state of charge.

    -Bill

    Hi guys...I have this charge controller and am very pleased with it. I ordered the remote meter and my wife make fun of how much I look at it. I'm still very new at the solar & battery world and Bill's statement that "voltage is not really a good indicator of state of charge" caught my eye. I've always just looked at the battery voltage displayed on the meter as my reference. What more should I be concerned with and/or checking to understand the true state of my batteries. I'm especially curious because I'm adding a Xantrex ProWatt 600W inverter to my setup and want to make sure that I'm only using it at the right times.

    Thank you, gentlemen, for providing guidance to us new guys!
    Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: Morningstar MPPT 15 question

    It's like this: Voltage at rest (no current going in or out) is a fairly accurate representation of SOC on a new, unabused battery. After that it gets tricky. When loads are on there draw will affect the SOC but this may not show up in the Voltage reading as the function of Amp hours available vs. Voltage shown is not linear. In other words a battery can hold 'X' Volts against a current draw for 'Y' minutes and then it will suddenly start to go down very rapidly. Where and how and when depends on the particular battery and operating conditions.

    To get a truly accurate measurement you need to take specific gravity readings of every cell and compare them to the known original values for those cells when the batteries were new and fully charged. Probably not going to happen and can't in retrospect. Besides, you can't take SG readings on sealed batteries.

    Enter the Battery Monitor. If installed and programmed correctly it keeps track of the Amps flowing in and out over time and compares the tally with the 100% value to see what the SOC is "on the fly". If it isn't set up right to begin with it's also inaccurate of course.

    Voltage actually does work if you know the system and have monitored it for a long time. You can get a fair idea of how much power you use in a day and when 'X' Volts @ "5:00 PM" means "start the gen or the 'frige shuts down at 2:00 AM".

    But any method of determining SOC takes planning and monitoring to know just how well it works on your particular system. This is why we repeatedly recommend not running things too close to the limit (either limit) and making sure you have a back-up power source (i.e. generator) in case you goofed the math.

    Margins are what you want. Big, wide margins for error.
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  • porch13
    porch13 Registered Users Posts: 68 ✭✭✭
    #13
    Re: Morningstar MPPT 15 question

    Thank you for the great information and quick reply! Since my batteries are less than a year old and have not dipped below 12.4 volts, it sounds like I can use voltage at rest as a pretty good indicator of the state of my batteries. Also, I only plan to run the inverter mid-day during full sun to charge a laptop or two. I'm guessing this will be a pretty small hit to the batteries.
    Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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  • boB
    boB Solar Expert Posts: 1,032 ✭✭✭✭
    #14
    Re: Morningstar MPPT 15 question

    You can actually tell something about a battery by noting its voltage with no load on it.

    For instance, if you have what is supposed to be 12V battery and you measure say, 6.0 volts across it,
    it is dead.

    boB
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #15
    Re: Morningstar MPPT 15 question
    porch13 wrote: »
    Thank you for the great information and quick reply! Since my batteries are less than a year old and have not dipped below 12.4 volts, it sounds like I can use voltage at rest as a pretty good indicator of the state of my batteries. Also, I only plan to run the inverter mid-day during full sun to charge a laptop or two. I'm guessing this will be a pretty small hit to the batteries.

    that's not totally true for if you drained your battery to 50% soc and recharged it up to 12.4v, your battery is not fully charged.
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  • porch13
    porch13 Registered Users Posts: 68 ✭✭✭
    #16
    Re: Morningstar MPPT 15 question

    That makes sense. According to my meter, the lowest voltage my batteries have seen is 12.4 volts. The only load they ever currently see is the circuitry on a propane fridge, a small radio, and a few lights.
    Northern Arizona...4050 Watt off-grid system - Outback FP1 - Rolls 605 in a 48V bank
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