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full_mosey's avatar
full_mosey
Explorer
May 31, 2015

MPPT Solar Controller Driveway Test

The weather forecast for tonight is 'mostly clear' and for tomorrow 'mostly sunny'. After that, the forecasts all include various degrees of cloudy without any mention of sunny. Today, Sunrise is 6:14AM and Sunset is 8:35PM. I want to make the best use of this short window.

Here is a list of the components of the solar system:

SA. 170W poly as 2 x 85W, 18.3Vmp, 4.69Imp, 22.7Voc, 5.12Isc.
TPA. Turnigy Power Analyzer.
MPPT. Morningstar Corp. SS-MPPT-15L with temp comp cable.
AGM. Johnson Controls 31C 100AH AGM
MMS. Magnum MMS 1012 inverter/charger with temp-comp cable. And yes, there are two cables on the AGM!

Connected like this:

SA -> fuse1 -> TPA -> fuse2 -> MPPT -> AGM -> MMS.

The SA is not tilted, plus the driveway is negative tilted to the North.

I plan two Voc tests to determine the characteristics of Voc around Sunrise and Sunset.

Test#1:
At dark-thirty(~5:44AM) I will connect fuse1 while leaving fuse2 pulled. I will record one hour of video of the TPA display. If the Voc has not reached 40V, I will record another hour.

Test#2:
This is a to be a recording of Sunset Voc starting at 8:00PM until the TPA shuts down due to lack of SA Voltage.

Test#3:
At noon, I plan to connect the Travel Trailer to the MMS and run the Air Conditioner. The AC is a 5k and usually draws 600W including the 50W fan. Fuse2 will be inserted.

Would anyone care to guess how long this might go? The MMS has a 10V LVD.

HTH;
John

29 Replies

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  • JiminDenver's avatar
    JiminDenver
    Explorer II
    May 31, 2015
    Even tracking the solar will only cover about a third of the amps being pulled from the bank. There is some recovery time the compressor cycles but when it isn't you will be pulling an additional 20-25 amps from the battery. Have the compressor run constantly and not be tracking with the solar and I'd say a hour is pretty good.
  • BFL13's avatar
    BFL13
    Explorer II
    May 31, 2015
    I suppose I meant things like allowance for heat loss as a "constant"
  • full_mosey's avatar
    full_mosey
    Explorer
    May 31, 2015
    BFL13 wrote:


    ....

    Do the TPA and the Kill-A-Watt use different constants?
    Do you suspect something does not match from previous results?

    You do good tests. I still have the info about AGM and high amp draws in mind that I remind folks about who want to run their microwaves, but only have room/weight allowance for two batteries.


    Thanks for the complement.

    I'm not sure what constants are.

    Yes, I spent Thu and Fri setting up the test environment. On Thu there was a brief period of partial Sun where I tried the Air Conditioner for 3hrs . KAW recorded .87 KWH and the TPA recorded 412 WHs. Using the formula 50x + 550y = 870, I solve x as 3hrs fan time, or 150WHs, and y = (870-150)/550, or 720/550 = 1.3hrs of compressor time. Afterwards I discovered a warm connection which I corrected.

    During these two days I also got comfortable with video capturing and I now know how many hours I can record.

    I plan to report power in Watts and WHs as I do not have any capability of capturing AHs. It should be interesting.

    HTH;
    John
  • BFL13's avatar
    BFL13
    Explorer II
    May 31, 2015
    full_mosey wrote:
    BFL13 wrote:
    The title says "controller test" but I can't figure out what you are testing for. Maybe I missed something.


    Test#3 is to sufficiently deplete the AGM thereby giving the MPPT a chance to produce power. I intend to compare the Kill-A-Watt's reading of WHs consumed by the Air Conditioner against the TPA's reading of WHs drawn by the MPPT.

    HTH;
    John


    Do the TPA and the Kill-A-Watt use different constants?
    Do you suspect something does not match from previous results?

    You do good tests. I still have the info about AGM and high amp draws in mind that I remind folks about who want to run their microwaves, but only have room/weight allowance for two batteries.
  • full_mosey's avatar
    full_mosey
    Explorer
    May 31, 2015
    westend wrote:
    With one 100AH battery, I'd guess an AC run of 1-1 1/2 hr. Your AGM will be pretty well discharged with this test.


    I'll give you another guess.

    Keep in mind, with fuse2 in place, the MPPT will be offsetting some of the power used.

    HTH;
    John
  • full_mosey's avatar
    full_mosey
    Explorer
    May 31, 2015
    BFL13 wrote:
    The title says "controller test" but I can't figure out what you are testing for. Maybe I missed something.


    Test#3 is to sufficiently deplete the AGM thereby giving the MPPT a chance to produce power. I intend to compare the Kill-A-Watt's reading of WHs consumed by the Air Conditioner against the TPA's reading of WHs drawn by the MPPT.

    HTH;
    John
  • westend's avatar
    westend
    Explorer
    May 31, 2015
    With one 100AH battery, I'd guess an AC run of 1-1 1/2 hr. Your AGM will be pretty well discharged with this test.
  • BFL13's avatar
    BFL13
    Explorer II
    May 31, 2015
    The title says "controller test" but I can't figure out what you are testing for. Maybe I missed something.

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