Morningstar TriStar 45 MPPT Battery Sense reading error

Hi all.

I have a very frustrating issue with my new Morningstar 45 TriStar MPPT controller.
The battery sense voltage displayed on the remote digital meter does not match the voltage reading taken at the controllers internal "Battery sense" terminal block, which is where the "Battery sense" wire terminates.

The voltage displayed on the controllers remote meter is .50 volts below the measured voltage at the controllers internal "Battery sense" terminal block.

Morningstar tech support e-mailed me to disconnect the feature, which I felt was an unacceptable ans..

Persisting, tech support e-mailed me that the voltage measured at the controllers internal "Battery sense" terminal block should match the remote meters "Battery Sense" displayed voltage.
I was instructed to inform them if the voltages did not agree.
I replied to the e-mail that the measurements did not agree, and were off by .50 volt, I never heard from them again... (7 days ago)

I did request a replacement controller from the dealer (at my shipping expense) and when I hooked it up the remote meter measured a .08 voltage drop which is what I expected, BUT after 24 hours the meter again started to reported a voltage drop approximately .50 volt.

I'm at whits end at this point. Morningstar confirms in their e-mail, that voltage measured at the controllers internal " battery sense" terminal block should match what the controllers remote meter displays, yet it does not.

On a perfectly charged battery bank measuring 12.76 volts, the controllers remote display meter displays a "Battery sense" voltage of 12.26, switching the remote display to "Battery" the voltage reads 12.7,
which agrees with my multimeter.

I'm running 7 feet of #4 AGW between the controller and the battery bank of six T-105RE's, and while i've been told my voltage drop is not significant, it is no excuse to disable a feature in order for the product to function correctly. The Tristar uses the "Battery sense" voltage to control charge voltage rates.

I''m using a Fluke 175 multimeter for testing.

Both controllers have a manufacture date after 10/2011

Any advise, anyone...


  • waynefromnscanadawaynefromnscanada ✭✭✭✭ Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Morningstar TriStar 45 MPPT Battery Sense reading error

    Just wondering about the temperature of your batteries. If they're cold enough, it's possible (a guess) that the way the controller boosts charge voltages for a cold battery, is by "modifying" the sensor reading so the controller will push the actual (real) voltage higher. But if this is the case, surely the Morningstar tech support would know that. If they don't, they should.
  • ArtStreamArtStream Registered Users Posts: 2
    Re: Morningstar TriStar 45 MPPT Battery Sense reading error

    Thanks for responding.

    Yes, an interesting theory, but as you said, the tech would know that.

    But a remote display battery reading of 12.2v, it's enough to get anyone to stand-up and notice.

    Can anyone confirm a multimeter voltage reading taken at the controllers internal "battery sense" terminal block with the displayed remote meter voltage?

    I've read so many good things about Morningstar, but i'm not feeling the love?
  • WindsunWindsun ✭✭ Solar Expert Posts: 1,164 ✭✭
    Re: Morningstar TriStar 45 MPPT Battery Sense reading error

    A few things to check:

    1. Insure that no current is flowing through the sense cable, at most perhaps 2-3 milliamps. You should be able to measure that with your Fluke.
    2. The sense cable should be something like #18 to #20 AWG copper electrical or phone cable type wire. It will work with wire size down to about #32, but small sizes are mechanically fragile. Using other than copper can cause a false reading - essentially the junction can act like a thermocouple and generate a few tenths of a volt.
    3. Check the cable going to the remote meter, if picking up EMF it can cause read errors in the meter. Some meters can also be mounted on the controller itself, if yours can be, try that and see if the error persists.

    It sounds like it is not the controller is the problem but the meter. It may have an internal error or fault in the analog to digital conversion.

    One thing you did not mention was the actual voltage at the battery with the Fluke.
  • K1ngN0thingK1ngN0thing Solar Expert Posts: 27
    EDIT: Replied to wrong thread.
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