Quality products showing conflicting data

AkoAko Registered Users Posts: 162 ✭✭
For 4 months i have ben using a Morningstar TS60 PWM Charge controller with the correct settings for my new AGM batteries , today i connected new Victron products and im getting different feedback , the voltage on the Victron is 0.28v lower than on the Morningstar and the temperature on the Victron is 1.5c lower , the difference has been constant from charging on Absorption at 28.8 volts to late at night with a voltage or around 25volts . The Morningstar use a temperature probe that is taped to the side of the batteries but the Victron one is connected to the Negative lug of the batterie so that could explain the discrepancy but the voltages are taken from the same point on the bus bar . Is it normal to have different products return different voltages , both im sure have high degrees of accuracy .

I have another TS60 so im going to swap them over tomorrow and see how the voltages and temperature compare the the Victron .
1050 Watt 24v Array . BP and Atersa 72 cell Panels 
Morningstar TS-60 Charge Controler
4 x 6v 400 Apm/Hr Trojan L16 AGM
Solener 1500w Pure Sinewave Inverter

Comments

  • mike95490mike95490 Solar Expert Posts: 9,582 ✭✭✭✭✭
    I don't like post mounted thermal sensors.  They can be tricked by ohmic heating between the post and the terminal clamp.

    Chinese Proverb:  A man with a watch knows what time it is. A man with two watches is never sure.

    The same with thermal sensors !!


    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,640 admin
    A 1.5F difference between two different temperature "probes" on industrial units  (not calibrated/designed for precision temperature measurements)--I believe that to be within the typical margin of error. Typical commercial temp sensors are only within +/-1C/2F of actual).

    Quick discussion of NTC (and PTC) temperature sensors:

    https://www.seeedstudio.com/blog/2020/10/27/thermistors-ntc-and-ptc-thermistors-explained/

    What was the reported temperature? If 25C/77F, then that is usually "Standard Conditions" and the the temperature offset issue between Victron and other brands of controllers (earlier thread) would not be an issue... (temperature offset would be zero Volts @25C).

    Of course, with Victron only supporting a max of -0.0027 mV/C/C (vs -0.005 V/C/C for most other controllers)--That would cause the Victron to have higher Temperature corrected voltage >25C and lower voltage for <25C...

    The difference of 0.28 volts (out of ~14.x volts nominal bus voltage)--That I would like to see closer (less than 0.1 volt difference would be nice). Some solar charge controllers had a calibration function in the setup menu. And there is always the possible issue of voltage drop vs wire AWG and current...

    Have you measured the voltage at the Charge Controller Vbatt terminals (check with a good volt meter to ensure that the voltage is nearly the same on both units and not affected by voltage drop, current, poor electrical connections, and such).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AkoAko Registered Users Posts: 162 ✭✭

    Was going to enable DSS on Cerbo but it says that MPPT that use CAN BUS wont work from it for temperature or sense . I have connected power cables to it and ran the RJ45 between it and the Cerbo but i cant get it to show on either VRM or Victron Connect App . 


    It appears I made a basic error , when scrolling through the settings to make the necessary charging adjustments I came to the screen with a thermometer on it which had no figures , there was no mention in the manual about an inbuilt temperature sensor however it appears there must be as there was another Temperature shown with a Battery symbol which was also blank prior to connecting the sensor cable , after connecting the cable both screens contained figures , one just had a Thermometer symbol and was 1.5c lower than the Morningstar , the other had battery and a thermometer symbol and was around 0.5c which is acceptable .


    The other problem with this MPPT is that it wont show on VRM , plugged into the Cerbo correct with the Blank RJ45s used on the spare connections on CAN BUS and inside the MPPT .


    I believe the Victrons voltages to be correct , the MPPT , Multiplus and the Cerbo all take their power from the same place , a busbar which has the same voltage as the battery bank . The log shows the Morningstar voltage to be the higher , its the voltage that controls Absorption , float etc , this is where I think the problem is . Following BBs suggestion I took a reading at the charge controllers battery terminal , it was 0.15 volts higher than the Battery , I dont know where the voltage on the Victron VRM comes from , it could come from the Cerbo GX power supply or the power supply to the Multiplus inverter . The Multiplus DC in terminals are 0.01 lower due to the cables so if its there then its easy to remedy .


    I have attached screenshot of the 2 min log when the Morningstar Controller was connected directly to the battery bank , at 15.10 today I turned off the Array and ran a sense wire between them , the Morningstar Charge controller voltage was then around 0.16v higher than the sense voltage or battery , really strange .


    The screenshot of both the Morningstar and Victron VRM was taken last night and the actual voltage physically taken at the time was agreed with the sense voltage which was 0.17v lower then the Morningstar showed




    1050 Watt 24v Array . BP and Atersa 72 cell Panels 
    Morningstar TS-60 Charge Controler
    4 x 6v 400 Apm/Hr Trojan L16 AGM
    Solener 1500w Pure Sinewave Inverter
  • AkoAko Registered Users Posts: 162 ✭✭
    More to try and consider but im going through everything to try to reconcile the anomalies .Think im having some luck with both problems , followed BBs advice and physically checked the voltages at the batteries , the battery leads are ample and short without any voltage loss so i have never needed to use sense wires . I took readings at Battery then removed the leads that ran from them to the charge controller , the voltage was identical at both ends 28.6 however once connected i took a reading again at the Charge Controller battery terminals and it was was 28.8 , very strange , i would have expected them to be the same , if there was to be a variation then it should be lower not higher .

    The Victron Blue Solar MPPT problem with Temperature has been solved with a firm wear update , the limit has now been raised from 3.5mv/C/c to 5mv

    I believe the problem with different voltages is due to using a Bus bar , the charge controller feeds it and the Victron equipment is powered from it , the voltage at the Morningstar charge controller is higher as its charging Batteries and the Victron equipment is consequently higher because of it . Fitted a sense wire to the Victron and it solved the problem , took voltage reading from batteries not Bus bar .
    1050 Watt 24v Array . BP and Atersa 72 cell Panels 
    Morningstar TS-60 Charge Controler
    4 x 6v 400 Apm/Hr Trojan L16 AGM
    Solener 1500w Pure Sinewave Inverter
  • BB.BB. Super Moderators, Administrators Posts: 32,640 admin
    In commercial computer systems, we use voltage sense wires for power systems quite often. There are not that many solar power based chargers that have remote voltage sense options. For batteries where charging voltage is very important--It is typically addressed by using short/heavy copper cables to make up for the lack of sense wires.

    With near zero current flow, the voltage should be near identical with both ends of the cables. For heavy/max current flow, then there is the V=I*R voltage drop. If R is small (heavy/short cables, heavy short bus bars), then Vdrop will be low(er).

    Bus bars are "kind of assumed" to be heavy copper (or brass, aluminum, etc.)--But they are only as heavy as purchased. You can do things such as, when there is heavy current flow from charging or AC/DC loads, and use your DMM to measure the voltage at each end of the bus bar/cable/etc... And see how much drop there is. One advantage is that you can use (for example) the 2.xxx voltage scale and get higher accuracy on the voltage drop. I.e., you can measure 0.008 volts on the low voltage range vs trying to compare 12.8 or 12.6 volts. The last digit on digital meters is that all that accurate/repeatable.

    Also, when measuring very low voltage (i.e., 0.001 volts or so), even measuring between copper cable, tinned leads, and brass busbar can have a thermal couple effect/offset... The nickle (or whatever) meter leads and the different metals where contact is made--Any differences (i.e., meter leads are contacting two different metals), you can have that thermal couple offset.

    Also you can have the issues of "electrical noise" from the charge controller, AC inverter draw, and DC loads can affect the readings too (a true RMS reading meter--Root Mean Square--Can give more accurate readings in "noisy" environments...

    In the end--Don't tear yourself apart over these relatively small voltage measurements/differences. You are looking for "bigger stuff". I.e., are you seeing 14.2 to 14.4 volts for several hours (ideally at least once or twice a week on solar) to ensure the battery bank is correctly charged. Float voltage around 13.6 to 13.8 (typical). And resting voltage (after 4+ hours or so), you see somewhere between 12.8 and 13.2 volts... And (suggestion) that you do not see the battery bank drained below 11.5 volts (continuous current draw--Surge current may drop down towards 11.0 volts or less for a few seconds or minutes in some cases).

    Very happy to hear that you fixed the Victron temperature offset value/limitation with a firmware update.

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