Changed from PWM to MPPT

Ako Registered Users Posts: 184 ✭✭
After three years of monitoring my PWM system daily with a Morningstar Charge controller and becoming very familiar with the input im quite surprised at how only changing to a Victron MPPT unit changes everything .

Previously i could almost predict the Incoming charge , Voltage and Amps on a regular sunny day here in Spain would be within certain parameters , 31-33 volts and 32-36 amps , simply by changing only the Charge controller the voltages have increased to around 40v and the Amp crashed to around 20 Amps , the strange thing is that the system changes from Bulk to Absorption around the same time of day and with the same amount of Amps going into the batteries , i didnt think the batteries would charge as quickly with far less amps going in as i understood that batteries needed amps and the voltage was only the means of transporting them .

Despite the strange reversal of Volts/Amp input he Cumulative daily input has not changed at all however Charging has , before my system would go into float maybe once a week , now it enters float daily and remains there for several hours and because of the way the Victron system splits the way it displays production between Load and Charging the batteries often show less than End Amps going in and they are often shown to be Idle , previously it came close to end amps but not quite .

I bought the MPPT so that when the time came to change batteries i could use Lithium and have my panels rewired to produce the higher voltages they require , i really didn't think it would see any changes leaving them as they are . Im hoping that when winter comes this change in the charging regime works to make the system a little bit more efficient as i think it will be a while before i need to replace my bank .
2240 Watt Array  4 x 460 Watt Mono Panels + 2 x 200 Watt Panels
Victron Smart 150-70 MPPT Charge Controller
24 volt Battery Bank 4 x 6v 400 Amp/Hr Trojan L16 AGM
LiFePO4 Lithium 100 Amp/Hr Battery for Backup
Victron 1600w Multiplus Compact Inverter/Charger
DC to DC Charger ( Non Isolated )


  • BB.
    BB. Super Moderators, Administrators Posts: 33,500 admin
    Is the 32v/34a vs 40v/20a the solar input voltage and current?

    Power wise:
    • 32v * 34a = 1,088 Watts
    • 40v * 20a = 800 Watts
    If the above is solar array output, what is the Vbatt output of the controller (voltage and current)?

    One issue--The voltage and current values from solar charge controllers seems to be less than accurate for many models. Typically (from stuff I have read years ago), at best 10% accuracy (and frequently read "high" values)--Solar array V&A readings may even be less accurate.

    Another issue, what is the Vmp of your array? Ideally, you want Vmp-array to be around 2x Vbatt charging... For 24 volt battery bank, the array Vmp should be around (2*29v) 58 volts... If the array Vmp is only a few volts above Vbatt--Then the MPPT controller behaves more like a PWM charge controller. MPPT controller need something like 2-7 volts minimum above Vbatt to begin to work their "MPPT Magic".

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Options on panels are typically in the range of 0.93 to 0.95 of so current should not 'crash' with MPPT controller. 

    If you got 32-36 amps PV current on PWM controller you should get about 95% of that amount on MPPT controller.

    MPPT controllers require some overhead voltage of over maximum battery voltage to operate properly.

    31-33 vdc  PV voltage on PWM is a bit high for 24v lead acid batteries assuming charging is in full bulk mode.  

    40v on PV while on MPPT controller should be enough panel overhead voltage above battery voltage.

    Sounds like you may have some issues on how panels are connected, different facing directions, or partial shading.