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Thomas Pfeifer avatar image
Thomas Pfeifer asked

BlueSolar Charger MPPT 75/15 Battery Current limited to 14.2 A?

Hi, I have a ~250 W(peak) solar panel connected to a 12 V lead carbon battery via a BlueSolarCharger MPPT 75/15 - which should deliver up to 15 Amps / 220 Watts continuously (if enough sun is shining and battery or load voltage is below MPPT output voltage).

However, I noticed in the VRM data, that the MPPT current is never going above 14.2 Amps and the PV Power is not exceeding 190 Watts. Is that current limit intentional? How can I adjust the maximum battery current to 15 Amps? The MPPT has the most recent firmware installed.

Thx in advance,
Thomas

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2 Answers
Stefanie (Victron Energy Staff) avatar image
Stefanie (Victron Energy Staff) answered ·

Hi @t.pfeifer,

how do you measure the current or do you rely on the information provided by the VictronConnect up? Please also consider that the MPPT itself has, compared to a DMM or BMV a rather rough estimate of current.
14.2A is pretty close to the limit of what the 75/15 can output. When you add cable losses etc. I think this is all you can get out of your MPPT.

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Thomas Pfeifer avatar image Thomas Pfeifer commented ·

Hi Stefanie, as I said: I am looking at the data provided by the MPPT itself (connected to a Venus GX, sending its data to VRM Portal via Internet). As the MPPT datasheet indicates a maximum current of 15 Amps and my PV voltage is well above 20 .. 25 Volts, I would expect to see 15 Amps / 220 Watts somewhen.

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klim8skeptic avatar image klim8skeptic ♦ Thomas Pfeifer commented ·

Got a link to your solar panel? Model. photo, website...??

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Thomas Pfeifer avatar image Thomas Pfeifer klim8skeptic ♦ commented ·

Hi, the PV module is a Sharp NRQ258H. A datasheet can be downloaded here: https://www.sharp.co.uk/cps/rde/xbcr/documents/documents/Marketing/Datasheet/1803_NQR258H_Mono_BackContact_Datasheet_EN_V5.pdf

I noticed in the spec, that the maximum power is rated at 258 Watt under Standard Test Conditions (STC, 1000 W/m², 25 °C) - but only 189 Watt under Nominal Operating Conditions of Cell (NOCT, 800 W/m², 47,9 °C). Might this explain my observations of limited charging power of the MPPT 75/15? Could the PV power increase over 190 Watt only on a sunny winter day? (Sorry, I am not a PV expert)

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Thomas Pfeifer avatar image
Thomas Pfeifer answered ·

Hi everybody! I found out something, which I would like to share (without understanding the details)

I checked the MPPT settings via VictronConnect App: Maximum Charging Current was set at 15 Amps, and the Load Output operating mode was set to "Battery Life".

As we do not have connected anything to the Load Ouptut of the MPPT, I changed the Load Output operating mode to "Always Off".

Now I can see in the VRM data, that the Solar Charger battery current goes up to 15 Amps under full load (as written in the MPPT spec). However, the PV yield is still around 190 Watts only - which is probably equivalent to the nominal power output (I mixed up the STC vs. NOCT power rating of the module, see comment above).

I guess that one of the Victron experts might explain this behaviour - however, I am fine now with the solution.


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ripper avatar image ripper commented ·

Watts is V multiplied by current A. Your volts are too low when you have a set max amperage. Lead batteries typically go up to 14.4 or higher. Multiplied by 15, you have your desired 220 W.

Battery amps is solar yield minus load. The higher the A, the bigger the error. Although nothing goes out the load out it thinks it does and deducts that from your battery amps. Nothing to worry about.

You have put more solar power on your charger than it can use, so it limits on good days and can get more on bad days. Also reasonable.

However your battery voltage barely rises during the onslaught auf full PV input. Do you have a other than lead battery technology or is your battery way too big and soon destroyed because you cant fill it up in time? The voltage during low PV yield is on the lowside for lead.


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Thomas Pfeifer avatar image Thomas Pfeifer ripper commented ·

Sorry, I didn't give the complete system set-up in my problem description: Its an off-grid power supply for an AC load (on MultiPlus), with 2 x 160 Ah / 12 V lead carbon battery (in parallel), charged by MPPT 75/15 on a 250 WP PV Panel plus a 100 W Fuel Cell. During the timeframe shown in the VRM diagrams, the AC load was drawing ~350 W, therefore the DC bus voltage (~battery voltage) is in the range <12.5 V. Under such conditions and with sufficient sunlight, the MPPT should provide maximum current to the DC bus. I was basically wondering, why I do not get the 15 Amps - but figured out that is was depending on the "Load Output" settings of the MPPT. However, from your remarks I understand that the maximum PV power will only be drawn, when the battery is charged at no load, and reaches its end of charge voltage. Thanks for clarification.

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