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rick79 avatar image
rick79 asked

Blue Solar MPPT 150/35 charging 55.5 volts LiPo battery (15 cells)

I have 6 solar panels (~300W each, MONO) for a ~72 volt PV system (series).

The solar panels are connected to MPPT150/35 which is charging a 15 cell LiPo battery system. 55.5V nominal.

Abs 62.40V, Float 61.96V / Battery level set at 48V (no other option for 55.5)

Temperature cutoff and compensation disabled.

The 55.5V battery is required. I cannot go to 48V battery.

Problem:

As expected, when there is a >5 volt delta between PVv and BattV the charger is in status Bulk. (i.e. PVv=64.5 and BattV=58.2V); However no power, or very minimal (1-20watts if any) is going to the battery. No errors are present.

I note than when the battery level decreases to certain levels, i.e. PVv=64.8V and BattV=57.81V the charger starts to pass some power but still less than expected (i.e. 500W)


Some thoughts:

Is the system firmware trying to protect a 48V battery (which I don't have) or do the Absorption and Float settings take care of that? I don't get any high battery voltage alarm.

Is the system physically incapable of producing battery charge voltages over 58V?

Any other ideas why I'm not getting any charge at higher battery levels (58V+)?

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1 Answer
Mike Dorsett avatar image
Mike Dorsett answered ·

The "48V" battery setting for the MPPT is a nominal voltage. If you select custom battery type from the configuration menu, and then enter in your desired Abs and float voltages, max charging current etc, then the system should work ok.

The MPPT will start when the PV voltage is >5V above the battery voltage as you point out, and will continue to operate down to ~1V above the battery voltage.

However, you should consider re-configuring your modules to give a much higher PV input voltage to the MPPT - it will work more efficiently. I would expect a 300W module to have a rated max power voltage of around 45V and an open circuit voltage of <50V. The aim would be to achieve an open circuit voltage of between 120 - 140V corrected for temperature. As you don't state the model number of the module, I can't check this.

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rick79 avatar image rick79 commented ·

Understood, will look into reconfiguring the panels. Is it a matter of not enough voltage differential? I thought 5v delta is all that was needed(?), and I don't see more than a few watts under 10 watts at some higher battery levels.

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niklas-schauberg avatar image niklas-schauberg rick79 commented ·

we need the panel's datasheet to assess this. maybe your idle voltage is high enough but it droppes to far for powering the charge.

this is why there is a Voc (open circut / idle) and a Vmpp (maximum power point / load) value stated at you datasheets

my gut feeling says you need at least a 2s3p configuration of your 6 panels. maybe 3s2p but be careful your Voc must never exceed 150V with your specific MPPT!

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