question

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New SmartSolar MPPT 100|20 not charging in full sunlight as well as old PWM charger

I replaced a Renogy PWM charger with a SmartSolar MPPT 100|20 charger and in full sunlight, the old PWM charger was charging at the same voltage (13.5V) but almost 2 amps more current (I have 3 PVs (two 100w and one 160W) with open voltage around 20v and a single 105AH 12v LiFePo battery).

The PWM was at 100% (PV voltage same as battery) while the MPPT determined a PV of 15.3V was best. I noticed in the morning, the MPPT ramps the PV voltage between 15.3 and 18V (to determine the best PV operating point?). Is the 15.3v floor (~1.8v greater than the battery) the lowest that the MPPT can work into the 13.5 battery voltage, and that the PWM works better as the PV's best operating voltage is below 15.3? If so, then would connecting the PVs in Series help?


mppt smart solar
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4 Answers
klim8skeptic avatar image
klim8skeptic answered ·

Differences between MPPT and PWM chargers.

Please read the notes at the end of the technical specs, Smart Solar mppt manual.

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pmikep avatar image
pmikep answered ·

1) Mixing different panels can be problematic. In series, you are limited to the lowest panel current. (So shading can kill an entire series array.) In parallel, you are limited to the lowest panel voltage.

2) IIRC, the Victron MPPT's require a highish differential voltage to start. But once started, the voltage differential can be as low as a few tenths of a volt. So if it's pushing current, it's working.

3) It could be that the Victron MPPT might be performing better (that is, more accurately) than your old PWM. That is, it might be that your old PWM was cooking your battery with too much current. (Assumes that you have all the voltages set up the same. AND that your old PWM was reading those voltages the same as the MPPT.) It might be rash to conclude that simply because your old PWM delivered 2 A more that it was "better." Really it's Watts in (V x I) that matters. Not just I.

4) If not #3, then in your case of mixed panels, I expect that trial and error is the only way to find which configuration (series or parallel panels) is best for you. (Perhaps "best" being defined as which gets you to 100% SOC fastest.)

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mgotcha avatar image
mgotcha answered ·

Thank you for the information. The specs did not indicate what the min in-out diff was and the Victron never attempted to try a PV voltage less than 15.3V. The mix of panels is a wild card and overall the MPPT does deliver more power overall (better during morning, evening and overcast conditions). It also regulates the battery voltage much better at 100% SOC (The PWM was jumpy/noisy at 100%)

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mgotcha answered ·

Update: I purchased another 160W PV (total 2ea 160W and 2ea 100W) and wired the like panels serial and paralleled those two serial pairs (40v open) and performance was much better.

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