Borneoboy
New Member
That will probably mean panels in series and a 24v battery pack. Altogether more than double my modest budget for my 12v starter system, don't you think?
New 300-watt solar panels 8.9amp 31v open
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RCinFLA
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PWM controllers have been given a somewhat bad rap.
PWM controllers are not that much less yield from MPPT controller if used on a 12v or even a 24v battery system and if the panel voltage is selected for a 12v/24v battery.
MPPT controller require a few volts overhead voltage on panel Vmp for series switch and buck coil converter regulation operation which eats up some of power conversion advantage for a lower voltage system. When battery needs charging the PWM switch will just be continuously ON so the panel will just be placed at battery voltage. Some MPPT controllers just stop switching and effectively turn into a PWM controller when panel voltage gets close to battery output voltage to reduce its buck switcher overhead voltage loss,
By the numbers, for an 18v standard 100 watt panel. Voc = 21v, Vmp = 17.2v, Isc = 6.3 amps, Imp = 5.8 amps
1) PWM during charging a LiFePO4 with about 3.3v per cell X4 = 13.2 vdc
Panel voltage = 13.6 vdc (0.4v controller switch drop overhead from battery)
Panel current = 6.0 amps ( little higher then Imp, little less then Isc)
Net charging power to battery = 13.2v x 6.0 amps = 79.2 watts
2) MPPT controller
Panel voltage = 17.2v (probably optimistic with panel heating, likely lower)
Panel current = 5.8 amps
MPPT buck converter overhead from Vmp = 3.5 vdc (this does not change much for higher voltage systems which is where MPPT has greater advantage)
Net power to battery = 13.7v (17.2v Vmp - 3.5v MPPT overhead) x 5.8 amps = 79.5 watts
MPPT has 0.3 watts ( 0.4% ) advantage for a 12v battery system. This will get greater at higher battery voltage systems.
MPPT has a practical advantage as it can use much higher panel voltage then battery without too much additional power loss.
PWM controllers are not that much less yield from MPPT controller if used on a 12v or even a 24v battery system and if the panel voltage is selected for a 12v/24v battery.
MPPT controller require a few volts overhead voltage on panel Vmp for series switch and buck coil converter regulation operation which eats up some of power conversion advantage for a lower voltage system. When battery needs charging the PWM switch will just be continuously ON so the panel will just be placed at battery voltage. Some MPPT controllers just stop switching and effectively turn into a PWM controller when panel voltage gets close to battery output voltage to reduce its buck switcher overhead voltage loss,
By the numbers, for an 18v standard 100 watt panel. Voc = 21v, Vmp = 17.2v, Isc = 6.3 amps, Imp = 5.8 amps
1) PWM during charging a LiFePO4 with about 3.3v per cell X4 = 13.2 vdc
Panel voltage = 13.6 vdc (0.4v controller switch drop overhead from battery)
Panel current = 6.0 amps ( little higher then Imp, little less then Isc)
Net charging power to battery = 13.2v x 6.0 amps = 79.2 watts
2) MPPT controller
Panel voltage = 17.2v (probably optimistic with panel heating, likely lower)
Panel current = 5.8 amps
MPPT buck converter overhead from Vmp = 3.5 vdc (this does not change much for higher voltage systems which is where MPPT has greater advantage)
Net power to battery = 13.7v (17.2v Vmp - 3.5v MPPT overhead) x 5.8 amps = 79.5 watts
MPPT has 0.3 watts ( 0.4% ) advantage for a 12v battery system. This will get greater at higher battery voltage systems.
MPPT has a practical advantage as it can use much higher panel voltage then battery without too much additional power loss.
Last edited:
Borneoboy
New Member
Thanks for that - I see lots of advantages for using MPPT in future... for the present I am stuck with PWM and wonder, given the panel and inverter data above, how many 300 watt panels to connect (in parallel).
4 should be OK in theory (36 amps max) but maybe 2 or 3 would be wiser to start with...
I can always use the spare panel to charge the battery (ies) through another separate charge controller couldn't I?
Borneoboy
New Member
This from the inverter/charger manual.
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