MPPT vs PWM Charge Controller for 12 volt portable panels

[astrocamper]

The advantage for series is if you portable array is going to be some distance away from your RV mounted controller. The lower amperage and higher voltage means the effect of voltage drop over the long wire will be less.

I am building a portable array out of 2 parallel strings of 3 watts panels in series. It will be used to give me a tilt up assembly that can directly face the sun and also be used as supplemental solar if my trailer is parked in the shade. The 52 volts DC and 5.72 amps will easily go over a longer cable with out much loss from voltage drop.

I went with the 50 watt panels because I can store them as a 2x2x0.75 foot cube and the weight is not a problem.

[PbdBlue]

Originally Posted by creativepart

Even with only 300w of panels we see +1200aH/day of charging when needed.

Do you mean watt\hours? 1200ah would require something approaching 200 amps from the solar panels. 300 watts would be more like ~16 amps.

[creativepart]

Originally Posted by PbdBlue

Do you mean watt\hours? 1200ah would require something approaching 200 amps from the solar panels. 300 watts would be more like ~16 amps.

Oops, I sure do mean kwH - 1.2kwH. I had to recheck my Victron history. Thing is, I start the day when boondocking around 95% SOC after running the gen 30 min or so for breakfast. Then the solar charger brings it back up to 100% pretty quickly after that and keeps it there.

I'm happy to see that little 300w system can keep my 4-100w AGM batteries at or near 100% SOC throughout the day. During the day we'll have our residential 3-door fridge, a fantastic fan, a few chargers, internet routers and hotspots going. Even some TV during lunch maybe. By 5pm or so the sun is less productive for us and SOC starts to drop into the lower 90% range. Just in time to make dinner and run the generator for aprox 90 min so we can go to bed with 100% SOC again. Normally, we wake to between 86% and 89% SOC. It depends on whether or not we have to run the heater at all during the night.

More solar panels and more battery amp hours would be great sure. But we're doing pretty well with our small system.

I plan to add a 4th 100w panel and once my AGMs give up the ghost - they're only 2-years old - I plan to replace with LiPo batteries.

[GyroGypsy]

Originally Posted by C.Martin

Your pair of panels will now ADD voltage, whilst AMPS remain the same.

Sorry. Universal Conservation of Energy laws means if the panel array output voltage increases, then the output current must be proportionally reduced. The MPPT controller is simply a computer DC-DC converter. It converts whatever input POWER (I x V) from solar array to appropriate volts and amps for the battery.

[Pappion]

Originally Posted by GyroGypsy

Sorry. Universal Conservation of Energy laws means if the panel array output voltage increases, then the output current must be proportionally reduced. The MPPT controller is simply a computer DC-DC converter. It converts whatever input POWER (I x V) from solar array to appropriate volts and amps for the battery.

I like your explanation.

It is an efficient DC-DC switching supply that constantly seeks out the best power point match of the panels. So it harvests more power and delivers it more efficiently than a PWM.
However these circuits consume some power too. My EPSOLAR Tracer MPPT controller drops down to PWM mode when Solar power is low.
PWM is like a simple switch that is rapidly turned on and off. Cheap and simple for small setups. Generally not for series panels, or large voltage drops from panel to battery.