So I currently have 300w(2 each 150w panels), a Samlex 30a Controller. It feeds 4ea. 6v batteries in series and paralleled. My rig came prewired for Solar. It has the Samlex panels and the Samlex wiring from the panels to the controller. Then the pre-wire from the controller to the battery is 8ga. Probably about ten feet from the controller to the battery. So my plan is to add one more panel and add an MPPT controller. Thinking I will move the controller closer to the batteries, say with in 5 feet and use 6ga. wire. I will rearrange the layout of the 2 panels that are there to allow room for the new panel and the installation of a Fantastic Vent over the bed for ventilation. There is tons of room in the truss area to run wires and with the new hole in the roof for the Fantastic Vent this will ease the wire running too. So, my questions are:1. What's the best MPPT Controller out there?2. When I put the third 150w up on the roof, how do I gather up all the solar output wires from the panels and get them into the controller? Thinking most of the Controllers have one or two input ports for the panels.3. Are most cables from the panels large enough? Seems to me these are 10ga. from my Samlex panels? 4. Are all panel cables interchangeable? Are there aftermarket cables that are 8ga? Would that be necessary if it were possible?5. When I move the controller down closer to the battery, the cables that come from the panel to the controller will now be longer. How much will that affect the charging with longer cables from the panels to the controller?Thanks in advance!

Are those 150w panels "12v" or "24v" is the first question. Second is what is the brand and model of the controller (Edited) you have now, so we can read up on its manual for its specs etc.I can explain how MPPT works for "amps to the battery" vs PWM , but first answer my questions above. Thanks.

I would not go MPPT with a 12v panel system. If your panels have MC4 connectors you can get a 3 into 1 connector and some #8 MC4 cable for the run down to the controller.If the panels have the same ratings and you are going series I recommend a Morningstar MPPT controller. Others are good too.

"Ass-uming" 12V panels...#1: It depends on your criteria of "good" and your budget. Off the top of my head, EP 30 will do, subject to input volts limit (BFL probably remembers that number). Morningstar Tristar 45 will be nice, for much more money.#2: Controllers normally have ONE input for panels, i.e. Pos and Neg. Any combining of panel wires is normally done on the roof waay before the controller. In case of series it's just plugging panels pigtails one into another.#3: Normally, panel pigtails are #12 or #10. Plenty thick for series, not enough for parallel 3*150W.#4: Did you mean "MC4 extension cables"? Yes. Panel pigtails - not really, because they are normally soldered to the panels. Yes, there are #8 extension cables with the same MC4 connectors (again, "assuming" you have MC4 since you didn't tell this). No, #8 is not necessary for series 3*150W, but for parallel you might need to combine pigtails into #8 or #6 before routing into the trailer.#5: Will hardly affect in series. In parallel you might need combiner box and #6-#8 cable.

Victron MPPT seem to be well thought of.

BFL13 wrote:Are those 150w panels "12v" or "24v" is the first question. Second is what is the brand and model of the controller (Edited) you have now, so we can read up on its manual for its specs etc.I can explain how MPPT works for "amps to the battery" vs PWM , but first answer my questions above. Thanks.Mine are 12v panels and the controller is a SCC-30AB

Polishing up my Solar System | Good Sam Community

28 Replies

CA_Traveler
Explorer III
Nov 29, 2018
FWIW I use 70% efficiency for flat panels. So 450W * 70% is 315W usable watts.

While this can be factored into the wire size it's always best to use wire for the maximum rated power. ie 450W.

I've gotten more than 70% on July 1, clear sky, 1:00 PM, panels with their 4% slope facing south and Phoenix latitude. And less otherwise.

And trust me I try very hard to not be in Phoenix on July 1.
CA_Traveler
Explorer III
Nov 29, 2018
Almot wrote:
#3: Normally, panel pigtails are #12 or #10. Plenty thick for series, not enough for parallel 3*150W.
All good Almont answers but clarification on this one: The pigtails are spec'd for the panel and no need to change them which would void any warranty anyway. Use the same gauge wire to the controller for series but I'm assume (makes an ass out of u and me) the OP has 12V parallel panels.

OP For parallel panels the individual panels are connected usually in a combiner box on the roof or perhaps using MC4 2-1 Y or even 3-1 connectors. At that point the panel amps add together and the wire from the combiner to the controller has to carry the total amps and larger wire may be required to reduce voltage drop.

And assuming your wire to the controller is 8 gauge as you think then it is likely adequate for 3 panels.

Likely adequate? What does that mean? :@ It means we don't know because it's also length dependent which may be difficult to determine given the mfg installed the wire.

What to do: I'd connect the third panel to the other 2 and then with full summer noon sun check to see that I get the expected max amps. Unless you tilt the panels you can't do this during this during the winter. And most likely the mfg used the god awful Z mounts so you can't easily tilt the panels.
BFL13
Explorer II
Nov 29, 2018
http://www.samlexamerica.com/documents/manuals/11010-SCC-30AB-0912.pdf

Have to check this out first. Generally, I would stick with PWM with a 12v system, but not always. EG, with PWM voltage drop between panels and controller is not so important, so wirie gauge is less critical on that run. It is important controller to battery, but that is true for both MPPT and PWM.
Vintage465
Nomad
Nov 29, 2018
BFL13 wrote:
Are those 150w panels "12v" or "24v" is the first question. Second is what is the brand and model of the controller (Edited)
you have now, so we can read up on its manual for its specs etc.

I can explain how MPPT works for "amps to the battery" vs PWM , but first answer my questions above. Thanks.

Mine are 12v panels and the controller is a SCC-30AB
agesilaus
Explorer III
Nov 29, 2018
Victron MPPT seem to be well thought of.
Almot
Explorer III
Nov 29, 2018
"Ass-uming" 12V panels...

#1: It depends on your criteria of "good" and your budget. Off the top of my head, EP 30 will do, subject to input volts limit (BFL probably remembers that number). Morningstar Tristar 45 will be nice, for much more money.

#2: Controllers normally have ONE input for panels, i.e. Pos and Neg. Any combining of panel wires is normally done on the roof waay before the controller. In case of series it's just plugging panels pigtails one into another.

#3: Normally, panel pigtails are #12 or #10. Plenty thick for series, not enough for parallel 3*150W.

#4: Did you mean "MC4 extension cables"? Yes. Panel pigtails - not really, because they are normally soldered to the panels. Yes, there are #8 extension cables with the same MC4 connectors (again, "assuming" you have MC4 since you didn't tell this). No, #8 is not necessary for series 3*150W, but for parallel you might need to combine pigtails into #8 or #6 before routing into the trailer.

#5: Will hardly affect in series. In parallel you might need combiner box and #6-#8 cable.
time2roll
Nomad
Nov 29, 2018
I would not go MPPT with a 12v panel system. If your panels have MC4 connectors you can get a 3 into 1 connector and some #8 MC4 cable for the run down to the controller.

If the panels have the same ratings and you are going series I recommend a Morningstar MPPT controller. Others are good too.
BFL13
Explorer II
Nov 29, 2018
Are those 150w panels "12v" or "24v" is the first question. Second is what is the brand and model of the controller (Edited)
you have now, so we can read up on its manual for its specs etc.

I can explain how MPPT works for "amps to the battery" vs PWM , but first answer my questions above. Thanks.

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