I read something interesting I need clarification!

[Jchance]

While hunting for additional items for my budget solar system that I’m putting together for my RV, (to charge the single house battery that I have). I came across this below Q& A on a 40 amp PWM charge controller.
Specifications:

Nominal Voltage: 12/24V auto recognition

Rated Charge Current: 40A

Max. PV Input Power: 12V/600W, 24V/1200W

Max. PV Input Voltage: 55 VDC


Q:"max. pv input voltage: 55 vdc" so i cannot use two 29v panels in series with this controller?

Answer this question

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A: No, for two reasons. First is because the voltage is too high for the controller. Also, with a PWM charge controller, only the AMPS are used to charge the battery, so putting panels in series is a complete waste of the second panel. The incoming power would just get converted to the same number of amps at a lower voltage. To run panels in series (with the exception of two 12v panels and a 24v battery) you need an MPPT charge controllersee less

the part I’m questioning is this sentence;
“putting panels in series is a complete waste of the second panel”

So bottom line, I should spring for an MPPT? I’m just trying to charge a single battery.

 

[2009Bounder2020]

yes get mppt

 

[DerpsyDoodler]

While hunting for additional items for my budget solar system that I’m putting together for my RV, (to charge the single house battery that I have). I came across this below Q& A on a 40 amp PWM charge controller.
Specifications:

Nominal Voltage: 12/24V auto recognition

Rated Charge Current: 40A

Max. PV Input Power: 12V/600W, 24V/1200W

Max. PV Input Voltage: 55 VDC


Q:"max. pv input voltage: 55 vdc" so i cannot use two 29v panels in series with this controller?

Answer this question

---

A: No, for two reasons. First is because the voltage is too high for the controller. Also, with a PWM charge controller, only the AMPS are used to charge the battery, so putting panels in series is a complete waste of the second panel. The incoming power would just get converted to the same number of amps at a lower voltage. To run panels in series (with the exception of two 12v panels and a 24v battery) you need an MPPT charge controllersee less

the part I’m questioning is this sentence;
“putting panels in series is a complete waste of the second panel”

So bottom line, I should spring for an MPPT? I’m just trying to charge a single battery.

If pwm sees a 12v battery, it will take the power it receives from the panels (if 29.xx is the panel‘s vmp), say 29.xx volts at 10a, it will chop the voltage down to 12 (no conversion, just a crude blunt axe) and send 10a at 12v to the battery. If it’s a mppt controller, the controller will convert the “extra voltage” into more amps at the charging voltage. So if receiving 24v at 10amps (made up number for sake of simplicity), it will convert to 12v at 20amps (minus some loss for inefficiency). Therefore, unless your panels are matched to your battery voltage, MPPT is an ideal option.

 

[chrisski]

If pwm sees a 12v battery, it will take the power it receives from the panels (if 29.xx is the panel‘s vmp), say 29.xx volts at 10a, it will chop the voltage down to 12 (no conversion, just a crude blunt axe) and send 10a at 12v to the battery.

I can’t verify the amperage you mentioned, but the PWM controllers I liked at, if at 12 volts, needed to be matched to “12 volt panels“ which are around 18 volts, but would not work off “24 volt panels” which read closer to 36 volts. So, as you add more panels to a PWM, at least the ones I looked at, would need to be in parallel, not series.

Being able to go series or parallel is another reason for an MPPT SCC.

 

[DerpsyDoodler]

I can’t verify the amperage you mentioned, but the PWM controllers I liked at, if at 12 volts, needed to be matched to “12 volt panels“ which are around 18 volts, but would not work off “24 volt panels” which read closer to 36 volts. So, as you add more panels to a PWM, at least the ones I looked at, would need to be in parallel, not series.

Being able to go series or parallel is another reason for an MPPT SCC.

i thought it was implied seeing as an MPPT will make use of the “extra” voltage, but is definitely better to explicitly state it. you, sir, are correct.

 

[bulrush]

If pwm sees a 12v battery, it will take the power it receives from the panels (if 29.xx is the panel‘s vmp), say 29.xx volts at 10a, it will chop the voltage down to 12 (no conversion, just a crude blunt axe) and send 10a at 12v to the battery.

Say whaaat? It just does a simple votage regulation with no increasing of the amps like in a transformer? I've seen voltage regulator chips. They just chop down the voltage to, say 3.3vdc, and the rest of the power is lost as heat.