PWM Vs Mppt Charge controllers

On my motorhome I have 3X100w panels feeding into a Renogy PWM controller. I think it is rated for 50VDC so I can add another panel.
What is the advantage of using a Mppt controller vs the pwm if I don't have any plans to have more that 400w.

Regards

Fred.

The PWM controllers that I have (cheap ones) are auto switching for 12v or 24v battery. But for 12v they say the input voltage is 25v or so and for 24v input limit would be 50v. I think they want to avoid seeing a large difference between the input and the battery being charged. The MPPT controllers allow larger differences (normally) and get slightly better performance when the is not strong on the panels.

Please include the battery voltage and if you have your 3 panels in series or if you have them in parallel.

Typical PWM controllers essentially just throw the panels across the battery and let the battery pull them down to its voltage so you have loss in power production since the panels are being run off Vmp.

The the duty cycle nature of PWMs comes into play too. Typically they connect the panels, and monitor the battery voltage. When it rises up to what ever point, the panels are disconnected, and then the voltage on the battery floats back down to the low threshold. Rinse and repeat as necessary. Usually this happens 25 times a second or more and there is a maximum / minimum duty cycle too so the battery is never 100% connected to the panels. The input capacitors in the controller will be maintained at a few volts over battery by this mechanism.

With PWM the further the panel Vmp is away from battery voltage the worse the power loss.

IMO if you are trying to wring every watt out of a solar array MPPT is the way to go but if the panels and battery are well matched and maximum power production isn't necessary PWM is a cheap and workable answer.

The PWM is a Renogy Wanderer and I have a 12v bank. Panels are parallel. The manual says optimized for 12v and 30A charging capacity.

Thx
Fred

So this is where it gets to be a little bit tricky. Remember you could always just buy another panel to get more power. With that being said Real life net gains are usually up to 30% more power for MPPT vs PWM in the Winter and up to 20% more power in the summer. This is with matched panels, good wiring practices and quality charge controllers.

I think other people are asking about parallel vs series panels as well. If you are willing to rewire your panels you could get more gains depending on shading, environment ect. Higher voltage with Mppt means less cable loss.

All thing considered I will usually say to add panels before changing controllers for the most bang for your buck. The next thing would be get rid of lead acid and keep every amp you throw at your batteries.

also if your panels are in the clouds and producing 10 watts each mppt wont get you any more solar gain, where another panel will do something.

Thanks. I plan to get a 4th panel and think later about changing the controller.

Regards
Fred

Watch this.

Mainly the gains for MPPT are highest with using domestic panels on vans, as those are ~45v not 18v max which is typical on 12v panels, or by series connecting panels.

12v panels with PVM controller and FLA batteries have minimal, but some gains by switching to MPPT

The greater the maximum power panel voltage is above the battery voltage, the greater the benefit of an MPPT over PWM will be.
To use some round numbers for easy math, lets say the panel puts out 18 volts at Vmp, current is 10 amps, and it's charging a 12 volt battery.
With an MPPT charger, the panel will run at 18 volts and 10 amps, so it will put 180 watts into the battery.
With the PWM charger, it will pull the panel down to the battery voltage, it will run at 12 volts, and 10 amps, and put 120 watts into the battery, 33% less than the MPPT.

If you put another panel in series, the new Vmp will be 36 volts at the same 10 amps...the new numbers will be:
MPPT runs at 36 volts and 10 amps, it will put 360 watts into the battery...double the single panel numbers.
PWM will STILL pull the panels down to battery voltage, so it's still at 12 volts and 10 amps, 120 watts...it sees no gain from the second panel...the greater Vmp voltage benefits the MPPT, but not the PWM.

If you put the second panel in parallel, it will have 18 volts Vmp, but 20 amps out, new numbers will be:
MPPT runs the panels at 18 volts, 20 amps, puts 360 watts into the battery.
PWM pulls down to 12 volts, at 20 amps now, puts 240 watts into the battery. It's making good use of the second panel now, but still trailing the MPPT by 33%.

Hope this helps you to understand the difference between MPPT and PWM.

Nicely explained. Thanks.
Looks like I will add a 4th panel AND an MPPT controller.

...And rewire solar into series? Its better for mppt. ?