Solar - anyone regret getting PWM charge controller?

Really like my Bogart SC2030 PWM coupled with Bogart's Trimetric. Works great for me. Only have 2 - 160 watts PV's and a Deka 8D 245ah AGM batt. Pretty basic system. Also have a Samlex 2000 watt inverter.

Cdash wrote:
MPPT sounds great, but comes at a cost, more than double. Enough to buy almost 200 watts of panels. I read about plenty of people that share that they are fully charged by noon or 1pm, with their MPPT controller. That means that the system has quite a bit more power than is required.

To me, it seems like a WPM could still charge the batteries, but may not do it till a little later in the day.

Is my thinking flawed?

Pieces of info are missing. You won't get an answer specific to your situation without providing more details. Several people talked/asked about your energy audit and planned panel wattage - this is what you should figure out first.

About fully charged by 1 pm with MPPT - the picture is bigger than that.

People with MPPT typically have more panel wattage. Plus, MPPT would harvest more energy – about 10-20% more – but there is also more wattage, these two effects work together.

Also - no matter what controller - if battery has been through all the charging stages and is 100% full by, say, 1 pm - it doesn’t mean that system has "more power than required". There is a huge difference in harvest on a good and bad day. On a good day you may get more than enough, and on a bad day - just enough. If you can barely make it full by sunset on a good day, then with any clouds you won’t get it full on that day.

When panel wattage is too low, neither PWM nor MPPT will charge battery full "later in the day" - it will never charge it full, period. You don’t want to leave it undercharged very often. OTH, there is no penalty – other than system cost – for getting it full earlier on some days.

"Cost more than double" – yes, sort of. You should compare controllers with same features. Also, consider that with MPPT you can wire panels in series -> thinner cable and no rooftop junction box -> simpler work and slightly lower wiring costs. Most important is the ease of install and no J-box, with MPPT. With 12V bank and panel wattage under 250W there are no savings on thinner cable and no need in J-box either.

Handy Bob’s blog is inspirational but it’s difficult to sift through the rant and get enough of useful info there. A bit dated, too.

server glitches again

Ductape wrote:
Fred, roof space is a limitation for some of us. I need all the power I can get in a limited footprint.

With limited roof space, you want to make sure that you are not putting the panels to close to the A/C unit or creating other shadows. MPPT is the way to go to get the most amperage when you are limited in solar panel wattage due to space considerations.

Still it is all a dollars equation, same as anything else.

You also want to check the square inches on one panel, and compare it to another. You want the highest watts per square inch that you can get (for a reasonable price), and stay away from flexible panels that only have about 1/2 the watts per square foot of crystal panels.

Good luck,

Fred.

PWM you get Isc as charging amps. Excess voltage is just clipped.

230w 24v 8.2 Isc panel $159
140w 12v 8.4 Isc panel $159

Either panel give you about 8.3 amps with PWM. Swap to MPPT to get 90%+ of full wattage.

Panels from SolarBLVD.com

A 17/18 volt panel will be great with pwm. The higher 20-30 volt panels will fail miserably with it, and will rock with mppt.
Assume the pwm controller will charge at the panels rated amperage. The mppt will (attempt) to convert excess voltage into current (amps) going into the battery. The higher the excess voltage, the more current it can convert. A 20 volt panel may generate 10% more current on mppt, a 30 volt panel will be closer to 50+%.

Yes, a poly 24V panel and an MPPT controller will harvest even in limited light. There might not be a lot of charge but there will be some. The other nice thing about MPPT controllers is that they usually have more adjustability for charge settings, along with battery temp compensation.

Slownsy wrote:
The way I see it the main resen for not using PWM is cheaper panels cheaper wire but more ekspensiv controller, and if partial shade less pover and bypass diodes also robs pover.

Not my experience. Bypass diodes can and have provided MORE power. For example with my 3 bypass diodes for each of my 3 panels in series I essentially have 9 panel sections at 90V (30V per panel and 10V per bypass section). I've gotten charging with only 2 sections in the sun - ie 20V. PWM with parallel panels would be no power.

I've seen my panels with partial shade ramp up in 10V increments from 20V to 90V as leafy shade leaves the panels. I know how bypass diodes work from research and actual logs from my controllers.

Yes bypass diodes have about a 0.5V drop. But with partial shade one of my serial panels with MPPT can be producing the given amps at 10V or 20V while an equivalent PWM panel would not produce any power.

Cdash wrote:
So basically, what I am getting from all of this is:

If you get a PWM you are happy with it and if you get a MPPT you are happy with it!

I appreciate the information and opinions, it seems that I can't really go wrong either way. Almost seems like I am better off picking my panels, and then the charge controller.

Yes, it seems overwhelming when researching some of this stuff. I would rule out the comments like you will get 30 % more with mppt or that you are being cheap because you dont buy the more expensive mppt. I would rather have more panels than put the money in mppt. A person can buy an mppt and it works great but another person buys pwm and it works great also. As I said in my last post I compare my pwm to my buddies mppt and he's not doing anything better than I am but he spent more and right now his controller is giving pwm performance.

His system is wired in parallel because he added panels as he went along. His mppt blue sky controller will take about 46 volts when the panels are wired in series. So ideally he could use say four 140 watt panels wired in series/parallel. Two pairs of panels wired in series and those two strings would then be wired in parallel. Mppt controllers give the most amp boost when they see the biggest difference in voltage between the panels and the controller.

If the same four panels were all wired in parallel he wouldn't get much better performance from an mppt because the voltage is low and may as well have an pwm. He started with one 140 watt panel then added a second 140 and then a 3rd 190 watt panel. He has a difference of .9 volts between the 190 and the lowest voltage 140 panel so the mppt cant lock onto the voltage signal. He also cant wire them in series because the total voltage would go over 46 volts. He could use his two 140 panels in series and stay under the 46 volt limit but he would only have 280 watts. Yes, he could add 2 more 140's in series and then parallel them with the old panels but they will probably default to the lowest amperage panel. Again, it's probably more important for mppt to have matched panels for best performance.

It seems like his best improvement would come from getting four new matched panels so as to get the most out of his controller. It's common for people to start out with a couple panels and add more later. This may be easier to do with pwm. As you add mismatched panels to pwm they will be pulled down or default to the lowest voltage of the group but the amps will all add up.

If you are mixing panels in series, the voltage isn't as critical (as long as it's under the controller limit) but the amperage is. If you are mixing panels in parallel, the amperage isnt important but the voltage is. If I was installing mppt I would be sure to fully panel it at the start of the build.

If you look at the difference of an MS mppt for $350 and say a Morningstar PWM for $145 you have enough money to buy 200 more watts of solar panels. There is no way that an mppt controller is going to give you the increased performance of 200 more watts of panels with pwm.

Now, if you want to go with a big system and use large dimension 24 volt panels you will get even more watts for your money but they often times dont fit the roof area as well as narrower 12 volt panels. With that large system you would absolutely go with mppt and get a controller that will run high voltage like over 100 volts. The Morning Star 60 amp mppt will run up to 150 volts. With that high voltage you will have low amperage in the wire so you can run one smaller wire all the way down to the controller and not use a combiner box on the roof to make the parallel connections. If you were doing a home install I cant imagine why they would ever use pwm because of all the long wire runs. Homes use big panels and long wires.

As mentioned above someone had a small roof area so they wanted all the bang they could get so they went mppt. If you have very limited space and can wire two panels in series to run about 40 plus volts that may be a better way to go. It will be more pricey for the given watts but they have no choice with limited roof area. Again, if those same two panels are wired in parallel he would probably get pwm performance. mppt wants to see high voltage and convert it to higher amps.

So it's not a urinating contest or you are being cheap or other bs, it's more about what will work for you and your needs. Mppt probably shines best in larger systems.

Have you done an energy audit?

Will your system grow as you realize how well solar works?


How much battery room do you have?

Do you have another EFFECTIVE source to charge the batteries if you have several bad solar days? What model converter do you have?

Will you invert heavy loads such as toaster, microwave, hair dryer etc?

Do you have a generator.

Will you consider running a generator along with your solar sytem?

NO, you are not a failure or cheap and your solar system is not a failure if you do supplemental generator charging. It's all just part of your choices in your energy management program. It's not one size fits all with many rv issues.




If I'm explaining any of this wrong others please help out.

The way I see it the main resen for not using PWM is cheaper panels cheaper wire but more ekspensiv controller, and if partial shade less pover and bypass diodes also robs pover. We have Bogarts PWM 30 A controller with temp censer and 600Watt of panels 2 6v 260A batteries wery happy. Considering adding 2 more batteries for microwave and partial air conditioning.
Frank.