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Old 03-24-2016, 02:47 PM   #31
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Originally Posted by Mustang65 View Post
PWM vs MPPT. Here is a video that helps show the difference. It is a 40 watt panel, but even at only 40 watts you see the benefits... now add another 200 watts to the input/output the difference looks even better.
Don
Interesting. Do you know why the input power changes when switching between PWM and MPPT?
The panel output should be the panel output no matter what is hooked downstream of it shouldn't it? Or do you think of the panel like a battery and the PWM controller is putting a larger draw on it thereby reducing the voltage?

That test certainly shows in MPPT's favor by 20-30% under those conditions. (Stressed battery)

Found this too....
http://www.schams-solar.de/download/...n-mppt-pwm.pdf

Shows that MPPT has a big advantage (40%) under shaded conditions. Testing procedures aren't exactly clear though. Showed 8% advantage to MPPT under most other conditions.
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Old 03-24-2016, 03:17 PM   #32
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Don, based on my configuration ( 2 100w panels in parrellel. ) would you covert to a MPPT controller?
I would look at it from your current usage/charging performance. If the PWM is meeting all your current needs, I would see no reason for upgrading to an MPPT controller. If you do a lot of dry-camping in the early spring or late summer fall (angle of sun), then it would help you. If you plan on adding more loads and longer dry-camping outings I would say go for it. If you do decide to upgrade to MPPT, temporarily wire them both in and switch between them at first to see what the actual benefits are. Then you can give us the actual numbers.

Oh, you asked if I would convert... I would probably say yes because I would pick up the 25% of loss from each panel.
Don
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Old 03-24-2016, 03:32 PM   #33
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Interesting. Do you know why the input power changes when switching between PWM and MPPT?
The panel output should be the panel output no matter what is hooked downstream of it shouldn't it? Or do you think of the panel like a battery and the PWM controller is putting a larger draw on it thereby reducing the voltage?
I would lean more to the internal resistance of the PWM and the MPPT controllers on the input side that is altering the panel output.

I have been monitoring my 250 watt panel output and granted there will be some loss due to panel temperature, but by the time the panels heat up the batteries are already in FLOAT mode, so there is no effect on the charging.

It will be interesting this summer (when we spend the summer in Hiawassee GA) as I am going to connect the Arduino to both the panel output and the MPPT output to monitor the voltages, amps, panel temp along with the suns power (insolation) in real time. Should have some interesting output to report back on.

Don
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Old 03-24-2016, 04:12 PM   #34
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Just found this after posting my question above. I have never read it explained like this before but it would explain the input power diferential and the 20-30% power boost seen when the batteries are discharged a fair amount.

MPPT vs PWM Charge Controllers
MPPT (Maximum Power Point Tracking) charge controllers are designed to harvest the maximum amount of power from the solar array. It is generally accepted that even the most basic MPPT controllers will provide an additional 10‐15% of charging capability compared to a standard PWM regulator. In addition this efficiency, there are several other important differences and advantages between PWM & MPPT technologies.pwm controller

PWM Charging

Traditional solar regulators featuring PWM (Pulse Width Modulation) charging operate by making a connection directly from the solar array to the battery bank. During bulk charging when there is a continuous connection from the array to the battery bank, the array output voltage is ‘pulled down’ to the battery voltage. The battery voltage adjusts slightly up depending on the amount of current provided by the array and the size and characteristics of the battery.

The Vmp (maximum power voltage) is the voltage where the product of the output current and output voltage (amps * volts) is greatest and output power (watts = amps * volts) is maximized. Module wattage ratings (e.g. 100W, 205W) are based on Pmp (maximum power) at Vmp under standard test conditions (STC). Using a nominal 12V system as an example, the battery voltage will normally be somewhere between 10 – 15 VDC. However, 12V nominal solar modules commonly have a Vmp(STC) of about 17V. When the array (having Vmp of 17V) is connected to the batteries for charging, the batteries pull down the output voltage of the array. Thus, the array is not operating at its most efficient voltage of 17V, but rather at somewhere between 10 and 15V.

Because these traditional controllers rarely operate at the Vmp of the solar array, potential energy is being wasted that could otherwise be used to better charge the battery bank and maintain power for system loads. The greater the difference between battery voltage and the Vmp of the array, the more energy is wasted by a PWM controller during bulk charging.

MPPT Charging

MPPT controllers are designed to quickly and accurately determine the Vmp (maximum power voltage) of the solar array. MPPT controllers ‘sweep’ the solar input to determine the voltage at which the array is producing
the maximum amount of power. The controller harvests power from the array at this Vmp voltage and converts it down to battery voltage, boosting

Copied from here...
MPPT vs PWM Charge Controllers

Good discussion by the way. I have learned something new and understand MPPT a bit better in the process. I still feel the need to give a little love to the lowely PWM controllers though....

Cheers
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Old 03-24-2016, 04:20 PM   #35
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I still feel the need to give a little love to the lowely PWM controllers though....

Cheers
Don't get me wrong.. as I say if the PWM controller is doing what you need it to, then there is nothing wrong with using one. I have always been one to try and extract every bit of power that is made available.. and that is my driving force.

Don
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Old 03-24-2016, 04:41 PM   #36
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And I'm a cheapskate so that is my driving force!

I am not toying with the idea of switching out my PWM controller at all. Just trying to present pro's and con's to other people reading here that are trying to make the decision. My SC-2030 and TM-2030 are paired and do exactly what I need them to do.
In reality this is almost a pointless argument anyway. If I was riding the cusp of getting my batteries charged each day and almost running them down each night then I would certainly gain from the 10-15% boost I would get from MPPT. As is I think I am charged shortly after mid day so any power after that is essentially wasted so I would just be wasting more with MPPT.

Another good read...
Frequently Answered Questions - Bogart Engineering

Click on the MPPT vs PWM question.

Here is another attractive low cost MPPT controller and it is built and designed in USA!
http://www.roguepowertech.com/produc...pt/mpt2024.htm

Looks like it has interesting logging capabilities built in too.


Cheers
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