mppt vs pwm

mena...!

that wasn't 17ampHrs for the day total
not 17amps charge rate

the remarkable part is he did it with 280w of solar
i've done it but i have 505w of solar

like he said, the LiFePo have a very slow voltage rise
which maintains the the voltage spread and gives the mppt something to work with

17A while it's raining? Wow!

jrnymn7 wrote:
I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

Sorry. Maybe I should have used a ;) instead of a :). It was just a little reference to the fact that every time the MPPT/PWM discussion comes up it gets stated that watts don't really matter; It's amps into the battery that count.

jrnymn7 wrote:
I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

That might be my fault. I hate Watts. I only like amps and amp hours. They are honest. Watts are sneaky mixtures of variables that can be presented to prove anything. A salesman's friend! :)

Shading
All panels parallel...output will be reduced only by the amount of the reduction of the panels that are shaded, this may or may not be the full output of these panels, depending on amount of shade etc...

Series is can of worms, two panels 17v at 4 amps in series produce 34v at 4 amps
The number of internal by pass diodes now play a major part in what happens
Panels with good by pass well drop output, from shade but still pass thru the amps from the sunny panel, do you might get 25v at 4 amps

Panels with poor low number of bypass diodes, might shut down most of the way and block the current, because there is no place for the amps from the sunny panel to pass thru aka around the shaded cells
Putting 3 or more panels in series requires no shading, or really good panel bypass diodes configuration

Series parallel attempts to give you the higher voltage and MPPT gains, yet limits the series to Paris of panels and puts the PAIRS in parallel so shading a panel doesn't kill the all the output
Shading one panel in one pair only reduces the output of one pair, not all the panels

Wait until people start getting attached to their LiFePo batteries!

I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

Thanks, PT.

Hi,

Here is a direct link to the page that 12thgenius is suggesting:

mppt vs pwm

It shows an average benefit from MPPT of about 18% over a seven day test. None of the test days were even close to perfect. However, they were also not hot days which may favor the MPPT side of the test.

KJINTF wrote:
Agreed a fair fight is difficult to setup

The fight becomes a completely different game with LFP batteries
The guy over at http://www.marinehowto.com/ did a PWM Vs MPPT test
Results a clear 20% gain from MPPT
Suggested reading material

For those of you that haven't looked at this here is a clicky. Click "tree view" then scroll down to the one titled MPPT vs PWM Controllers.

He uses identical panels tested simultaneously with different controllers. It was fairly lousy weather in May in Maine.

He also has some interesting comments about cheap (Chinese) controllers.

Here's a copy of the test results. For those of you who are "watts averse", notice that the results are in amps.:)