MPPT input voltage comparison

[BruceS]

Such a very well explained example or examples MUST be applauded!!
Top stuff Leslie!

To answer William...
The panels I bought exceeded the VOC allowed on my 48V 4000w Chinese PWM combo unit but fell in the allowed VOC for a similar rated one that was an MPPT one.

[native pepper]

Terry, wouldn't that chart be a lead acid test, which has very different charging parameters, voltage inputs and ability to take charge, compared to lifepo4 at high amperage inputs, as voltage rises in the cells. Is there a comparison chart with the same test conditions, which shows PWM will continue it's highest input voltages, as the battery voltages rise. Especially when the internal resistance when charging lifepo4 compared to lead acid, could be a major factor in lose of voltage.

Would like to see the same tests using lifepo4 storage, mppt and pwm comparisons. As said earlier, MPPT seem great for shady and cloudy conditions, PWM clear skies to maintain charge input voltages. Over a cloudy day, using the LA and lifepo4, would both mppt and pwm provide the same voltage inputs over the entire charge period and SOC. After all, bench tests never can replicate on site testing, in any way and are mostly designed to sell the product, as we are seeing with other industries.

Just read your post Leslie, excellent description that makes sense. Decided to not edit my post as didn't look like you addressed my questions, if they are still relevant.

[bagmaker]

GREAT post Firegirl Leslie, thanks so much, I have slapped my forehead for not noticing that its not comparing PWM with MPPT!!
Bruce can you change the thread header to MPPT input voltage comparison or something?

Ok some more trialling today but not much fascinating stuff. Poor, drizzly/rainy/overcast day, 20 odd degrees.
The results are all from charging at under 10 amps from either string all day it was that poor. Not sure if this sort of data is so reliable.

per Steves request I tried shading some panels and comparing outputs.
i have a heap of figure jottings over the day with a panel shaded, partly shaded, bulk input or floating input.
BASICALLY though, the higher voltage series string curcuit won out in all styles of test except when all panels unshaded (per original issue) by a 10 or 15%.

[T1 Terry]

A great post Leslie, very well explained. I understand they were just random examples, just from my testing on different types of panels, the voltage that panel makes its max amps deceases as it heats up but the amps don't decrease very much unless they suffer serious shading from a heavy cloud. Very light scattered cloud actually increases the amps output cause by reflection increasing the amount of "sun" the panel sees.

Native Pepper, if you are referring to the charts for the Morningstar MPPT controller, I doubt they used a battery at all and I doubt they used a solar panel either, they would have wanted to control an exact input current and voltage and maintain the 12.8v output so the load would have been varied to maintain that voltage. No doubt 12.8v was an optimal figure that gave the best results, I think most of us understand that no battery will stay at the same voltage while being charged. Lithium will hold a much steadier voltage between deeply discharged and close to fully charged, but this can still vary by more than 1v for a 12v battery although far less influenced by the rate of charge compared to lead acid batteries.
A tad too aggressive with the charging current can see a lead acid battery near fully discharged at under 11v suddenly rise to 14.8v without the state of charge having improved much at all, so using the theoretical 10v as the MPPT camp often do is extremely misleading. High current charging a small capacity lead acid battery can often lead to serious under charging because the controller drops back to float voltage too soon resulting in sulphation and that then makes the problem even worse.
I doubt any manufacturer will make a better solar lead acid battery charge controller that pulse charges rather than the constant current then constant voltage regime as most accept that lead acid batteries are gradually being replaced by lithium batteries, so research $$ (hopefully) is being directed towards the lithium chemistries. The major problem there is a lack of understanding just what each different lithium chemistry requires and that also depends on the use pattern.

T1 Terry

[native pepper]

Native Pepper, if you are referring to the charts for the Morningstar MPPT controller, I doubt they used a battery at all and I doubt they used a solar panel either, they would have wanted to control an exact input current and voltage and maintain the 12.8v output so the load would have been varied to maintain that voltage. No doubt 12.8v was an optimal figure that gave the best results, I think most of us understand that no battery will stay at the same voltage while being charged.

T1 Terry

Then the morningstar charts are worthless as evidence for charge realities for real life situations, which is understandable and aren't related to lifepo4 in any way. It would be nice to some real charts of different charge controllers in different weather situations, for both lifepo4 an lead acid, using mppt as apposed to pwm. But until then, it is all conjecture and personal preference.

Now the thread has been well explained by Leslie, my mppt controllers on the house pack, all show different current/voltage input during the day at times and it is rare for them to be the same for more than a few seconds. You can watch the shade go over by how the inputs change.

[T1 Terry]

As far as the current changing constantly when it's a bit cloudy, you should see the Victron BMV carry on when the sun/clouds play havoc with the panel output using the PWM SSR control, there is no processor delay, the reading change is close enough to instantaneous.

T1 Terry