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Old 22-01-2014, 03:55   #16
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Lots of confusion here.


Firstly a pwm regulator can never extract maximum power from any panel UNLESS the Vmp operating point of the panel at the given operating current happens to be close to the battery voltage at that time

Vmp is not significantly affected by illumination levels. It moves but not that much. Hence shading or low illumination or changing illumination is not a justification for or against mppt.

The regulation system used by mppt is not pwm its simply ( in almost all cases ) smoothed DC derived from a pwm switcher.

A pwm regulator as understood in solar regulators is really not the same at all compared to pwm used in switchers

Mppt even cheap mppt is always better then Pwm solar regulators once Vmp is more then 10-15% away from operating voltage point.

You can easily verify mppt operation with a simple multimeter.

In small panels the gain may not justify high cost mppt ( or course you could use low cost mppt )


There's no inherent reason mppt should be premium priced

Dave
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Old 22-01-2014, 04:16   #17
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Re: Quality of MPPT? How good/bad are the cheap ones

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Originally Posted by goboatingnow View Post
Vmp is not significantly affected by illumination levels. It moves but not that much. Hence shading or low illumination or changing illumination is not a justification for or against mppt.
Overall illumination does not move Vmp much, but minor shadows have a significant effect. The Vmp alters rapidly in most situations on a yacht. In addition the Vmp of multiple panels on yacht is often significant different due to variable shadowing. Cheap (and sometimes even expensive) controllers can lock on to one of the false humps in the net Vmp curve.

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Mppt even cheap mppt is always better then Pwm solar regulators once Vmp is more then 10-15% away from operating voltage point.
This assumes the Vmp is correctly tracked (and the self consumption is not greater than this gain).

If you are going to get a MPPT controller get a good one.
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Old 22-01-2014, 04:28   #18
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....Cheap (and sometimes even expensive) controllers can lock on to one of the false humps in the net Vmp curve.

This assumes the Vmp is correctly tracked (and the self consumption is not greater than this gain).

If you are going to get a MPPT controller get a good one.

Since we have little comparison data on Vmp tracking I would agree buy a " good one" however that's not the same as an expensive one.

I am always suspicious in electronics of retail cost as a metric of either quality or performance.

What's needed is a good set of tests on a series of mppt controllers. I have two chineese oem modules , both do quite good mppt tracking

There are a number of Integrated circuit solutions for mppt now, so we might see a convergence of approaches

False Vmp issues are easy enough to deal with, a good mppt always does a range scan rather then just looking for the next adjacent Vmp bump.

If you plot shading versus Vmp you will see that tracking the mppt point isn't that difficult.

Furthermore this tracking of more complex Vmp actually makes mppt more advantageous over pwm

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Old 22-01-2014, 04:44   #19
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Re: Quality of MPPT? How good/bad are the cheap ones

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What's needed is a good set of tests on a series of mppt controllers. I have two chineese oem modules , both do quite good mppt tracking
There is an example of a test here:
Another Newby : General Talk

It shows the non MPPT regulator (the PL 20) doing significantly better than the cheap MPPT.
This is not typical, but the gain from even a very good MPPT controller is only very modest, leading little margin from even brief periods of poor tracking which is seen in the cheaper regulators.
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Old 22-01-2014, 04:50   #20
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Re: Quality of MPPT? How good/bad are the cheap ones

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There is an example of a test here:
Another Newby : General Talk

It shows the non MPPT regulator (the PL 20) doing significantly better than the cheap MPPT.
This is not typical, but the gain from good MPPT controllers is only very modest, leading little margin from even brief periods of poor tracking.

But we have no idea in those test of where the VMP point was and even if the panel was capable of operating at Vmp. simple current comparison s in themselves are not really an indication of anything.

for example , you could have the system operating outside the Vmp point ( because the load cannot use the power) resulting in a larger quiescent power draw on the mppt type over PWM.

What I was saying is that at with a disparity between Vmp and Vop ( panel output voltage) mppts will always be capable of extracting more power, if the load can use it.


They are almost universal now in things like parking meters etc. ( which is where the OEM modules I have are designed for ) .


As a general comment, I would suggest users look at OEM mppt modules on a per panel basis , then one big overall Mppt on a system basis. better Vmp tracking, better panel matching, redundancy.

Of course this doesn't match some peoples "take it out of a box and use it"

dave
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Old 22-01-2014, 07:45   #21
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Re: Quality of MPPT? How good/bad are the cheap ones

[QUOTE=Nicholson58;1446736]For what its worth, Solar Bob was not keen on Blue Sky. Per his recommendations, We bought The Morningstar-TS-MPPT-45. Part of the decision was based on the high open circuit voltage of our panels 54 - VDC & 660 watts. Our batteries are 24 volts.QUOTE]

Could anybody help me to find "Solar Bob's" comments on Blue Sky? Or summarize what he didn't like about Blue Sky products? I was about to commit to a Blue Sky MPPT controller.
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Old 22-01-2014, 07:49   #22
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Re: Quality of MPPT? How good/bad are the cheap ones

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Could anybody help me to find "Solar Bob's" comments on Blue Sky? Or summarize what he didn't like about Blue Sky products? I was about to commit to a Blue Sky MPPT controller.
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Old 22-01-2014, 08:09   #23
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Re: Quality of MPPT? How good/bad are the cheap ones

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As a general comment, I would suggest users look at OEM mppt modules on a per panel basis , then one big overall Mppt on a system basis. better Vmp tracking, better panel matching, redundancy.
If each panel has its own controller, what is the point/purpose of the extra controller for the overall system? Each panel is already putting the maximum current into the batteries.

Unless you mean the individual controllers do nothing but track MPPT and do not do any voltage regulation, and the system controller is a more normal voltage regulation type.

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