Epicycler avatar image
Epicycler asked

Max Panel Voltage for MPPT

MPPT regulators have voltage and current limits. eg 100/30 is panel volts 100V, battery amps 30A.

The mppt algorithm controls the panel volts. Does the algorithm stop at 100V or can it look above 100V for the max power point and thus potentially overload and kill the circuit. Put another way, is there software protection at 100V in the mppt algorithm.

I ask because at present there is a tendancy to leave some freeboard between panel open circuit volts and regulator specification. Panels which have 100V open circuit volts would never expect to provide max power at 100V, always somewhat less. If connected while dark the regulator is never exposed to the panel open circuit 100V.

I realise there may be circuit constraints beyond the simple concept.

Not looking for a recommendation, just an explanation.

MPPT Controllers
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3 Answers
JohnC avatar image
JohnC answered ·

Hi Epi. The 100/ is a hardware limit. There *may* be protection from exceeding it on some models? But Victron specifically warn against it, as do all cc makers. It can be expected to damage the unit.

I think you're suggesting that this may never be reached in practice, but there's several ways this might occur:

* Disconnect or failure of the batts or wiring. Panel Voc goes to max.

* Li batt bms halts charging. Panel Voc goes to max.

* Batt charge tapers when almost full. Panel approaches Voc. Etc..

Panel Voc is specced at a standard temp (maybe 20 or 25C). Apply the temp coefficient for freezing weather and you'll soon see why 'freeboard' is recommended and applied.

Victron's mppt range is quite massive: Good reason for them all to exist, like 48V batts and larger panel arrays.

But the question you ask is valid. Sometimes we all need a little protection from our stuffups, well I do! :) Nor am I particularly famous for following 'rulez'. In this case, I comply unreservedly.

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Epicycler avatar image
Epicycler answered ·

thanks .... I wonder if anyone knows?

I have used mppt 100/30 for several years with panels fixed on RV roof with fixed wiring to mppt and battery.

I'm in process of adding a couple of portable panels which obviously at some stage will be connected to the additional regulator while the sun is shining.

I don't expect to be anywhere near the regulator spec - more headroom than with my fixed install.

But it has caused me to wonder about the fixed install. I shaded those during original install.

So, is the answer "yes" or "no".

1 comment
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Pat Davitt avatar image Pat Davitt commented ·

The reason their is no hard answer is that you are looking at the Possible versus the Probable. If your panels Voc is near 100V and your controller is rated for 100V; then, if the panels got cold enough, it is possible to over voltage the controller. Worst case is about 20%.

Is it probable? A lot depends on the climate where you live. If your winters are very cold and sunny, then probably. If you are in a more temperate climate, probably not.

Hope that helps,


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Epicycler avatar image
Epicycler answered ·


its a simple question about the mppt algorithm not a question about the operation of the panel.

Does the mppt algorithm limit its search range to <= 100V?

I understand the panel voltage the circuit sees may not be what we measure and the panel may behave beyond normally accepted limits. My panels have operated in a variety of conditions in 34 countries.

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