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chasen avatar image
chasen asked

Oversizing a PV Array (within max Voc and Isc) can do any damage to MPPT ?

Hello there,

I currently am using a BlueSolar MPPT 100/30 while my defect 150/60 is getting replaced.
At first I only connected 2 of my 4 BenQ 330W modules in parallel, but they are not getting the job done on cloudy days...
I am now considering connecting them all 4 in parallel. The modules' specified Voc is 64.9V, the Isc is 6.52A, getting in total about 27A, well below the 35A limit for max Isc...

With the colombian sun at midday, I sometimes got more than 1600W from my 4 x 330W modules, nearly doubling the nominal PV power specified for my 24V system with the MPPT 100/30.

Could this oversizing cause damage to the MPPT, although inside the permitted range of Voc and Isc? Could there be shortening of the lifetime of the device because of "abuse"? Will it get very hot?

Any clarification very appreciated, thanks in advance and greetings from Medellin.

oversizing mppt charge controller
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3 Answers
wkirby avatar image
wkirby answered ·

If you stay within Voc then you shouldn't damage the controller with an oversized array.
The controller will go to Max 30A and that will the be the maximum.

All you need to take care of is cooling. If you are hammering the controller at maximum power for many hours then it will probably get hot. You might even need to force cool it on sunny days until you get your 60A controller back.

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

To add to Warwick; see here:

https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/


It has a chapter about this. No; no damage. When too hot; the controller will derate itself.


Ofcourse, more cooling is always better.

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

And see the similar posts:

https://community.victronenergy.com/topics/oversizing+mppt+charge+controller.html

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chasen avatar image chasen commented ·

Hello WKirby, thanks for your reply!
The controller is in a completely shady, cool place around 20°C, attached to a massive wooden board.
You think the temperature could rise to critical levels?
Would it be enough cooling to attach it to some big metal sheet?

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thanar avatar image thanar commented ·

Hi; why is there a maximum Isc on the spec sheet then?

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ thanar commented ·

Hi @thanar,

The maximum Isc (input short circuit current on the PV panels) is a limitation of the reverse polarity protection within the MPPT for the PV array.

If you connect a PV array in reverse polarity that is below the short circuit current limit, then the MPPT has a protection circuit that will allow you disconnect the PV array, reconnect it and have the MPPT continue to operate without any damage.

If you exceed the PV array input current limit AND connect the PV array in REVERSE POLARITY, then there is likelihood of damage to the MPPT, and this damage in not a manufacturing fault and will not be covered by warranty.

Connecting a PV array in correct polarity that exceeds the PV input current limit is possible, and in some cases desirable, but comes with potential risks of damage to equipment if incorrectly installed, or later modified or adjusted by someone who is not aware of the situation.

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thanar avatar image thanar Guy Stewart (Victron Community Manager) ♦♦ commented ·

Thank you. Really appreciate the answer. We were arguing over this on the DIY Powerwalls facebook group.

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holdmyhand avatar image holdmyhand Guy Stewart (Victron Community Manager) ♦♦ commented ·

Hi, @Guy Stewart (Victron Community Manager)

I just wanted to ask a couple more questions about this point, as it confuses me in relation to other Victron statements.

I'm using a Smartsolar MPPT charge controller, and I would like to oversize my array, as I have a large surplus of solar panels available.

Obviously, you must stay within the maximum VOC limits so as to not damage the device. But can you confirm that it is harmless and perfectly OK to oversize the array and exceed the maximum short circuit current limit as long as the polarity is correct?

In other words, the ONLY risk or problem with this configuration would be the potential of damage in the case of reverse polarity connection?


I apologize if my question seems pedantic or tiresome, but I've been reading about this issue for awhile now, and the Victron product manuals, several of their system design blogs such as https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/ , and other resources state repeatedly that exceeding the short circuit current limit will damage the device (although there are footnotes which seem to indirectly imply that perhaps it might be okay as long as the correct polarity is ensured)

It would be extremely useful in my application to be able to take advantage of this undocumented feature.


Also, can you clarify whether it is safe to exceed the maximum short circuit current limit when a low array voltage configuration would push the input current high enough to violate the specification? I know this would be an uncommon scenario, but for example a 60-Voc array charging a 48v battery would be within the voltage specifications to operate the device, but it would exceed the Isc limit with enough panel strings placed in parallel.

My Victron dealer seemed unequipped to answer these questions and suggested that any talk about current limits was just a mistake in the manuals, and that only Voc mattered. (as many times as the Isc limit is mentioned in Victron documentation, it seemed unlikely to me to be included as a simple error)

Thank you very much for your consideration.

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Leslieanne avatar image Leslieanne holdmyhand commented ·
There is one other case. Have a look at the mppt error codes, 38 and 39. If the output voltage from the mppt spikes too high for whatever reason (misconfiguration, other charge sources, sudden disconnection of battery etc) then the mppt will short the panels for protection. If the input current at that moment is above specs it might then be damaged.
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filterguy avatar image filterguy Leslieanne commented ·

I looked up the codes and could not find an Err 39. could you provide a link?

This is what I found

----------------------------------------------------------------------------------------

Err 34 - PV over-current

The current from the solar-panel array has exceeded 75A. This error could be generated due to an internal system fault. Disconnect the charger from all power-sources, wait 3 minutes, and power-up again. If the error persists the controller is probably faulty. This error will auto-reset.

Err 38 - Input shutdown due to battery over-voltage

To protect the battery from over-charging the panel input is shut down. To recover from this condition first disconnect the solar panels and disconnect the battery. Wait for 3 minutes reconnect the battery first and next the panels.

A common reason for this error to occur is that the Battery voltage (12/24/48V) is set, or auto-detected, incorrectly.

Use VictronConnect to disable auto-detect and set the BatteryVoltage to a fixed voltage.

If the error persists the charge controller is probably faulty.

-----------------------------------------------------------------------------------------

It does not say anything about shorting the inputs. It says shutting down the inputs... to me, this means turning the input off and allowing no current.

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Leslieanne avatar image Leslieanne filterguy commented ·

Hi, link below. I often have some difficulty navigating my way through Victron's voluminous (and sometimes contradictory documentation, presumably because it regularly gets updated....). Easiest way to find things in the mix is to do a Google search!!!

https://www.victronenergy.com/live/mppt-error-codes

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ holdmyhand commented ·

Hi @HoldMyHand,

The statement I made above is as definitive as you will get officially from Victron, or any of the dealers.

It is also possible to damage the unit by exceeding the current limit in some circumstances even when correctly connected, but that is only likely to occur when well above the listed limit. The exact specification when that would occur is going to vary between different models of MPPT, conditions when the short circuit current event occurs, and other factors, so it is not published and should not be assumed.

Even if someone else has done it and reports that it's all working fine, your experience might be different.

The purpose of the specifications is to give certainty and a warranty backed guarantee to specific performance. It will have tolerances that can be pushed, but pushing them is not backed by us as a manufacturer.

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chasen avatar image
chasen answered ·

Hello mvader, thanks for the reply, I already had seen the blog entry and the entries in the topic but it didn´t seem clear to me if there can be damage. A local dealer warned me that there is a risk of damage (at least at longterm).

One more stupid question: The charger will heat up because of working at the limit, but the oversized PV generation will rather result in a "normal" heating of the modules (same as when the battery is already full), as they can not deliver the power, right?

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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ commented ·

Yes indeed; so; nothing to worry about. We dont; otherwise we would not advice this ;-).


Imagine a standard AC Battery Charger, connected to the utility: it doesnt blow up because there is a MegaWatt Power Station either. Its note a straight comparison; but still I like the analogy.



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chasen avatar image chasen mvader (Victron Energy) ♦♦ commented ·

Thank you mvader, thanks also to Warwick and Markus!
So I will connect the 4 modules in parallel on Friday with a good feeling, at least for the one month that I will be travelling and until I return with my new MPPT 150/60...

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Michael Connolly avatar image Michael Connolly chasen commented ·

Also why not add a fan to the output side and point it back at the controller. That way it will blow air in when the power is present!!

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markus avatar image markus ♦♦ commented ·

your modules don't get hot because they can't deliver their power. Equally like your AC wall plugs don't get hot, because they can't deliver their power to a small load ;o)

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chasen avatar image chasen markus ♦♦ commented ·

I rather mean, they don´t stay cooler than another black surface, which happens while delivering part of the radiation energy as electrical energy...
The discussion with my local dealer was, that the oversized power of the modules will be transformed to heat in the charger, which I think is not the case...

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markus avatar image markus ♦♦ chasen commented ·

Do they really get cooler? I don't know. But I don't think the photoelectric process will absorb heat.

But You are right, a MPPT charger will not get hotter, because of the connected modules. It get's hotter because of the load.

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chasen avatar image chasen markus ♦♦ commented ·

As I understand it, they dont get cooler, they just dont heat up as much as another surface of the same color as long as the electric energy flows. It is quite logical considering the energy conservation principle.

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filterguy avatar image
filterguy answered ·

There is a lot of debate on what limits the max Isc spec implies. The above statement from Guy Stewart is probably the most definitive statement I have found, but it would be good if it were more explicit about "but comes with potential risks of damage to equipment if incorrectly installed, or later modified or adjusted by someone who is not aware of the situation" Is this referring back to the comment about damage due to reverse polarity?

The ideal situation would be for Victron to update the manual to be more specific on what limits the Isc spec create.

Here are a few things to point out:

1) If the Voc is kept high, most system designs (including over-panel designs) would not violate the Isc spec.

2) If the Voc is low, it is possible to have non-over-panel designs that would violate the Isc, but otherwise meets all of the controller specs.

3) The Victron web site has an “MPPT Calculator” It is possible to put in configurations that would violate the Max Isc spec but the calculator says is OK.

4) In the manual it says:

"PV reverse current too high - Overcurrent does not necessarily damage the solar charger, but it will cause damage if the array produces too much current while, at the same time, the array has been connected in reverse polarity to the solar charger. Damage due to overcurrent is not covered under warranty. Refer to the solar chargers technical specifications for the maximum PV short circuit power current rating.“

6) At least some Victron distributors say you don’t have to worry about Isc, others say you do have to worry about it.

My current working assumption is that the Isc spec only comes into play during a reverse polarity situation.
You need to make your own assumption.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·

1) It should be assumed that at some point in the systems life it will experience a PV short circuit, maximum current event. The system should be designed so that event does not damage any equipment.


2) Indeed, and this is why I make the information above available. NOT so that people push their controllers with 200%+ short circuit current limit panel designs, but so that someone who has a system that is just over that short circuit current limit in some circumstances understands that it may be possible without immediately destroying their MPPT. Also to draw the comparison between the 'soft' short circuit current limitation, and the 'VERY STRICT' PV open circuit voltage limit (which will result in immediate destruction).

3) I will pass along a note to that calculator developer to see if that advice can be clarified to be in line with the other statements. Thanks.

6) Victron gives a lot a lot of independence to the distributors, they are the ones that will ultimately have to resolve the issues of their customers, so take the risks as to the system designs that they endorse. Some choose to be very conservative and strictly conformal to the published specifications, and their customers may require that. Others may prefer to know how far they can push their equipment, and use their own experience as a guide. Both can be successful strategies for the dealer and their customers.

Your assumption a useful guide, but it is not the complete picture, and the complete picture is not specified by Victron beyond the published spec.

It remains a somewhat ambiguous situation, because beyond the published spec which is clear and safe in all circumstances, deviation from that may or may not be depending on the individual situation with many variables.

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filterguy avatar image filterguy Guy Stewart (Victron Community Manager) ♦♦ commented ·

Guy,

Thank you for responding.

"1) It should be assumed that at some point in the systems life it will experience a PV short circuit, maximum current event. The system should be designed so that event does not damage any equipment. "

Are you confirming that there is circuitry in the Victron MPPT controllers that will short circuit the PV input under certain unspecified conditions?

If so, it would be good to understand any of these conditions so they can be avoided even if the Isc is not over the controller's spec.

It would also be nice to understand some of the engineering reasons for creating the short circuit. Is it a deliberate action to protect the controller or is it an unfortunate side effect of other aspects of the design?

If the Isc spec has implications beyond the reverse polarity situation, I highly recommend that this statement in the manual be updated.

"PV reverse current too high - Overcurrent does not necessarily damage the solar 
charger, but it will cause damage if the array produces too much current while, at the same time, the array has been connected in reverse polarity to the solar 
charger. Damage due to overcurrent is not covered under warranty. Refer to the 
solar chargers technical specifications for the maximum PV short circuit power current rating.“

If there is more to the Isc specification than the reverse polarity situation, the above statement is very misleading. Some people may be willing to accept the risk if they believe it is only an issue if they screw up and hook up the PV backward. However, if there are problems with Isc that can happen when the controller is properly connected, they may decide not to risk it.

In addition, the manual says:

4.3. PV array
The solar charger can be used with a PV configuration that satisfies both these two conditions:
• The maximum open circuit PV voltage can not exceed 150 or 250V, depending on the solar charger model.
• The nominal PV voltage should be at least 5V higher than the battery voltage.
The PV array can consist of mono- or poly-crystalline panels.

If there are additional conditions the PV array must satisfy, the above statement needs to reflect it.

The only reference I can find in any Victron documentation that implies there is more to the Isc spec is the document that defines error codes. Many people do not even know this document exists, let alone read it. (I did not know it existed till a forum member discussed it and I have been using Victron controllers for years.).

Note: When I went searching for the error codes, I found this on a distributers site...you may want to have them update it.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ filterguy commented ·

Hi @Filterguy,

"Are you confirming that there is circuitry in the Victron MPPT controllers that will short circuit the PV input under certain unspecified conditions?"

Yes, there are unspecified conditions that the MPPT controller will short circuit the PV array. This is not normally an issue in itself.

I do not know all the conditions that this would occur, and any speculation would be incomplete, so I wouldn't give guidance on how it could be avoided, instead it should be assumed that it will happen.

I think the statement from the manual is valid. Any attempt to expand upon it would provide additional assurances where Victron does not want to make any.

Indeed, anyone who is going beyond the specified limits is taking on the risk and responsibility of that. The clearest, and most likely risk is that of the reverse polarity connection - however that is not the only one. Anyone who is looking to design outside of the specification must accept that they are doing so in undocumented and uncertain conditions, where the many variables that are unknowable that then come into play may compromise their design.

The safe route is to follow the published specifications.

Forgive me for a crude analogy. If the published top speed of a car is 150 km/h, you are asking me what is likely to fail if that top speed is exceeded. We cannot know, could be the tires, the transmission, the suspension, or the aerodynamics and the wind that day. The car will go over 150 km/h if you push it - but how far, for how long, and what happens when the REAL limit is discovered is not always possible to foresee.

So the product is tested, and components maintained to the companies satisfaction that every FET, resistor, terminal connection, and microcontroller it will perform for a minimum of 5 years within those published specs. Beyond those specifications, we do not know and can not say.

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filterguy avatar image filterguy Guy Stewart (Victron Community Manager) ♦♦ commented ·

Thank you for the information.

I think the statement from the manual is valid. Any attempt to expand upon it would provide additional assurances where Victron does not want to make any.

I am not suggesting Victron make additional assurances. I am suggesting the manual be more explicit about not violating the Isc spec. The wording in the manual implies the reverse polarity is the only potential issue but you have helped me understand that there is more than that.

The same goes for the second part of the manual I referenced.

4.3. PV array
The solar charger can be used with a PV configuration that satisfies both these two conditions:

  
                       
    
                        
  • The maximum open circuit PV voltage can not exceed 150 or 250V, depending on the solar charger model.
    • 
                        
  • The nominal PV voltage should be at least 5V higher than the battery voltage.
    • 
                       
The PV array can consist of mono- or poly-crystalline panels.

If I build a system based on these instructions, I could end up with a configuration that does not meet spec. Consequently, there should be another bullet about not violating Isc.

Unless someone happens to find threads like this one on the community site or happens to read about Err38/Err39 in the obscure error code document, they would never understand the importance of the Isc spec. I have worked with Victron MPPT controllers for years and never stumbled across this information. Luckily, I don't think any of my designs violated the spec..... but I have to check them to make sure....particularly since it is possible to violate the spec without over-paneling, even when using the Victron on-line MPPT calculator


Now for a related question:
If the Array meets the following three requirements, are there any additional limits to the wattage of the array?

1) The maximum open-circuit PV voltage (Adjusted for cold temperatures) does not exceed the specification listed for the solar charger model.

2) The maximum short-circuit PV current is less than the specification listed for the solar charger model.

3) The nominal PV voltage is at least 5V higher than the battery voltage.

Thanks



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cristianc avatar image cristianc filterguy commented ·
Dear FilterGuy, This is one of the most interesting topic i have read lately, and i appreciate you trying to find a definitive answer to this question. I just want to ask you or anybody a related question. Lets say i configure a PV array with several parallel string, well above the Isc of the controller. Each string is fused of course, being over 2 paralel strings. Then i combine all parallel string using suitables cables that are 156%Isc rated. Now i have two cables that i can connect to the MPPT. What if i put a fuse rated for the max Isc of the MPPT (or slightly below) between the PV array and the MPPT? Then wouldnt i be ok for all the niche scenarios of when the MPPT can short its PV input? Thank You and forgive my english as i am not a native speaker.
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wkirby avatar image wkirby ♦♦ cristianc commented ·
This is not a good idea.

The fuse would very likey not open up until long after the damage is done.
Remember, a fuse cannot predict future short circuit scenarios, it can only respond to existing ones.
Better to stay within the published limits.

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