Will a 150 VOC array work ok on an EG4 CC with 120 minimum MPPT range?

[hwy17]

My friend's old Magnum charge controller burned up on a 4x4x37VOC array (150ish VOC).

Can they use a high voltage charge controller without rewiring their array, or will it dip below minimum MPPT too often?

 

[sunshine_eggo]

My ~150Voc array (3S * 47Voc) performs best at 110-115Vmp

 

[hwy17]

Would you expect a 120v minimum mppt cc would fall out of range and stop operating, or would it operate less than ideally at the 120v minimum?

 

[sunshine_eggo]

Would you expect a 120v minimum mppt cc would fall out of range and stop operating, or would it operate less than ideally at the 120v minimum?

I would assume the worst case unless the distributor/manufacturer guarantees otherwise.

 

[fafrd]

I would assume the worst case unless the distributor/manufacturer guarantees otherwise.

Uhhh, what?

If the MPPT range has a minimum voltage above Vmp of the string, it just means you will be losing some potential production.

String voltage will be higher than Vmp and hence current will be below Vmp (and power will be below maximum power point output).

The OP asked ‘Would you expect a 120v minimum mppt cc would fall out of range and stop operating, or would it operate less than ideally at the 120v minimum?’

The answer is that ‘no, a 120v minimum mppt would not fall out of range and stop operating’ and ‘yes, the mppt would operate less than ideally at the 120V minimum’ (assuming Vmp of the 4S string is below 120V).

How much potential output power will be lost operating above Vmp is tougher to estimate but output power should not in any case be much worse than:

Vmppt_min x Imp x [1 - (Vmppt_min - Vmp) / (Voc - Vmp)]

 

[hwy17]

I think that's worded a bit strongly in disagreement, fafrd. What sunshine said about expectation of functionality isn't totally contradictory with that. But I appreciate the additional additional input on the "it's supposed to work" side of opinion.

 

[sunshine_eggo]

The answer is that ‘no, a 120v minimum mppt would not fall out of range and stop operating’ and ‘yes, the mppt would operate less than ideally at the 120V minimum’ (assuming Vmp of the 4S string is below 120V).

How much potential output power will be lost operating above Vmp is tougher to estimate but output power should not in any case be much worse than:

Vmppt_min x Imp x [1 - (Vmppt_min - Vmp) / (Voc - Vmp)]

Given the model referenced, please cite your source that indicates it will work as you describe.

Oh. No model referenced. Nevermind.

If you're wrong, will you reimburse him?

Or do you think he should ask the distributor/manufacturer?

 

[fafrd]

I think that's worded a bit strongly in disagreement, fafrd. What sunshine said about expectation of functionality isn't totally contradictory with that. But I appreciate the additional additional input on the "it's supposed to work" side of opinion.

I don’t mean to be the least bit confrontational - I’ve never seen anything ever suggesting that a OV array can’t be driven at voltages above Vmp and believe the suggestion that an SCC may stop operating if Vmppt_min is higher than Vmp is incorrect.

If I’ve got that wrong I’ll apologize and correct my post in a heartbeat.

But whenever I see information being posted that I believe it not correct, I believe it is best to hit it between the eyes.

Absolutely nothing personal o te Ted towards sunshine_eggo - we’re all here to understand and to learn (which is most effectively achieved if we make an effort to keep the information being shared as correct as we can).

I’m pretty certain a solar string will operate properly at any voltage between Vmp and Voc (as well as voltages below Vmp), just at decreasing current levels.

A linear current degradation model from Imp to 0A at string voltage increasing above Vmp towards Voc isn’t perfect but puts a reality check on the levels of lost power we are talking about.

If Voc is 37V and a 4S string has a voltage of 148V, I’d guess Vmp is probably somewhere around 31V and 4S string voltage is around 124V.

Vmppt_min of 120V is below that, so no issue at all.

Even if the actual Vmp is higher than 30V and 4S string has Vmp slightly higher than 120V, the Los efficiency will be mini or.

The biggest issue when Vmp-min close to Vmppt_string is that any shading at all will cut output close to 0W (pretty much no ability to activate bypass diodes).

 

[Hedges]

Voc was quoted with panel at 25C. Hot day, panel 45C? 65C? expect 0.2% to 0.4% drop per degree, whatever temperature coefficient data sheet says. Voc drops maybe as low as 138V.

Any shadows, and output drops precipitously. I've tried, rewiring some 24s panels as 16s2p. Worked OK until slightly shadowed.

Data sheets of the inverters I use (Sunny Boy and TriPower) give a "Rated MPPT Voltage Range", 155 to 480V for 3kW model, 270 to 480V for 7.7kW model. But also "MPPT Operating Voltage Range" 100 to 550V, "Minimum DC Voltage/Start Voltage" 100/125V.

That model operates over a wider range than the earlier ones I used. Maximum MPPT current looks like the limiting factor. Minimum rated voltage x current x number of MPPT is just above inverter's wattage rating.

So long as Voc is above MPPT start voltage, I expect an MPPT to being operating and pull as low as minimum MPPT operating voltage to maximize power.

My 30kW TriPower, several times it started then shut off. There was a setting of 1500W minimum to operate, and I had connected a single 2500W string (with less than full light.) Setting 500W minimum it began operating, and continued as the sun set and power dropped below 500W.

 

[fafrd]

Given the model referenced, please cite your source that indicates it will work as you describe.

My simple midel for power output at voltages above Vmp conus from the I-V curves provided for any solar panel. Actually estimating data from the actual curve of the specific panel in question is best, but that simple linear current degradation I modeled provides a realistic estimate of magnitude.

Oh. No model referenced. Nevermind.

If you're wrong, will you reimburse him?

Just to be clear, you are asking me if he connects an SCC with Vmp_min of 120V (but Vmp_max above Voc_worst-case of the string, presumably meaning above ~150V) ) to a string of 4 panels with Vmp above 30V (but well below 150V) whether I will reimburse him the cost of his SCC if it blows up / gets damaged from connecting that string?

Yes I would,

Or do you think he should ask the distributor/manufacturer?

I’d never suggest someone not seek their manufacturers guidelines and recommendations if they have the time for that.

If the manufacturer says anything different than I’ve suggested, I live to hear what they state.

The requirements for Vmp_max and especially maximum input voltage ratings versus Voc_worst-case (coldest possible day) are much more critical guidelines as far as possible damage than anything regarding Vmp_min.

And after that, the next priority as far as avoiding damage is Isc max versus maximum current ratings.

Once you are certain your string cannot damage your SCC, the only other consideration regarding Vmp_min close to Vmp is startup of the array and especially whether it can produce any power despite the presence of shade on some cells / panels.

Of course, if Vmppt_min is way above Vmp (> halfway to Voc), then output current will be significantly reduced and output power with it (but the SCC will still function properly and will not be damaged).

 

[fafrd]

Voc was quoted with panel at 25C. Hot day, panel 45C? 65C? expect 0.2% to 0.4% drop per degree, whatever temperature coefficient data sheet says. Voc drops maybe as low as 138V.

Any shadows, and output drops precipitously. I've tried, rewiring some 24s panels as 16s2p. Worked OK until slightly shadowed.

Yes, precisely. If you are operating an SCC with Vmppt_min close to Vmp of the string, that leaves little/no latitude to activate bypass diodes and any shading can totally kill output.

But it won’t cause damage and the OP did not say anything about dealing with shading issues.

When Vmppt_min is close to Vmp of the string (either slightly below or slightly above), startup in the morning will be delayed and shutdown in the afternoon will be accelerated (and there will likely be no output at all until all panels are clear of shade).

Data sheets of the inverters I use (Sunny Boy and TriPower) give a "Rated MPPT Voltage Range", 155 to 480V for 3kW model, 270 to 480V for 7.7kW model. But also "MPPT Operating Voltage Range" 100 to 550V, "Minimum DC Voltage/Start Voltage" 100/125V.

That model operates over a wider range than the earlier ones I used. Maximum MPPT current looks like the limiting factor. Minimum rated voltage x current x number of MPPT is just above inverter's wattage rating.

So long as Voc is above MPPT start voltage, I expect an MPPT to being operating and pull as low as minimum MPPT operating voltage to maximize power.

Yes, exactly. Normal operation but possibly at reduced potential output levels (depending on how much Vmppt_min drives outout currevt down below Imp…).

My 30kW TriPower, several times it started then shut off. There was a setting of 1500W minimum to operate, and I had connected a single 2500W string (with less than full light.) Setting 500W minimum it began operating, and continued as the sun set and power dropped below 500W.

Yes, if there are other specs / requirements for proper function of the SCC other than voltages being within range (Vmppt_max > Voc_string), that can obviously impact functionality and is an entirely different discussion than the one started by the OP…

 

[sunshine_eggo]

My simple midel for power output at voltages above Vmp conus from the I-V curves provided for any solar panel. Actually estimating data from the actual curve of the specific panel in question is best, but that simple linear current degradation I modeled provides a realistic estimate of magnitude.

Do you know that the MPPT will behave in a manner that will yield those results? What algorithm does it follow below 120V? What algorithm does it follow above 120V?

Just to be clear, you are asking me if he connects an SCC with Vmp_min of 120V (but Vmp_max above Voc_worst-case of the string, presumably meaning above ~150V) ) to a string of 4 panels with Vmp above 30V (but well below 150V) whether I will reimburse him the cost of his SCC if it blows up / gets damaged from connecting that string?

Yes I would,

No. I didn't mean this at all. I meant what if it just performed like shit?

My response was to this question:

Would you expect a 120v minimum mppt cc would fall out of range and stop operating, or would it operate less than ideally at the 120v minimum?

I indicated I would assume the worst, i.e., stop operating without confirmation otherwise.

Nor did you mention damage:

The answer is that ‘no, a 120v minimum mppt would not fall out of range and stop operating’ and ‘yes, the mppt would operate less than ideally at the 120V minimum’ (assuming Vmp of the 4S string is below 120V).

I thought the context was pretty clear.

I'm assuming this is cheap Chinese shit where across all brands and models erratic behavior and low overall quality is well documented. I'm not assuming anything but the worst about them unless I get a guarantee from the distributor/manufacturer, and I'm not going to give anyone the impression that it may perform acceptably unless I KNOW otherwise.

 

[fafrd]

Do you know that the MPPT will behave in a manner that will yield those results?

I know how a properly designed MPPT for an SCC should function.

If you want to broaden the discussion to include SCCs/MPPTs that may not have been designed correctly, that’s not a discussion I’m interested in (nor one I feel the least bit qualified to participate in).

What algorithm does it follow below 120V?

It can’t go below Vmppt_min, that’s why it is the minimum voltage of the MPPT…

What algorithm does it follow above 120V?

A properly designed MPPT allows voltage to increase above Vmppt_min until power decreases.

The only real ‘algorithmic’ part of the entire affair is when the controller decides to search for higher power levels by allowing bypass diodes to activate. It does this by occasionally pulling string voltage back down to Vmppt_min (or some other lower voltage above Vmppt_min) and letting voltage increase to a new maximum power point.

No. I didn't mean this at all. I meant what if it just performed like shit?

As Vmppt_min increases further and further above Vmp and closer and closer to Voc, performance suffers more and more, from near-optimal to sh*t.

My response was to this question:
I indicated I would assume the worst, i.e., stop operating without confirmation otherwise.

A properly designed SCC MPPT will not stop operating when Vmppt_min is greater than Vmp of the string. Full stop.

Checking with a manufacturer for confirmation is never a bad idea.

But if they state anything to the contrary it means they did not design a proper SCC MPPT.

Nor did you mention damage:

I see you are correct that the OP was not explicitly asking about potential damage, so I apologize if I misinterpreted your response from that confusion on my part.

I thought the context was pretty clear.

I assume you are referring to the context you outline below. If you meant something else, thanks to clarify.

I'm assuming this is cheap Chinese shit where across all brands and models erratic behavior and low overall quality is well documented.

Could be, but since the OP stated nothing to that effect, I’m not sure that assumption adds to the discussion.

More to the point, poor quality of some cheap Chinese inverters is one thing but has nothing to do with how an SCC MPPT is supposed to function.

The only way an SCC MPPT will not function properly when Vmppt_min is greater Vmp of the string is because the SCC MPPT was improperly designed (which again, is a ‘context’ I don’t feel qualified to connect on)

I'm not assuming anything but the worst about them unless I get a guarantee from the distributor/manufacturer

You are allowed to assume anything you want, but I assume we’ve both engaged with this thread from a desire to assist the OP - isn’t it the OPs assumptions that should be important to the discussion rather than yours?

, and I'm not going to give anyone the impression that it may perform acceptably unless I KNOW otherwise.

And you are totally entitled to that position.

My position is that I can contribute the most by clarifying how a properly-designed SCC MPPT is intended to function,

A properly-designed SCC MPPT has no problem functioning properly when Vmppt-min is slightly higher than Vmp of the input string, certainly when we are talking about Vmppt_min of a few volts higher / < 10% higher than Vmp of the string and only on the case that output in the presence of partial shading is not a priority.

 

[sunshine_eggo]

My position is that I can contribute the most by clarifying how a properly-designed SCC MPPT is intended to function,

How does this help the OP?

You're assuming it's properly designed.

You actually don't know how it will perform. You know how it should perform. There's a difference.

Let's talk about "proper design"... Why is there a 120V limitation at all? A properly designed MPPT shouldn't restrict MPPT operation until something much closer to peak battery voltage.

 

[fafrd]

How does this help the OP?

You're assuming it's properly designed.

You actually don't know how it will perform. You know how it should perform. There's a difference.

Yup. One is worth discussing / clarifying, the other is not (certainly not on the case that that is not what the OP had explicitly requested).

Let's talk about "proper design"... Why is there a 120V limitation at all? A properly designed MPPT shouldn't restrict MPPT operation until something much closer to peak battery voltage.

You are correct that Vmppt_min must almost always be several volts higher than the voltage of the battery being charged (in fact, my SCC specifies Vmppt_min as ‘Vbat + 2.0V)’).

But there are clear reasons / advantages that lead many properly designed SCC MPPTs to require Vmppt_min levels significantly higher than that absolute minimum associated with the need to charge batteries with voltages above Vbat:

Higher minimum input voltage translates to lower maximum input current which translates to lower cost (smaller wire sizes) and/or higher charging efficiency (lower I^R losses).

An SCC supporting the widest possible voltage range for Vmppt will cost more and/or will have lower charging efficiency specifications than one restricting Vmppt_min to voltages which are a % of Voc / Vinput_max rather than some minimum voltage level above Vbat.

And since you are the one who brought up cheap Chinese inverters, lowering cost and inflating / maximizing specifications in general (and especially efficiency specifications) are both things many Chinese manufacturers are suspected of being motivated by .

 

[sunshine_eggo]

And what happens if your particular MPPT isn't at least +5V above battery voltage (assuming a particular brand)? It doesn't function at all, yet you assume the unspecified unit will function fixed at 120V. Why?

You sure will fight hard and spout much to avoid saying, "I don't know," eh?

Assumptions upon assumptions, and you even stoop to equate "cheap" to "properly designed."

 

[fafrd]

Let's talk about "proper design"... Why is there a 120V limitation at all? A properly designed MPPT shouldn't restrict MPPT operation until something much closer to peak battery voltage.

By the way, Schneider solar equipment is properly designed and certainly does not qualify as ‘cheap Chinese junk’: https://www.altestore.com/static/da...PT-100-600-and-MPPT-80-600-Datasheet_2022.pdf

Vbat of 24 and 48 VDC.

MPPT voltage range of 195 to 510 VDC.

 

[fafrd]

And what happens if your particular MPPT isn't at least +5V above battery voltage (assuming a particular brand)?

I don’t believe I’ve ever seen a requirement for Vbat + 5V for Vmppt_min, but whatever it is, when the PV array is unable to increase string voltage to Vmppt_min, there will be no charge current driven to the battery. With very weak solar energy / light, the solar panels will be unable to put out full Voc and if whatever open circuit voltage they can succeed to put out is below Vmppt_min (Vbat + 5V in your case), the SCC will remain in standby state waiting for sufficient solar power to begin charging…

It doesn't function at all

It functions just fine (and as intended), it just cannot begin charging yet. And since string voltage will approach Voc as solar energy / light increases, and since Voc > (Vbat + 5V) (in this case and in any sensible case), it is just a matter of waiting until there is sufficient solar power to drive string voltage above Vbat + 5V so battery charging can start.

, yet you assume the unspecified unit will function fixed at 120V. [nb]Why?[/b]

Because I understand how SCCs with MPPTs work. I’m starting to worry that you do not.

Voc is ~150V and Vmppt_min is 120V, so charging will not begin until there is sufficient solar energy to drive string voltage above 120V (which it must if it is a clear day delivering anything close to NOCT by midday).

So shading may cause it to remain in standby, an overcast day may cause it to remain in standby, but if panels are hit by sufficient solar energy to approach anything close to NOCT without any shading, string voltage is guaranteed to increase to 120V or more where charging can begin.

You sure will fight hard and spout much to avoid saying, "I don't know," eh?

I’m really at a loss to understand what you would like me to admit I don’t know. I’m assuming the SCC MPPT has been properly designed. If it has not I don’t know anything about that and don’t care to engage in the discussion.

Other than the voltages supplied by the OP - what else is there to know?

Assumptions upon assumptions, and you even stoop to equate "cheap" to "properly designed."

You are going to have to point out to me where I said anything cheap has been properly designed.

Anything properly designed has been properly designed.

High-cost products have a lower likelihood of being improperly designed.

Many lower-cost products have been properly designed (at least as far as the implementation of the SCC MPPT functionality) and those that have not will ultimately fail in the marketplace.

I have an interest in helping members understand how a properly designed SCC MPPT should function.

I have no interest in attempting to understand how an improperly designed SCC MPPT might or might not function (especially when the OP has not stated what SCC they have and expressed any concerns as to whether it’s been properly designed / implemented or not).

 

[hwy17]

And I was worried this post wasn't gonna get seen...

Thank you guys for the detailed answer.

I'm gonna tell them if they would like to rewire the array then a high voltage CC can probably work in the meantime on the 150v array, but no guarantees about EG4.

If they don't want to rewire, it looks like the Midnite Classic might be best, as its hyper VOC feature explicitly allows high (160ish) VOC excursion.

 

[Hedges]

Let's talk about "proper design"... Why is there a 120V limitation at all? A properly designed MPPT shouldn't restrict MPPT operation until something much closer to peak battery voltage.

Or HV DC rail, if it was a hybrid.

My friend's old Magnum charge controller burned up on a 4x4x37VOC array (150ish VOC).

Can they use a high voltage charge controller without rewiring their array, or will it dip below minimum MPPT too often?

Just an SCC, not a hybrid. In that case, voltage closer to Vbat would be expected.

Does the SCC support Imp & Isc from the 4s4p array?
If getting a high voltage charge controller, why not just rewire as 8s2p? should be trivial.
(But not good for a 250V max SCC, needs to be 350V max or higher.)

I don’t believe I’ve ever seen a requirement for Vbat + 5V for Vmppt_min, but whatever it is, when the PV array is unable to increase string voltage to Vmppt_min, there will be no charge current driven to the battery.

Most MPPT need at least that, because they are buck converter and need a bit of headroom for IR voltage drop.

I'm gonna tell them if they would like to rewire the array then a high voltage CC can probably work in the meantime on the 150v array, but no guarantees about EG4.

Good.

If they don't want to rewire, it looks like the Midnite Classic might be best, as its hyper VOC feature explicitly allows high (160ish) VOC excursion.

Midnight Classic 150, 200, 250 allow Voc up to rated voltage + Vbat (so not just 10V higher, 160is for the 150V model.)

I think they detect over-voltage, where FET is exposed to Voc - Vbat. So they do NOT start switching buck converter, which would expose FET to full Vbat (each time FET switch turns off, after having turned so so current is going through inductor, it flies down from Vbat to zero volts.)

The higher voltage Classic cost more and process fewer watts, so lower voltage model would be preferred.

If his array is nominally 150V, then under nominal conditions the SCC won't operate. In cold weather it won't operate. HyperVoc means nothing happens at all until voltage drops lower, like when panel heats up. There should be some voltage headroom between Voc and SCC rating.