Over paneling a charge controller

BarryFields · March 2022

My Renogy rover 60 has two limitations. No more than 150volts Vmp and no more than 3200 watts input.

My panels have a Vmp of 20.4 @25degrees. With a temp coefficient of -.29%. By my calculations, in my 48 volt system, it would have to be a bright sunny day close to absolute zero to get to 150 volts. Should not be a problem here in Tennessee. Are my calculations correct?

My main question is this. If 5000 watts are available, will the controller only process 3200 watts and ignore the rest OR will it try to process all of it and burn up?

In bulk mode the controller is in MPPT mode. In absorb and float it is not in MPPT mode. If it is not in MPPT mode, does that mean it is n PWM mode?

Thanks in advance for your input.

mike95490 · March 2022

Controllers burn up for several reasons, among which are
Overvoltage Voc

overheating - trying to reduce 140VDC to 12VDC , the larger the conversion requirement, the hotter they run
In theory, as they get hotter, there is supposed to be power cutback to reduce heat

Over-paneling - where the panels are so large they cannot possibly be controlled by the controller, and it is unable to
regulate the output voltage to the battery. Some controllers can be overpaneled at a low voltage and be OK, but if the same array was wired to higher voltage, the controller smokes.

Stay within the CC sizing calculator for best results

BarryFields · March 2022

mike95490 I asked three specific questions. It is ok for you to say "I don't know".

mike95490 · March 2022

BarryFields said:

.... By my calculations, in my 48 volt system, it would have to be a bright sunny day close to absolute zero to get to 150 volts. Should not be a problem here in Tennessee. Are my calculations correct?.........

No. Absolute Zero in Fahrenheit is -459.76 degrees

How many panels do you have? 3 in series, 5 in series ? 5S3P All in parallel ? you never mentioned wattage or other specs of whatever panels you have

Most controllers have a Voc not to exceed rating. None that I know of use Vmp.

I do not memorize settings for all possible components. List the particulars, don't link to a site, because I don't follow links off site.
You need to list the specs for :
Controller
PV panels Voc, Vmp, Isc, Imp,

So, no, I cant help with the data given, and no one else can, if they are honest.

If the manual says 3200w, 3300 watts could void the warranty. Most controllers have NVRAM to record warranty exclusion data.

mike_s · March 2022

BarryFields said:

Renogy rover 60...

My main question is this. If 5000 watts are available, will the controller only process 3200 watts and ignore the rest OR will it try to process all of it and burn up?

RTFM? "PV Overcurrent: The controller will limit the battery charging current to the maximum battery current rating. Therefore, an over-sized solar array will not operate at peak power."

mike95490 · April 2022

Warren93nature said:

It is possible to over-panel a charge controller, you just have to put a higher wattage into the charge controller than it is rated for.

Very feasible to overpanel, but you may have to replace the burnt out controllers often, IMHO

fratermus · April 2022

BarryFields said:

My main question is this. If 5000 watts are available, will the controller only process 3200 watts and ignore the rest OR will it try to process all of it and burn up?

The controller will limit output to demand, up to the rated output.

if you need 60A it will deliver 60A (assuming it can make that much)
if you need 70A it will deliver 60A

This limiting (clipping, etc) is achieved by moving the panels off their maximum power point on the power curve. It can go either direction but in practice Vpanel is typically moved toward Voc. Example: my panels are rated 30.1Vmp but in float right now the controller has them at 35.8v.

It may not be intuitive, but this question and the next are two sides of the same coin. Backing off harvest to limit power to the rated output (this question) and backing off harvest to avoid overshooting Vabs/Float (next question) are done the same way.

BarryFields said:
In bulk mode the controller is in MPPT mode. In absorb and float it is not in MPPT mode. If it is not in MPPT mode, does that mean it is n PWM mode?

It is still power point tracking, it just isn't selecting the maximum anymore. It is selecting the power point that matches demand. You can watch this happen by observing panel voltage during absorp/float.

Photowhit · April 2022

BarryFields said:

My Renogy rover 60 has two limitations. No more than 150volts Vmp and no more than 3200 watts input.BarryFields said:

If your controller says "...no more than 3200 watts input". Don't hook up enough panels to bring in more than 3200 watts. Basically a 3200 watt or smaller array. Yes solar arrays typically produce no more than 75% of their rated power, but can in cold weather produce their panel rating.

BarryFields said:
My main question is this. If 5000 watts are available, will the controller only process 3200 watts and ignore the rest OR will it try to process all of it and burn up?

Apparently NOT yours. If it says limit input to 3200 watts, follow the instructions.

Another option would be to invest in a MPPT charge controller that will allow over paneling. I believe the Schneider Conex, MorningStar and Midnite Classic all allow for over paneling. I'd suggest the Midnite Classic, been using 2 for 10 years now.

BarryFields said:
My panels have a Vmp of 20.4 @25degrees. With a temp coefficient of -.29%. By my calculations, in my 48 volt system, it would have to be a bright sunny day close to absolute zero to get to 150 volts. Should not be a problem here in Tennessee. Are my calculations correct?

We need to know how you intend to wire the panels. Understand that boB Grudel who designed early Outback MPPT charge controllers one of the first effective designs, and the Midnite Classic, still a 'classic' more than 10 years in production. Helps people who want to use MPPT type charge controller by giving some basic info often not found from other designers. For MPPT controllers to work effectively they need to have about 30% higher input voltage to output voltage. for a 48 volt lead acid system, that would charge at around 60 volts that would be about 78 volts. Even with a VMP of 20 volts the effective (normal) voltage under load would likely not reach 78 volts in strings of 4 panels. I would suggest strings of 5 or more panels.

BarryFields said:
In bulk mode the controller is in MPPT mode. In absorb and float it is not in MPPT mode. If it is not in MPPT mode, does that mean it is n PWM mode?

Yes, perhaps. I think in most (perhaps better?) MPPT type controllers, the incoming is still reduce using power point tracking, but delivered/output using Pulse Width Modulated, to maintain the correct system voltage. Certainly the system would benefit while in absorb stage.

Perhaps boB will pop in and deliver a bit of knowledge.

BB. · April 2022

And remember that for "cold" panels and controllers, you are looking for Voc (voltage open circuit) cold value (don't want to over voltage the controllers when there is no charging current required).

For "hot" panels, you are looking for Vmp-array-hot value... Vmp (and Voc) fall as the panels get hot... You want to make sure your "hot panel" array still has sufficient Vmp voltage to optimally operate the charge controller.

-Bill

Vic · April 2022

Some MPPT CCs have limits on maximum array power, and several have limits on PV array total string Isc. Generally these CCs are believed to have relatively slow output (battery) current limiting.

Some Schneider CCs, like the 150 V, 60 Amp SCC:
"Max. array short-circuit current 60 A (48 A @ STC)" from this Spec Sheet:
XW-SCC.pdf (solar-electric.com)

The Renogy maximum array size spec is probably an attempt to state a similar limitation in a less-technical manner.

As photowhit stated, CCs like the MidNite Classics (and the venerable Outback MX-60) have no such stated limits, and can be over-paneled, within reason.

As an aside, one disadvantage of a large degree of over-paneling an MPPT CC, is that it tends to increase the average PV input voltage to the CC, due to current limiting, usually results in less loading (less current than the actual Maximum Power Point voltage) of the PV array. So, the CC that is limiting output current, is operating at close to its maximum rated current, and at a higher input voltage, both of these factors increases the CC operating temperature.

FWIW, IMO, and so on. Vic

BarryFields · May 2022

When I make an error, I admit it. My initial post stated Vmp. It should have said Voc. So 4panels in series 20.4 x 4 = 81.6 Voc. 150v max - 81.6 = 68.4 volts 68.4 / -.29 = 235 degrees C. 235 degrees - 25 degrees = -210 degrees C to get the panels to 150 Voc. Absolute zero is -273 degree CELSIUS.

I stand corrected.

As I revere actual facts rather than assumptions and extrapolation, I contacted Renogy directly. Below are the highlights of that inter-reaction

.

RENOGY 4/7
If you are running 5000W and the max is 3200W at 48V.
On page 29 it says The controller will limit the battery charging current to the maximum battery current rating. Therefore, an over-sized solar array will not operate at peak power.
So yes it might just ignore the excess, and a double flashing white "PV indicator" will show: The oversized PV system is charging the battery bank at the rated current.
Barry 4/8
I was looking for a more definite answer than what the unit "might" do.
Let me repeat the question.Is the following statement true?
If the Rover 60A has 5000 watts of Solar panel power connected to it, the unit will process 3200 watts and ignore the rest and will continue to to do so with no damage to the unit.
Please, no "mights" or "maybes".
Renogy 4/25
I received a reply from our Technical Department.
The controller will not send a charge out, however the amount of power that the contorller is receiving with no output will cause the controller to fail and creates a potnetial hazard.
Renogy 4/29
Dear Barry Fields,
as what we have talked about over the phone, the Rover 60 charge controller will still continue to run the solar system as long as it is not exceeding the 150V input voltage limit.
Renogy 5/5
Dear Barry Fields,
As we discussed over the phone. Yes, the charge controller will stop working and cut off when experiencing an error.

I would appreciate any objective analysis. It appears there is still a incongruity in the answers.

mike95490 · May 2022

I am not the controller designer and cannot say if it will throttle back, fail gracefully, fail spectacularly.

Marc Kurth · May 2022

The voltage being applied to the battery is what will determine the current that the battery will draw. Wouldn't the charge controller simply modulate its output voltage to the battery bank as required in order to avoid exceeding its own maximum current rating - regardless of how much energy is available behind it? Or, is it done on the input side resulting in heat generation, hence the reason for potential burnout?

Obviously, you cannot exceed the maximum input voltage of the charge controller. I'm only asking about the current.

Example: A 2 amp battery charger plugged into 120v 20 amp circuit will not burn up when connected to large battery representing a large load. It simply modulates the output voltage to the battery to cause the battery to draw the max amps that the charger can handle.

Dave Angelini · May 2022

Hey Marc !
It is pretty much as Mike wrote. A really top notch MPPT can easily current limit its input circuitry and protect itself. I almost always put 8.5KW of solar on the 100 adc mppt charger from schneider. It is built to deal with 20 to 25 percent over paneled. Still have an 80 amp from 2011 when they designed the first 600vdc mppt for batteries in the world.

boB · May 2022

"Perhaps boB will pop in and deliver a bit of knowledge."

I thought I had seen this thread a while back ?...

What an MPPT CC will typical do to limit battery output current and power into the battery is the same thing it does when it is regulating battery voltage for Absorb and Float etc... It raises the PV input voltage more towards Voc or "open circuit"...

Voc or open circuit is just that... It is open and no current and no power. BUT in-between the maximum power point voltage of the panel(s) and Voc, it is in-between and so it is variable output power. Most controllers do it this way as far as I know.

When you say "PWM" I know that you mean.... Like a PWM charge controller which means that the CC does not actually reduce the PV input voltage to the battery voltage, but switches the PV to battery connection on and off and on and off maybe a hundred times per second or more. BUT even MPPT charge controllers use "PWM" as in Pulse Width Modulation to vary the output voltage and current.

It's just that an MPPT controller or "Buck Converter" (it Bucks the input voltage down) is just slightly more complicated in that it can reduce the PV input voltage efficiently by varying the duty cycle to make the "average" DC voltage a fraction of the input voltage.
50% duty cycle would take 100V input and reduce it to 50V output. By varying the output current, voltage with varying duty-cycle percentage, this also changes the PV input voltage. So if the battery and its loads need more current than the PV can supply, the controller will move that input voltage down and up until it finds the PV voltage that yields maximum output power and try to keep it running at that PV input voltage until it needs to "Re-Track" and find a new Vmp. The PV's Vmp will usually change with temperature and less so with irradiance. How that PV voltage is moved around to find the Vmp is subject of many different patents and algorithms. The typical Perturb and Obvserve (P&O) is an old tried and true method for instance.

MPPT controllers usually run at ultrasonic frequencies (above hearing range) greater than 20 kHz typically and must use a transformer or inductor in its output filter which limits instantaneous current to the output and on to the battery.

That is part of it anyway.

boB 🌜

BB. · May 2022

There is also something else to watch for... The input side of a MPPT (and PWM) controller has a maximum current rating of some sort...

Typically, the max input current may be the same as the output rated max current (i.e., 60 amps out, 60 amps max in). Or, I have seen the max rated input current at 80% of rated output current... I.e., 60 amps max output current. and max input of ~48 amps from array...

That second rating... I am not sure where the 80% comes from... The NEC has a 80% derating for solar (i.e., a PWM controller which cannot control output/throughput current--They say to only design for 80% max current). This probably makes sense to "allow" the controller to have "head room" for the times when the sun (reflections from clouds and ground/sand/water) can have more than rated current.

Personally, when charging a battery bank and you can have "hours" of max/rated charge into a battery bank (AC genset, over paneled MPPT controller, etc.)... The 80% derating for continuous current (things such as Gym Lighting--Constant current/power for hours at a time) I suggest for Wiring and Circuit Breakers... I.e.:

60 amp rated output * 1/0.80 NEC derating (or x1.25) = 75 amp rated branch circuit...

This not only "works" for wiring (keep it from gradually overheating)... It also makes sense for circuit breakers too... The normal NEC/UL circuit breaker/fuse ratings are at 100%+ of rated current, will eventually trip (will vary--Minutes to hours depending on specs). And will not trip at 80% or less of rated current... So running for "hours" at 80-100% of rated current--You are in the zone of "possible" "false" trips. Running at 80% or less of rated breaker/fuse current--Just one less thing to "go wrong" in your system (and cause loss of current).

For MPPT controllers--They are rated for max output current--So is 80% NEC derating needed (i.e., rated for 60 amps, use 60 Amps max)? I think not--Running at 100% rated current is fine... But many (some/most/all?) controller are rated at 25C for specifications... And will generally have some derating curve if running at 100% rated current as ambient temperature rise... But in this case, most (all?) MPPT controllers simply reduce output current to keep from overheating.

Running hot--There is the engineering rule of thumb--For every 10C/18F increase in temperature (typically 25C/77F), the "life" of the product is cut by 1/2... Running 35C = 1/2 life. Running 45C = 1/4 life... Etc... And also, thermal cycling can be a big issue... I used to "break" disc drives decades ago by cycling twice a day in their "spec range". "Bad" design would fail in several weeks of cycling. "Good drives" would never fail in month+ times.

Anyway, back to where I was heading... You need to look at the max input current rating when "over paneling" an MPPT controller. When an MPPT controller is over paneled... You want to make sure that Voc-array-cold, as above, does not "over voltage" the array on very cold days. But you also need to look at Imp/Isc (current max power, current short circuit) do not exceed the input wiring side rating of the controller...

In normal operation the MPPT controller should never exceed the max Ipanel input current (if array is property designed for Vmp ratings). But you also need to make sure that if the MPPT controller fails (internal short circuit of some sort) does not "fry" the controller input wiring and wiring from the array will not fail... So that, for example, would require a circuit breaker (or fuse) on the output of the solar array to limit the available branch circuit maximum current to controller max input rated current.

For example, an MPPT controller should work just fine when connected to a large battery bank (has been done for systems that have 24-48 VDC battery banks, but need a 12 volt battery bus/bank too (such as for HAM radios). Just need an array "output breaker" (mounted at/near the array combiner box) to protect the wire run from the array to the MPPT controller...

So, for example, you have a 2x larger (wattage/current) array (solar panels cheap, batteries and genst fuel expensive)--Just protect the array output to MPPT solar power wire run.

I believe boB (current Midnite co-founder/designer) once posted here that a (relatively low) resistance "balance" ballast (stupid typo. -BB) resistor from Battery Bank to Vpanel input of (some?) MPPT controllers is a good thing (limit switching current peaks?). Solar Guppy, years ago typed about using MPPT controllers to drop from 24-48 VDC Banks to 12 volt banks--And that he had no issues at all (Solar Guppy, a now mostly "retired" poster here, did design/test a fair number of MPPT based solar products in his engineering life).

When going from "just big enough" solar array to an "oversized" array--We are getting into the "issues" where the array starts looking like a version of a battery bank (i.e., Battery Bank => Voltage source and large surge current; "right size" soar array => current source--Cannot pull more current from solar panels than the amount of sun on panels--To "over sized" solar array => much more "surge" current available--looking more like a battery bank Voltage/Current characteristics).

This is where "details" matter... Doing something "different", and you can trip over these "buried"/"hidden" issues.

-Bill

Dave Angelini · May 2022

Exactly Bill ! The only controller I use has a limit of 29 adc on the 600vdc input. The 100 adc controller output mppt also current limits.

If you get too much solar, more than 8500 watts coming in, the mppt can't move the MPV far enough/fast enough to protect or current limit the input circuitry.

I still think Mike said it best about how it was designed and how it can fail.

Over paneling a charge controller

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