Going slightly over the max MPPT voltage

[ricardocello]

Take it from someone who designs electronic circuits for a living, a properly designed 100 volt rated input that safely tolerates 100 volts isn't going to smoke at 100.68 volts.

Would you use 50V rated capacitors for a 48V power supply?

Good designs double the capacitor voltage ratings.
There are reasons the ratings exist, and why conservative “defensive engineering” is preferred.

 

[timselectric]

This group is uniquely passionate about VOC.

More passionate about saving the magic smoke.
Once it gets out, you can't get it back in.

 

[timselectric]

Just as an example, the EG4 18k inverter

No point in drifting into the imaginary world. lol

 

[Minimoose]

Hi,

I am looking at adding a victron 100/30 to manage one of my strings. The VOC from my string would be 100.68V. Would that extra 0.68V fry or substantially shorten the lifespan of the controller? The 150V version is almost twice the price!

Most have over voltage and reverse polarity protection. At least mine do. In the hot weather I can series four 24.3 VOC on a 100 volt controller. But in the winter it will flash overvoltage and go into protection mode. No harm done. I usually just series/parallel and no issues.

 

[bolhuijo]

Good for you. Don't forget that almost all manufacturers publish this as a hard limit. The only exception that I can think of is Midnite with their HyperVoc protection.



Please cite your source for this claim. I'll use that when trying to get warranty from Victron if I ever over-volt my MPPT.

I believe the idea is that electronic components all have recommended operating conditions, and then absolute maximum ratings. The 1st one (100 Volts) is where the manufacturer warranty stops, and the 2nd one is closer to the magic smoke point. So almost nobody believes that 100.68 Volts will kill it but Victron has no obligation to help you at that point.

boilerplate from a data sheet: "Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, and do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions"

 

[robbob2112]

I would bet that tollerence is ±1% ... heck I would bet the panels have ±2% or higher

 

[ksmithaz1]

The problem with tolerances is they are cumulative. That is why it is always best to stay well within them.

 

[robbob2112]

Nagh, run the ragged edge

 

[crossy]

All this ^^^.

Plus don't forget your panel Voc also has a tolerance

 

[mciholas]

Would you use 50V rated capacitors for a 48V power supply?

No, of course not. 63 or 75 WVDC might work based on the circuit needs, depends on the nature of the circuit. A transorb clamping the voltage input would be a good thing to be able to cover, for example.

Good designs double the capacitor voltage ratings.

That "good design" means you are using more caps with higher ESR for being too conservative. The caps already have a margin above working voltage in their design, so when you start piling on too many safety margins, it can get excessive and lead to bad design in the end.

There are reasons the ratings exist, and why conservative “defensive engineering” is preferred.

The existence of safety margin in engineering is exactly why 100.68 volts isn't going to blow up a 100.00 volt rated input. This is what the OP wants to know, and that's the answer to the question.

Mike C.

 

[Hedges]

I wouldn't worry about 0.68V on top of 100V.
I would worry about 16V on top of 100V (possible cold temperature and temperature coefficient of Voc.)

If I used historical record cold and PV panels temperature coefficient and that came out 100.68V, I wouldn't worry about it (too much) with premium equipment.

Chineseum, if not under the watchful eye of a Tier-1 OEM, then I'd recommend lots of extra margin.

Any reason not to use a different series/parallel PV panel configuration, or a higher voltage rated MPPT? Get one that will support additional panels. Are you running near rated current or wattage? That will shorten life, for any quality level. Select one to run cooler.

 

[Y2JB]

Thanks for all the info, i'll get the 150

 

[shadowmaker]

Deye engineers told me to go with 16S with my panels (gave them specs). This was before I had no knowledge what Voc even means. Hard limit for my Deye is 800V and I have witnessed voltage to go up to 808V. At that point there was fault code: DC overvoltage and inverter stopped working and voltage immediately started to drop, slowly though. About two-three minutes later voltage dropped under 780V and Deye started working again.

Haven't done anything to it (still 16S) and there are many overvoltage faults occurring spring time (-30C or lower temperatures, sunny days). Don't know how long it's going to last, but it has been fine for over a year now and ~15MWh produced/Deye.

Don't recommend anyone to do this at home! I understand risk and just want to see how much abuse these sh*tty Chinese inverters can take.

 

[cdsolar]

@sunshine_eggo convinced me to go to the 150/35 MPPT instead of a 100 a bit ago largely on the same discussion.

I saw a max voltage of 99 based on colder temperatures in January. A few degrees cooler may have fried the 100... Glad I went with the 150.

 

[wpns]

You’ll only slightly destroy it. Kinda like being a little bit pregnant.

As an EE I’m on the side of “if that’s after your worst case calculations then you are fine”, but experience suggests that Murphy’s Law supercedes calculation, and more margin is always good.

 

[timselectric]

I thought that I had left enough buffer at 11s. But the first winter I had an over voltage on a cool sunny morning. Luckily, my Growatt was able to shut down instead of melt down. I changed it to 10s, and never had another problem.
I had originally planned on 12s, before I knew about temperature coefficient.
If I had, this would have been a different story.
If you choose to gamble, you have to be prepared to lose.

 

[Brucey]

@sunshine_eggo convinced me to go to the 150/35 MPPT instead of a 100 a bit ago largely on the same discussion.

I saw a max voltage of 99 based on colder temperatures in January. A few degrees cooler may have fried the 100... Glad I went with the 150.

I have two 150/35s they work great.Good bang for buck. Hopefully the smartsolar version with BT connectivity to Victron connect for settings changes.

 

[cdsolar]

Yes mine is Smart solar with bt. But, I am lazy. I don't want to go out to the barn to check on it, Bluetooth doesn't go that far. So I use Victron Connect on my android and connect to it through VRM and can see it all and make changes too.

 

[utkvols]

Buy once, cry once was my thought process. I would rather buy the 150 than buy a 100 and a 150

 

[Brucey]

Yes mine is Smart solar with bt. But, I am lazy. I don't want to go out to the barn to check on it, Bluetooth doesn't go that far. So I use Victron Connect on my android and connect to it through VRM and can see it all and make changes too.

Yes, that's the reason I went with the cheaper smartshunt versus bmv-712 which has better bt range. With VRM, limited by BT range no longer matters.

 

[mciholas]

I thought that I had left enough buffer at 11s. But the first winter I had an over voltage on a cool sunny morning. Luckily, my Growatt was able to shut down instead of melt down.

Shutting down and unloading the panels makes the voltage rise. Keeping the panels under load lowers their voltage. So shutting down wasn't necessarily making things "safe", it could be making things worse as far as voltage tolerance.

The MPPT could protect the input in an overvolt case by loading the panels down with more current thus lowering the voltage. It could do this even to move the panels off the max power point by going to a higher current and lower voltage operating point.

I had originally planned on 12s, before I knew about temperature coefficient.
If I had, this would have been a different story.

Maybe, maybe not. There can be a surprising amount of headroom in the ratings and even going 9% above them (12 panels versus 11) is not assured to damage anything. I actually doubt that would have caused a failure.

If you choose to gamble, you have to be prepared to lose.

All electronics are a gamble, it just depends on what the odds are. Being 0.68% above the rating is not a meaningful change in the odds.

Mike C.

 

[timselectric]

Shutting down and unloading the panels makes the voltage rise. Keeping the panels under load lowers their voltage. So shutting down wasn't necessarily making things "safe", it could be making things worse as far as voltage tolerance.

Shutting down, disconnected the panels from the charger.
Making it safe.

The MPPT could protect the input in an overvolt case by loading the panels down with more current thus lowering the voltage. It could do this even to move the panels off the max power point by going to a higher current and lower voltage operating point.

It was already at max current draw.
Which is why the voltage was high.

Maybe, maybe not. There can be a surprising amount of headroom in the ratings and even going 9% above them (12 panels versus 11) is not assured to damage anything. I actually doubt that would have caused a failure.

11 panels was already too much.
12, would have definitely been a different story. (About 60v over)

All electronics are a gamble, it just depends on what the odds are. Being 0.68% above the rating is not a meaningful change in the odds.

No one here thinks that less than 1% over is a problem.
But it leaves no margin of error. Which will more than likely become a problem in colder temperatures.

 

[Madcodger]

I tend to think of voltage limits on SCCs the same way I think of the edge of a cliff. Even a little bit past that, and you probably won't get a second chance to make the same mistake on that unit.

 

[mciholas]

It was already at max current draw.
Which is why the voltage was high.

That's not how the IV curve works on solar panels.

Max volts occurs at zero amps.



An MPPT can make any voltage it wants from Voc to zero by controlling the current load. Just staying at max power is about 20% under open circuit voltage. If the inverter goes to zero amps, it lets the voltage go to max. If there isn't some switch/relay to the panels that opens on shutdown (which is unusual), then shutting down exposes the unit to the max volts.

Mike C.

 

[timselectric]

Some MPPT's have the ability to protect themselves from small over voltage situations.
And some don't have any protection.
But the ones that can, still have their limits.
The listed operating range usually allows a 10% cushion below the VOC.
Plan to stay in the operating range (in all temperatures), and things will be fine.
If you choose to push the limits, that's entirely up to you. (It's your money)
But, it's never going to be our recommendation.