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Max VOC - How strict?

Watts Happening

Watts Happening

I call it like I see it.
Joined
May 3, 2022
Messages
809
If you had panels with 52.1v Voc and 43.3v Vmp, would you be worried connecting them to a Victron 150/85?

I understand this ends up at 156.3v Voc, on a 150v charge controller, but I'm wondering just how "sketchy" this really is. A big part of me wants to think a Victron charge controller isn't going to melt over a 6.3v excess, but I also don't want to break anything needlessly. Strings of 3 panels sound much more attractive than 2.

Thanks!
 
Some manufacturers (e.g. SMA) record highest PV voltage in NVM. That way they can say, "It's your fault!"

One where it isn't a hard number is Midnight Classic. Those detect over-voltage and suppress operation, survive up to spec + battery, e.g. 150 + 48 = 198V

you're considering exceeding spec based on data sheet Voc, which is under STC, 25 degrees C? Definitely don't do that. Expect ~ 15% higher voltage in cold weather (you can calculate exactly.) Midnight Classic would just sit there and do nothing under even nominal conditions, until temperature rose in the sun and voltage dipped below 150V.
 
Run 2 panels in series instead of 3. Get thicker PV wire to keep voltage drop reasonable.
 
From a teardown video on youtube Victron 150V MPPT uses 150V rated IRFI 4321 mosfets. At -40C temperature and 150V this mosfet goes into avalanche breakdown or basically starts conducting small current while turned off. Depending on dissipated heat it can destroy itself. Here is reverse breakdown voltage vs temp chart for IRFI 4321.

ds.PNG

If you can guarantee that charge controller will always operate at above +10C temp you could get away with running 156 Voc but the problem is at low temp your panels will make more voltage while the mosfet tolerates less voltage at lower temps, so you have a compounding effect working against you.
 
For a 150v max VOC, I’d be looking at 40v VOC panels if running 3 in series. They make many high wattage panels in that VOC range, down side is the higher current means larger conductor.
 
The moment you mentioned Victron, it’s like no way, full stop, Do not pass Max OCV!
Probably the most efficient unit out there. They start making power when they say they will and they can die if you don’t believe the end. MPP’s are a bit more forgiving but not when you’re already over V at normal temps. You’ll smoke it for sure when the panels are cold and making more voltage.
 
You know, there are so many people that are in this same situation where it’s just so close(and tempting) where it’ll be OK for 99.5% of the time( but that .5% will kill the mpp several times a year). Does someone make a voltage dump or some kind of a limiter? If not, perhaps a smart fella should make one?
 
Skypower said:
You know, there are so many people that are in this same situation where it’s just so close(and tempting) where it’ll be OK for 99.5% of the time( but that .5% will kill the mpp several times a year). Does someone make a voltage dump or some kind of a limiter? If not, perhaps a smart fella should make one?
Click to expand...
A stack of big ol' diodes would kill volts for you, but they need to be rated above the ISC current of the panels.
 
Diodes in series will introduce undesirable power loss. Better to make a voltage clamp circuit by switching on resistor load in parallel with solar panels once voltage gets close to 150V.
 
AntronX said:
Diodes in series will introduce undesirable power loss. Better to make a voltage clamp circuit by switching on resistor load in parallel with solar panels once voltage gets close to 150V.
Click to expand...
Is a resistor load not an undesirable power loss? The case in point is 156.3 VOC into a 150V max device. Killing about 10 volts would seem appropriate, no matter what the method.
 
Vmp well under 150V, so switching off the resistor below 145V would mean no loss.

A stack of zener diodes would clamp voltage, but the wattage that has to be dissipated could be excessive. Maybe enabling a transistor/resistor circuit.

Might be better to short out one PV panel (or diode-bypassed section of a panel) and let the watts be lost in PV cells rather than separate component.

156.3V x 1.15 = 180V (estimate of cold weather Voc), so killing 30V is necessary.
 
voltage limit is hard as a rock.... amps not so much, just remember the SCC only take what i can use ( max amps)
 
Hedges said:
Some manufacturers (e.g. SMA) record highest PV voltage in NVM. That way they can say, "It's your fault!"

One where it isn't a hard number is Midnight Classic. Those detect over-voltage and suppress operation, survive up to spec + battery, e.g. 150 + 48 = 198V

you're considering exceeding spec based on data sheet Voc, which is under STC, 25 degrees C? Definitely don't do that. Expect ~ 15% higher voltage in cold weather (you can calculate exactly.) Midnight Classic would just sit there and do nothing under even nominal conditions, until temperature rose in the sun and voltage dipped below
Click to expand...
 
you can go over on your Amps (it’s called overpaneling) but you can’t go over on volts. So overpanel, the only thing in over paneling is you have to pay attention to the cables. A 10awg wire can handle 30amps. So if you solar controller says it can handle 800w you can over panel and add 1000w or higher. This is recommended for maximizing your system. Some people would even add 1500w. Just make sure you have the right gauge wire.
 
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