NOOOO......It all has to do with the VOC max and temperatures. The Axpert's topology is a bit dated and The MPPT range is 60-115V DC. The PV Max is 145 V DC. So for the MPPT to function properly between 60 and 115V and as @plonkster has highlighted  30% higher than battery Voltage. 60 cell panels have a Voc  max of  36-38 V. The also have a temperature coefficient of about -0.31 to -0.33%/°C. So roughly for every 3 or 4 degrees that it is below 25°C there is 1V increase in panel voltage. Not much but with the cold weather we are having early tomorrow morning might test whether your installer did his homework. A Canadian Solar 275W at -10°C Voc max will be 4 V higher than the same panel at 25°C. Not much on its own but have 10 panels in series we now talking 40V. Even 3 panels in series will be 12V higher at -10°C.

I am often told "Ja Ja..... but you need 1000W/m2 insolation and the panels themselves need to be open circuit".  How many times does an Axpert  MPPT not restart? In that moment it is open circuit. The highest voltage I have recorded is 123V on 250W Yinglis which have a temperature compensated max of 128V. 

Four 60 cell panels  are going to have a temperature  compensated Voc of 165V plus. Dangerous territory to my mind.

Play with the PV Array Sizing tool I designed a while back.

 

 

I saw 135V the other day. That's across 3 x 72 cell Canadian Solar panels, on a cold morning (about 6 °C). My calculations shows I'm about 5V shy of the max MPPT voltage (150V) at the very peak.

Tuesday morning. I love VRM. I have the date and time too, not quite what I would have expected!

8 minutes ago, plonkster said:

I'm about 5V shy of the max MPPT voltage (150V) at the very peak.

How does your MPPT handle it if it goes over the max voltages?

Limit it, switch off or blow up?

3 minutes ago, The Terrible Triplett said:

Limit it, switch off or blow up?

It blows up. As far as I know in any case. Absolute max is 150V. Above 145V it won't even start up.

11 minutes ago, plonkster said:

It blows up.

I just remembered ... once connected a 440w array to a 12v with max 400w Nominal PV power.

Could not understand why I never got more than 400w, till @Chris Hobson popped my bubble by pointing out the max watts for the 12v system. Cost me to change to 24v.

Manual says: PV over-voltage will auto-reset after PV-voltage has dropped to safe limit. 
On the brochure: If more PV power is connected, the controller will limit input power.

However, a PV array with a higher sort circuit current may damage the controller - THIS is the one to watch.

 

2 minutes ago, The Terrible Triplett said:

However, a PV array with a higher sort circuit current may damage the controller - THIS is the one to watch.

I don't exactly want to test it. There is something that the controllers sometimes do, in such cases it might short the input as a protection measure. This means that the full short circuit current of the panel flows through the cables, but since that is pretty close to normal operation it only heats things up a bit. It also does this for polarity protection. I'm not quite sure which of these measures are implemented on which controllers. Some of the cheaper controllers have less goodies than the higher end ones. I'm not trying it out, as I already said :-)

Thanks. Voc is about 37 or 38VDc on most 250 to 330 panels I have seen, so based on this 4 panels in series on an Axpert would be BAD in SA. If I have had up to 160V on 3 panels (getting more than 1000/m2), that would mean nearly 200V on a string of 4. Got it. I getting "kleva" er

6 hours ago, KLEVA said:

Voc is about 37 or 38VDc on most 250 to 330 panels I have seen

Careful there!

60 module panels (often 200 - 250W) will normally have operating voltage of around 32Vp and and open circuit of around 36Voc.

72 module panels (often 275-330W) will normally be around 36Vp and 42 45Voc

The 145Voc limitation of many MPPT will allow 3x 60mod series panels with no problem but you are pushing the envelope with 3x 72mod panels - I wouldn't like to be the lab rat, I think it is a good idea to avoid published operating limits when you have no idea of the safety margin allowed.  

Edited August 12, 20188 yr by pilotfish

18 minutes ago, pilotfish said:

72 module panels (often 275-330W) will normally be around 36Vp and 42Voc

275W is the changeover point. I've seen 60-cell 275Wp modules. I haven't seen 60-cell 300Wp modules, those are almost exclusively 72-cell (I guess).

My 72-cell Canadian Solar's have a Voc of 45V. Three of them on a 150V controller is safe, but just barely so. At 145V you'd be playing solar roulette :-)

Yay... Voltage roulette is the best game ever

3 hours ago, KLEVA said:

Yay... Voltage roulette is the best game ever

Kindred spirits we are. Go ahead ... you know you want to! (cwl)

 

If it says 150v max, and I make it so that it never ever exceeds that, even on the best solar day ever ... that is within the published recommended standard as per the manufacturer. Basta with the rest.

I paid good money and are sticking to the MAX of 150v/35amps as per their ENGINEERS that is ok to run at up to 150/35amps max, not one volt/amp more, WITH the temperature also kept in line as per their specs (all that is my responsibility), I would think they designed it to handle the max 150/35amps and not get warranty claims, nuisance blowouts. 

And in some cases a manufacturer is so bold to give a 5 year warranty to boot. Or they block startup at 145 and above and limit the production  ... 

My point is, if the manufacturer says that for X year/s they warrant that if you follow their laid down T&C's to the T, you are good to go. 

We can always play it save and go bigger like 250v at a rather steep price tag. :-) 

Wow this topic has brought some interesting things up and most of it i do not understand.

Would my Axpert 5kva inverter be in danger with my array of 3X330w JA panels. What would the the max volts be that this will create?

Don't think so @Leonc, even above their max of 40V+/panel (at over 1000l/m2) this only gives you 120V per string, so well within spec. We were just playing with the idea of 4 panels per string, and what the guys are saying above is that this can maybe jump the line (4 panels might be able to hit 160V, which is above spec). So it seems everyone is saying stay with the 3. The Axperts MPPT can work down to lower voltages than the on-grid systems it seems. And my experience with 3x250W panels per string did work quite well, my smoke released Axpert is mainly due to input issues with supply rather than the panels.

Another thought, what does the MPPT charger efficiency curve look like for the battery voltage you are charging? On my outback it's peak efficiency is at about 70v (a max input of 150v ), at max pannel current for a 48v battery pack. Which means two pannels not three in a string for me anyway.

Edited August 13, 20188 yr by seant

3 hours ago, KLEVA said:

can work down to lower voltages than the on-grid systems it seems

Depends entirely on the design of the thing. Some of the more expensive MPPTs have incredible ranges, eg the 250V SmartSolar units start at Vbat+5V and goes up to 245V. All the blue controllers start at Vbat + 5V (though once started they will work as low as Vbat + 1V). The Solis GTIs start up at 80V. The Fronius Primo as well.

If this is your cup of tea, it might also make sense to read up about continuous mode vs discontinuous mode on a buck converter. Continuous mode yields better efficiency and less noise.

@seant, Not sure, but what panels are you using? Surely a MPPT controller would select it's best - based on the 250-330W panel example, most of those work around 30-32V (up to a Voc of 40), so unless you have full light to your panels you could be losing under slightly low light conditions. A 3 panel string would be able to work when shaded by cloud/tree but a 2 panel might only be able to work if full sunlight? My experience was that even on semi-cloudy days I was still getting power. I think 2 can't get the best on an Axpert, how low can the Outback go?

@plonkster - Just got stung a bit with Imeon, it wants 140+V, but even serialising my existing 6 panels wan't enough to keep it using it's best (even though it was within spec). I had to add more panels to the series to get it closer to the max of 400V that its max. It's MPPT still keeps it around 230V, but at least getting the rated W now. Big difference since the Axpert would get 1400-1600W for the same panels that the Imeon could only get 800W out of. Adding panels (ie: increasing the Voltage to closer to the Imeon optim), and immediately got the 2000+W (11panels in Winter, expecting 2900W in Summer)