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Too close for comfort..? PV Voltage.

jamiegreen

Solar Enthusiast
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Nov 8, 2021
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Getting round to doing the final wiring on my Canadian Solar panels soon, they run at 37.7 OCV, 265W X8.
I have a MorningStar 60a MPPT running a 24v lifepo4 bank.

It sure would be nice to run a 4s2p setup on the panels, my problem is that comes to 150.8V. The max input of the tristar is 150v.
temperatures here generally dip to around -5 and at worst -10, but I haven't seen it that cold.. yet.
Too close? Potential damage? Do I already know the answer and just want confirmation..? Maybe.

Worst case I have to go with a 2s4p setup.. bit of a pain with all those Y branches etc, don't really want to buy a combiner box.
 

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hello!

nice array! looks really powerful ☀️

some people say look at the historic lowest temperature and prepare for 1 degree Celsius below that and calculate the Voc of panels given Voc at STP or NOCT with specified operating temperature and specified voltage change coefficient.

personally i would recommend using at the very least, the exact historic lowest temperature

up to 5 degree C below historic record lowest temperature is probably the furthest i would go with safety super optimizing
 
Horrifying. You NEVER exceed max PV voltage.

Not sure what country, so don't know if you mean -5/-10 °F or °C. Either way, your panel Voc will be over 150V.

At freezing, your panels will produce 161V.

For a 4P array, you need over-current protection on each string. Either get a combiner box, or put fuses in each string.

This table has the NEC correction factors. You need to divide your MPPT max Voc number by the appropriate number in this table:

 
Horrifying. You NEVER exceed max PV voltage.

Not sure what country, so don't know if you mean -5/-10 °F or °C. Either way, your panel Voc will be over 150V.

At freezing, your panels will produce 161V.

For a 4P array, you need over-current protection on each string. Either get a combiner box, or put fuses in each string.

This table has the NEC correction factors. You need to divide your MPPT max Voc number by the appropriate number in this table:

Thanks for link... eerr, yes that could indeed bring me to 170v. Guess thats decided then.
I'll have another look at combiner boxes.. I just like to keep the amount of IP65 (weather rated) components to a minimum.
 
Thanks for link... eerr, yes that could indeed bring me to 170v. Guess thats decided then.
I'll have another look at combiner boxes.. I just like to keep the amount of IP65 (weather rated) components to a minimum.

Single ~$10 MC4 fuse in each string is sufficient and fast/cheap. a 4-1 combiner box is going to cost you $.

This:


or a Midnite Solar MNPV4 (+ breakers) are good options. Spendy, but good.
 

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Going with in line fuses.. does this look about right to you?..Just a quickie.
downside of inline fuses is that you can't disconnect a live panel without possible excitement. You are much better off with a combiner box and breakers. You can do the fuses now, and do a combiner box/breaker setup later, but it is very worth it. It makes finding a bad panel a lot easier as you can easily switch off all by one string to see who is the guilty party.
 
I've connected/disconnect 3S 72 cell panels dozens of times in full sun. I've never experienced even a hint of excitement, but I agree on the awesomeness of the combiner. I have a MNPV6.
 
The downside of lower voltage and more strings, be careful with keeping your string current in check with proper conductor size.

8 - 285w panels in 2S4P looks like around ~30A DC (conservative) going to the SCC. This is where a combiner box is nice to upsize that home run conductor to the SCC.
 
Doesn’t look easy unless a full rebuild of that nice ground mount he has already.
 
Webo solar has a nice sale on Midnite MNPV boxes and breakers at the moment. I just purchased one two weeks ago.
 
Doesn’t look easy unless a full rebuild of that nice ground mount he has already.
Looks like the horizonatal purlins might be unistruts. If so, a simple extension could be bolted onto one end to add one more panel. Yes, it will look odd. but it will work.

Alternatively, replace the TriStar controller with a controller that handles higher voltage. I'm wiring similar panels 4S2P because I use Midnight 200 controllers.

BTW, I very much like that rear post/rod for adjusting array angle with the telescoping rod. Never thought of that. That appears to be an elegantly simple way to adjust the seasonal solar array position. Don't think I could make it work though with my rotating arrays.
 
Missed some notifications sorry!

combiner box/breaker setup later, but it is very worth it.
I've been thinking on it, making up my own combiner box actually works out around the same price as in line fuses, only downside is an ugly white box shoved on the frame lol, using a fairly standard ip65 UK style consumer unit with slight modification and replaceable fuse type breakers. But then I thought it wasn't worth the hassle... now I don't know.

I've never experienced even a hint of excitement
I live in the UK... I probably wouldn't struggle to find a dull day if I had to disconnect, although I do already have a main manual disconnect fitted, just can't be seen in photo.

be careful with keeping your string current in check with proper conductor size.
I already had this in mind when burying my cable 800mm down in 3" conduit, Its 10mm SWA over 25 meters so more than capable whichever panel arrangement.
Can you add one more panel and go 3s3p?
....No, lol. its too much hassle, aside from these are somewhat "older" panels now, very difficult to find in the UK, I don't want any odd looking out of place panels, although I agree it would have been ideal. I build the frame specifically for 8 panels, and with the serious weather conditions up here I wouldn't want to stress it any more anyway.
Alternatively, replace the TriStar controller
Honestly really don't want to do this, I bought it brand new about a year back, its been in the box since, only now really getting things into action. Yes it would have been nice to have a victron that could communicate with my other victron equipment, but when it comes to charge controllers I put Morningstar in a different class to most.. so I would like to keep it.
BTW, I very much like that rear post/rod for adjusting array angle with the telescoping rod. Never thought of that. That appears to be an elegantly simple way to adjust the seasonal solar array position. Don't think I could make it work though with my rotating arrays.
Thank you, I mean in all honestly those 2 rear supports were an afterthought, after fully assembling without them I soon realised my box section etc was on the thin side, and the whole thing had too much twist and flex in it, those 2 rear supports solved all that and I haven't long had 60mph winds which it handled no problem at all.


Another fusing question, when fusing all 4 strings individually, would you still fit a main fuse after this handling the complete array?
 
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