Hitting max voltage limit on my CC, help?

[Guest]

Hello. I am not sure if this is the perfect place to post this question, so if there is somewhere better please let me know.

We have an outback FlexMax 80 cc that is rated up to 145 volts (150 max).

I am trying to wire 8 solar world 245 watt panels 4 ea. in series/parallel (1960 total watts) to charge a 24v bat bank. The FlexMax 80 is rated up to 2000 watts for a 24v bat bank.

The problem that I am running into is the Voc for each panel is 37.7 which puts it at 150.8 just over the "damage" warning for the cc.

The panels are 8.16 Imp, 30 Vmp, 37.7Voc. I don't want to burn up our cc so my question is:

Is there any inline diode (like a zener diode) that I could put on it to limit it to 144 or 145 volts?

or is there any other safe way to hook up these panels to this cc?

I am not overly familiar with Voc. From what I understand it is when the panels are not under load. Is there any way I can keep the panels under a small load before the cc so they never produce the full 37.7 Voc? On cold mornings before the sun even hits them directly they shoot right up to 147 volts. After they warm up the come back down, but about half our year here it is cold enough where they produce these higher voltages in the morning and the colder it is the longer it takes for them to warm up which means less power, plus I would never chance it and leave them connected to the FlexMax just in case they could burn it up...

any my help is appreciated. Thank you.

There is no Zener Fix. A Midnight Solar "clipper" could work, but that is pretty expensive. Also Midnight Classic 200 or 250 would work.
Magnum PT-100 has 185V max solar input
http://www.magnum-dimensions.com/pt-...rge-controller
And - you did post in some unrelated topic, and us Mods can't move posts to their own threads. So this is locked, and I will start a new thread for you. and come back and delete this. Mike

[sensij]

Two options... put in a 9th panel so you can do three strings of three panels each, or rewire them so you have 4 strings in parallel of two panels each. Either option will require each string to have its own over-current protection... a combiner box or in-lines fuses are typical.

The FM80 can be over-paneled, so 2000 W is not a hard limit. If your array is capable of providing more than that, the controller will limit itself to 80 A output. Although you may clip a small amount of power in the middle of cool, sunny days, you'll be thankful for the extra energy produced in the morning, afternoon, and when the clouds are out.

[Guest]

Thanks Sensij,

The nine panels was an option I was considering. We have 10 of those panels, only 8 are in that specific array so getting a ninth one up there just for a year or under is actually a bit more work than I was hoping to do. I also figured the fm80 could handle 2205 watts becaus it would only be 113.1 Voc at 24.48 Imp in, but unfortunately 91.88 Imp out to charge the 24v bat bank. So I figured to stay away from that because I really don't like just burning off the extra 11+ volts and it would probably wear the fm80 more.

Just looking back at all my figures I just came across a 32 amp configuration that I think is what you are talking about. I apologize, I have been pretty under the weather and my brain just isn't too clear.

I had 32 Imp written down but no voltage. If I did 2 panels in series that would be 75.4 Voc @ 8.16 Imp. X 4 parallel that would be 32.64 Imp @ 75.4 Voc, 60 Vmp. Correct? (And that just took me about 30 minutes to wrap my head around)

If that is correct I have no idea why I did not just use that. But half of the things I've done for the last week have been pretty much the same. I actually fried our internet router when I hooked up the polarity backwards 2 days ago. And I marked and color coded everything extra (which I usually don't even do) and still hooked it up backwards... I have literally been spending hours on this really baffled that I couldn't get 8 panels hooked up to this easily.

That is the exact way and still not too bad of a load for 30' of 8 awg wire. And no excess voltage or amperage. (Thank goodness I didn't go through the hassle of trying to get a ninth panel close to the other ones...)

I am going to have to go through everything and make sure I didn't miss or mess anything else up.

i am am sorry if I took up any of your time. And I appreciate the help. Thank you so much.

[sensij]

Thanks Sensij,

The nine panels was an option I was considering. We have 10 of those panels, only 8 are in that specific array so getting a ninth one up there just for a year or under is actually a bit more work than I was hoping to do. I also figured the fm80 could handle 2205 watts becaus it would only be 113.1 Voc at 24.48 Imp in, but unfortunately 91.88 Imp out to charge the 24v bat bank. So I figured to stay away from that because I really don't like just burning off the extra 11+ volts and it would probably wear the fm80 more.

Just looking back at all my figures I just came across a 32 amp configuration that I think is what you are talking about. I apologize, I have been pretty under the weather and my brain just isn't too clear.

I had 32 Imp written down but no voltage. If I did 2 panels in series that would be 75.4 Voc @ 8.16 Imp. X 4 parallel that would be 32.64 Imp @ 75.4 Voc, 60 Vmp. Correct? (And that just took me about 30 minutes to wrap my head around)

Yeah, your math is good. In the 2S4P arrangement, from the point the four strings are combined, you'd want the conductor ampacity to be 1.56 * Isc * 4, and double check the voltage drop, too.

In the 3S3P configuration, the FM80 doesn't "burn" off extra volts when it goes into current limiting mode. It moves the operating voltage of the PV circuit to something between Vmp and Voc, which produces less electrical power than Vmp would, and stays within the 80 A output limit (or whatever limit below that you choose to set). The extra power that is lost is just a small amount of irradiance distributed over the entire area of the array that isn't converted to electricity, and doesn't meaningfully affect the cell temperature (the photon to electron conversion is already <20% efficient at Vmp, so dropping it slightly doesn't hurt anything), .

[Sunking]

You only have two options, take it or leave it.

1. 2 panels in series
2. 3 panels in series.

Take your pick. It means with 2 in series you can work with 2, 4, 6, or 8 panels max. With 3 in series means 3, 6, or 9 max panels. Easy peasy, take your pick.

[Guest]

Thanks again Sensij,


I see what you are saying about the extra amps. I still would hate to loose even that little bit when I don't have to. We live off grid and tend to frown on wasting anything if it can be helped.

I am actually quite embarrased that I posted that question when the answer was so obvious and literally right in front of me... Well I hope it at least helps someone else down the road, or gives someone a good chuckle.

Thanks again, take care.

[sensij]

Thanks again Sensij,
I see what you are saying about the extra amps. I still would hate to loose even that little bit when I don't have to. We live off grid and tend to frown on wasting anything if it can be helped.

You are welcome! Instead is focusing on what is wasted, think about it another way. The amount lost to clipping might be 1% of annual production. So, you could think of that 9th panel as a zero waste 242 W panel instead of a 1% waste 245 W panel, and that is equivalent effect on the overall economics of the system.

If every hour of every day was clear and sunny, the economics of clipping might be different. In the real world, you can over-panel a fair amount before it stops being worth it, especially if you can aim some panels SE and some SW to stretch out your charging day.