Very close to max wattage on my Classic 200

Wbuffetjr1 · October 2017

Just installed my system this past Summer. I have 9 Solarworld 345 watt panels connected in 3 strings of 3 for a total of 3,105 watts. I have a Classic 200 charging a 48V battery bank. The "max allowable wattage" on the Classic 200 is 4,080 watts. So far, I have seen a high power of 4,024 watts produced in the logs. If this thing happens to get up to say 4,100 watts can it damage my charge controller or will the Classic protect itself by limiting the power??

mcgivor · October 2017

Probably not, a quality company would have conservative maximums, Midnight is a quality company, so the maximum wattage seen would probably be a transient high and safeguards are more than likely incorporated, Midnight users please comment.

Horsefly · October 2017

Chad - It looks to me that the Classic 200 limits its output current to 79A, according to the spec. Even if your PV array may be capable to produce more power than would translate to 79A, it will only produce what the CC pulls. The Classic will limit what it converts for your batteries, so there really isn't anything you can do to damage it with "too much power". At least not if you 3 x Voc can't ever get above the 200V limit of the Classic 200.

Steve

Estragon · October 2017

Going a little over 200v on a classic200 is okay. From 200 to 248v it stops charging, but lives on to charge when the voltage drops without letting the magic smoke out.

As others mentioned, the classic won't normally draw more than rated even with more panel. To a point, extra panel is a good thing for lightly overcast days. Like pretty much any electronics though, running it at full rated output for long periods can make them hot internally and shorten lifespan.

Photowhit · October 2017

Estragon said:

Going a little over 200v on a classic200 is okay. From 200 to 248v it stops charging, but lives on to charge when the voltage drops without letting the magic smoke out.

To add to what Estragon is saying the VOC is in danger of dropping into the Hyper VOC range for the Midnite classic, it's usually in the early morning when the panels are cold. Once the sun warms them the VOC will drop. So the time you are in the "Hyper VOC" range is when the panels aren't very productive so little to no loss!

Wbuffetjr1 · October 2017

Thanks everyone!

I am still slightly confused. I just don't see how to predict what these panels are going to do at this altitude. The Classic sizing tool for the 200 says my system is good for hyper VOC down to -93C. However, I am assuming that number isn't going to be the same for me at 10,000'. Surely I will still have plenty of cushion, but is there anyway to calculate a more correct number?

Bottom line is I don't want to damage anything this Winter when there is no easy way to get up there regularly to keep an eye on the system.

Photowhit · October 2017

We might be able to call on the All mighty @boB ! To give some insight, but I think you're fine.

Photowhit · October 2017

I guess I should explain, boB is boB Gudgel who diesgned the Classic and is a forum member here.

They also have their own forum at;
http://midniteftp.com/forum/index.php

BB. · October 2017

Voc-cold is NOT the result of sun (any sun, from weak morning sun to full noon-time sun) is the same... It is the temperature of the cell... Usually, the worst case is morning sun on a cold panel/solar cell (note that radiative cooling can bring cell temperatures down further--Like frost can form on an open field even if ambient temperatures are above freezing). Once you get "normal" sun on the panel, the cells generally are generally above ambient temperatures.

Any sort of loading will bring down Voc (voltage open circuit) voltages towards Vmp (voltage maximum power) or lower... But we want to be sure that your system will not "self destruct" under normal conditions. And that you do not have to pull the fuses/open the array breakers on frosty mornings to protect the charge controllers.

-Bill

Estragon · October 2017

To give you a sense of winter sun can do to panel temps, last Jan I during a cabin visit I cleared the snow off the arrays. The bottom layer was the sort of wet sticky stuff that falls early in winter, and by Jan it was pretty crusty and stuck on. A fair bit was still stuck on, but I got about 50% clear.

Even at -25°c and with a bit of a breeze, it took less than an hour for the rest to melt.

At altitude, I suspect you could see better current in thinner, dry air, but not higher voltage vs sea level at equal ambient temps.

boB · October 2017

10,000 feet, eh ? The modules should put out a bit more up that high. Less air for cooling too. I know that Classics have been operating up at that high of altitude but I haven't been to any of those installations so I'm not sure what to expect.

Maybe just try it and report back ? The Classic may limit itself, current-wise. If it does limit the current, it does this by raising the input voltage and so the Classic MAY get a bit hotter.

boB

Wbuffetjr1 · October 2017

Thanks again for all the insight. I will have a load on the system every day throughout the winter. I will be running a 1/3hp electric motor on a timer for 10 hours every day. Timer kicks on a couple hours before sunrise. If I am hearing BB correctly, that will help keep things reigned in. I would think any extra heat in the room from the classic would be welcome up there through the Winter.

boB - I can definitely report back. I am new to solar and the classic so I cannot remember, do the logs show max amps also? Is that all I would be looking for?

Thanks everyone!

BB. · October 2017

Voc is, in some ways, a theoretical figure. Any loads on the panel can lower the voltage (a bit)... However, since we have no control over the how the charge controller operates (sweeping current for MPPT function, "restarting" at the sun rises, etc.).

I would suggest that you do not push the limits.

HOWEVER, Midnite for (most?) of their controllers has a high voltage safety mode. Basically, if the array hits maximum input voltage, the controller shuts down and protects itself to (for example) 150VDC+Battery Voltage. HyperVOC:

http://midnitesolar.com/pdfs/whyHyperVOC.pdf

-Bill

Wbuffetjr1 · October 2017

Bill, I hear you and I was actually trying NOT to push the limits. I knew the panels would produce a little more than the rated wattage, but I had no idea it could be 30% more! Now I find myself pushing the limits and I am not sure what to do.

I suppose as long as the controller shuts down to protect itself then I will be ok. Although I am sure putting the controller through that regularly can't be good for longevity.

BB. · October 2017

In terms of output wattage... It is Vmp*Imp... Cold panels, Vmp rises and does support higher output power for an MPPT type charge controller.

In general, good quality MPPT controllers will limit their output current to rated levels--Safely and reliably.

However, obviously, the more energy you pump through the charge controller, the more heat that is generated. Midnite controllers (and others) will reduce power throughput if the controller temperatures rise above programmed limits.

And, at 10,000 feet, the air is much thinner and most electronics/motors/etc. should be derated to because of the lack of ability of of high altitude air to carry heat away.

If you want to get full performance of the solar array--You may need to split it (say in 1/2) and run two charge controllers in parallel to charge the one battery bank (that is perfectly OK).

Or, possibly other design changes (Classic 150's have lower input voltage, but higher output current ratings). You are already at 48 VDC battery bank--So you cannot go to a next "higher standard voltage" battery bank.

-Bill

Estragon · October 2017

Splitting the array with a second classic also has the advantage of some redundancy for when a controller fails.

If you do stay with the single classic, you might want to inspect it regularly to make sure vents don't get blocked. I haven't had a problem yet, but I have to think a warm classic might make a nice nesting place for a critter.

Wbuffetjr1 · December 2017

Just figured I would post an update.

At 12:30 pm yesterday the system apparently hit it's current limit. Class Amps were 80.2 and Power was 4.2k watts. There was an upwards arrow with a line above it in the information bar on My Midnite. First time I have seen it do that since I got it hooked up to My Midnite on 11.7.17. I have also only seen >4,000 watts in the log one other time. I'm assuming if it current limits just a handful of times per year it won't be THAT hard on the Classic. I was surprised it happened in the middle of the afternoon.

I will thoroughly inspect everything each time I am there. The system is in it's own ICF structure that is built very tight. Hoping to totally keep pests out. I will throw some poison in the crawl space for good measure tho.

arby · December 2017

Can't you screen the crawl space. Seems a bit over the top to poison animals with bait. My inverter was damaged by a mouse and her offspring but I was to blame. I left a small end panel off. If the CC and inverter etc. are all in proper shape, a mouse cannot get into them.

mcgivor · December 2017

Be careful with poison if you have dogs or cats, secondary poisoning can lead to an......how do you put it, an ugly death of your pets. My problem is geckos, lost an inverter due to their seeking a nesting spot, used mosquito net on the replacement, lessons learned.

littleharbor2 · December 2017

Birds of prey can also be poisoned by eating poisoned rodents.

arby · January 2018

mcgivor said:

Be careful with poison if you have dogs or cats, secondary poisoning can lead to an......how do you put it, an ugly death of your pets. My problem is geckos, lost an inverter due to their seeking a nesting spot, used mosquito net on the replacement, lessons learned.

Ugly death is what any animal gets, mouse or dog.

Very close to max wattage on my Classic 200

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