Limiting Solar Charge Current from the Charge Controller

[Sunking]

So with your particular panel wattage your saying Adding a 10th panel & putting them 2s5p would push the Midnite over its maximum amps?

Complete nonsense and proves you do not know what you are talking about. All MPPT CC are Buck Converters and as such input current is always lower than output current, and input voltage must be higher than output. Putting more panels in series raises the Input Voltage and lowers the Input current. Output is unchanged. The higher the input voltage, the more efficiency the controller is period. That is why you use the manufactures efficiency tables to determine the sweet spot which you refuse to believe. * * * *

[travissand]

Sun-king has forced me to explain myself far deeper then I wanted to in fear of people thinking I am a fool. I wonder how efficient the 48 volt inverters are compared to the 24 volt. My 24V sw4024 inverter the 5000w system seems to consume around 200w more than it puts out. I have not checked the other brand 24 volt inverter in the other system.

My 4260w system has 6 solar panels in parallel on one charge controller and six identical solar panels in the 2s3p configuration on the other charge controller. I did the parallel configuration for the sole purpose of comparing which one brings in more power to finally get to the bottom of that particular debate. Everybody theorizes and talks and uses calculators and talks and talks and talks but I could find nobody that actually tried it so I had to do it myself because I'm a curious person.
So on the parallel array I'm bringing in 40 volts at 9 amps per panel for a total of 54 amps, thats 2,160 watts. 40v X 54 amps = 2,160w.
Now onto the series parallel setup. Each of the 3 sets of panels is putting out 80 volts at 9 amps.
9 amps X 3 sets is 27 amps.
80V X 27 = 2,160w.

According to the voltage calculator the watt loss is only about a half of one percent and comes out to:
9w in the parallel set up.
4.5w in the series parallel setup.

That's a such a small difference.

On the parallel set up I'm not losing as much power to heat therefore the end result is 17 Watts more into the batteries then the more common series parallel setup. That is negligible on a system of this size. I am impressed on the efficiencies in the DC voltage converter in the midnight.

Everything is close together and I did every wire run using the voltage drop calculator and kept my losses lower than the average person.

https://www.calculator.net/voltage-drop-calculator.html

Take note that in each of these two configurations they are still only 9 amps going through each set of wires coming from the panels. My string combiners sits next to the charge controllers and the short wire that has to carry twice as many amps and runs between the midnight and the string combiner is maxed out in gauge for the lug on the Midnite and it's short enough to be a negligible power loss difference.

Yes I had to run more wires costing $0.50 ft from the solar panels a further distance because I didn't put the string combiners on the roof and simply run one more expensive thick wire which I didn't have. Running a lot of 10 gauge turned out to lose about the same as running a single 4 gauge. It was more labor than anything else the wire was cheap. The fact is the purely parallel setup is putting more watts into the batteries and I have proved it by doing this for myself and watching the Midnites side by side.

Sunking has some good points about the cost. Especially with the the need for double string combiners and Breakers which I was lucky enough to have plenty of unconventional electrical supplies for free. Not to mention the extra labor cost you would have to pay an installer to run so many more thicker wires. Yada yada yada it's all been covered elsewhere.

Now when it comes to 24 vs 48. People come on come on go with 48. You need more power than you realize. Why don't we have 120 or 240 volt DC? Danger?
Would 120V DC be more efficient to convert to AC?

[travissand]

To my knowledge Matrix started with a 24 volt system and wants to change the 48 but hasn't found the opportunity .

My 24 volt inverter for the 4,200w system was not my choice but was available free and upgrading would have required purchasing a 48 volt inverter which I would rather have but not if I have to pay for it. I'd rather buy an extra $700 Midnite than a $1,700 48 volt inverter. Consider High shipping cost to Hawaii. a Midnite fits in a $20 flat rate box. Inverter shipping starts at $140.

I'm glad Sunking is calling out the Ridiculousness of the oversized 24-volt setups so the noobs don't get confused but not everyone on a large 24 volt system is a fool. A lot of them started small and found it cheaper to expand then switch over. The 4200 watt system was designed around the inverter and a bunch of spare parts that we had laying around. The 5000 watt system I bought slightly used from a guy who was leaving the island. It originally cost $13,000 + Hardware. He designed it not me. He started with 2500 watts on a single Midnite which was a decent match for his 24-volt system. Shortly after he decided to double his solar and batteries.
I got what I think is a pretty good deal for a total of $5,000.

5000 watts of solar $4,600
sw4024 $1,800
42kwh of batteries $3,000
2 Midnights $1,400
automatic generator start module $?
2 string combiner boxes with Midnite Breakers $?
2 whizbangs $?
2 iota 40 amp battery chargers $550
10000 watt generator $2,000
DC combiner box $125
System control panel LCD $300
and every wire nut bolt washer railing and piece of conduit which transferred seamlessly to my roof. It even came with the main service connect wires to go from the inverter to my breaker panel. He was a kind and generous man.

[travissand]

And we do not care what a fool think. Only a fool would run 4200 watt system @ 24 volts requiring 2 extremely expensive charge controllers. Smart money would run 48 volt battery using only 1 very expensive controllers and save a ton of money money on unnecessary wiring and hardware.

You are so foolish you do not even know that running at 39 volts vs 90 volts is causing you to lose 400% more power on your wiring, and the significant cost of over coming the losses. All you have done is taken the heat off the controller, and put even more heat on your wiring robbing you of power.

You can disagree with me all you want, but it is at your expense. All you have done is pissed away a lot of money and gained nothing. A Fool and their money will soon be parted.

This is Matrix thread, and I have walked him through the design process for over a year and I bet if he were asked would thank me and ignore your foolish advice.

I know you know what you're talking about so you need to rethink what you just said. My wires are not getting hot and I am not losing any potential energy in one system versus the other. The power difference is negligible it's only the heat in the charge controller that's different

[travissand]

And the reason I used the configuration I chose based on my needs and midnite solar's configuration tool. At 3S3P, this was the largest array I could build for 24v with a single CC and not exceed their spec recommendations for wattage etc. If I tried to go 4S2P I was leaving power on the table, and if I tried to go 5S2P midnite tool said it would be too much

So with your particular panel wattage your saying Adding a 10th panel & putting them 2s5p would push the Midnite over its maximum amps? Even then that would be only on the rare occasion during summer at High Noon and the Midnite would simply amp limit itself for that brief time. It would run cooler and you would get more average kilowatt hours per day having the extra panel. Or like I said before it would run really cool if you put them all in parallel provided you had around 40v panels. All that rewiring is probably not worth it though.

In my circumstances I've already maxed out the charge rate of my batteries so when I add more panels I could add enough panels to the existing charge controllers to double the maximum allowed and it would only help me off peak hours & during cloudy days when I otherwise could have only been harvesting 400 watts. Doing this double Overdrive would it raise my cloudy day Harvest to 800 watts. Of course I could not be taking advantage of those extra available 4,000 Watts during peak hours to dump into hot water heating or car charging but I'm not quite there yet anyway. Actually I'd rather Mount them on a Sun Tracker with their own charge controller and study the Harvest difference between the fixed mounted panels but now I'm rambling.

[Sunking]

I don't care what Midnite spec sheet says about efficiencies

And we do not care what a fool think. Only a fool would run 4200 watt system @ 24 volts requiring 2 extremely expensive charge controllers. Smart money would run 48 volt battery using only 1 very expensive controllers and save a ton of money money on unnecessary wiring and hardware.

You are so foolish you do not even know that running at 39 volts vs 90 volts is causing you to lose 400% more power on your wiring, and the significant cost of over coming the losses. All you have done is taken the heat off the controller, and put even more heat on your wiring robbing you of power.

You can disagree with me all you want, but it is at your expense. All you have done is pissed away a lot of money and gained nothing. A Fool and their money will soon be parted.

This is Matrix thread, and I have walked him through the design process for over a year and I bet if he were asked would thank me and ignore your foolish advice.

[travissand]

. Going lower than 90 volts will just make it run hotter and less efficient.

obviously I've already disagreed with you. In case you didn't catch that. I've got two solar arrays connected to the same battery Bank. Each solar array has six 355w panels and has a maximum power output at 39 volts. Each array has its own Midnite 150. One array is all parallel and the other one is series parallel.
I can most definitely guarantee you the parallel unit runs cool. Often actually cool to the touch. And the other one is uncomfortably hot and I can only stand touching it briefly during peak hours.
I don't care what Midnite spec sheet says about efficiencies. I've done it. In the real world with a 24 volt system it runs cooler with 39 volts coming from the panels then 78 volts . I also get more kilowatts per hour into the batteries from the parallel setup

[Sunking]

And the reason I used the configuration I chose based on my needs and midnite solar's configuration tool. At 3S3P, this was the largest array I could build for 24v with a single CC and not exceed their spec recommendations for wattage etc. If I tried to go 4S2P I was leaving power on the table, and if I tried to go 5S2P midnite tool said it would be too much

Matrix you have done well, Warm Fuzzies to you. You did your homework, read the manual, examined the specs, and asked good questions.

[Matrix]

And the reason I used the configuration I chose based on my needs and midnite solar's configuration tool. At 3S3P, this was the largest array I could build for 24v with a single CC and not exceed their spec recommendations for wattage etc. If I tried to go 4S2P I was leaving power on the table, and if I tried to go 5S2P midnite tool said it would be too much

[Sunking]

Matrix said in post 1 Quuestion#3
"FET's can get 63*C during charging) (right now even with the CC's internal fans, AND an external fan on the CC running all day the FET's can get 63*C during charging)"

OK but to the point.

With any MPPT controller one needs to look at the efficiency curves to find the Vmp for maximum efficiency voltage input. Otherwise you are cheating yourself out of power. For the MS Classic 150 is 90 volts at any battery voltage. Two panels in series is not going to give you 90 volts Vmp, it takes at least 3 GT panels in series to do that or up to 4 to 5 x 12 volt panels in series. If you want to error would be on the high side of 90 volts. In order of efficiency from most to least is:

90 Volts
100 Volts
110 Volt
120 Volts.

You would never want to go lower than 90 volts. You could get away with it on 12 and 24 volts, but not 48 volt battery. But if you think going lower than 90 volts is going to make it run cooler, think again and look at the specs. Going lower than 90 volts will just make it run hotter and less efficient.

[travissand]

Please explain how you could possible know that?

Matrix said in post 1 Quuestion#3
"FET's can get 63*C during charging) (right now even with the CC's internal fans, AND an external fan on the CC running all day the FET's can get 63*C during charging)"

[Sunking]

You're charge controllers are getting up to 145 degrees Fahrenheit.

Please explain how you could possible know that?

[travissand]

You're charge controllers are getting up to 145 degrees Fahrenheit. I've got ten 250w panels so that is 2 in series X 5 sets. You have 3 in Series so your panel voltage is likely much higher and your charge controllers are working much harder. I wouldn't like those temperatures I'm sure they can handle them just fine still though I just don't like it. If I were in your shoes I'd probably buy a 10th panel and rewire them 2 in series or if a single panels voltage is sufficient I'd put them all in parallel.
I have an identical system where I didn't put any panels in series & the charge controller is pretty cold. Both charge controllers are pushing 96 amps each into the batteries often. I had to run a hell of a lot of wires for the system that had all parallel panels but it was worth it for the experiment. Both charge controllers charge the same battery Bank so I can watch the midnights real-time wattage and I'm getting more power from the parallel setup.
So which method is better? I still haven't determined that because the series system gets a head start because it reaches charging voltage sooner in the morning and before the parallel system can catch up the batteries are full. Lol. it's pretty much negligible and has more to do with how hot you want your charge controller to run. With two or three panels in series I guarantee that ants won't be living in that charge controller. But that can be accomplished with a mothball as well
I'll attach December's daily high temperature chart from the Midnite I have connected to the 2 * 5 array.

[Matrix]

Thanks SK. That was my other thought. By limiting charge I would slow down charging to the point it might not finish on solar. Right now with the array I have I get a fully charged even on partly cloudy days

[Sunking]

Matrix FWIW C/6 is not going to hurt L16's. No reason to spend more money on something you do not need. Most likely outcome is you just slow things down so much that in shorter sun hour days your batteries never get fully charged. Just monitor water use and if it gets excessive, than take another look. Until then relax.