Limiting Solar Charge Current from the Charge Controller

[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]

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.

[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]

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]

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?

[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. * * * *

[PNW_Steve]

FWIW the way it is intended to limit charge current is panel wattage.

To clarify..... We should panel for Winter and then take panels offline in the Summer?

[Sunking]

To clarify..... We should panel for Winter and then take panels offline in the Summer?

No, you size the panels for winter. In summer no changes, you just do not utilize the extra energy available or find ways to use it.

[Mike90250]

To clarify..... We should panel for Winter and then take panels offline in the Summer?

No, the controller just does not utilize the excess panel power - IF you have limited it to the design specs. Putting way too much panel (3x would be too much) into a controller, can cook even a well made MPPT when it reaches the limit of what it can throttle back.

[travissand]

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. That makes you a fool.

Why must you insist on me being a fool? I don't know why you think I don't know how a buck converter operates. You are jumping to conclusions again. Since you've been back you appear to be a different more angry person. You quote me when I say adding a 10th panel could push him over his Midnight's max? That's kind of what Matrix set himself. What does that have to do with your rebuttal?
To my knowledge Midnite says the higher the incoming voltage the lower the efficiency but they don't make a big deal of a negligible loss. If Matrix adds another panel as he quoted himself that would put his Midnite into amp limit mode.
I was quite clear and I'll reiterate adding a panel to a system increases the max amperage the controller can put out if you're still under its Max. With matrix's particular panel wattage The Sweet Spot was 9 panels and the calculator recommended 3 in series versus all in parallel. Midnight's calculator tool could be in error when it comes to parallel versus series parallel. This becomes obvious when you punch in the specs for a 40 volt panel on a 12-volt system and it still forces you to put some in series. Matrix was worried about the heat that's why I brought up what I learned with my experiment. I wonder if anyone's done any long-term temperature experiments to see how much life you actually shave off of the charge controller by running it hot but within spec?


It's okay for you to be completely ignorant to the fact that I have done the experiment and I know for myself what runs cooler and what puts out more power. I understand you aren't here measuring things yourself and that's okay. Why are are you preaching about input voltage must be higher than output voltage, obviously I'm bringing in 40 volts and putting out 24. Midnite recommends incoming voltage at 30% more then maximum expected charge voltage. So if I'm equalizing at 31 volts I need 40 volts in which is exactly what I have.

[travissand]

The order a solar system should be designed in is first the batteries according to your storage need.

then size the charge controller according to the batteries Requirements no skimping on this one..

Then after you've done all that make sure you get enough panels to satisfy the batteries requirements and if you can afford two or three times that requirement it will help you greatly on cloudy weeks. Of course greatly oversizing the panels only works with charge controllers that can deal with the oversized solar panels properly and if you really have that many extra Watts you may as well add another charge controller and dump power somewhere that saves you money

[travissand]

The higher the input voltage, the more efficiency the controller is period.

I know you have a lot of things understood but more you speak here in this thread the less faith I have in you. Here's a quote straight from the Midnite webpage "With MPPT controllers the higher the input voltage the less efficient they are."

if you want to see for yourself go to the classic string sizing tool do a calculation and read the notes.

http://www.midnitesolar.com/sizingTool/

[SunEagle]

You know you have a lot of things understood but more you speak here in this thread less faith I have in you. Here's a quote straight from the Midnite webpage "With MPPT controllers the higher the input voltage the less efficient they are."

if you want to see for yourself go to the classic string sizing tool do a calculation and read the notes.

http://www.midnitesolar.com/sizingTool/

In basic electrical circuitry the higher the voltage the more efficient a piece of equipment runs as long as you do not exceed the voltage rating.

Now for Midnite they may have a lower voltage limit where they peak on efficiency but for most charge controllers that is not true.

So I hope you and Sunking can come to an agreement as to what voltage provides the highest efficiency because you are both correct yet are still arguing with each other.

[travissand]

In basic electrical circuitry the higher the voltage the more efficient a piece of equipment runs as long as you do not exceed the voltage rating.
.

We're not talking about a 24 volt system versus a 48 volt system. We all agree a 48 volt system is more efficient than a 24 in every way.
Yes I agree with your statement but that is not what we're talking about here. We're talking about for a 24v system what voltage incoming is the most efficient. Sun King is saying the higher the better with the only limit i assume being the high incoming voltage spec for the charge controller.. I am saying the closer to battery voltage the better.

I trust Midnite when they say it works best when the voltage is at least as high as 1.3 times the highest expected charging voltage. My test showed for a 24 volt system an incoming voltage of 40 was better than an incoming voltage of 80 in my climate with my weather type. Which is 4000 FT elevation temperature between 45 and 65 degrees day and night. Ocean views both sunrise and sunset. And mostly sunny to partly cloudy with little to no rain year round.

I originally was thinking putting 3 in series and taking huge advantage of the voltage conversion might even be able to charge off of really dim light. But the amount of amps coming from panels in that situation is so low it's negligible and it's dwarfed by the continuous heat loss in the larger conversion.
Solar panels are limited by their amps that's why a pwm system has such huge losses. On a pwm 24 volt System a 40 volt 9 amp panel would only put out battery voltage at 9 amps which is a huge loss of potential power versus a mppt system which would bring in 40 volts at 9 amps. Where the mppt takes the best Advantage is where the battery voltage varies. For example my 24 volt battery range is between 24 on up to 29. An mppt controller will very it's voltage conversion to put out the right amount of Volts for the situation. A pwm can't do that, a pwm simply connects and disconnects the panel there's no voltage conversion at all and no way to increase the amperage out higher than the amperage in. It's within this tiny range between 24 and 29 that an mppt gains the majority of its advantage in a 24 volt system. For some reason Midnite wants me to have at least 40 volt panels so that's what I have. Something about the way the buck converter operates requires this. Any higher than that and the charge controller gets unnecessarily warmer.

[SunEagle]

We're not talking about a 24 volt system versus a 48 volt system. We all agree a 48 volt system is more efficient than a 24 in every way.
Yes I agree with your statement but that is not what we're talking about here. We're talking about for a 24v system what voltage incoming is the most efficient. Sun King is saying the higher the better with the only limit being the high incoming voltage spec for the charge controller.. I am saying the closer to battery voltage the better. I trust Midnite when they say it works best when the voltage is at least as high as 1.3 times the highest expected charging voltage. My test showed for a 24 volt system a incoming voltage of 40 was better than an incoming voltage of 80 in my climate with my weather type. Which is 4000 FT elevation temperature between 45 and 65 degrees day and night. Ocean views both sunrise and sunset. And mostly sunny to partly cloudy with little to no rain year round.
I originally was thinking putting 3 in series and taking huge advantage of the voltage conversion might even be able to charge off of really dim light. But the amount of amps coming from panels in that situation is so low it's dwarfed by the heat loss in the conversion. Solar panels are limited by their amps that's why a pwm system has such huge losses. On a pwm 24 volt System a 40 volt 9 amp panel would only put out battery voltage at 9 amps which is a huge loss of potential power versus a mppt system which would bring in 40 volts at 9 amps. Where the mppt takes the best Advantage is when the battery voltage varies. For example my 24 volt battery range is between 24 on up to 29. An mppt controller will very it's voltage conversion to put out the right amount of Volts for the situation. A pwm can't do that, a pwm simply connects and disconnects the panel there's no voltage conversion at all and no way to increase the amperage out higher than the amperage in. It's within this tiny range between 24 and 29 that an mppt gains the majority of its advantage in a 24 volt system.

I agree with what you state concerning PMW CC's. They waste a lot of wattage due to how they work (amps in = amps out).

Since I do not have hands on experience with any Midnite CC's I will bow to those with more experience. But based on what I have read concerning MPPT type CC's they work very well with an input voltage that if it stays below their max input rating yet can be much higher then the battery voltage they are charging.

Again the Midnite CC that you have may be different when it comes to input voltages but when you are discussing electrical circuits at any voltage the higher it is on the wires the lower the losses and higher the efficiency of the circuit..