I need help understanding the amperage of my PV arrays

Guda

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Maximum power W 250
Open circuit voltage V 37.6
Voltage at pmax V 30.3
Short circuit current A 8.85
Current at pmax A 8.27
Max system voltage V 600
Fuse A 15

I've got 2x 6s pv arrays 1x 3s in parallel. East tilt 3s, summer tilt 6s, winter tilt 6s. All in parallel.

How is my amperage up to 58.02a? I should be under 30a according to how I thought series worked. The volts go up in series, the amps go up in parallel. Each series set should only be putting out 180v & 8.85a

I'm Cornfused af

Thanks guys for like the 17 thousandth time
 

GMB

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This video explains the math behind parallel and series connections with solar panels.

 

Guda

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This video explains the math behind parallel and series connections with solar panels.
That doesn't help at all but thx any way.

That video says what I say. It does not explain why my amps are over 58.
 

Bud Martin

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How did you measure the current? Did you put on DCA clamp-on meter on the PV wire feeding the SCC to check the current? It sounds like you are looking at batt charging current that SCC converts the PVinput to batt charging Voltage/current.
 
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svetz

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On a cold day you can exceed STC, but your numbers don't make sense for the configuration stated.

I'm guessing (OP wasn't crystal clear) that you have 18 panels, which you believe are in 3 parallel strings of 6 panels in series.
With Vmax=30.3V and Imax=8.27, what you expect is:

PanelString 1String 3String 3
130.3V and Imax=8.2730.3V and Imax=8.2730.3V and Imax=8.27
260.6V and Imax=8.2760.6V and Imax=8.2760.6V and Imax=8.27
390.9V and Imax=8.2790.9V and Imax=8.2790.9V and Imax=8.27
4121.2V and Imax=8.27121.2V and Imax=8.27121.2V and Imax=8.27
5151.5V and Imax=8.27151.5V and Imax=8.27151.5V and Imax=8.27
6181.8V and Imax=8.27181.8V and Imax=8.27181.8V and Imax=8.27

Then when you add up the amps from all 3 strings, you expect 8.27x3=24.81 amps.

What you see is 58 Amps, but you didn't tell us the measured voltage. Ideally the wattage is less than 4500. I'd suggest measuring at each panel/string to see where the voltage is wrong.

Let's say it was 3 in series and 6 parallel... then you'd have 50 amps at 90V. That's a closer to what you're seeing. Take a look at this thread and see if it helps: What does it mean to have solar panels in parallel and series?

Hope that helps and please be careful!
 

JoeHam

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The only way that makes sense is if you are measuring current after the MPPT SCC.

An extremely unlikely possibility is that the wrong label was applied.

Either way just separate one panel from the group and measure it to be sure what is going on.
 

SolarQueen

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I'm not offering any ideas on the current (other than as others said, are you measuring the output of the charge controller?). My concern is having strings of 6 in series wired in parallel with a string of 3 in series. That will pull the voltage of the whole array down. Did you measure the volts? I'm guessing it would be really low, as the 3 would pull down the 6. Maybe it has something to do with the funky readings.
 

Hedges

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"I've got 2x 6s pv arrays 1x 3s in parallel. East tilt 3s, summer tilt 6s, winter tilt 6s. All in parallel."

A bit confusing, saying "arrays" when you may mean "strings"

Do you mean this:

(3 panels in series) || (6 panels in series) || (6 panels in series)

Where "||" mean in parallel
?

Do you have 15 panels?

"Each series set should only be putting out 180v & 8.85a"
"Open circuit voltage V 37.6"
6 of these in series 6 x 37.6 = 225.6 Voc at nominal 25 degrees C.

1) I hope your charge controller is good for at least 250Voc
2) Better unplug the panels before weather gets any colder, because you only have 10% headroom. I allow 16% voltage headroom for -15 degrees C.

"Voltage at pmax V 30.3"
6 x 30.3 = 180Vmp (what you're expecting)

"Current at pmax A 8.27"

"Short circuit current A 8.85"

So you're correct that each string should put out 8.85A maximum into short circuit.
The 180V is point of maximum power, but 225V no-load
Both at 25 degrees C.

If you have a series string of 3 panels under no load, it will generate 8.85A of current flow but all leaks through the solar cells because no current is being drawn externally.
When you parallel two more strings, each 6 panels in series, they will be pulled down to (just over) 3 x 37.6V = 113V. Each will dump its current into the string of 3 panels. That will be something between 8.27A and 8.85A, call it 8.5A.
So 8.5 + 8.5 = 17A will backfeed the string of 3 panels, causing accelerated damage to those cells.
Since they are rated to have 15A fuse, this isn't enough current to damage wires or interconnect; it is only 10% over.

When you connect a charge controller, it will settle to some voltage between 3 x 30.3 = 91V and 3 x 37.6V = 113V, maybe 105V
It will put out about 8.5 + 8.5 + 8.2A = 25.2A

What are your charge controller specs?
You should probably have 5 series strings of 3 PV panels each. With a 15A fuse for each string.
Measure Voc of each string before connecting it, make sure they are similar (or close to zero volts between the two MC cables you're about to connect.)

What is your battery voltage?
 

Guda

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How did you measure the current? Did you put on DCA clamp-on meter on the PV wire feeding the SCC to check the current? It sounds like you are looking at batt charging current that SCC converts the PVinput to batt charging Voltage/current.
I am looking at the Midnite SCC display. It got to 58.2a & started throwing a max amp code

On a cold day you can exceed STC, but your numbers don't make sense for the configuration stated.
It is cold

Then when you add up the amps from all 3 strings, you expect 8.27x3=24.81 amps.
Only correction is the East string is only 3pv. Other than that thats the math I was working with.

What you see is 58 Amps, but you didn't tell us the measured voltage. Ideally the wattage is less than 4500. I'd suggest measuring at each panel/string to see where the voltage is wrong.
Incoming voltage is about 180v. Battery was at 44.5v. Watts were around 2500w.

Let's say it was 3 in series and 6 parallel... then you'd have 50 amps at 90V. That's a closer to what you're seeing. Take a look at this thread and see if it helps: What does it mean to have solar panels in parallel and series?
Yup, all good there. Each parallel string is in series.

My concern is having strings of 6 in series wired in parallel with a string of 3 in series. That will pull the voltage of the whole array down
I used ideal diodes. Think that stops that.
Did you measure the volts? I'm guessing it would be really low, as the 3 would pull down the 6. Maybe it has something to do with the funky readings.
My volts have stayed around 180v-200v. They start in the morning at around 200v & then they drop to 180v when the amps come up.

"I've got 2x 6s pv arrays 1x 3s in parallel. East tilt 3s, summer tilt 6s, winter tilt 6s. All in parallel."

A bit confusing, saying "arrays" when you may mean "strings"
Got it

(3 panels in series) || (6 panels in series) || (6 panels in series)
Correct

1) I hope your charge controller is good for at least 250Voc
Yes, Midnite 250

If you have a series string of 3 panels under no load, it will generate 8.85A of current flow but all leaks through the solar cells because no current is being drawn externally.
When you parallel two more strings, each 6 panels in series, they will be pulled down to (just over) 3 x 37.6V = 113V. Each will dump its current into the string of 3 panels. That will be something between 8.27A and 8.85A, call it 8.5A.
So 8.5 + 8.5 = 17A will backfeed the string of 3 panels, causing accelerated damage to those cells.
Since they are rated to have 15A fuse, this isn't enough current to damage wires or interconnect; it is only 10% over.
I have ideal diodes installed. Thanks to Wills video where he talks about how a fire can start by back-feeding current. Not trying to have another fire.

What are your charge controller specs?
You should probably have 5 series strings of 3 PV panels each. With a 15A fuse for each string.
Measure Voc of each string before connecting it, make sure they are similar (or close to zero volts between the two MC cables you're about to connect.)
Currently I have 1 Midnite 250. I will be switching over to MPP AIO. At that point I'll rewire into 3pv per strings, I'll have 5 of those.

What is your battery voltage?
35v-46.8v

But hopefully soon I'll be building a normal 48v battery.

Thank you all! Still confused on how my amps have doubled. Hopefully some info I have provided will unlock the mystery
 

JoeHam

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My bet is that you are looking at the OUTPUT from the Midnite 250.

The max current OUTPUT of that unit (if i am looking at the right one) is 63 amps. Quite possibly you exceeded that on a cold morning to trip a fault.

Please, please, please measure at the panels with a multimeter as suggested.
 

Guda

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My bet is that you are looking at the OUTPUT from the Midnite 250.

IMG_0748.JPGI

In that screen where it says 4.2a is where is said 58.02. On the left side there was a amber lED & where it says Bulk MPPT it said Max Amps.

Please, please, please measure at the panels with a multimeter as suggested.
How exactly should I do that? I don't have the clamp multimeter. What do I unplug & where do I prob. I'm pretty sure I know the setting.
 

SolarQueen

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That's the battery side, so the output. You would expect it to be higher than the input. In that picture it is dropping the volts by 4, so it would increase the amps out by 4. It is easy to figure out the amps in by dividing the watts by the volts. In the picture you are showing, the input watts is 178W and the volts in is 177.3V. That's 1A coming in. The output is 42.5V, 1/4 the input voltage. So the output current is 4X. 42.5V x 4.2A = 178W! Same as the input, so you are not losing power.

Unless you have a really good meter that can measure over 30A, don't measure with the probes. Most average multimeters can only handle 10 or 20A.

Did the display say Amp Limit? The 250 has an output max of 63A. You were getting close to the limit at 58A. If more power than that is coming in, it will limit the output. Likewise if it is getting too hot, it will limit the output to cool down. Looks like me like everything is working well.
 

Guda

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That's the battery side, so the output. You would expect it to be higher than the input. In that picture it is dropping the volts by 4, so it would increase the amps out by 4. It is easy to figure out the amps in by dividing the watts by the volts. In the picture you are showing, the input watts is 178W and the volts in is 177.3V. That's 1A coming in. The output is 42.5V, 1/4 the input voltage. So the output current is 4X. 42.5V x 4.2A = 178W! Same as the input, so you are not losing power.
Sweet!

Unless you have a really good meter that can measure over 30A, don't measure with the probes. Most average multimeters can only handle 10 or 20A.
Okay, thank you.

Did the display say Amp Limit?
I believe it said "Max Amps". There was a amber light as well.
The 250 has an output max of 63A. You were getting close to the limit at 58A. If more power than that is coming in, it will limit the output. Likewise if it is getting too hot, it will limit the output to cool down. Looks like me like everything is working well.
Awesome! Okay so I need to look in the settings to find out how to see amps coming in. I thought all that info was "in". I didn't realize it was 2 sided.

Much thx to everyone!
 

SolarQueen

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Awesome! Okay so I need to look in the settings to find out how to see amps coming in. I thought all that info was "in". I didn't realize it was 2 sided.

Much thx to everyone!
I don't think it tells you how many amps in. You just need to do the math, watts in divided by volts in.
 

Hedges

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Yes, Midnite 250


I have ideal diodes installed. Thanks to Wills video where he talks about how a fire can start by back-feeding current. Not trying to have another fire.

That's good!

OK, doesn't backfeed the short string of 3.
But that string probably won't ever contribute any power.

With 15 identical panels I would have wanted to do 3 strings of 5 panels, but your orientations don't support that (unless you can move one panel from each string of 6 over to the string of 3). So I suggest 5 strings of 3. Then all panels should contribute.

A lower voltage Midnight (only for shorter strings) would be rated for higher battery current.
Adding another Midnight should let you get all the power from your arrays, avoid clipping.
A combination of angles, e.g. more panels facing East, maybe some panels facing West, should reduce peak amps but produce power more hours, to fit within the existing Midnight specs.

The diodes have to stay cool enough so they don't fail. "Ideal Diodes" have the advantage of lower voltage drop, less power dissipation.
Fuses would be more reliable.
Circuit breakers, if polarized, I wouldn't trust for backfeed protection.
 

Guda

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I don't think it tells you how many amps in. You just need to do the math, watts in divided by volts in.
Got it! Much thanks!
But that string probably won't ever contribute any power.
It does. As soon as the suns up its hitting 300w-600w. I think all said I have about $300 in everything for that series.

With 15 identical panels I would have wanted to do 3 strings of 5 panels, but your orientations don't support that (unless you can move one panel from each string of 6 over to the string of 3). So I suggest 5 strings of 3. Then all panels should contribute.
When I switch to the correct battery I'll be able to use my MPP AIO. runs 145v 80a for input. At that point I'll make 5 strings out of my 3. 3s5p. I have about 40 PV total. 15 deployed. Once the roofs are done I'll be adding 1 large "main" array & a West array also. West will be 3s. Main will be 3s5p ish. I've got a big big sky.

A lower voltage Midnight (only for shorter strings) would be rated for higher battery current.
Adding another Midnight should let you get all the power from your arrays, avoid clipping.
I plan on adding 3 more MPP 3000w AIO to complete this system. I'll probably get one more right after the battery so I can run 240v.
The diodes have to stay cool enough so they don't fail. "Ideal Diodes" have the advantage of lower voltage drop, less power dissipation.
Fuses would be more reliable.
Circuit breakers, if polarized, I wouldn't trust for backfeed protection.
I thought I needed both. I have both ideal diodes & 30a fuses on 2 strings. The other string has a diode & 30a breaker. I bought breakers but they only run 145v. That will be another bonus of getting the correct battery, a nice combiner box with all those features & more. Plug'n play.

I learn like 15 new things a day thanks to yall!
 

GSXR1000

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number of panels x watt of panel / battery voltage
is your output amps and that is what you are seeing
 

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JoeHam

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View attachment 30141I

What do I unplug & where do I prob. I'm pretty sure I know the setting.

Glad you got sorted out @Guda. As suspected, and with a happy ending.

However, in the future if you have problems I always like to start simple. That means start checking individual components. To test one panel you would just unplug it from the array and stick your multimeter leads in the MC4 connectors.

Set on voltage (with a high enough range selected) to read voltage to see that value.

Then set it on the highest amp setting to see short circuit amperage.

Even my freebie Harbor Freight meters can handle most any single panel. If the panels had tested properly then you would know that things weren’t adding up (literally) and you would know it’s the SCC.

I suspected user error reading the info from the SCC output from the start.

I’m something of an expert on user error 😎

Glad it didn’t result in letting the magic smoke out. I have experience in that arena also.
 

Hedges

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I thought I needed both. I have both ideal diodes & 30a fuses on 2 strings. The other string has a diode & 30a breaker. I bought breakers but they only run 145v. That will be another bonus of getting the correct battery, a nice combiner box with all those features & more. Plug'n play.

I learn like 15 new things a day thanks to yall!

Having both fuse and diode isn't any harm. I figure a diode can fail shorted, so better to have a fuse in series.
Some vendors sell 2-pole breakers, to be wired in series so 145 + 145 = 290V or similar.
I don't trust the breakers for backfeed protection if they are "polarized", only work in one direction.
Fuses work, if rated for DC and rated for at least Voc of the string.

30A fuse sounds like too much. What does label on panel say? Since the panels put out 10A, I would have expected 20A or so. (but maybe it does say 30A)
 

Guda

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Glad you got sorted out @Guda. As suspected, and with a happy ending.
I needed a win

However, in the future if you have problems I always like to start simple. That means start checking individual components. To test one panel you would just unplug it from the array and stick your multimeter leads in the MC4 connectors.
I thought the pv had to be hooked up to get a reading. I've tried to prob a pv & nada. I'll play with it again.

Even my freebie Harbor Freight meters can handle most any single panel. If the panels had tested properly then you would know that things weren’t adding up (literally) and you would know it’s the SCC.
Good to know

I suspected user error reading the info from the SCC output from the start.

I’m something of an expert on user error
I'm a expert at making errors 🤓

Glad it didn’t result in letting the magic smoke out. I have experience in that arena also.
I did all the math & was super careful wiring. I am making every effort to be safe. I need to become a multimeter ninja tho
30A fuse sounds like too much. What does label on panel say? Since the panels put out 10A, I would have expected 20A or so. (but maybe it does say 30A)
You are correct. I need 15a breakers. I can swap out the fuses for 15a for now. I am adding a combiner box once I get my new battery built. At that point all my breakers will be the correct 15a per string.

I've been confused by this for months. Thats why I have 30a fuses/breakers, is because I was reading the display wrong & adjusting my parts accordingly.

Much thanks!
 
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