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Help in understanding new DIY solar setup - voltage drop from panels to SCC

Keepingfaith

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Nov 26, 2021
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Hi Everyone,
Honestly: I am not an electrician and understanding 12V has been a challenge - I am very new but just like learning and growing. Like most people here I started to build my own portable solar generator because of Will Prowse's YT videos. Fast forward 8 months of thinking I have this all figured out (my own arrogance) I thought all I had to do is crimp, plug and play...uh, not quite! I bought Will's book which was helpful - so I took that and tried to create a 24V system. I won't bore you with my setup - only the relevant parts: Panels, SCC, batteries, fuses, and wiring. I know that pictures are good so I have included one. More reading is required but I don't know which topic to tackle. I may have the wrong fuses but I'm willing to put myself out there for utter ridicule...but hopefully I learn something new. :giggle:

question in a nutshell: why the major voltage reduction reported by SCC - is it because of my inputted values that I clearly don't understand?

Dilemma: From what I understand, the panels are supposed to bring in around 38 V each when not connected to anything and around 31V when it is (according to the panel specs). Wired in series I scope around 112-115 Volts on the multimeter just before I plug them into my generator, great! However, when I plug the panels into the SCC it reports around 26-35V incoming...it'll flash that it recognizes around 103V and then a few seconds later it'll read around the 20-35V mark. The amps are around 0.6A incoming. So, clearly I don't understand electricity and their values....I think. I've learned how to program the SCC through the MT50 - but some of the terms I don't understand (but will read up on)...here are my values I've inputted: It was hard to get a spec sheet from SOK (I'm not a FB user for their page) - so i found one from a reseller to get my values.

Batt. Type: User
Batt. AH: 206 AH
Temp. Comp Coef: 0
Rated Voltage: 24V
Over Volt Disc.:29V
Over V Disc: 29V
charge Limit: 28.9V
over V Rec: 28V
Equal Chg: 27V
Boost Chrg: 27V
Float Chrg: 26.5V
Boor Rec:26.4V
Low V Rect: 23.2V
Under V Rect: 24.1V
Under V Warn: 24V
low V disc:22.4V
discharge limit:22V
equalize time: 10min
boost time: 180min
Screen Shot 2021-12-16 at 11.28.55 AM.png
 
when I plug the panels into the SCC it reports around 26-35V incoming...it'll flash that it recognizes around 103V and then a few seconds later it'll read around the 20-35V mark
If the battery(ies) are fully charged it won’t charge them

If the sun isn’t ideal the load of the batteries will reduce the apparent voltage to a point

scope around 112-115 Volts on the multimeter
plug the panels into the SCC it reports around 26-35V incoming...it'll flash that it recognizes around 103V and then a few seconds later it'll read around the 20-35V mark.
That is normal. The batteries according to the spec above are nominal 24V, right? So it will charge them at a voltage that is higher than static voltage but 29V or lower according to your specs above.

Basically your open circuit voltage is ~104 at say 5A for the panels. The SCC converts that to 28V at like 16A. That’s what the mppt does. Utilizes the max power available and outputs max ideal charging volts and amps.
 
Please bore us with the details. We need to know EXACTLY which solar charge controller you have. Please provide the full specs or a link to them.
Wow, so many wonderful people to help and advise...and so quickly too! I am grateful.:)

Hehe, I'm so sorry. I honestly never post anything anywhere...sorry if I omitted details! The charge controller is an Epever 50A charge controller. I found these links to directly access its specs/information/manual. Please let me know if you require more information. Also, would you recommend any specific site or book so I don't bother you wonderful people with silly questions?


I certainly don't want to get banned...the below is not an affiliate link...just where I bought it. honest!

Thank you
 
If the battery(ies) are fully charged it won’t charge them

If the sun isn’t ideal the load of the batteries will reduce the apparent voltage to a point



That is normal. The batteries according to the spec above are nominal 24V, right? So it will charge them at a voltage that is higher than static voltage but 29V or lower according to your specs above.

Basically your open circuit voltage is ~104 at say 5A for the panels. The SCC converts that to 28V at like 16A. That’s what the mppt does. Utilizes the max power available and outputs max ideal charging volts and amps.
Thank you for taking the time to respond so fully 12VoltInstalls! Just to help my own confusion :p I wanted to clarify that the settings I placed originally in my post was what I thought should be the values based on the attached document. Some values I couldn't change for some reason - even though I followed the Epever manual of cascading restrictions from manual:

The following rules must be observed when modifying the parameters value in user battery type (factory default value is the same as sealed type):
* Over Voltage Disconnect Voltage > Charging Limit Voltage ≥ Equalize Charging Voltage ≥ Boost Charging Voltage ≥ Float Charging Voltage > Boost Reconnect Charging Voltage. 

* Over Voltage Disconnect Voltage > Over Voltage Reconnect Voltage 

* Low Voltage Reconnect Voltage > Low Voltage Disconnect Voltage ≥ Discharging Limit 
Voltage. 

* Under Voltage Warning Reconnect Voltage > Under Voltage Warning Voltage ≥ 
Discharging Limit Voltage. 

* Boost Reconnect Charging voltage > Low Voltage Disconnect Voltage.


Also, thanks to another user, @SteveSS , I was able to get an actual download of the SOK battery specs I have...I've attached them here.

Ok, so I'll need to read & understand apparent voltage next. Thank you. According the SOK doc. each battery has a Nominal voltage of 12.8 - so does that mean the combined nominal is 12.8*2= 25.6 Volts?

The more I unpack my understanding (one painful step at a time - but worth it!) I realize that perhaps my settings on the SCC are not correct. The reason I say that is the MT50 reports that the battery is only half full...I included a pic for brevity. Maybe I'm in over my head...I've struggled so far and just want to know if the SCC is faulty or is my thinking faulty!

Thanks again for all your help. I am dedicated in understanding this all.
 

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You didn't provide EXACYLY which CC you have. The CC has a model number.
 
After looking at your wiring diagram I'd like to point out a few things I see that are unrelated to your original question (I hope you don't mind).

You have a 50A fuse between the SCC and the bus bars. Since you have a 50A SCC you probably want a bigger fuse to avoid possible nuisance trips. 60A would be a good choice. 75A would also be safe since you have 6AWG wire.

Your 3000W inverter may be too big for your batteries. If you look at the specs for the SOK batteries you will see that they are rated for 100A max continuous discharge. If you were to actually put a 3000W load on your inverter that would attempt to pull 3000W / 24V / 0.85 = 147A. Obviously 147A is a lot more than 100A. To stay within the battery specs you should try to stay at 2000W or below. There is a rumor that the SOK can actually safely discharge at a higher rate than 100A and that SOK may update the specs with a higher number. Something to keep in mind.

Related to the last paragraph is your battery fuse at 300A. While 1/0AWG wire (assuming high quality pure stranded copper with 105ºC rated insulation) can be fused up to 300A, I would suggest a smaller fuse. Since your inverter might pull 147A with a 3000W load, your fuse should be more like 200A. No sense fusing at the wire's max when not needed. A smaller fuse gives a better margin of safety.
 
You didn't provide EXACYLY which CC you have. The CC has a model number.
Oh boy...so sorry, I feel terrible. You are so correct...The model number is a Tracer5415AN. Boy I'm feeling so new to the Internet :p
 
After looking at your wiring diagram I'd like to point out a few things I see that are unrelated to your original question (I hope you don't mind).

You have a 50A fuse between the SCC and the bus bars. Since you have a 50A SCC you probably want a bigger fuse to avoid possible nuisance trips. 60A would be a good choice. 75A would also be safe since you have 6AWG wire.

Your 3000W inverter may be too big for your batteries. If you look at the specs for the SOK batteries you will see that they are rated for 100A max continuous discharge. If you were to actually put a 3000W load on your inverter that would attempt to pull 3000W / 24V / 0.85 = 147A. Obviously 147A is a lot more than 100A. To stay within the battery specs you should try to stay at 2000W or below. There is a rumor that the SOK can actually safely discharge at a higher rate than 100A and that SOK may update the specs with a higher number. Something to keep in mind.

Related to the last paragraph is your battery fuse at 300A. While 1/0AWG wire (assuming high quality pure stranded copper with 105ºC rated insulation) can be fused up to 300A, I would suggest a smaller fuse. Since your inverter might pull 147A with a 3000W load, your fuse should be more like 200A. No sense fusing at the wire's max when not needed. A smaller fuse gives a better margin of safety.
Hi @rmaddy - I don't mind in the slightest! Quite the opposite, I'm grateful for the knowledge and experience you all bring. So, huge THANK YOU. I totally agree with the 50A fuse... I ordered all the parts through Amazon and have been buying/returning things as I learned more. I read at Renogy's site that it'd be OK to fuse to the CC's rating but also read in many places to place one that is 1.5 - 2 times higher. I will do that.

I'm certainly not justifying my purchases for the inverter, Will Prowse mentioned to overkill the inverter for future expansion...not sure if I'd do that soon or not but I'm a planner...almost to the point of analysis paralysis - truly! I will keep the load in mind though as I need to be aware of that.

I only had the 300A fuse handy... I bought a 225A terminal fuse - which just arrived today! I learned so much in one day from you and the others. I only hope to help someone else out - when I have experience and something worth to say!

Thank you so much for the suggestions and the knowledge sharing @rmaddy - I hope you all don't laugh at my portable setup if I send in a picture of it... I omitted the 24-12V converter, 12 V fuse block, shunt, fans, and 12V socket w/USB...as I thought that would be irrelevant to my question.
 
That's good. You didn't blow it up. The 5415 is rated for 150V PV open circuit.

Check your connections. Does the inverter work? Will the inverter output 100W>
 
That's good. You didn't blow it up. The 5415 is rated for 150V PV open circuit.

Check your connections. Does the inverter work? Will the inverter output 100W>
Yes, thankfully! I ran a hair dryer (1500W?) for about 2 minutes and the inverter fans didn't kick in. I then put the hair dryer on the 'super' heat setting and then the inverter fans came on. I haven't tried to run more than that yet. Connections are solid and tight. No heat noticed on the wire when running the hair dryer load.

So, I'll ask another silly question. Could the SCC be damaged? All other replies here make me think the SCC is operating as expected. Should I drain the batteries a bit more to test the SCC functionality? I appreciate your patience in helping me understand just all the things I don't know. I appreciate it.
 
Try powering the CC up again.
1. disconnect solar.
2. disconnect battery.
3. connect battery.
Does the CC know there's a 24V battery attached? Are there any fault codes displayed?
4. connect solar.

You could connect just one of the panels directly to the battery by removing all the wires from the CC and then connecting the two positive wires together and the two negative wires together. If it's sunny the voltage at the battery should slowly start to rise. Check with voltmeter. This test will determine if the wiring is OK and if the battery is OK.
 
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That's good. You didn't blow it up. The 5415 is rated for 150V PV open circuit.

Confirming the above info. The PV input voltage is acceptable, it is well below the Max PV Input Voltage of the solar charge controller.

If the PV cables are measuring 115 volts before being inserted into the solar charge controller and then those same cables are measuring only 35 volts after being connected to the solar charge controller, then something is wrong.

On the other hand, if the multimeter is taking those measurements on the input and output sides of the solar charge controller then the values are completely normal. However, what the display for the solar charge controller is showing indicates a battery at a low state of charge, being charged by voltage that is lower than I would expect to see.
 
Try powering the CC up again.
1. disconnect solar.
2. disconnect battery.
3. connect battery.
Does the CC know there's a 24V battery attached? Are there any fault codes displayed?
4. connect solar.

You could connect just one of the panels directly to the battery by removing all the wires from the CC and then connecting the two positive wires together and the two negative wires together. If it's sunny the voltage at the battery should slowly start to rise. Check with voltmeter. This test will determine if the wiring is OK and if the battery is OK.
Thank you for the troubleshooting tips, Cal, super helpful. I'll have to try that tomorrow unfortunately. I will report back as soon as I can what I find.:)
 
On the other hand, if the multimeter is taking those measurements on the input and output sides of the solar charge controller then the values are completely normal. However, what the display for the solar charge controller is showing indicates a battery at a low state of charge, being charged by voltage that is lower than I would expect to see.
Sorry @HRTKD I am not catchin' what you're throwin' - I'm slow at this - could you kindly explain just a bit further what you mean? How could I do what you're suggesting please? Thank you again for your time and patience.
 
The picture of the SCC display shows only 25.90VDC, that cannot be normal when having 3 panels in series that has Voc of 38Vdc, 31Vmp.
In full sun, your reading of 112-115Vdc when not connected to the SCC, then it drops down to only 25VDC may indicate you have high resistance in the wiring of the panels.
Is the panel string is connected directly to the SCC without any fuse/breaker/junction box, etc?
Can we see the pictures of your setup?
Can you try just 2 panels in series?
 
Sorry @HRTKD I am not catchin' what you're throwin' - I'm slow at this - could you kindly explain just a bit further what you mean? How could I do what you're suggesting please? Thank you again for your time and patience.

@Bud Martin understands where I'm going with my thoughts.

If you measured 115 volts on the PV cables then the solar charge controller should also be reporting that same voltage, or something very close to it. Since it isn't reporting that then something is wrong.

Is it a problem with the solar charge controller, the panels, the cable or the connections? Since you measured 115 volts with your meter, I would start looking at the connections. That's the easiest thing to check.
 
If the PV cables are measuring 115 volts before being inserted into the solar charge controller and then those same cables are measuring only 35 volts after being connected to the solar charge controller, then something is wrong.
picture of the SCC display shows only 25.90VDC, that cannot be normal when having 3 panels in series that has Voc of 38Vdc, 31Vmp.
In full sun, your reading of 112-115Vdc when not connected to the SCC, then it drops down to only 25VDC may indicate you have high resistance in the wiring of the panels.

I guess I can’t see where he mentioned panels were fully exposed to the sun?
Maybe I missed it.

I assumed partial clouds or something

These are good points I overlooked
 
The picture of the SCC display shows only 25.90VDC, that cannot be normal when having 3 panels in series that has Voc of 38Vdc, 31Vmp.
25.9V is close to what would be seen in PWM mode. With MPPT the voltage at the input to the CC should be close to 3 * 31V = 93V
 
25.9V is close to what would be seen in PWM mode. With MPPT the voltage at the input to the CC should be close to 3 * 31V = 93V

Does that solar charge controller have a PWM mode? I have no idea. I downloaded the manual yesterday and quickly scanned it for a couple items I wanted to check. I didn't see anything about a PWM mode, but I wasn't looking for that either.
 
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