diy solar

diy solar

Charge controller shuts off every few minutes then comes back on

SolarNoah

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Mar 20, 2021
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Hello! I have been having an issue with my charge controller that I have been unable to resolve. Any insight would be very much appreciated.

System (only what's relevant):
  • Two, 300w 24v solar panels in series. 30 amp inline fuse before charge controller.
  • 60 amp renogy rover MPPT charge controller that goes to a 40 amp fuse
  • 12v lithium batteries
  • *everything listed above is running on 10awg wire (using the same wire that came with the solar panels)
  • smart battery monitor

Issue:
  • Batteries charge like normal in the morning. Around mid-day (seems to be when I'm pulling 27+ amps), my charge controller goes into a strange cycle.
    • It charges the battery (usually gets around 90% charged), shuts off (the charge controller doesn't show any warning lights, it just shows that it isn't receiving any sun), then turns itself back on.
    • This cycle usually repeats every few minutes until either (1) the batteries are fully charged, or (2) I block the solar panels to reduce the incoming sunlight.
    • Photo attached showing a few minutes of this on the battery monitor app. Absolutely no power is coming in at the low points. My batteries are just draining. I just didn't have much running when I took this photo.

I have been on the phone with renogy all week and haven't had much luck. So far, I have:
  • checked for loose wires
  • checked for hot wires. The wires coming out of the charge controller and going to the battery were warm, but not hot.
  • messed around with the settings on the charge controller
  • reset the charge controller
  • scoured the internet for any similar issues... but have come up empty!
I have had this system running well for a few months, but recently have moved to a place that gets more sun (I'm in a campervan). I assume this may have something to do with it.

The only things I can think of are:
  • There is an issue with my charge controller. Renogy said this may be the case. I'm under warrantee, so can swap it out if needed.
  • Something with the wiring? Maybe I need to be using a higher gauge? That said, I don't know why this would cause the controller to shut off like this. I know 10awg wire isn't ideal, but I called renogy when I set this up; they didn't seem to think the 10awg wire would be an issue...
  • Something going on with one of my fuses?

Thanks for reading this far! Really hoping someone is able to shed some light on this.

Cheers,
Noah
 

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What Lithium batteries are you using?

I think you may be exceeding the charging current limit and the BMS is shutting off. 600 watts at 12 volts in 50 amps. That is a lot of charge current for many 12 volt LFP packaged batteries.
 
BMS over voltage limit would be my first guess too. What BMS are you using?
Your battery could be out of balance or your charge limit could be set too high.

edit: The individual cells in the battery can get out of balance and one cell can go above the cell voltage limit. The BMS shuts down charging to save the cell.
The charge controller only knows the voltage of the whole battery.
 
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1) Provide the battery specs; BMS settings if it's a programmable smart BMS, or the BMS info provided otherwise, every bit counts.
2) The Settings you have programmed into the SCC
 
If it isn't the BMS (very good chance it is), run the system on just one PV panel at a time. This could rule out a bad panel or an over voltage situation.
 
Thanks, all. I am using two 12v battleborn batteries, wired in parallel. I set the charge controller settings as follows:
  • OverVolDsc 14.7v
  • ChgLimtVol:14.6v
  • EquChgVol: 14.4v
  • BstChgVol: 14.4
  • FltChgVol: 13.6v
  • BstChgRev: 13.2v
  • LowVolRev: 12.0v
  • UndVolWrn:11.5v
  • LowVolDsc: 11.0v
If it helps, yesterday the batteries were at 13.34v when the on/off cycle started happening.

I also have the batteries connected to a 40amp DC-DC battery charger (for when the car is running), so I have seen the batteries accept upwards of 40 amps at a time without issues.

I will try running the system on one PV panel at a time later, once the sun is a bit stronger. The idea here is to see if one panel may malfunction once its output reaches a certain level? So If this was the issue, I would still be seeing the SCC shutoff, but at a much lower amp output?

Thanks so much for all of the responses already. Please let me know if any other information would be helpful.

Edit: when the SCC turns off, the PV indicator is not lit up.
 
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What Lithium batteries are you using?

I think you may be exceeding the charging current limit and the BMS is shutting off. 600 watts at 12 volts in 50 amps. That is a lot of charge current for many 12 volt LFP packaged batteries.
This is the first system I have set up, so I may not fully understand.

The solar panels are 600 watts at 24v. The positive lead leaving the SCC has a 40amp fuse attached to it that is not popping, so I know it is not exceeding 40amps.

I left more details in my comment above. Thanks!
 
The panel voltage is higher than 24 volts. And even if it was just 24 volts going into a 12 volt battery, the output of the charge controller would be about half the voltage, but at nearly twice the current. Good charge controllers do switching DC-DC conversion that is over 95% efficient. But with two BattleBorn 100s, they should take over 50 amps without a problem, so it is more likely that the batteries are just fully charged and the charge current is shutting off from the BMS units in the batteries. Like ArthurEld said, the cells may have come a little out of balance, and a single cell could be going over voltage even though the external post voltage is fine for 4 cells in series. This can be an issue with LFP cells as the voltage of each cells starts to climb quickly right as it reaches full charge. The internal BMS does have balancing, but it is likely very low current. If it is a balance issue, I can only think of two easy ways to get the cells back top balanced without tearing open the battery.

My first idea is just changing your charge controller settings for a day or two and see if it will bring them inline.
You said the cycling started when the batteries were at 13.34 volts. If the cells are perfectly balanced, that would be 3.335 volts each. That is basically fully charged on LFP. And the protection shut off probably happens when a cell reaches 3.65 volts. For one cell to jump up that much sounds very bad, but it really isn't. Just a 5% state of charge difference up there is enough for that to happen. One way to possibly balance up the cells would be to set the absorption voltage to just 13.3 volts, below where it started to cycle, but allow 3 hours of absorption. If the voltage just hangs there at 13.3 without shutting off, the charge current should be tapering down as the internal BMS tries to balance the cells.

If the first way does not work, then we need to get more drastic. This is going to be very slow.
Apply a very low current limited charge setting of under 100 ma and voltage limited to under 14 volts. That will try to bring all of the cells up to 3.5 volts, but at a low enough current that the BMS balancing can hold the already full cell(s) from going to over voltage. If this also triggers a shut off, you will need to run even less current and maybe lower the limit voltage even more. A decent CC/CV power supply should work just fine for this. The idea here is that the balancer in the internal BMS can pull some current from the cells that are going too high in voltage. As long as the charging current is less than the balancing current, the BMS can stop the full cell from getting any more charge current while the other cells can still charge. If the charge current is too high, even 100 ma more than the balancer current can easily push a full cell to the 3.65 volt BMS shut off level.

The only problem with this is that LFP cells do get stressed about 3.5 volts, so don't leave the battery up at 14 volts for more than a day at a time. You should be able to pull power from the battery, but stay above 50%, and then slow charge it up a few times, and that will also help bring them back into balance without stressing the high voltage end as much. A day or two at 3.5 volts per cell is not a big deal, but try not to leave them up there for a week at a time. Every manufacturer recommends storing LFP batteries at 50% charge to extend their life.
 
The panel voltage is higher than 24 volts. And even if it was just 24 volts going into a 12 volt battery, the output of the charge controller would be about half the voltage, but at nearly twice the current. Good charge controllers do switching DC-DC conversion that is over 95% efficient. But with two BattleBorn 100s, they should take over 50 amps without a problem, so it is more likely that the batteries are just fully charged and the charge current is shutting off from the BMS units in the batteries. Like ArthurEld said, the cells may have come a little out of balance, and a single cell could be going over voltage even though the external post voltage is fine for 4 cells in series. This can be an issue with LFP cells as the voltage of each cells starts to climb quickly right as it reaches full charge. The internal BMS does have balancing, but it is likely very low current. If it is a balance issue, I can only think of two easy ways to get the cells back top balanced without tearing open the battery.

My first idea is just changing your charge controller settings for a day or two and see if it will bring them inline.
You said the cycling started when the batteries were at 13.34 volts. If the cells are perfectly balanced, that would be 3.335 volts each. That is basically fully charged on LFP. And the protection shut off probably happens when a cell reaches 3.65 volts. For one cell to jump up that much sounds very bad, but it really isn't. Just a 5% state of charge difference up there is enough for that to happen. One way to possibly balance up the cells would be to set the absorption voltage to just 13.3 volts, below where it started to cycle, but allow 3 hours of absorption. If the voltage just hangs there at 13.3 without shutting off, the charge current should be tapering down as the internal BMS tries to balance the cells.

If the first way does not work, then we need to get more drastic. This is going to be very slow.
Apply a very low current limited charge setting of under 100 ma and voltage limited to under 14 volts. That will try to bring all of the cells up to 3.5 volts, but at a low enough current that the BMS balancing can hold the already full cell(s) from going to over voltage. If this also triggers a shut off, you will need to run even less current and maybe lower the limit voltage even more. A decent CC/CV power supply should work just fine for this. The idea here is that the balancer in the internal BMS can pull some current from the cells that are going too high in voltage. As long as the charging current is less than the balancing current, the BMS can stop the full cell from getting any more charge current while the other cells can still charge. If the charge current is too high, even 100 ma more than the balancer current can easily push a full cell to the 3.65 volt BMS shut off level.

The only problem with this is that LFP cells do get stressed about 3.5 volts, so don't leave the battery up at 14 volts for more than a day at a time. You should be able to pull power from the battery, but stay above 50%, and then slow charge it up a few times, and that will also help bring them back into balance without stressing the high voltage end as much. A day or two at 3.5 volts per cell is not a big deal, but try not to leave them up there for a week at a time. Every manufacturer recommends storing LFP batteries at 50% charge to extend their life.
Thanks for the detailed response. I really appreciate it. The only thing I don't understand, is that this cycle seems to be completely connected to how much power is flowing from the solar panels. I can sit comfortably all day pulling 15amps and the battery will reach 100% charge (14.6 volts then slowly dropping down). The only trigger for the issue seems to be surges of sun.

Is it just the sudden surge that throws the one cell over voltage and triggers the BMS? In other words, it would be normal for the batteries to reach 100% SOC if they receive a more constant low power? Right now, I am looking at my battery monitor and the voltage shows 13.46. The issue hasn't surfaced yet today.

If that still all sounds right, I'll give your first suggestion a shot today! Just to confirm, which of these setting would I modify to change the absorption voltage to 13.3v? The BstChgVol? There is also a setting to change the "Bst-time." I should change this from 2 hours (where it is now) to 3?
  • OverVolDsc 14.7v
  • ChgLimtVol:14.6v
  • EquChgVol: 14.4v
  • BstChgVol: 14.4
  • FltChgVol: 13.6v
  • BstChgRev: 13.2v
  • LowVolRev: 12.0v
  • UndVolWrn:11.5v
  • LowVolDsc: 11.0v

Sorry- I realize these are basic questions. The manual for the SCC isn't too helpful and I am a beginner to all of this.

If this doesn't work, I'll look more into your second suggestion. Thanks again.
 
From Battleborn:
Our charging parameters consist of the following:
  • Bulk/absorb = 14.2 – 14.6 V
  • Float = 13.6 V or lower
  • No equalization (or set it to 14.4 V)
  • No temperature compensation
  • Absorption time is 20-30 minutes per battery (if it’s an option)
So you can tinker with your settings safely provided they are below the Max specified by Battleborn.
I would go 14.2 Absorb/Bulk, EQ Off or 13.0 for as short time as possible, Absorb time to 15 minutes.
 
Do you know at what voltage the charge controller maxes out?

if the cells are nigh full, it would be easy for your panels to exceed 90V, especially if the weather is cool.
 
Thanks for the detailed response. I really appreciate it. The only thing I don't understand, is that this cycle seems to be completely connected to how much power is flowing from the solar panels. I can sit comfortably all day pulling 15amps and the battery will reach 100% charge (14.6 volts then slowly dropping down). The only trigger for the issue seems to be surges of sun.

Is it just the sudden surge that throws the one cell over voltage and triggers the BMS? In other words, it would be normal for the batteries to reach 100% SOC if they receive a more constant low power? Right now, I am looking at my battery monitor and the voltage shows 13.46. The issue hasn't surfaced yet today.

If that still all sounds right, I'll give your first suggestion a shot today! Just to confirm, which of these setting would I modify to change the absorption voltage to 13.3v? The BstChgVol? There is also a setting to change the "Bst-time." I should change this from 2 hours (where it is now) to 3?
  • OverVolDsc 14.7v
  • ChgLimtVol:14.6v
  • EquChgVol: 14.4v
  • BstChgVol: 14.4
  • FltChgVol: 13.6v
  • BstChgRev: 13.2v
  • LowVolRev: 12.0v
  • UndVolWrn:11.5v
  • LowVolDsc: 11.0v

Sorry- I realize these are basic questions. The manual for the SCC isn't too helpful and I am a beginner to all of this.

If this doesn't work, I'll look more into your second suggestion. Thanks again.
I would dial down ChgLimtVol, EquChgVol, and BstChgVol all to just 14.0 volts. Your batteries seem to be very close to completely full, so this will likely result in low current until you start pulling some load and take some energy out of the batteries.
 
From Battleborn:

So you can tinker with your settings safely provided they are below the Max specified by Battleborn.
I would go 14.2 Absorb/Bulk, EQ Off or 13.0 for as short time as possible, Absorb time to 15 minutes.
Thank you very much. Do you mean just for this testing or generally (after the cells get rebalanced, if that is the issue)?
 
Do you know at what voltage the charge controller maxes out?

if the cells are nigh full, it would be easy for your panels to exceed 90V, especially if the weather is cool.
When the issue was happening last time it was in the mid-70s. However, this was the reading during the few minutes the SCC was providing power. I am going to start monitoring this much more closely and will follow up with the voltage right before it crashes.

If this is the issue, do you know if this is dangerous at all? Or is it something I can live with?
 
I would dial down ChgLimtVol, EquChgVol, and BstChgVol all to just 14.0 volts. Your batteries seem to be very close to completely full, so this will likely result in low current until you start pulling some load and take some energy out of the batteries.
Thanks! I'll give this a shot tomorrow- at this point the sun is already low in the sky. Assuming the SCC doesn't crash while running these settings, I'll let it run like this for a few days and will then revert to my old settings. Or the settings suggested by Steve_S (based on battleborn guidance). I will update this thread shortly. Thanks again. I really appreciate all of your help.
 
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