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diy solar

Charge controller shuts off every few minutes then comes back on

we got this all figured out?
Thanks for checking in.

Not quite... after a few back and forths with Renogy (and some more testing) I am pretty sure it is an issue with the charge controller. Renogy wants the unit back for testing, before they give me a new one. I’m relying on it for power now (in an RV), so can’t send it back in for a few months.
For now, I’ve taped over part of a panel and haven’t had the issue since.

I’ll update once renogy does their testing. I’m still under warrantee for another year.
Thanks,
Noah
 
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
Looks like the controller is cycling for a minute every minute. That's sounds like proper charging for a certain type of battery have you reprogrammed the controller for what type of cells you are charging ? Is it hitting the high voltage cutoff ? Maybe from your move it needs to be reprogrammed. I'm sure renogy would have asked I guess. And a fuse will either work or not work. Relays bounce back and forth.
 
Thanks for checking in.

Not quite... after a few back and forths with Renogy (and some more testing) I am pretty sure it is an issue with the charge controller. Renogy wants the unit back for testing, before they give me a new one. I’m relying on it for power now (in an RV), so can’t send it back in for a few months.
For now, I’ve taped over part of a panel and haven’t had the issue since.

I’ll update once renogy does their testing. I’m still under warrantee for another year.
Thanks,
Noah
Sounds like maybe a bad cell causing you to lose your series run I've read some panels can bypass bad cells or shady cells without compromising the rest of the panels in series. Have you tried disconnecting the taped over panel from the run and test the remaining panels ?
 
I have the same problem. I am using Rover MMPT 40A charge controller. This one charges at 12.9v for 3 or 4 seconds, then it stops. It will repeat this circle all day.
 
if the controller show "day" icon and then "night" icon, I found it is caused by mu fuse breaker.

Then I check its specification. It's working temperature is between -10 c to 50 c. The up limit is 50c (122 F) which is too low in Myrtle beach.
 
I have this same problem. I'm using a 60a techfine mppt charge controller. My controller goes off when output amps is above 37a. My 3 panels are connected in series. 350w each. I'm using 8eve 3.2 100a cell with 120a jbd smart BMS.
 
if the controller show "day" icon and then "night" icon, I found it is caused by mu fuse breaker.

Then I check its specification. It's working temperature is between -10 c to 50 c. The up limit is 50c (122 F) which is too low in Myrtle beach.
Myrtle Beach SC? 122 ambient? Nah. Add more ventilation, if that’s the case.
 
This vicious cycle puzzles me maybe from another angle (not just Renogy) in this scenario:

1) Batt gets near fully charged, but being slightly unbalanced, one high cell triggers the bms cutoff. Essentially for a moment to the controller there is no battery.

2) Panel awakens the sleeping bms.

3) But now, when many controllers always insist you have the battery connected first, this sequence means the panel has been connected first out of sequence and perhaps the controllers don't act right after the reset?
 
This vicious cycle puzzles me maybe from another angle (not just Renogy) in this scenario:

1) Batt gets near fully charged, but being slightly unbalanced, one high cell triggers the bms cutoff. Essentially for a moment to the controller there is no battery.

2) Panel awakens the sleeping bms.

3) But now, when many controllers always insist you have the battery connected first, this sequence means the panel has been connected first out of sequence and perhaps the controllers don't act right after the reset?
This usually isn't the case, scc's hold their settings for some time.
Battery first is usually required for the initial connection. After that, if nothing changes, or the battery isn't disconnected for extended periods, it isn't a problem.
 
I have this same problem. I'm using a 60a techfine mppt charge controller. My controller goes off when output amps is above 37a. My 3 panels are connected in series. 350w each. I'm using 8eve 3.2 100a cell with 120a jbd smart BMS.
In most of these similar cases we are seeing, it is a cell that is a little out of balance causing the BMS to interrupt charging. With LFP cells, the sharp knee when fully charged causes the highest charged cell to "run away" and trip the BMS.

The first thing to try is to lower your maximum bulk and absorb charge voltage settings and see if the systems acts better. And watch the cell voltages when it drops to absorb charging. Due to the nature of LFP cells, even if they appear to be perfectly balanced at 3.2 to 3.2 volts, one or more cells could be at a significantly higher state of charge. As the charge controller continues to charge the system, one just hits the top knee first, and it's voltage climbs sharply. Even thought the entire pack voltage is still well below the absorb voltage, the one high cells causes the shut down. Even a 2 amp active balancer might not be able to keep the running cell from causing the trip.
 
As a diagnostic - we don't know if the BB's were new or pre-owned.

It is not clear that either of them has been charged individually with a charger. Even if placed in parallel, this is a good idea to isolate any particular problem first.

The 40A dc-dc charger may be bulk charging, but not charging enough to simulate the bms-disconnect as seen when the SCC is used.

Are these first-owner batts? Even if not, does charging on an AC charger duplicate the bms disconnect?

If there is no ac available, how about this: Use a lower-wattage panel on an *individual* BB, and see if that gives the possble bleeder resistor a bit more time? Rinse and repeat with the other.
 
This vicious cycle puzzles me maybe from another angle (not just Renogy) in this scenario:

1) Batt gets near fully charged, but being slightly unbalanced, one high cell triggers the bms cutoff. Essentially for a moment to the controller there is no battery.

The BMS will cutoff charge, but discharge should still be active. So the SCC should still have full access to "see" the battery.
 
The BMS will cutoff charge, but discharge should still be active. So the SCC should still have full access to "see" the battery.
The possible problem is that the BMS turns off charge only by acting like a diode. That allows current to still flow out, but not in. So what happens when the charge controller tries to push power in? The diode looks like an open circuit and the voltage will rise. If the charge controller was supplying only 120 watts into a 12 volt battery, we are talking about 10 amps, so no big deal. But when the load is removed, the current falls. The DC to DC converter in the charge controller is essentially a constant power device, If the current fell to 1 amp, the voltage would then try to go to 120 volts. Hopefully, there is enough capacitance to slow the voltage rise, and the control electronics will see the rise, and reduce the output power and switch to CV mode at the set absorb voltage, but that is not guarantied. If the Charge controller is using a basic buck DC to DC converter from a 100 volt (or even higher) solar array, the voltage could spike up very quickly when the load disconnects, and it could exceed the BMS mosfet ratings and even damage output components in the charge controller. There is a good reason they don't want a solar panel connected without a battery connected. Designing the circuit to safely handle this situation will certainly add to the cost. I am sure they try to make it somewhat capable of taking the surge, but the fact they warn not to do it in the manual shows that they don't want to cover it if it fries. This is another reason I like having 2 battery banks with separate BMS units. The odds of one BMS hitting a fault is pretty good, but two of them at the same time, not so much.
 
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