Power surges when battery is full - any ideas?

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Small Cabin Forum / Off-Grid Living / Power surges when battery is full - any ideas?


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outdoorsinnature Member	# Posted: 19 Sep 2026 07:23am Reply I have a 12vdc system. When the battery reaches full charge I notice a surge, hearing a surge in the fans blowing stronger, as soon as the battery is full. That is not the only indicator. I have a digital display for my MPPT. What the voltage shows is a drop after full, which is expected when it goes to open circuit voltage, shutting off the panels, but then it will have sudden surges, now and then when 'floating' between off and trickle charge, sometimes as high as 18V volt range, which causes my lifepo4 battery's BMS (shutoff voltage is 16V, to cause a total shutdown to protect itself for a second or two before it goes back down again. I asked the battery manufacturer what this might be and they didn't have any more information to tell me other than what I already knew "it sounds like you have something causing a power surge in your system". So any ideas what may be causing this surging? Conversely is there a device I could get to regulate the voltage so it won't go above a point where it would cause the system to shut down? thus circumventing the need to find the cause? Also how bad is it to leave it on with this surging happening? At the moment I do not feel comfortable leaving it on and going out where I will be away from it for a long time - which sucks long term having to be around all the time while it is charging. Currently the battery will fully charge within a few hours, and so I just switch the solar disconnect off when I would be going outdoors anyway but it is not going to charge that quickly as winter approaches and sets in. So would like this resolved so I can feel ok to leave it unsupervised again. Just to make clear that the surge does not happen when the battery is charging; only when it reaches full and the mppt goes to float/shutdown.

Steve_S Member	# Posted: 19 Sep 2026 11:53am Reply If this is 12V LFP Battery you are overcharging & causing BMS to disconnect, resulting in the surge/spike. The working voltage range for a 12V LFP Battery Pack is from 2.800V to 3.450V per cell (11.2V to 13.8V) Max Voltage going into the battery should NOT exceed 3.500V per Cell X 4 Cells means 14.0V MAX. This si your Bulk Charging Voltage. FLOAT should be set to 13.7V (3.425V per cell) which will allow the cells to balance up which is dependent on the BMS within the pack, if it has balancing capability or not... Normally at this voltage the cells will comfortably balance out. BMS will shut down once a cell reaches 3.650V in the pack. This is for safety and should never be reached. Low Voltage Cutoff for your Inverter needs to be set to 2.700 VPC (volts per cell) or 10.8V ---------------- You will have some line loss & resistance in the wires, so you do need to do a voltage test at the Solar Controller Terminals, the Inverter/charger terminals & at the battey pack terminals. Note the different voltages and adjust accordingly. Remember the Battery Voltage is the most critical & therefore is the target to adjust your equipment for. * Use a good quality Digital Multimeter that is at least 2 decimal accurate showing you 12.24V for example. 3 Decimal accurate DMM are available but they are more $$$, 2 decimal are more common and much less $. AMPERAGE IS CRITICAL ! When Charging do NOT exceed max amps allowed by the battery. With LFP that is typically 0.5C-Rate or in other words, a 100AH Battery can be Discharged up to 100A but can only be charged up to 50A (0.5C) Max Current. As the battery reaches FULL Voltage (working range) of 3.400-3.425VPC (13.6V-13.7V) the amperage will fall as the cells top off. This can drop to 0A but usually it should kick off @ 5% or 5A of total capacity in AH. * Solar Controllers & Inverter/Chargers usually have a setting for amperage cutoff points. WITHOUT KNOWING WHAT GEAR YOU HAVE, IT IS NOT POSSIBLE TO PROVIDE MORE DETAIL. * I am familiar with Tier-1 Products like Midnite, Samlex, Victron and so on... SPECIAL NOTE ! The BMS is a Failsafe System & Cell Manager. It is NOT supposed to control the battery charge/discharge unless there is a fault. Allowing it to do so IS causing potential harms and increases risks. It is importat to properly configure your components (Solar Controller, Inverter/Charger) so they do their job safely & properly. --- I check in here randomly, not regularly. I can answer some questions but I have responded to numerous points on such here & left an extensive trail of documents, guides, tables & charts pertaining to solar systems, batteries & more. I can try to answer some questions but I woudl need far more detail in order to properly answer. See below: Req Info: * Battery Types, Make, Model, Capacity. * Solar Controller(s) Make, Model etc * Inverter/Charger, Make Model * A Diagram/Schematic of setup is helpful. * Wiring used from Solar Controller to Battery to Inverter/Charger... Gauge, Lug Types, DIY or Commercially supplied. IF Commercial, links needed. * What Fuses/Breakers are used & where are they. !!! (link to any/all products used if possible) !!! ALTERNATELY, You can goto https://diysolarforum.com/ and you can post your information as I suggested you provide, plus the problems you are experiencing and some will chime in (too many opinions) including from some of us hard core types. I have left a vast trove of guides, docs, manuals etc on that forum that you can use as well. WARNING There are many "Bench Experts" there and lately some who just love to "mess with folks" use critical thinking... I, like many have backed away from there when it got "dark", no point in dealing with that stuff, real life has plenty. Good Luck, hope it helps Steve

outdoorsinnature Member	# Posted: 20 Sep 2026 06:24am Reply Thanks but how are you so sure that it is overcharging that is the root cause? My MPPT has settings specifically to prevent that. It is Tracer bn4215.

outdoorsinnature Member	# Posted: 20 Sep 2026 06:27am - Edited by: outdoorsinnature Reply Oh and I totally agree with you about the diysolarforum. It really is the best place I found for targeted advice on the subject matter but sadly also lots of trolls too which makes it love/hate, and like you have had to back far away on more than one occasion and have currently been on a break for months, swearing off the place, due to the 'darkness' you speak of which is precisely why I posted here rather than there. It is always questionable whether I want to know something bad enough to post there and probably get frustrated in the process at the annoying comments that will also come as well as the good advice. It is probably 50/50 really great advice, annoying trollish/negative comments which I find soul draining so have to fortify myself to post there and try and exhaust other fora before resorting to posting there.

FishHog Member	# Posted: 20 Sep 2026 07:54am Reply I have a 12v system with a tracer mmpt and have never seen this. My gut tells me it’s your mmpt, which is either something in your settings or an internal fault. Can’t see this being a battery caused issue. I’d swap the mmpt and if that doesn’t fix it then you have a spare for when you will need one.

Steve_S Member	# Posted: 20 Sep 2026 10:44am Reply With regards to overcharging, you said it here. Quoting: outdoorsinnature now and then when 'floating' between off and trickle charge, sometimes as high as 18V volt range, which causes my lifepo4 battery's BMS (shutoff voltage is 16V, to cause a total shutdown to protect itself for a second or two before it goes back down again. MPPT controllers need to be setup/programmed, their defaults are terribly generic and not really appropriate... Max Charging voltage should not be more than 14.0V but 13.8V is optimal for Bulk/Absorb while float should be programmed to 13.7V. Transition to Float should occur when the battery can only take 5A (5% of 100AH capacity) The Tracer BN Manual says: Manual Link HERE: https://www.epever.com/upload/file/2103/Tracer-BN-Manual-EN-V2.0.pdf 3.3 Battery Type 1) Sealed (Default) 2) Gel 3) Flooded 4) User You will have to go and program the USER battery settings for LFP. There does not appear to be a setting for LFP. Settings below should work just fine. -------------------- Over Voltage Disconnect Voltage 15.0 Charging Limit Voltage 15.1 Over Voltage Reconnect Voltage 14.0 Equalize Charging Voltage 13.8 Boost Charging Voltage 13.8 Float Charging Voltage 13.7 Boost Reconnect Charging 13.8 Low Voltage Reconnect Voltage 10.4 Under Voltage Warning Reconnect Voltage 10.4 Under Volt. Warning Volt 10.8 Low Volt. Disconnect Volt 10.4 Discharging Limit Voltage 10.6 Equalize Duration (min.) 0 Boost Duration (min.) 2 Manual link is above and that can guide you as t how to configure your SCC from a PC or Phone App if it's capable. Hope it helps, Good Luck. Steve

outdoorsinnature Member	# Posted: 20 Sep 2026 11:30am - Edited by: outdoorsinnature Reply Quoting: Steve_S You will have to go and program the USER battery settings for LFP. There does not appear to be a setting for LFP. I am aware of that. I did all the research (on diysolarforum with many experienced users giving feedback) before connecting it up 2 years or more ago. I didn't just wire it up on default and hope for the best. It was fine for long before this happened, which is a relatively recent occurrence during the whole time I have used it. I got someone on diysolarforum who is a respected member (Mike something with an aeroplane helmet profile pic you may know him if you have been there a while, Mike Fitz I think) to give me the lifepo4 settings which were confirmed as good by other members on there. This is not something that has happened the whole time I have had the MPPT. I have had it 2 years or more and did not notice such behavior until maybe the last 6 months or so and was fine with those settings all the time up to now. I looked and the overcharge disconnect is 14.8V and overcharge limit is 14.7V. So perhaps it is not kicking in for some reasons which causes the BMS to have to be the last line of defense?

outdoorsinnature Member	# Posted: 20 Sep 2026 11:32am Reply Quoting: FishHog I’d swap the mmpt and if that doesn’t fix it then you have a spare for when you will need one. I am not a proponent of buy replacements before even trying to figure out what might be wrong with the existing one. Wasteful and feeds throwaway culture.

FishHog Member	# Posted: 21 Sep 2026 07:39am Reply Seems you’re offended by people’s suggestions so I’ll move on. Good luck. But for the record, I don’t believe having a backup for a critical part is wasteful.

gcrank1 Moderator	# Posted: 21 Sep 2026 09:57am Reply I agree with Steve's profile settings. If you have not gone through the verification/reset of ALL the parameters you do not KNOW that the settings are correct now. Not verifying and assuming may well be biting you.

outdoorsinnature Member	# Posted: 22 Sep 2026 04:20am - Edited by: outdoorsinnature Reply Quoting: gcrank1 If you have not gone through the verification/reset of ALL the parameters you do not KNOW that the settings are correct now. Not verifying and assuming may well be biting you. I just don't quite get the rationale. If they were verified by others as good when I first set them up and if it worked fine for 2 years or so then the settings won't have changed on their own to something else will they? It just seems like barking up the wrong tree? Anyway, here they are for verification if you would kindly take a look: Temperature compensation , set to 0 or disabled Charging limit voltage 14.7 Over voltage disconnect 14.8 Over voltage reconnect 14.6 Equalizer charging voltage 14.2 Float charging voltage 13.5g Boost charging voltage 14.2 Boost reconnect voltage. 13.2 Low voltage disconnect 11.0 Low voltage reconnect 12.5 Under voltage warning 11.5 Under voltage warning reconnect 12.5 Discharge limit voltage. 11.0 Over discharge disconnect 10.5 Equalizing duration 10 min Boost duration 30 minutes

Brettny Member	# Posted: 22 Sep 2026 03:35pm Reply Quoting: outdoorsinnature I am not a proponent of buy replacements before even trying to figure out what might be wrong with the existing one. Wasteful and feeds throwaway culture I believe you can do a factory reset.

Steve_S Member	# Posted: 22 Sep 2026 04:32pm Reply His settings are "not bad" and should cause no harm... It also should not allow spikes at the battery with those settings either. If there was an SCC failure, it would be very obvious because it would fail outright or fry in a most stinky manner. Battery Cells in production should never be charged above 3.500V per cell, X4 Cells for 12V = 14.0V MAX. Cross that line will trigger runner cells that can run up to 3.650 in a hurry, a place you should not go. LFP Allowable Voltage Range is 2.500-3.650 Volts. Working Voltage Range is 2.800-3.400 Volts, per cell. 4 Cells for 12V, 8 Cells for 24V and 16 Cells for 48V. Assuming all connections, fuses etc are tight & in working order, it leave only one point of potential here... The Battery itself... IE A BATTLEBORN Death Pack for one... Those are so damned dangerous, well outted and so they are suing everyone who outted them. There have been soe other terribly dubious batteries that made it to market (with or without UL etc certifications). A failed/failling BMS would present several other problems till it died outright but it would be very evident as a chain of things would all go wrong at once. OP has not mentioned what his gear is other than the SCC. He has not identified the Make/Model of the batteries or anything else. None of this can be divined... --------------- Off to hunt House-Hippo's and Ookpiks with the new .556 Have fun folks.

outdoorsinnature Member	# Posted: 1 Oct 2026 04:40am - Edited by: outdoorsinnature Reply Quoting: Steve_S His settings are "not bad" and should cause no harm... Thanks for the details. In the meantime I have been in contact with the SCC manufacturer who have been very helpful in the past with troubleshooting issues. In this case they are not giving much help. They just told me that the SCC is not made for Li batteries so that is why it won't work. An easy way for them to get rid of relieve themselves of responsibility for solving the issue. For the battery it is Fogstar Drift 105ah. Very well regarded batteries here in the UK from the research I did before purchasing. I had also been in contact with them a while before. They come with a 10 year warranty supposedly and the guy just told me it was nothing to do with the battery and to look elsewhere in the system.

gcrank1 Moderator	# Posted: 1 Oct 2026 09:55am Reply Id start at the total beginning as if doing it all as a new install. Nothing to lose at this point other than your time.

wiki21 Member	# Posted: 1 Oct 2026 12:16pm Reply Classic blame game. If the SCC isn't Li-compatible, no setting will fix it, get a Li-ready controller and move on.

wiki21 Member	# Posted: 1 Oct 2026 12:18pm Reply Classic blame game. If the SCC isn't Li-compatible, no setting will fix it, get a Li-ready controller and move on.

gcrank1 Moderator	# Posted: 1 Oct 2026 06:44pm Reply Well, I had good luck using a gel-bat setting on my charger, the profiles were 'close enough' for me without having to buy a dedicated LFP charger that (imo) charges too high at 14.6v

FishHog Member	# Posted: 2 Oct 2026 07:49am Reply Epevers might not have a LifePo4 program but they are user programable as the OP seems to have done. Although I still think it’s the SCC. I have 2 Epevers programmed and am not having any issues.

paulz Member	# Posted: 6 Oct 2026 11:48pm Reply I too had 2 Epevers up until recently when I switched to the Victron. Supposed to grab more juice but hard to tell with my shaded lot. Still use one Tracer to keep thr generator battery up. Had the Epevers user programmed too for LFP, no issues.