• Have you tried out dark mode?! Scroll to the bottom of any page to find a sun or moon icon to turn dark mode on or off!

diy solar

diy solar

12V battery only charging to 13.4

Yes, I write novels (and it took me long enough to write it didn't take and post)


It looks like you built a 12v battery with cells 4p4s using a single 4s BMS. Are the jumper wires you are using between battery clusters large enough to carry the current? I see a 3000w inverter in the picture which is 235amps - which calls for a fuse at 300amps and wire capable of handling that many amps - i.e. 2/0 or 4/0 welding wire. I can't tell from the pictures but that looks like only 2awg or so based on relative size.


If you want to run smaller than that you can, but it needs a fuse to blow if you exceed it.... I would suggest a 3 fuse MRBF holder to be able to break the amps if there is a short. I suggest the 3 holder because it attaches with wire verse being bolted directly to the terminal. And the type cells you have with the double terminal have been reported to have the terminals break off so you don't want to have any force that bends them up and down or side to side.

You need to install the rest of the bolts into the battery terminals or you are asking for corrosion and hot spots. Did you use no-ox-id special A or similar on all of your terminals and bus bars? If not you are asking for trouble down the road.

For your charging issue -

From what you are saying it sounds like you didn't use a bench power supply to bottom balance them before assembly. And you didn't top balance them either. Which means the COVP is going to be hit and you will stop charging. This will happen frequently until you have fully cycled them probably for months.

A couple of other notes -

There aren't any separators between cells in case you rub through the blue shrink-wrap - In any application that is recommended and in a mobile application it is required to have separators.

It looks like the cells are sitting straight on the wood platform - it needs to be lined with something non-conductive and smooth to prevent rubbing damage under them... you can easily cause a vent from rubbing a hole in the bottom - there is a recent thread on the topic where that happened.

Compression and restraint - a hotly debated topic - but the cells expand and contract as they charge and discharge - this is going to cause them all to move apart from each other - rubbing the bottoms and applying force to the bus bars. I can't tell from the pictures if they are just copper with a kink covered in shrinkwrap or if they have a metal braid under there. I suspect just metal from the uniform shape of them all. If so that means they will be constantly pulling and pushing on the terminals everytime you charge/discharge and it will eventually break a terminal off.

So, to fix things to not be a hazard to yourself and your loved ones -

  • remove them all from the bay
  • disassemble everything
  • bottom balance all the cells - look up what that means as it has been described many times
  • top balance things - look up what that means as it has been described many times
  • clean everything
  • apply no-ox-id special A to bus bars and terminals
  • line the wood shelf with something smooth and slick so they can slide without damage
  • use separators between cells - there is special foam for this
  • re-assemble them using 2 screws per terminal - packs of 4 at a time so you can lift them
  • make sure your wire guage is large enough for the connections between or use flat bus bars instead
  • use a torque wrench on all the bolts - make sure all the metal is wrapped in electrical tape or heatshrink so you don't cause a short - having both bolts in and as finger-tight as you can before torquing should prevent shear problems
  • provide some sort of restraint or compression - with them at middle charge they will be the flattest - so require the least force they expand as they either charge or discharge from the middle SOC - there is a white paper on this to read if you think that is wierd
  • fuse with a class T or MRBF as close as possible the the positive post of the pack
  • Make sure ALL wires connected to the pack are restrained within 4 inches of it so there is no force applied to the terminals.
  • Make sure the battery is attached to the bottom where it sits so it can't slide around as a unit.
  • PUT a plastic cover over the top of the battery to shield ALL the metal bits - a single dropped wrench or wire or a bump that touches any part of it to the overhead metal vents and you are looking at Disaster - vent hydrogen, spark, BOOM or kerwhump (the sound it makes when the air catches on fire.... think gas grill that didn't light for a bit, then it catches)

To be honest - you should really have the battery in a case sealed up and vented to the outside - so nothing can go wrong - this might mean rethiking where it goes. I also think if you don't follow all the suggestions above you are asking for a fire.
 
Last edited:
Sorry, didn't read the whole thread, but your rvs converter/charger is probably designed for lead by default. Lead charges lower than LiFePo4. It may also feature charging parameters that can damage a LiFePo4 bank. I also have a 4s4p 12v LiFePo4 bank, BTW. Do your bms have Bluetooth? You can see how much juice is being drained at any time. If you don't have bt, then you should have a sophisticated battery monitor, known as a coulumb counter battery gauge. Vitron makes sever nice ones. They are cheaper brands too. But you need to make sure your charger is able to be adjusted for proper charging of LiFePo4 prismatic cells. This is vital.
 
Yikes! Do NOT move the RV without removing the battery and rebuilding it properly.
It is not mobile! it sort of works lol gotta make do with what we have at the moment. We will be able to replace things in the next couple months. It's been a rough winter for us. First year off grid, in a very cold climate.
 
It is not mobile! it sort of works lol gotta make do with what we have at the moment. We will be able to replace things in the next couple months. It's been a rough winter for us. First year off grid, in a very cold climate.
don't replace anything till you figure out the problem, people like to spend other people's money. answer the questions asked of you, and you will eventually figure out what's going on
 
4 batteries with 4cells each, one BMS
Your pictures show 1 battery (4P4S as originally stated) and 1 BMS (as it should be).

There are some oddities. What are the wires coming off the middle of the battery? Or is this just a long "bus bar"?
Screen Shot 2025-01-17 at 10.20.07 AM.png

Probably not your issue but you should get the bus bars to all lay flat and not one end on top, the other end on bottom so that the connecting surfaces are not parallel.
Screen Shot 2025-01-17 at 10.23.10 AM.png

I have a lot of experience with batteries made with multiple cells in parallel and then connected in series like you have done. The trick is to get each of your parallel group capacity totals to be equal to each other.

If all your cells are the same capacity or even close you should be fine. Having 4P groups "should" help random cell groupings because more cells would mathematically be more likely to have a more even distribution. If you were unlucky and ended up with your 4 weakest (lowest capacity) cells in the same 4P group, then that groups total capacity would determine your overall battery capacity.

This "could" be your issue if the BMS is cutting out with over volt for a given 4P group that hits 3.65V when the other 4P groups are a much lower voltage. Do you know if the BMS is cutting out and stopping the charge?
 
Yes, I write novels (and it took me long enough to write it didn't take and post)


It looks like you built a 12v battery with cells 4p4s using a single 4s BMS. Are the jumper wires you are using between battery clusters large enough to carry the current? I see a 3000w inverter in the picture which is 235amps - which calls for a fuse at 300amps and wire capable of handling that many amps - i.e. 2/0 or 4/0 welding wire. I can't tell from the pictures but that looks like only 2awg or so based on relative size.


If you want to run smaller than that you can, but it needs a fuse to blow if you exceed it.... I would suggest a 3 fuse MRBF holder to be able to break the amps if there is a short. I suggest the 3 holder because it attaches with wire verse being bolted directly to the terminal. And the type cells you have with the double terminal have been reported to have the terminals break off so you don't want to have any force that bends them up and down or side to side.

You need to install the rest of the bolts into the battery terminals or you are asking for corrosion and hot spots. Did you use no-ox-id special A or similar on all of your terminals and bus bars? If not you are asking for trouble down the road.

For your charging issue -

From what you are saying it sounds like you didn't use a bench power supply to bottom balance them before assembly. And you didn't top balance them either. Which means the COVP is going to be hit and you will stop charging. This will happen frequently until you have fully cycled them probably for months.

A couple of other notes -

There aren't any separators between cells in case you rub through the blue shrink-wrap - In any application that is recommended and in a mobile application it is required to have separators.

It looks like the cells are sitting straight on the wood platform - it needs to be lined with something non-conductive and smooth to prevent rubbing damage under them... you can easily cause a vent from rubbing a hole in the bottom - there is a recent thread on the topic where that happened.

Compression and restraint - a hotly debated topic - but the cells expand and contract as they charge and discharge - this is going to cause them all to move apart from each other - rubbing the bottoms and applying force to the bus bars. I can't tell from the pictures if they are just copper with a kink covered in shrinkwrap or if they have a metal braid under there. I suspect just metal from the uniform shape of them all. If so that means they will be constantly pulling and pushing on the terminals everytime you charge/discharge and it will eventually break a terminal off.

So, to fix things to not be a hazard to yourself and your loved ones -

  • remove them all from the bay
  • disassemble everything
  • bottom balance all the cells - look up what that means as it has been described many times
  • top balance things - look up what that means as it has been described many times
  • clean everything
  • apply no-ox-id special A to bus bars and terminals
  • line the wood shelf with something smooth and slick so they can slide without damage
  • use separators between cells - there is special foam for this
  • re-assemble them using 2 screws per terminal - packs of 4 at a time so you can lift them
  • make sure your wire guage is large enough for the connections between or use flat bus bars instead
  • use a torque wrench on all the bolts - make sure all the metal is wrapped in electrical tape or heatshrink so you don't cause a short - having both bolts in and as finger-tight as you can before torquing should prevent shear problems
  • provide some sort of restraint or compression - with them at middle charge they will be the flattest - so require the least force they expand as they either charge or discharge from the middle SOC - there is a white paper on this to read if you think that is wierd
  • fuse with a class T or MRBF as close as possible the the positive post of the pack
  • Make sure ALL wires connected to the pack are restrained within 4 inches of it so there is no force applied to the terminals.
  • Make sure the battery is attached to the bottom where it sits so it can't slide around as a unit.
  • PUT a plastic cover over the top of the battery to shield ALL the metal bits - a single dropped wrench or wire or a bump that touches any part of it to the overhead metal vents and you are looking at Disaster - vent hydrogen, spark, BOOM or kerwhump (the sound it makes when the air catches on fire.... think gas grill that didn't light for a bit, then it catches)

To be honest - you should really have the battery in a case sealed up and vented to the outside - so nothing can go wrong - this might mean rethiking where it goes. I also think if you don't follow all the suggestions above you are asking for a fire.
Thank you for all of the tips! Once winter is over, we will have the time and funds to re-do the whole setup legitimately. I will look into how we can top balance them. I read much mixed advice for compression. Is there a source you recommend to get this information at? I did notice one of the terminals did bend. Those terminals are very interesting to me. Are you saying to put a fuse between the jumpers? There is a 300a fuse between the inverter and the battery, but it is very cheap. It's also closer to the inverter than the batteries. The inverter cable hooks directly to the fuse, and then goes to the bank. We put nothing between the bus bars and terminals. And yes they're cheap, no metal braiding. The easily bend. They just came with the batteries so we used them.

I didn't top balance, because we cannot locate our plug in battery charger and there is also a lot of opposing views on that. I thought it would be fine. We just got the BMS last week, and were still only charging to 13.4(which oddly is the cut off for the same type of converter that is lead acid capable).

I also didn't know the fuse should be as close to the main positive as possible. Didn't know they needed anything to keep them from corroding.

What do mean restraining the cables 4" from the pack? You mean like bolting them to something? None of those cables are welding cables and have absolutely no give whatsoever. I was concerned about the battery terminals, but it's all we have right now. I had no idea the air could catch on fire!

I appreciate this so so much because I don't want to harm anyone. My dad has been our guidance on this project. He is a PEE... But he is also very redneck and has a "that will do" type attitude. We can probably aquire some different jumper wires, and get the bank properly separated, secured or enclosed. I'm not sure where else we could enclose the batteries at. Some RV people say under their benches, but we are only borrowing this RV and want to do as little permanent altering as possible. Thank you for taking the time to offer guidance to keep us all safe. I know time is valuable so I really appreciate it.

We will start with a balance and see if that helps the charging.
 
Sorry, didn't read the whole thread, but your rvs converter/charger is probably designed for lead by default. Lead charges lower than LiFePo4. It may also feature charging parameters that can damage a LiFePo4 bank. I also have a 4s4p 12v LiFePo4 bank, BTW. Do your bms have Bluetooth? You can see how much juice is being drained at any time. If you don't have bt, then you should have a sophisticated battery monitor, known as a coulumb counter battery gauge. Vitron makes sever nice ones. They are cheaper brands too. But you need to make sure your charger is able to be adjusted for proper charging of LiFePo4 prismatic cells. This is vital.
We just bought a new lithium charger, but oddly enough our batteries only charge to 13.4- the voltage for lead acid. We have called intellipower 3 times and they said nope it charges at 14.46.... except multimeter says 13.99 and 14.03. it does have a Bluetooth. I will try to find out where it states current current draw. There is a place that shows where the amps are when charging. I turn discharge off while we're running the generator, so I believe that is a good sign it's the charging amperage. We have been advised to get a shunt or monitor. We will get one as soon as we can. From what others are saying, I believe I need to start with a top balance.
 
It's not the air, it's the hydrogen (and other toxic and flammable) gasses that are vented from a failed cell that will go up in a fireball. Google for LFP battery fires to get an appreciation for the danger.
I was under the assumption lithium didn't vent. I don't know why I thought that. I thought they internally combusted often from over charge. Wouldn't I know if a cell was failing via BMS?
 
I read much mixed advice for compression. Is there a source you recommend to get this information at?
Use the search function on this forum, and prepare to be overwhelmed by the amount of contradictory information you will receive. From a first approximation, don't worry about it and solve your other problems first, you can optimize for compression after you deal with the safety issues.
 
And yes they're cheap, no metal braiding. The easily bend. They just came with the batteries so we used them.
That's fine, they are probably copper, which is highly conductive but bends easily. Be really careful with torque on the terminals, depending on your source (and acquisition timeframe) you can tear the terminals right off the cells if you are not careful"
 
I was under the assumption lithium didn't vent. I don't know why I thought that. I thought they internally combusted often from over charge. Wouldn't I know if a cell was failing via BMS?
You might know if a parallel group of 4P cells was having an issue, but one cell in that group shorting internally would have 4 cells in parallel able to dump thousands of amps into the shorted cell, so you might receive no warning at all.
 
I also didn't know the fuse should be as close to the main positive as possible.
You want to be able to protect the battery from shorts. If the main positive fuse is far from the battery, there's no overcurrent protection for the wire and one side of the fuse holder should a short to ground occur before the fuse.
 
Didn't know they needed anything to keep them from corroding.
Depending on your environment, and it feels like yours is semi-outdoors, corrosion can occur on and between current-carrying conductors. Something like https://www.amazon.com/NO-OX-ID-Special-Electrical-Contact-Corrosion/dp/B00HDF9EXE can help both improve conductivity and prevent corrosion. On the other hand, any silicone grease will protect from corrosion and be squeezed right out of the interface if you bolt (or crimp) copper to copper. But see 'terminal torque' above.
 
Your pictures show 1 battery (4P4S as originally stated) and 1 BMS (as it should be).

There are some oddities. What are the wires coming off the middle of the battery? Or is this just a long "bus bar"?
View attachment 270842

Probably not your issue but you should get the bus bars to all lay flat and not one end on top, the other end on bottom so that the connecting surfaces are not parallel.
View attachment 270844

I have a lot of experience with batteries made with multiple cells in parallel and then connected in series like you have done. The trick is to get each of your parallel group capacity totals to be equal to each other.

If all your cells are the same capacity or even close you should be fine. Having 4P groups "should" help random cell groupings because more cells would mathematically be more likely to have a more even distribution. If you were unlucky and ended up with your 4 weakest (lowest capacity) cells in the same 4P group, then that groups total capacity would determine your overall battery capacity.

This "could" be your issue if the BMS is cutting out with over volt for a given 4P group that hits 3.65V when the other 4P groups are a much lower voltage. Do you know if the BMS is cutting out and stopping the charge?
Yes that long cable is a jumper wire 🤦‍♀️ we ran out of lugs and had to make do with something we had laying around. I honestly had no idea all the bolts weren't in place.

I was reading the logs in my BMS app and I saw one over voltage error. Couple days ago. But it's not common so I would just assume that yes, this may be an issue but something else is going on as well. This morning the BMS shut down charge and discharge due to low temp. But as I was reading the logs, it also said short circuit protection. I'm thinking we need to legitimately re-wire everything, and get better quality bus bars... What makes me think there is a short inside the fifth wheel, is this was happening with our old lead acid batteries. We also had zero power for 4 days because of a bad ground. Finally found it, so it is likely other cables are too old as well.
 
What do mean restraining the cables 4" from the pack? You mean like bolting them to something? None of those cables are welding cables and have absolutely no give whatsoever.
If the cables move relative to the battery terminals, you can tear the terminals right off the batteries (see above). Your batteries are sitting on a wooden furniture dolly, which means they could move...
 
Are you absolutely certain your converter is compatible with LFP _AND_ that it's set for LFP properly?

I am certain as it says right on the front lithium only. The cover states it puts out 14.6V the dudes at intellipower said it has two settings, one at 14.6 and trickle charge state 13.something. I have only seen 13.99 and 14.03 when I take readings at the converter.

I do know they make the same model but for lead acid.
 
If the cables move relative to the battery terminals, you can tear the terminals right off the batteries (see above). Your batteries are sitting on a wooden furniture dolly, which means they could move...
We put wheels on it so we could move it if needed. They're currently locked closed. I didn't really consider the pressure could make things slightly move. We got a lot of work to do! Thank you for pointing out the obvious
 
Oh man I didn't know they made kits!! That sounds very simple THANK YOU!
Many folks here like the:
cases, at least in the 48V rack mount style, though I'm sure Luyuan has too many options!
 
Depending on your environment, and it feels like yours is semi-outdoors, corrosion can occur on and between current-carrying conductors. Something like https://www.amazon.com/NO-OX-ID-Special-Electrical-Contact-Corrosion/dp/B00HDF9EXE can help both improve conductivity and prevent corrosion. On the other hand, any silicone grease will protect from corrosion and be squeezed right out of the interface if you bolt (or crimp) copper to copper. But see 'terminal torque' above.
Thank you for the link! I will get it ordered. It is semi outdoors.
 

diy solar

diy solar
Back
Top