Lithium Battery question

Van Living Forum

Help Support Van Living Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Cy_5th

Member
Joined
Jan 30, 2024
Messages
15
Reaction score
3
Location
Bay Area, California
51.2V 210ah Renogy. Is it ok to stay on shore power and let the charge say go to 100%. The tech at dealer texted me that once the total voltage goes to 53.2 it wont charge anymore.

My first crack at it I let it charge to 100%. It was fine. That night I was plugged in and sometimes mid night it didn't charge anymore or the rest of the next days. Even alternator charge. Mobile tech came out and did a reset and it worked.

Right now I'm im plugged in at a pedestal the soc is 88% and the total voltage is 54.1.

There's this protection mode too I've read? And How to get back to recovery? All new to me.

Any links to an existing thread that has more info than the manual.

What not to do?
 

Attachments

  • PXL_20240208_224543236.jpg
    PXL_20240208_224543236.jpg
    2.1 MB · Views: 0
Last edited:
How long will you be on shore power? Unlike lead acid batteries;
LiFePo4 batteries do not like being held in a constant state of 100% charge. If you’re going to be on shore power for an extended period I would draw the lithium battery down to at least around 50% charge and hold it there; maybe even 30% of full charge.

INTJohn
 
How long will you be on shore power? Unlike lead acid batteries;
LiFePo4 batteries do not like being held in a constant state of 100% charge. If you’re going to be on shore power for an extended period I would draw the lithium battery down to at least around 50% charge and hold it there; maybe even 30% of full charge.

INTJohn
Ok yes. I just edited my text that lead me to this post. I did charge to 100%. Left came back then plugged in again. Middle of night it didn't charge nor the alternator way. Tech guy came out and showed me how to reset the battery .
 
In my 48volt lithium battery that I built, the normal charge cut off is 56volts. Some prefer to set this a bit lower. The batery charge is being controlled by a circuit board in the batery called a BMS ( battery monitor system) It can be set in various ways such as when to stop charging... once my battery hits "full" and the charging stops it will float in the 53 volt range, which is normal. Voltage cannot be used to tell how much charge is in the battery.

Most batteries will stop allowing input voltage and your charge controller could also be controlling some aspects of it.
 
Is that the other control panel. One of my setting says stop at 54.0v. so it will stop the shore power from coming in? The start setting is set at 52.0v meaning it will start the shore power to charge again when it hits 52.0. with that I don't have to go outside and turn the circuit breaker switch off when I get to that sweet spot. That sweet spot can be that settings I see on the control panel. That BMS will cut it off or it will start at low voltage that it's set.
 
Last edited:
Right now I'm im plugged in at a pedestal the soc is 88% and the total voltage is 54.1.

Your LiFePO4 battery has 16 cells in series. When charging, each cell will be full at ~3.65V, and your charge controller should be set to stop charging near this level...IF you want your batteries fully charged. 3.65x16 is 58.4V. On my controller this is called the "charge limit".

When you remove the charge (and any loads) from your now full batteries, the voltage will slowly drift down to ~3.35V per cell, or 53.6V for your pack. This is the voltage of a full battery at rest.

In a typical use case if you want to maximize your capacity, you'd stop charging at 58.4V, but maintain it at a higher voltage than 3.35V, rather something in the 3.45V per cell range (55.2V), if you are using electricity and still have charge available.

If you have plenty of capacity, then a charge limit of 3.55V (56.8V) is fine, and you could maintain it 3.40V (54.4V). You only lose a couple % and it's a bit easier on the batteries.

It's very difficult to tell the charge level of a battery of this type by voltage alone, even if you are able to let it rest for an hour or so. The curve of voltage vs SOC is nearly flat between 10-90%. Only at near full charge or zero charge does the SOC become obvious. You probably have a monitor that measures current in and out, which will give you a much better measure of SOC once it has been calibrated to your system.

If you are in a situation where you have shore power, I'd drain the batteries to 90% SOC or less (as low as 30%) and disconnect them. Just run on shore power, then hook the batteries up again when you leave. If disconnecting the batteries completely isn't possible, see if you can set your system to maintain a certain charge level.

My first crack at it I let it charge to 100%. It was fine. That night I was plugged in and sometimes mid night it didn't charge anymore or the rest of the next days. Even alternator charge. Mobile tech came out and did a reset and it worked.

Each battery has a BMS that protects the cells from overcharging among other things. Typically they will cut off at ~3.75V per cell. This is a safety feature, not a charge controller. YOU SHOULD NOT USE THIS AS YOUR LIMIT! Your limit should be set by the charge controller at a lower level.

I'm guessing that your BMS tripped because of too high a voltage on one or more cells. It would be good to know what your pack voltage was when this happened. The BMS should balance your cells, but I recently got a battery that failed to do this, and one of the cells was far out of balance. Consequently the BMS would cut out when the pack voltage was far below the recommended charge limit (13.9V rather than 14.6V), and it got worse with time rather than better. If you have something similar going on, then at least one of your batteries, or cells, or BMSs is defective and needs to be replaced.

Are you interested in doing some testing?
 
Last edited:
Thanks for your reply. I'm still getting my head wrapped around this. Let me study this with your reply in mind. It's been flawless since. I would like to know how I can tweak this to set the charge limit. The only panel that allows me to do this is here. If I keep it on shore power it can go to 100% if I let it. I switch the inverter off when I get to 90%. Instead of going outside in the cold to switch the breaker off.

Id be interested in testing. I need to learn this stuff.
 

Attachments

  • PXL_20240212_150237204.jpg
    PXL_20240212_150237204.jpg
    2.7 MB · Views: 0
First question... what is this system? Looks pretty complex!

You'll need to read the manual I think and try to figure it out and go from there. Happy to answer question about what I know. I understand a bit about LiFePO4 batteries and the solar controller I have since I recently installed it in my rig... but mine is simple and bare bones. I don't have shore power or charging from the alternator.
 
Top