Question re. my LiFePo batteries

[rajid]

I apologize for the length of this post! I'm hoping someone with some experience with LiFePo batteries can give me some help!

A while back, I switched to LiFePo batteries and also changed out the power distribution/controller for one which would support the new batteries.

I was reading that it's not good for LiFePo batteries to leave them connected to a charger. Supposedly, it's better to leave them around 60% charge. So, I disconnected the charger and left a small number of LED lights on to slightly discharge the batteries over a few days. They seemed to be discharging very slowly, but then suddenly one day I saw a very rapid drop-off, leaving the voltage far below 12 volts, such that everything stopped operating! As you can see from the graph, it was discharging slowly and then within 1/2 day, it suddenly dropped off a cliff!

I was concerned about this, because I have also read that Lithum batteries of all types do not like being drained completely down! I hooked up the charger immediately but, as you can see from the 2nd graph, it only came back up to 11.17 volts; not enough to run anything. It stayed this way, while connected to the charger, for about 2 weeks until I finally connected the trailer to my F150 truck to take it out for a trip (knowing we simply would not have power unless we stopped at a full-hookup campsite).

When I arrived at the campsite, I was amazed to see the batteries operating again! As you can see from the 3rd graph, during the course of the afternoon, the batteries suddenly jumped from around 11 volts, up to 12.64 volts, and later jumped again, up to around 14 volts. I don't know what would have caused these jumps.

So, in short, I'm concerned a few issues here:
1) why the sudden discharge below 12 volts when there was very little drain on the batteries and they had been draining slow before?
2) why would the batteries only charge to around 11 volts and stay at that level for about 2 weeks, not gaining anything more?
3) why did the voltage suddenly jump from 11, up to 12.6, and then later jump again up to around 14 volts?

Thanks for any answers you can provide to these questions!

[Soppy]

There is nothing wrong with your batteries and they are acting normal. The LifePo4 voltage curve is very flat between 20% - 80%.
I would suspect the voltage readings have not been properly calibrated. A 12v LifePo4 battery will read 12.8v @ 20% capacity and 13.4v @ 90% capacity. At 10% they will be 12.0v then drop very quickly to 10v @ 0% capacity.
When charging the voltage will be very constant just above 13v till they reach 90% , then rise quickly when they approach 100%.

The 11v you are reading should actually be above 13v.

The only sure way to know your capacity is to fully charge the batteries then put a load on them and monitor the amp hrs till they reach the desired capacity. For a 200ah battery , fully charge them, then remove 60 ah and that will give you 70% capacity remaining.

[SafariBen]

Is it possible the shunt is hooked up incorrectly? like something is not going through the shunt? The battery seems fine, but the state of charge reading is wacky. Possibly set for a wrong AH rating, or not reset, zeroed out.



The charger that brought them to 11v was either extremely undersized, or not set correctly, or just not working at all.

[rajid]

Originally Posted by SafariBen

Is it possible the shunt is hooked up incorrectly? like something is not going through the shunt? The battery seems fine, but the state of charge reading is wacky. Possibly set for a wrong AH rating, or not reset, zeroed out.



The charger that brought them to 11v was either extremely undersized, or not set correctly, or just not working at all.

Well... As I always say, "It's a quantum physics world. Anything is possible!"
I'm including a photo of my battery box wiring. You can ignore the red wire which terminates outside of the batteries at the top and also the extra red and black wires which exit the box on the right side of the picture (they're an extra connector which I need to store inside the box in case it's needed.

I think I have it wired according to the VIctron wiring diagram "5B", which I'm attaching as well. I'm going to attach the "aux" wire to the positive of the 2nd battery. I guess I just never got around to doing that. I think it just allows the shunt to tell if one or the other batteries are not charging correctly, but maybe it will have an effect on the percent charged reading. I'm also going to see if there's some calibration which I need to do. Previously, I didn't see any, but I'll look again.

The charge controller is a Progressive Dynamics part which they said was a direct replacement for my previous unit.

https://www.amazon.com/dp/B002OR4242...asin_title_0_1

[TacomaJoe]

I think that the "5B" diagram is for 6V batteries in series. You have 12V in parallel.

One thing I see is that the split washer on the shunt does not look compressed and could be a loose connection.

[SafariBen]

Yes, that connection looks loose. The aux goes to the midpoint of two series batteries, which you don't have, so I assume the aux is not needed. Double check everything for tightness, and see how it goes I guess.

[Persistent]

Lots of good advice above.

The shunt is probably not compatible or needs calibration with Lithium voltage and current profile.
Loose connections are also a possibility.

RV lithium batteries have a built in electronic device called a BMS. It protects the batteries against abuse that may damage the cells inside.

Different battery designs do things differently. See Will Prouse Utube videos.

Many will disconnect the output when voltage drops to minimum cutoff voltage. That may be near 12.6 volts. Deep discharge will usually not damage the cells if they are charged up again in a month or so. The BMS disconnects. Output voltage drops to zero.

Measure the voltage directly on the battery terminals using a cheap digital voltmeter. See attached chart for resting voltage estimate of percent of charge.

[Stircrazy1]

Originally Posted by rajid

I apologize for the length of this post! I'm hoping someone with some experience with LiFePo batteries can give me some help!

A while back, I switched to LiFePo batteries and also changed out the power distribution/controller for one which would support the new batteries.

I was reading that it's not good for LiFePo batteries to leave them connected to a charger. Supposedly, it's better to leave them around 60% charge. So, I disconnected the charger and left a small number of LED lights on to slightly discharge the batteries over a few days. They seemed to be discharging very slowly, but then suddenly one day I saw a very rapid drop-off, leaving the voltage far below 12 volts, such that everything stopped operating! As you can see from the graph, it was discharging slowly and then within 1/2 day, it suddenly dropped off a cliff!

I was concerned about this, because I have also read that Lithum batteries of all types do not like being drained completely down! I hooked up the charger immediately but, as you can see from the 2nd graph, it only came back up to 11.17 volts; not enough to run anything. It stayed this way, while connected to the charger, for about 2 weeks until I finally connected the trailer to my F150 truck to take it out for a trip (knowing we simply would not have power unless we stopped at a full-hookup campsite).

When I arrived at the campsite, I was amazed to see the batteries operating again! As you can see from the 3rd graph, during the course of the afternoon, the batteries suddenly jumped from around 11 volts, up to 12.64 volts, and later jumped again, up to around 14 volts. I don't know what would have caused these jumps.

So, in short, I'm concerned a few issues here:
1) why the sudden discharge below 12 volts when there was very little drain on the batteries and they had been draining slow before?
2) why would the batteries only charge to around 11 volts and stay at that level for about 2 weeks, not gaining anything more?
3) why did the voltage suddenly jump from 11, up to 12.6, and then later jump again up to around 14 volts?

Thanks for any answers you can provide to these questions!

just a couple questions, did you set the jumper for the li mode when you replaced the converter, and did you set the smart shunt to Li and recalibrate it? just from looking at the graphs it doesn't look like it was recalibrated or switched over and it is still trying to display a lead acid type setup.

[rajid]

Originally Posted by TacomaJoe

I think that the "5B" diagram is for 6V batteries in series. You have 12V in parallel.

One thing I see is that the split washer on the shunt does not look compressed and could be a loose connection.

Yes, you're right. My mistake. I disconnected the extra wire again. Thanks.

[rajid]

Originally Posted by SafariBen

Yes, that connection looks loose. The aux goes to the midpoint of two series batteries, which you don't have, so I assume the aux is not needed. Double check everything for tightness, and see how it goes I guess.

Thanks for pointing this out. I have tightened up all of the connections.

[rajid]

Originally Posted by Persistent

Lots of good advice above.

The shunt is probably not compatible or needs calibration with Lithium voltage and current profile.
Loose connections are also a possibility.

RV lithium batteries have a built in electronic device called a BMS. It protects the batteries against abuse that may damage the cells inside.

Different battery designs do things differently. See Will Prouse Utube videos.

Many will disconnect the output when voltage drops to minimum cutoff voltage. That may be near 12.6 volts. Deep discharge will usually not damage the cells if they are charged up again in a month or so. The BMS disconnects. Output voltage drops to zero.

Measure the voltage directly on the battery terminals using a cheap digital voltmeter. See attached chart for resting voltage estimate of percent of charge.

I have now located the detailed instructions and set up the shunt configuration values to what they suggest for liFePo. Thanks.

[rajid]

Originally Posted by Stircrazy1

just a couple questions, did you set the jumper for the li mode when you replaced the converter, and did you set the smart shunt to Li and recalibrate it? just from looking at the graphs it doesn't look like it was recalibrated or switched over and it is still trying to display a lead acid type setup.

I have now verified that, yes, I set the jumper to "LI" for lithium. There's no specific configuration for setting the shunt to Lithium, but the instructions do give suggested values for various parameters. I have now verified that these are set according to the instructions. Thanks.

[SafariBen]

Did you find a setting for battery bank amp hour capacity?

[Stircrazy1]

Originally Posted by rajid

I have now verified that, yes, I set the jumper to "LI" for lithium. There's no specific configuration for setting the shunt to Lithium, but the instructions do give suggested values for various parameters. I have now verified that these are set according to the instructions. Thanks.

usealy for the shunt you have to do a re-install which involves setting up the AH capacity and such again. I would have to know the brand and model of the shunt to look it up to be sure.. but I know my setup I have to redoo the install procedure whan I chage batteries size or type.