Battery Voltage Fluctuations and Charging Issue

[Jamesb-uk]

Hello people,

I current have a Renogy 12v 50Ah lithium battery that I dont think is working correctly.

The battery is kept in the back of my van to run 12v accessories (water pump and led lights) and I charge the battery in my home using mains chargers (either Noco Genius 5 or an Optimate lithium 2amp charger).

The voltage is monitored using a small accessory that is attached directly to the battery terminals and appears to match multimeter readings.

Issue 1
- Battery only seems to get to arround 13.66 volts before charging stops. My understanding is maybe a cell is reaching a high voltage and the BMS is cutting the charging path? If the cells are inbalanced, how can this be fixed with a sealed battery? Is this a warranty issue on the battery? If the voltage drops to 13.4 after charging should I be concerned it stopped charging at 13.66v?

Issue 2
- The battery voltage under zero load can suddenly and randomly drop from say 13.3v to 12.8v? It usually jumps back at some point, as shown below, but again what might cause something like this?

Any help would be appreciated. Renogy suppport is terrible and they ask basic questions like is my charger set to Lithium mode.

 

[sunshine_eggo]

Issue 1
- Battery only seems to get to arround 13.66 volts before charging stops. My understanding is maybe a cell is reaching a high voltage and the BMS is cutting the charging path? If the cells are inbalanced, how can this be fixed with a sealed battery? Is this a warranty issue on the battery? If the voltage drops to 13.4 after charging should I be concerned it stopped charging at 13.66v?

Correct. Cell imbalance causes capacity loss. 13.4V is still a high-ish state of charge, so it may not be a big deal, but it's definitely not optimal.

More regular charging/cycling may correct it. If you have a charger or source that can be set for 13.6-13.8V, it might help to balance the cell simply by holding it at elevated voltage.

Issue 2
- The battery voltage under zero load can suddenly and randomly drop from say 13.3v to 12.8v? It usually jumps back at some point, as shown below, but again what might cause something like this?

12.8-12.9 is a common BMS protection or standby voltage. It's not the actual battery voltage, but it's what the BMS reports. If a small load or charge restores the actual voltage, it's just a characteristic of that BMS and not a concern.

 

[mikefitz]

the voltage drops to 13.4 after charging

That's an almost full voltage, however not being able to charge higher than 13.66 suggests significant cell inbalance, perhaps reducing battery capacity. The BMS is shutting down the charge path, then recovering, repeating continuously shown on the graph.

randomly drop from say 13.3v to 12.8v?

Renogy batteries have strange BMS protection that puts the battery in sleep mode after a while if no charge or discharge is taking place, this is what you may be seeing.

Any help would be appreciated

Your chargers are not ideal for charging despite their claims. The Victron range are fully programmable for charge voltage,

Victron Energy Blue Smart IP65 Charger - 12V 4A (Bluetooth Built-In)

Victron Blue Smart IP65 12V 4A professional charger with built-in Bluetooth and 7-stage charging algorithm. Ideal for scooters, motorcycles & classic cars.

www.12voltplanet.co.uk

This is comparable to your existing chargers. ( note with a 50Ah battery you could charge at higher currents safely, suggest up to 20 amps, limit 50 amps)

Hopefully the battery will become better balanced over time, being able to a high charge voltage ( just slightly lower that the BMS protection level) for several hours may speed up this process. Alternative your existing chargers connected for many hours may help.

The issues you are having is not unusual and common with Renogy batteries. You could ask for a replacement but it may have the same issues.

A reputable battery supplier in the UK is Fogstar, they understand their products and quickly resolve any issues. Unfortuantly they don't stock a 50Ah battery,

Lithium Leisure Battery | Fogstar UK

‘Fogstar Drift’ Lithium Leisure Battery | All models include Grade A EVE Prismatic LiFePO4 cells, High Discharge JBD BMS, Bluetooth, Heating | Lowest Prices in the UK. 10 Year Warranty.

www.fogstar.co.uk

 

[Jamesb-uk]

Correct. Cell imbalance causes capacity loss. 13.4V is still a high-ish state of charge, so it may not be a big deal, but it's definitely not optimal.

More regular charging/cycling may correct it. If you have a charger or source that can be set for 13.6-13.8V, it might help to balance the cell simply by holding it at elevated voltage.



12.8-12.9 is a common BMS protection or standby voltage. It's not the actual battery voltage, but it's what the BMS reports. If a small load or charge restores the actual voltage, it's just a characteristic of that BMS and not a concern.

Many thanks for your reply. I will review purchasing a Victron IP65 charger and see if that does a better job of charging.

In regards to the BMS going into standby, when I apply a load, 95% of the time the voltage drops even further (see below) and then returns to 12.8, and then randomly pops back up to 13.4. Are you saying it should go from 12.8 back to 13.4 when the load is applied?

In regards to balancing, are you saying if I set the charger to say 13.7v, it may give some of the other cells times to charge up to that level whilst not triggering the cut off for the high voltaged cell?

Thanks again. Starting to wonder if AGM wouldve been less complexity!

 

[sunshine_eggo]

Many thanks for your reply. I will review purchasing a Victron IP65 charger and see if that does a better job of charging.

Very capable charger. Can also work in "power supply" mode where it just outputs a constant voltage. Great for holding a battery at elevated voltage for balancing or for waking up a discharged battery that's in protection mode.

In regards to the BMS going into standby, when I apply a load, 95% of the time the voltage drops even further (see below) and then returns to 12.8, and then randomly pops back up to 13.4. Are you saying it should go from 12.8 back to 13.4 when the load is applied?

The typical behavior is to restore the voltage to the true voltage.

In regards to balancing, are you saying if I set the charger to say 13.7v, it may give some of the other cells times to charge up to that level whilst not triggering the cut off for the high voltaged cell?

Not just charge to but hold at an elevated voltage in the 13.6-13.8V range. It may trigger cut off, but it should still balance the cells.

Thanks again. Starting to wonder if AGM wouldve been less complexity!

Yes. LFP batteries are almost always imbalanced upon receipt (must be shipped at < 30% charge for hazmat requirements, and it's rare a consumer receives a battery < 60 days since build - ample time to go out of balance) and failure to regularly charge to full (a couple times a week) just makes it worse.

Once balanced and operating normally, it should be superior to AGM especially since you're lugging it in and out for charging...

 

[Jamesb-uk]

Very capable charger. Can also work in "power supply" mode where it just outputs a constant voltage. Great for holding a battery at elevated voltage for balancing or for waking up a discharged battery that's in protection mode.

Thanks. I have just bought the IP65 10amp version, should be good for my current 50Ah battery and if I ever change to a 100Ah battery it won't be too slow! I'll let you know how I get on. So the aim is to be able to charge up to around 14.4v (3.6v x 4) ?

 

[sunshine_eggo]

Thanks. I have just bought the IP65 10amp version, should be good for my current 50Ah battery and if I ever change to a 100Ah battery it won't be too slow! I'll let you know how I get on. So the aim is to be able to charge up to around 14.4v (3.6v x 4) ?

14.2-14.4 w/o triggering protection is sufficient.

 

[featherlite]

Can also work in "power supply" mode where it just outputs a constant voltage. Great for holding a battery at elevated voltage for balancing or for waking up a discharged battery that's in protection mode.

Thanks for that info. It seems that no matter how much time I spend on this forum, I learn something new quite often,

 

[Jamesb-uk]

The typical behavior is to restore the voltage to the true voltage

Im starting to think the BMS in this battery is junk. With a load applied the voltage is going down even more, it was sat quite happy at 13.48 last night.

I’ve got it on charge with the Victron at 14.2v but no current is flowing, is the battery full but bms showing lower voltage for some reason?

 

[sunshine_eggo]

Im starting to think the BMS in this battery is junk. With a load applied the voltage is going down even more, it was sat quite happy at 13.48 last night.

I’ve got it on charge with the Victron at 14.2v but no current is flowing, is the battery full but bms showing lower voltage for some reason?

At #1, BMS over-volt protection likely engaged. Voltage dropped to 12.8-12.9 while in protection mode.

At #2, the offending cell(s) likely dropped in voltage to release protection, so the charger engaged again, and triggered protection again.

 

[Jamesb-uk]

At #1, BMS over-volt protection likely engaged. Voltage dropped to 12.8-12.9 while in protection mode.

Should probably add, at point 1 the battery was not connected to anything. Based on previous comments I'd guess the BMS has gone into some kind of standby mode and would be expected to return to 13.4 when a load is applied. Instead the voltage drops further with the load.

Point 2 was me trying to charge it from the 'fake' low voltage, seeing if it would cause it to jump back to 13.4.

It has now come back to 13.4 on its own accord. All seems a bit random, maybe I should just disconnect the voltage monitor and let it do its own thing...

 

[sunshine_eggo]

Should probably add, at point 1 the battery was not connected to anything. Based on previous comments I'd guess the BMS has gone into some kind of standby mode and would be expected to return to 13.4 when a load is applied. Instead the voltage drops further with the load.

Makes sense.

Point 2 was me trying to charge it from the 'fake' low voltage, seeing if it would cause it to jump back to 13.4.

Looks like it went well beyond that, and protection mode engaged.

It has now come back to 13.4 on its own accord. All seems a bit random, maybe I should just disconnect the voltage monitor and let it do its own thing...

LOL... maybe so.