Weird behavior from new 200ah Renogy lithium battery

[pseudo]

Hey all,

Just set up a basic solar system on my van. Not my first but first time using lithium.

2x 100w in series, Victron 100/20 mppt and one of those 200ah Renogy batteries with bluetooth.

Absorption at 14.2 for 1 hour, float at 13.6

I haven't moved into the van yet so the electrical system has only had very little use but it's been connected and parked outside for a couple of weeks.

There's a weird thing going on where some nights but not others, as soon as the sun goes down, the battery voltage gradually decreases to about 13V or slightly below, without any loads whatsoever. Other nights it settles around 13.3-13.4 and stays there until sunrise which I believe is the expected behavior.

Any ideas what's going on? Is the battery likely faulty?

Also, on the Victron controller app's History page, I've seen the maximum battery voltage on some days reach up to 17V! If I check the Trends tab soon afterwards I can see the spike in the graph but if I don't look for a few hours the high battery voltage still shows on the History tab but seems to have been smoothed out of the graph in Trends.. Is this normal behavior?

And lastly, how much difference in voltage between cells is deemed acceptable? On the Renogy app, with the battery at 100%, cells 1 and 4 are at 3.5V, while 2 and 3 are at 3.3V.

Here are a few screenshots showing the behaviors described above

A few normal nights followed by one night where the battery seemingly self discharges (with a short period where it jumps back up to the expected voltage then starts decreasing again):



That same bad night followed by the same thing happening the following night:



Battery voltage reaching 17.14V:



History page showing battery max voltages reaching high 15 to 16+ volts on multiple days:



Any input is much appreciated!
Thanks

 

[sunshine_eggo]

Hey all,

Just set up a basic solar system on my van. Not my first but first time using lithium.

2x 100w in series, Victron 100/20 mppt and one of those 200ah Renogy batteries with bluetooth.

Absorption at 14.2 for 1 hour, float at 13.6

Those should be sufficient.

I haven't moved into the van yet so the electrical system has only had very little use but it's been connected and parked outside for a couple of weeks.

There's a weird thing going on where some nights but not others, as soon as the sun goes down, the battery voltage gradually decreases to about 13V or slightly below, without any loads whatsoever. Other nights it settles around 13.3-13.4 and stays there until sunrise which I believe is the expected behavior.

Any ideas what's going on? Is the battery likely faulty?

Imbalanced. Confirm that your batteries do not go dormant after 24 hours. There is a "feature" on some Renogy batteries that renders them unusable IMHO.

Also, on the Victron controller app's History page, I've seen the maximum battery voltage on some days reach up to 17V!

Here's your problem. One or both batteries are imbalanced. The batteries are cutting charge off causing the controller battery voltage to spike before it can clamp down on the current.

If I check the Trends tab soon afterwards I can see the spike in the graph but if I don't look for a few hours the high battery voltage still shows on the History tab but seems to have been smoothed out of the graph in Trends.. Is this normal behavior?

And lastly, how much difference in voltage between cells is deemed acceptable? On the Renogy app, with the battery at 100%, cells 1 and 4 are at 3.5V, while 2 and 3 are at 3.3V.

3.5V is fully charged.
3.3V is not fully charged.

Confirmed cause for 17V spike.

You likely need to discharge them a bit - until all voltages are below 3.3V.
Set MPPT current to 1A
Set absorption to 13.8V for 6 hours.
Set float to 13.79V.

Let them sit this way for several days. Try 14.2V again.

 

[mikefitz]

Welcome to the wonderful world of Renogy.
I think you have one battery, the latest with Bluetooth.
The battery is entering protection due to cell inbalance and shutting down the charge path. There is still energy in the output stages of the controller , and with light loads on the 12v system, a voltage spike occurs.
This seems to occur when the battery volts is just over 14 volts, try reducing the charge, absorbtion volts, in 0.1 steps from the existing 14 .4, until the problem stops occurring. Extend the absorbtion time to allow time for the ballance circuits to work. If necessary reduce down to 13.8 volts.
Don't take the BMS readings as accurate, one decimal place is not much use and Renogy admit there may be calibration and rounding errors. For example the cell reading of 3.3 may actually 3.39.

The odd effects you are seeing overnight may be due to the Renogy 'go to sleep mode'. If there is no current Into or out from the battery it takes a rest. It could also be the protection on cell overvolts, this turns the charge path off but you still see volts lower than actual.
After a while the internal volts fall below the recovery level and the BMS will restore the path and the volts become actual.

I type real slow and mr sunshine has posted advice, however I think we sort of agree on the issue and the solution.

Mike

 

[Texas-Mark]

History page, I've seen the maximum battery voltage on some days reach up to 17V!

This may be from the BMS opening and the open circuit voltage spiking. Possibly from cell imbalance.

 

[pseudo]

Awesome, thanks for the replies.
How would I check to see if the battery is going into shelf mode? It shouldn't be since it's getting a charge from the controller every day, right??

You likely need to discharge them a bit - until all voltages are below 3.3V.
Set MPPT current to 1A
Set absorption to 13.8V for 6 hours.
Set float to 13.79V.

Let them sit this way for several days. Try 14.2V again.

1A max charge current? (Currently set to 20A I think) Or tail current?

Any idea approximately how long it might take? Any way to tell if it's been successful since the BMS cell voltages are so imprecise? Just try my original settings again and see if the symptoms persist?

 

[sunshine_eggo]

Awesome, thanks for the replies.
How would I check to see if the battery is going into shelf mode? It shouldn't be since it's getting a charge from the controller every day, right??



1A max charge current? (Currently set to 20A I think) Or tail current?

1A max charge current.

Tail current disabled.

Any idea approximately how long it might take?

No. 3.5 vs. 3.3 suggests significant imbalance. In a perfect situation, a balancer can bleed off about 1 Ah/ 24 hours of continuous balancing.

If that's 3.45 vs. 3.34 and rounded, it's less of a big deal.

13.8V is 3.45V/cell, which should get a battery to 98%+ SoC.

Any way to tell if it's been successful since the BMS cell voltages are so imprecise? Just try my original settings again and see if the symptoms persist?

Yep. Again, also worth discharging at least a little bit prior to the new attempt.

 

[pseudo]

1A max charge current.

Tail current disabled.



No. 3.5 vs. 3.3 suggests significant imbalance. In a perfect situation, a balancer can bleed off about 1 Ah/ 24 hours of continuous balancing.

If that's 3.45 vs. 3.34 and rounded, it's less of a big deal.

13.8V is 3.45V/cell, which should get a battery to 98%+ SoC.



Yep. Again, also worth discharging at least a little bit prior to the new attempt.

Follow up question if you don't mind.

Is there a way to achieve this without limiting the charging current so much?

I discharged the battery to a little bit below half according to the Renogy app - just below 13.2v at rest, and have set the cc to the settings you recommended.

Over the last (somewhat overcast) day and a half, the battery amp hours as reported by the Renogy app have not increased a single bit. At this rate it looks like it could take weeks to charge back up and I'm going to need to use my system before then..

 

[mikefitz]

My suggestion of reducing the charge volts to 14.0 volts, or slightly lower if the battery still enters protection, and just using the system with normal charge currents, could be a more convenient method.
Many of the low cost batteries have unbalanced cells and 99% of the users don't know or care that the battery enters protection mode, and even the battery suppliers often state, 'its normal'.
In most cases the battery meets the users requirements and gradually gets Into better balance.

Mike

 

[sunshine_eggo]

Follow up question if you don't mind.

Is there a way to achieve this without limiting the charging current so much?

I discharged the battery to a little bit below half according to the Renogy app - just below 13.2v at rest, and have set the cc to the settings you recommended.

Over the last (somewhat overcast) day and a half, the battery amp hours as reported by the Renogy app have not increased a single bit. At this rate it looks like it could take weeks to charge back up and I'm going to need to use my system before then..

I would have expected the discharge to 3.3V/cell to not require 50% of the capacity, and 50% is not "discharge a little bit"

Increase charge current to maximum, charge to 13.8V and hold there.

@mikefitz's method is another option. With routine use and daily charging to full, the battery will eventually balance itself. Personally, I like to avoid cutting the chargers off in this manner, and the hope is that 13.8V minimizes the spikes and maximizes the balance time.

 

[pseudo]

I would have expected the discharge to 3.3V/cell to not require 50% of the capacity, and 50% is not "discharge a little bit"

Increase charge current to maximum, charge to 13.8V and hold there.

@mikefitz's method is another option. With routine use and daily charging to full, the battery will eventually balance itself. Personally, I like to avoid cutting the chargers off in this manner, and the hope is that 13.8V minimizes the spikes and maximizes the balance time.

Well I'm not sure how accurate the Renogy app is..

I wasn't planning on discharging it by that much but after 2 days of just working on my laptop running on the inverter it hadn't dropped by much so I left the laptop plugged in overnight with a 4k video playing and music playing on the speakers and that did the trick ?

I have about a week to try and get this sorted properly, if not I'll do as mikefitz says and just use the system at slightly reduced voltage while keeping an eye on it.

But you're saying put charge current back to 20A but keep everything else as before? 13.8 for 6 hours, then 13.79?

 

[sunshine_eggo]

But you're saying put charge current back to 20A but keep everything else as before? 13.8 for 6 hours, then 13.79?

Yes. The goal of a small discharge and 1A charge was to ensure that charging was happening during balancing. SOME BMSs only balance during charging.

 

[pseudo]

Just checking in to make sure everything looks as it should..
It's been a couple of days that the battery charge has topped out. The Renogy app says battery is at 83.8% and that hasn't changed in two days. Cells are still showing 2x 3.3 and 2x 3.5
Victron logs show voltage being held at 13.8 all day and it gradually drops to 13.6 overnight.
Charging current is essentially permanently at 0A. Is this normal? Can balancing take place when there's no charging current?

 

[mikefitz]

The Renogy battery has a 'shelf mode' that shuts the battery down if it sees no activity , current in/out over 1 amp.
You need to load the battery, say 2 amps or greater to 'wake it up' and then use normally, don't restrict current and use a suitable charge voltage, Renogy suggest any voltage between 13.8 and 14.4 can be used.
Whenever the charge current falls to zero the battery is in protection and no balance effect will take place.
The Victron graph showed that charging was taking place 'three days ago', revert to the charge settings you used then.

a)Discharge the battery to wake it up.
b)Let the Victron charge.
c)If the Renogy goes into protection, charge current falls to zero, reduce the charge voltage, go back to a)
d) if a sucessful charge without Renogy shutdown, just continue using the battery at the sucessful charge voltage with a long absorbtion time.
e) after a week or so increase charge volts and evaluate, if battery enters protection go to a), else go to d). (no need to charge higher than Victron default of 14.2)

Read page 14 of the instructions for the Renogy 200ah battery.

Mike

 

[sunshine_eggo]

Just checking in to make sure everything looks as it should..
It's been a couple of days that the battery charge has topped out. The Renogy app says battery is at 83.8% and that hasn't changed in two days. Cells are still showing 2x 3.3 and 2x 3.5
Victron logs show voltage being held at 13.8 all day and it gradually drops to 13.6 overnight.
Charging current is essentially permanently at 0A. Is this normal? Can balancing take place when there's no charging current?

It may be time to incrementally increase the absorption voltage until you observe the voltage spikes.

Mike has provided some good iterative steps to pursue.

 

[pseudo]

Ok thanks guys, I appreciate the help.

I'm going to plug the fridge in and leave it running all day and night and keep absorption at 13.8 for now and eventually raise it 0.1V at a time to see what happens.

Is it safe to keep absorption time at 6 hours for the long term or is it putting undue strain on the battery?

Should I leave float at 13.79 or put it back down to 13.5-13.6?

Is the fact my battery is "stuck" at 83% just because of the reduced absorption voltage?

The Victron graph showed that charging was taking place 'three days ago', revert to the charge settings you used then.

The settings hadn't changed. 4 days ago I'd increased the charge current from 1A back to 20A to speed up the charging after having discharged the battery and it charged for a couple of days until it hit 13.8V then it started doing what you see the past couple of days but I didn't change anything..

 

[mikefitz]

Set float to 13.4 or 13.5 for long term charging.
Having examined the graph again it seems you have no loading on the battery, its charging to about 13.8, holding that during the day, and a slight fall overnight to 13.6 volts.
To ensure the balance processing has more time, the battery needs to be discharged below the balance threshold, then charged. Renogy don't specify this but usually balance occurs over 3.4 v per cell or around 13.6 volts. Renogy do specify balance only occurs when charging, (page 14).
It's not too clear how the 'shelf mode' operates and how this effects things.

 

[pseudo]

Set float to 13.4 or 13.5 for long term charging.
Having examined the graph again it seems you have no loading on the battery, its charging to about 13.8, holding that during the day, and a slight fall overnight to 13.6 volts.
To ensure the balance processing has more time, the battery needs to be discharged below the balance threshold, then charged. Renogy don't specify this but usually balance occurs over 3.4 v per cell or around 13.6 volts. Renogy do specify balance only occurs when charging, (page 14).
It's not too clear how the 'shelf mode' operates and how this effects things.

Still working on balancing the cells with no obvious progress so far, but with my fridge running 24/7, and bulk set to 14V, I haven't experienced any more voltage spikes or weird discharge at night anymore.

I have a new one for you though.

Since yesterday, during bulk charging, the panel wattage drops very briefly every 10 minutes on the dot. Any idea what could be happening? No clouds, no shade and at regular intervals to the exact second.