New Lithium Battery - charging and reading graphs

immanence

Hi all,

I got MPPT settings from the battery manufacturer and set up a Victron smart shunt, and at first it was reading 100% plugged into shore power. I figured it needed some calibration though, and now I am seeing a steady drop in capacity. To me this looks like a I have a slow draw and shore power isn't charging the battery at all. Or is this just the limits of the AGM WFCO (2021 tab bd, I believe it is the AGM WFCO - someone said you can tell by the two letters on the serial number. Mine were DC I think.)

Here are examples of what I am seeing in the Victron app:

immanence

Yoshi_TAB

Hi,

When you first hooked up to the battery, when it's  known to be fully charged, did you can sync. the smart shunt to 100% ? Then your fully charged battery is syncd at 100% and the percent SOC should match the voltage.   Your solar looks like it's a fully charged battery.

Even when on shore power, your WFCO will supply the 12V systems in your TAB with amps to power them.  Any remaining amps will go to charge your battery.  The parasitic draw in your trailer is estimated to be about 0.75 amps.  Is anything else running like a light, TV, radio, etc.  Something is running resulting in a deficiet of -1.69A.  

The WFCO is either 8735P , 8735LIS or 8735AD.  My '21 is a 8735P (for lead acid battery only).  I believe there may be some later model '21s with the LIS or AD, for lithium batteries..but not sure.  Look inside the cover for the WFCO model.

Most people only see 85-90% charge with a 8735P.  For some reason mine will get to 100%, but very slow.

As an experiment, pull each of the 12V fuses in the WFCO and record the change in current.  As you pull each one (except the bottom 2) , record the amps and you can see which device is draining the battery.   Eventially it should get to zero and go to positive to indicate your battery is being charged.

Here is chart of the estimated  number of amps for all the 12V devices.

AnOldUR

Yoshi_TAB said:

Most people only see 85-90% charge with a 8735P.  For some reason mine will get to 100%, but very slow.

I had thought that was strange until recently. When I plugged into shore power my LiFePO4's went to 87% overnight and I thought that was it. Over the next few weeks I notice it's slowly gone up to 99%. I'll still have to use my NOCO to top off when time is important, but it's nice to know it won't always be necessary.

@immanence there's something that looks strange to me in your Victron app screenshot. The voltage reading on your SmartShunt is reading 13.25V but the reading on your SmartSolar is 13.80. Mine are usually within about .01V of each other as seen by the 13.49V and 13.48 readings below. Anyone care to comment on this?

Also, you may know this, but if you hit the up/down arrow to the right of the device on the app, it will give you an expanded view.

Marceline

Are you 100% sure that the SmartShunt is wired correctly? As @AnOldUR says, your readings look strange. The SmartShunt and SmartSolar monitor some different data, but the voltage readings should be the same. And that 1.69A draw is odd if you have everything off in the trailer.

Yoshi_TAB

Hi,

Can you put a meter on the battery to see which value is corect?

A 70% SOC lithium battery is about 13.2 V , so that seems right.  Correct?

Could the solar settings be off?

If you look at his install post that shows pictures, it looks wired correctly.  But always worth checking.

otr_320

Yoshi_TAB said: Most people only see 85-90% charge with a 8735P.  For some reason mine will get to 100%, but very slow.

AnOldUR said: I had thought that was strange until recently. When I plugged into shore power my LiFePO4's went to 87% overnight and I thought that was it. Over the next few weeks I notice it's slowly gone up to 99%. I'll still have to use my NOCO to top off when time is important, but it's nice to know it won't always be necessary.

Here's a possible explanation for what you're experiencing.

WFCO converters have a bad habit of only operating in 13.6v absorption mode (vs 14.4 - 14.6v bulk mode), which increases charge times considerably.  13.6v will eventually charge a lifepo4 battery to ~100% SOC assuming the 12v loads on the WFCO converter are minimal. Any additional loads will reduce available charge current, further increasing charge times, and in some cases prevent the lifepo4 battery from ever achieving a 100% charge.

Another contributing factor is the voltage drop due to undersized wiring used in many RV's--including NuCamp.  Although the WFCO converter may produce 13.6v at its output, voltage drop due to undersized wiring can reduce the voltage at the battery terminals to less than 13.6v, preventing a lifepo4 from obtaining a 100% charge.  This voltage drop is why some folks only achieve a 85 - 90% SOC.  A lifepo4 battery needs at least ~13.6v to charge to 100% (there's some debate as to the specific voltage necessary to achieve 100%).

I believe most folks would be very surprised to see how much faster the batteries in their 320's would charge with a 35a converter that does go into 14.4v (or 14.6v) bulk mode properly.  When charging a 12v lifepo4 battery from 0 to 99% charge times are typically twice as fast at 14.4 - 14.6v vs. 13.6v.  Depending on the size of the battery bank (and other external loads) it can sometimes take a lifepo4 battery hours to charge from 99 to 100% at 13.6v.  At 14.4v - 14.6v, it may only take a matter of minutes.

FYI for those using an WFCO that is not going into 14.4 - 14.6v bulk mode: Most BMS's in 12v lifepo4 batteries perform their cell balancing functions when charge voltages hover above 14.0 - 14.2v or so (varies by manufacturer).  Since most WFCO's rarely go into 14.4 - 14.6v bulk mode, this means the BMS in a 12v lifepo4 battery will not have the voltage (or the time) necessary to perform important cell balancing functions.  Over time your lifepo4 battery may lose ah capacity due to imbalanced cells.  If the imbalance becomes excessive, the BMS's balancer may not have the current capacity to recover, even if the proper voltage is applied at a later time.  This could result in a permanent loss in battery ah capacity (unless you're willing to open the battery case and manually balance the cells).  Just something to keep in mind.

immanence

@otr_320 on that final 'fyi' note: is that why products like the Victron smart charger advertise extending battery life? In practice, do you think the smart charger will have a big effect there?

immanence

Hey all,

I think that draw was an anomaly, because I am now in there with a couple of lights on and the draw is .75.

That being said, I just don't think any power is going to the battery. Could it be the battery bms?

I just checked battery with a multimeter. The Smart Shunt is accurate. Also confirmed that I have the 8735P. 

Going to look into battery bms, but is there anything else I should check as well?

immanence

Hmm. I was going to try jumping the bms, but it sounds like the fact that the smart shunt is reading voltage suggests it isn't a bms issue.

I feel like it can't be my wiring because I am plugged in to shore power and that is working... But the power isn't going into the battery for some reason when WFCO is switched on.

Checked the 30 amp on the WFCO. It isn't blown.

Power coming in, just not being sent to battery (not even slowly).

Yoshi_TAB

Hi,

A couple things to check.

Check WFCO AC power breaker branch #1 (to the right of the Main) and see if it tripped.  The converter/charger AC power to charge the battery is wired into this breaker.

Check fuses #6 and #7 in the WFCO and see if they are blown.  Both of these have to be good.  #6 is for the battery converter power and #7 is the reverse polarity.  The #6 may be the one you already checked.

Have you plugged something into a 110V  outlet inside the TAB to make sure the shore power is working as it should?

Here's a trouble shooting chart from WFCO.

New Flow Chart for WF-8700 Series (wfcotech.com)

What brand of battery do you have?

immanence

@Yoshi_TAB thanks that flowchart is great! Fuses are good, breakers are good. 110v outlets work.

Battery is LiTime 230ah. Starting to think it is battery bms... But I haven't read enough about those to know. I did read that they need to be reset sometimes by applying some power directly to the battery. But shouldn't the WFCO already be doing that?

I have a small battery jumper. Should I try hooking that up to the battery and see if giving it a jolt does anything?

immanence

@Yoshi_TAB and everyone else, well this is an anticlimactic ending... I wanted to make sure all the other components were working so I turned off the WFCO and unplugged the trailer. Power off, that is good. Turned the WFCO back on, battery power works, great! So I plug the trailer back in... And now the battery is taking a charge.



I think that may have given the bms the jolt it needed, and I am thinking low temp charging protection triggered, so it needed some kind of reset. Just my hypothesis.

Will Prowse confirmed that the low charging protection does work pretty well on this battery, and while it wasn't cold when I was working on it we did have some cold weather recently. 

Supposed to be 35 tonight and I am thinking that l will leave it plugged in and see if it is still charging in the morning. Though 35 might not trigger the protection anyway (particularly since this is pretty well insulated inside the trailer).

Thanks for the support all, sorry it didn't end up being a more rousing victory...

Though the MPPT and smart shunt discrepancy is still out there, which is weird. I set the settings for both smart shunt and MPPT according to LiTime parameters, but maybe I got one wrong on there (probably the MPPT since earlier I confirmed via multimeter that the smart shunt is reading correctly).

Yoshi_TAB

Great..that should have occured to me, because I am  been plagued by that exact issue.  I usually have to do that same iteration to get my charger working.

I don't know enough about the logic in the charging circuit board, but my theory as to why the charging circuit does not automatically start at voltages above 13V is because the voltage for a lithium battery at 70% or even down to 20-30% SOC is still  higher than a fully charged lead acid battery (12.6V) so the charger never starts to charge.  The charger circuitry does not detect a discharged battery at voltages above 12.6V so a charging cycle doesn't auto start....don't know if that is  right, but my theory.  I've asked WFCO and never get a good answer.

My winter project is to install a victron standalone charger and disconnect the WFCO battery charger.  It will also help with the cell balancing issue discussed above.

immanence

@Yoshi_TAB my wife said: "So... You unplugged it and plugged it back in?" I was like, it was harder than that..!

I will try to monitor what you describe and see if I can lend some evidence there.

Which charger are you thinking? I was wondering about that as a solution, but the smart chargers end in a 3 prong, so I was wondering if there would be a way to permanently hook one up into the system. I guess if on shore power you can always just run the outlet out of a seat and plug it in to your own ac outlets!

otr_320

immanence said:

@Yoshi_TAB and everyone else, well this is an anticlimactic ending... I wanted to make sure all the other components were working so I turned off the WFCO and unplugged the trailer. Power off, that is good. Turned the WFCO back on, battery power works, great! So I plug the trailer back in... And now the battery is taking a charge.

@immanence, the 13.29v charge voltage and 10.65a of charge current shown in your screenshot appears to show your 35a WFCO 8735 converter charging in absorption mode.

This is a perfect example of what I was discussing in my previous post---the WFCO's inability to charge in bulk mode.

If your WFCO 8735 was charging properly in bulk mode (while charging a lifepo4 battery at 0 - 98% SOC), voltage would be hovering around 13.6 - 13.8v and current would be at or near the 8735's maximum rated charge current of 35a (this assumes minimal voltage drop between the converter and battery).  As the lifepo4 battery approaches 100% SOC this charge voltage would rapidly increase from 13.6 - 13.8v to 14.4 - 14.6v (charge current will drop to zero or near zero at the same time).

To put this current disparity into perspective, 10.65a of charge current in absorption mode will take almost 22 hours to charge a 230ah battery from 0 to 100% SOC.  It would take slightly less than 7 hours if it was charging at or near 35a in bulk mode.

A significant difference in charging performance.

otr_320

Yoshi_TAB said:

I don't know enough about the logic in the charging circuit board, but my theory as to why the charging circuit does not automatically start at voltages above 13V is because the voltage for a lithium battery at 70% or even down to 20-30% SOC is still  higher than a fully charged lead acid battery (12.6V) so the charger never starts to charge.  The charger circuitry does not detect a discharged battery at voltages above 12.6V so a charging cycle doesn't auto start....don't know if that is  right, but my theory.  I've asked WFCO and never get a good answer.

I see the logic you're trying to use; however, the key point you're missing is the internal resistance of a lifepo4 or lead-cell battery at any given SOC.

A charger, any charger, sees a lead-cell or lifepo4 battery as simply a variable resistor. 

A discharged lead-cell or lifepo4 battery presents LOW resistance to a charger.  Low resistance allows charge current to flow.  

A fully-charged lead-cell or lifepo4 battery presents HIGH resistance to a charger.  High resistance prevents or restricts the flow of charge current.   

If you're familiar with Ohms Law it should help clarify this relationship.

Simply having the charger's output voltage higher than the voltage of the battery is not enough to allow charge current to flow.  The internal resistance of the battery must ALSO be low (i.e., battery discharged) at the same time . . . to allow charge current to flow.

Yoshi_TAB

Hi @otr_320

Thank you for the explaination.  It's helpful to better understand what's going on. 

So the charger never starts because the voltage (and resistance)) of the lithium battery does not drop enough below the voltage of the charger to allow current to flow.  Correct?

Like the OP, when the lithium battery voltage drops, the charger will never start on its own, but when powered off and on,  the charger will start.  Why do you think that happens?

I never had the issue with the charger not starting  with lead acid batteries, is it  because their voltage is always lower than lithium batteries (for the most part).   Is that correct?

What delta voltage would you have to see to get 25-35 amps out of a charger (even for a lead acid battery)?

Yoshi_TAB

immanence said:

Which charger are you thinking? I was wondering about that as a solution, but the smart chargers end in a 3 prong, so I was wondering if there would be a way to permanently hook one up into the system. I guess if on shore power you can always just run the outlet out of a seat and plug it in to your own ac outlets!

Hi, My plan is to add a new outlet for the charger to branch 5 in the WFCO.  The WFCO allows for 5 circuits but only 4 are being used.  Branch 4 has a breaker that is taking up two slots (one is blank).  It can be split into a tandem breaker to allow for two circuits.  The WFCO manual allows this.

otr_320

Yoshi_TAB said:

Hi @otr_320

Thank you for the explaination.  It's helpful to better understand what's going on. 

So the charger never starts because the voltage (and resistance)) of the lithium battery does not drop enough below the voltage of the charger to allow current to flow.  Correct?

Like the OP, when the lithium battery voltage drops, the charger will never start on its own, but when powered off and on,  the charger will start.  Why do you think that happens?

I never had the issue with the charger not starting  with lead acid batteries, is it  because their voltage is always lower than lithium batteries (for the most part).   Is that correct?

What delta voltage would you have to see to get 25-35 amps out of a charger (even for a lead acid battery)?

@Yoshi_TAB, my previous post was primarily trying to clarify basic charger/battery operation---and not so much address the specific problem you and the OP are experiencing.

I'll try and take a stab at what may be occurring based on your above, short description of the problem.

The WFCO 8735 is advertised as a 3-stage charger (13.2v float, 13.6v absorption, and 14.4v bulk).

As you know, most WFCO converters are unable to properly transition from 13.6v absorption to 14.4v bulk mode, significantly reducing charge current.  It's possible the WFCO is also experiencing a float/absorption transition problem.

For whatever reason, the WFCO may be inadvertently transitioning to 13.2v float mode.  If the voltage of the 12v lifepo4 battery is somewhere between 13.21 - 13.40v, the WFCO will not produce any charge current because the charger output voltage (13.20v) is **lower**  than the battery voltage.  When you turn the WFCO off, then on, you may be creating just enough inrush load to force the WFCO into 13.6v absorption mode.  At that point, the charger's output voltage (13.6v) is **higher** than the battery voltage allowing charge current to flow.

Without going into another negative rant about WFCO converters, suffice to say, replacing your WFCO with a Progressive Dynamic, Victron, or other proven converter/charger should eliminate both of these problems.

immanence

@otr_320 yeah that 10 amps quickly went to 5. Now this morning (the next day) it is at 3.5 amps at 13.56v. I don't think I need to jump on it, but this is pushing me towards adding a smart charger.

@Yoshi_TAB that is awesome, that is a great tip! Would you then add the outlet in the same compartment as the battery? Seems like there should be space next to the run going into the section with the air8, though the cord on the charger is probably long enough that you could put it anywhere. Might be somewhere more convenient to have another outlet.

rh5555

One more thing to think about:  I also have the LiTime 230Ah batteries and have been charging them with a Victron Multiplus II.  When a Litime battery thinks it is fully charged, its internal BMS reduces the charge current to zero (or really close).  The transition is quite sudden, one minute they're charging at 10 Amps, the next minute, zero.  So zero observed charge current might just mean the battery thinks it's fully charged.

otr_320

rh5555 said:

 . . . . I also have the LiTime 230Ah batteries and have been charging them with a Victron Multiplus II.  When a Litime battery thinks it is fully charged, its internal BMS reduces the charge current to zero (or really close).  The transition is quite sudden, one minute they're charging at 10 Amps, the next minute, zero.  So zero observed charge current might just mean the battery thinks it's fully charged.

I believe you're using two 230ah batteries, right? I'm almost certain one of your LiTime BMS's is activating a high voltage disconnect (HVD).  Your comments that the "transition is quite sudden" and it was "charging at 10 Amps, the next minute, zero" describe an HVD perfectly. When an HVD occurs the BMS abruptly disconnects all charge current to protect one or more cells in the battery.  The BMS reconnects charge current once all cell voltages fall below the BMS release voltage for the HVD.  I might add, the BMS charge mosfets are not capable of "reducing" charge current.  They're strictly ON or OFF devices--there's no in-between.  

Assuming you don't have the absorption voltage in your Multiplus set too high, odds are the cells in one of your LiTimes batteries are not well balanced. Some of the cells are charging to 100% SOC sooner than others.  The cells already at 100% SOC will continue to activate the HVD until the cells at a lower SOC (voltage) "catch-up" with the cells that are 100% SOC.  Hopefully the balancer in your BMS can rectify the imbalance.

rh5555

So how does the HVD differ from "Fully Charged Disconnect "?  High Voltage Disconnect sounds kind of scary, like you're trying to charge with too high a voltage...

Interestingly the LiTime batteries just call for charging at 14.4V ± 0.2V (which is what I'm doing) all the time.  No mention of Bulk vs. Absorption charging.  I assume that the BMS takes care of this by cutting off the charge when a battery is full.

I am indeed using 2 LiTime batteries in parallel and I will write up my experiences with the Victron Multiplus sometime soon.  I did discover that charging a single LiTime 230Ah battery at 120A causes its BMS to get confused.  It did sort itself out after discharging the battery a little (LiTime's suggestion).  I would suggest limiting the charge current to about 60A per battery.

otr_320

rh5555 posted: LiTime batteries just call for charging at 14.4V ± 0.2V (which is what I'm doing) all the time.

A High Voltage Disconnect (HVD) can occur even if you're charging a 12v 4s lifepo4 battery at significantly LESS than 14.40v, say 14.00v.  Here's two examples that will hopefully clarify how unbalanced cells cause an HVD to occur.  In both examples the battery is being charged at 14.00v.  Both have the same ah rating.  Typically any cell voltage >3.650v will activate an HVD.  Example #1 are unbalanced cells that experience an HVD.  Example #2 are balanced cells that do not experience an HVD.

#1.  Cell voltages (12v 4s battery being charged at 14.00v with UNbalanced cells)

Cell #1: 3.499v

Cell #2: 3.651v ***BMS activates HVD*** 

Cell #3: 3.349v

Cell #4: 3.501v

---------------

Total:  14.000v

#2.  Cell voltages (12v 4s battery being charged at 14.00v with well BALanced cells)

Cell #1: 3.501v

Cell #2: 3.499v

Cell #3: 3.498v

Cell #4: 3.502v

---------------

Total:  14.000v

Same relatively low 14.00v charge voltage in both examples, but two completely different results--one bad, one good.  The battery in Example #2 could probably be charged as high as 14.55 - 14.58v without experiencing an HVD.  The battery in example #1 will have less ah capacity than the battery in Example #2.  This is because any battery with cells in series is only as strong as the weakest cell (SOC & ah capability are both factors).  In the DIY lifepo4 world, Cell #2 in Example #1 is what they call a "runner".  

rh5555 posted: "I assume that the BMS takes care of this by cutting off the charge when a battery is full."

You're assumption is incorrect.  When a lifepo4 battery is being charged, the BMS only monitors individual cells for excessive voltage, charge current for overcurrent conditions, and possibly battery/cell temps.  As I mentioned to @Yoshi_TAB in an earlier post, the internal resistance of a cell/battery (along with voltage) determines the amount of charge current.  When a cell or battery becomes fully charged its internal resistance ramps up very high, high enough to stop nearly all charge current.  

A lifepo4 battery with well BALanced cells: all the cells will reach 100% SOC at approx. the same time---with ZERO assistance or intervention from a BMS.

A lifepo4 battery with UNbalanced cells: the cells do NOT reach 100% SOC at the same time. This can cause wide fluctuations in voltage (and current) from one cell to another (see Example #1 above).  This will typically require the BMS to intervene with an HVD to prevent one or more cells from being damaged from excessive voltage.  

rh5555 posted: High Voltage Disconnect sounds kind of scary, like you're trying to charge with too high a voltage...

High Voltage Disconnects can be scary if you're concerned about obtaining the rated ah capacity from your battery/cells.  Unbalanced cells reduce the ah capacity of the battery.  If the cells are not excessively unbalanced, the balancer in most BMS's should be able to resolve the imbalance. 

rh5555 posted: So how does the HVD differ from "Fully Charged Disconnect "?

I've explained what an HVD is.  I've programmed a number of BMS's---I've never heard the term "Fully Charged Disconnect" before.  Ball's in your court. 

rh5555

OK.  I think I get it.  I was thinking of the whole battery as a single element, rather than 4 internal cells connected in series.  The term High Voltage Disconnect had me confused - I was charging at the recommended voltage, how can that be too high?  If it were called High Cell Voltage Disconnect, I would have cottoned on sooner.

It seems you are familiar with BMS systems: I had this interaction with LiTime - perhaps you can explain what was going on here:

Me:

Hello,

I ordered a LiTime 12V 230Ah Plus Low-Temp Protection LiFePO4 Battery, Built-in 200A BMS, Max 2944Wh Energy - 2 Pack. 

I charged both batteries until the BMS indicated they were 100% charged by not accepting any more charge current.

I let the batteries rest for several hours with nothing connected to them.

One battery reads 13.3V (which is about what I expected), but the other battery reads only 12.8V.

This doesn’t seem right, please advise.

Their Reply:

We would like to clarify that It is our new protected functions of the battery BMS ：Stop Over-charging.

Please try to discharge with a small load for a few minutes and then continute to re-charge the battery to see if the resting voltage will be ≥13.33V.

As per our laboratory and customer feedback survey found that MPPT, car chargers and other chargers do not stop charging after the fully charged which has been resulting in frequent voltage oscillations.

To solve this protection mechanism, the battery only needs to be charged properly after the first discharge.

We feel sorry do not inform you the new functions in time, please try to discharge with the 100W loads for a few minutes  at highger 2A current.

Your understanding will be so much appreciated.

otr_320

rh5555 posted: I was charging at the recommended voltage, how can that be too high?

My last post explained how that's possible in detail.

--------------------------

I find it suspect that your 13.30v battery read 13.30v a few hours after supposedly charging to 100% SOC. You're charging at 14.40v, right?  Never timed it, but I do know it takes at least a day for my 12v lifepo4's to go from 14.20 - 14.40v before eventually resting around 13.35v (this is with the battery completely disconnected---zero parasitic).

In your message to LiTime, you mentioned verifying 100% SOC based on the "BMS indicat(ing) they were 100% charged by not accepting any more charge current". As a I mentioned in my first post, charge current (and voltage) also go to zero when a BMS activates an HVD.  Be sure not to confuse the two.

As for the problem with your one battery reading 12.80v, without knowing the individual cell voltages you're troubleshooting blind.  Assuming you didn't exceed maximum charge current or try to charge in cold weather---the HVD is the only remaining protection that would prevent your battery from charging higher than 12.80v.  Of course, a bad BMS could be at play, too.  The response from LiTime was cryptic at best.  Any luck with their suggestion to discharge/charge?

Are you using a Victron Shunt?  May want to discharge each battery (solo) to Low Voltage Disconnect (LVD), then charge.  The "trend" data while charging would be very helpful for troubleshooting purposes.

Good luck!