Unexpected challenge in finding LiFePO chargers compatible with your battery

[djm45]

I have a BougeRV 100Ah 12V battery with heater protection and high voltage protection. It has an upper charge voltage limit of 14.45V enforced by the BMS. I got a AmpereTime charger 14.6V 30A for LifePO batteries. The charger never was able to charge the battery even though it have changing stages for charging. A trickle charger could. There does not appear to be control over what the AmpereTime (now LiTime) voltage is for charging. So did I unexpectedly buy the wrong charger? I returned it to AmpereTime and they quickly refunded my money (great interaction with the support people but no answer to the voltage issue). I tried search the forum for this dilemma, but could not find a solution (somewhat new at this). OTOH, the Victron Blue Smart IP67 charger seems to suggest control over charging levels (spec sheet gives a charging range of 13.5 - 14.2 V). Would their charger work with a 14.45V battery limitation?

I guess the idea that one needs to drill down to determine compatible chargers is something I naively wasn't expecting. Or, that the battery folks can give you a list of compatible chargers?

 

[mikefitz]

The Victron Smart IP 22 or IP 67 range have preset values that can be selected or user settings for a charge profile. Having Bluetooth connection to an app makes programming easy and gives access to charge conditions.
Either of these chargers would perform well with your battery.
For an instalation indoors the IP 22 unit is recomended,

Blue Smart IP22 Charger - Victron Energy

The Blue Smart IP22 Charger is the new professional battery charger with built-in bluetooth. Find a Victron Energy dealer near you.

www.victronenergy.com

 

[djm45]

Awesome! Thank you for your suggestion. I guess if you want compatibility, you need a quality product.

 

[John Frum]

It has an upper charge voltage limit of 14.45V enforced by the BMS.

Is the battery really tripping on pack over-voltage of 14.45 volts?
Or is it tripping on cell over-voltage of 3.65 volts?
If its the former, that is a bit weird.

 

[djm45]

Is the battery really tripping on pack over-voltage of 14.45 volts?
Or is it tripping on cell over-voltage of 3.65 volts?
If its the former, that is a bit weird.

Sorry I missed your response earlier. The battery specs sheet says to protect battery, charging voltage ≥14.8V will stop charging. However, in an email from the battery people, they said it kicks in at 14.45 volts. When I reduced the charging voltage to 14.2V, it charged successfully (ending at 14.2 V according to the Victron charger). The actual battery ends up about 13.1 VOC. I am now curious why the ending voltage is so different than the ending charge voltage. If I look at lithium battery voltages to estimate the SOE, it suggests that it is only at 40% capacity. Is that surprising? Or, do I have (cranial) cross wires, i.e. misunderstanding of this process.

 

[John Frum]

Sorry I missed your response earlier. The battery specs sheet says to protect battery, charging voltage ≥14.8V will stop charging. However, in an email from the battery people, they said it kicks in at 14.45 volts. When I reduced the charging voltage to 14.2V, it charged successfully (ending at 14.2 V according to the Victron charger). The actual battery ends up about 13.1 VOC. I am now curious why the ending voltage is so different than the ending charge voltage. If I look at lithium battery voltages to estimate the SOE, it suggests that it is only at 40% capacity. Is that surprising? Or, do I have (cranial) cross wires, i.e. misunderstanding of this process.

You didn't really answers my questions.
Makes it hard to converge on understanding.

 

[djm45]

You didn't really my questions.
Makes it hard to converge on understanding.

I think you meant a whole battery versus an individual cell. I am talking about the whole battery. Is that what you mean?

 

[John Frum]

I think you meant a whole battery versus an individual cell. I am talking about the whole battery. Is that what you mean?

Does the battery have a smart BMS?
If yes, it should indicate whether its a pack over-voltage or a cell over-voltage.
Can you tell us which event is ocurring?

 

[djm45]

Does the battery have a smart BMS?
If yes, it should indicate whether its a pack over-voltage or a cell over-voltage.
Can you tell us which event is ocurring?

Yes, my battery does have a BMS. The only indication I had from the original incident was a flashing light on the charger indicating a problem. I then contacted the battery people and they said it was a "charging overvoltage protection issue" and that was built into the battery. No reference anywhere to a "cell over-voltage" or "pack over-voltage". Is pack referring to the collection of cells that represent the battery? I guess semantics may be the challenge for me. I am a novice at this.

 

[John Frum]

Yes, my battery does have a BMS.

The key word is "smart".

The only indication I had from the original incident was a flashing light on the charger indicating a problem. I then contacted the battery people and they said it was a "charging overvoltage protection issue" and that was built into the battery. No reference anywhere to a "cell over-voltage" or "pack over-voltage".

I'm guessing you don't have a "smart" bms.

Is pack referring to the collection of cells that represent the battery?

Yes.

I guess semantics may be the challenge for me. I am a novice at this.

That is ok.

 

[John Frum]

However, in an email from the battery people, they said it kicks in at 14.45 volts.

This battery is just not very useful if the pack over-voltage disconect triggers at 14.45 volts.

When I reduced the charging voltage to 14.2V, it charged successfully (ending at 14.2 V according to the Victron charger). The actual battery ends up about 13.1 VOC.

Is the BMS still disconnecting?

 

[djm45]

No. I was able to charge it when I lowered the max charge voltage to 14.2V. I think I might edge that up a bit and see what happens.

One final curiosity: Are the LiFePO4 SOC charts that label % charge by voltage level very accurate?

 

[John Frum]

No. I was able to charge it when I lowered the max charge voltage to 14.2V. I think I might edge that up a bit and see what happens.

If you can charge to 14.2 volts with an aborption timeout of ~30 mintues then the battery is usable.
You mentioned earlier that the battery settled to 13.1 volts open circuit.
That is not good.
The settled open circuit voltage should be ~13.6 volts.
I would let that battery sit for a week or so and see if it drops even more.
You may have a lemon.

One final curiosity: Are the LiFePO4 SOC charts that label % charge by voltage level very accurate?

Some are better than others.
Charge and discharge curves are usually better than those color coded tables.
Here are some fairly representative charge/discharge curves courtesy of @Off-Grid-Garage

Hithium 280Ah

Shared with Dropbox

www.dropbox.com

 

[djm45]

Very helpful comments and observations. BTW BougeRV has sent a replacement battery so I am anxious to see how things play out with a second gen battery. At least with respect to their original BMS. Major thanks.

 

[Steve_S]

A 12V Battery Pack typically has 4 cells, so a 12V/100AH battery usually has 4x100AH cells within.
Some companies will produce these with 8x50AH cells by having 2 cells in parallel. This is not that uncommon btw.

14.2V ÷ 4 = 3.55V per cell. This is 0.15V above the Working Voltage Range and gains you nothing.
13.6V ÷ 4 = 3.4V per cell. This is the TOP of the Working Voltage Range and perfectly acceptable.
LFP always settles post charge and depending on how saturated the charge is it will vary somewhat. If charging just cuts off @ 14.0V then all you have is a "Surface Charge" and that will settle even lower.

The EndAmps/TailCurrent for a 12V/100AH battery is 5A for charging. If you are charging at 14.0V (3.5Vpc) starting at 50A, once the pack reaches 14.0V the amps will begin to decrease from the internal resistance as that increases. When the EndAmps of 5A is reached (the cells are full) and then charging should be transitioned to Float for final topping & balancing which takes a trickle.

Absorb: 13.8V for 15 minutes (3.45vpc) (some call this boost) (Absorb Timer is typically 10 minutes per 100AH of capacity)
Equalize: OFF
Float 13.7V (3.425vpc)
MIn Volts: 10.6V (2.650vpc)
Max Volts: 14.3V (3.575vpc)
Rebulk Voltage: 12.8V (3.200vpc)
End Amps: 5.0A (*1)
(*1): End Amps is calculated (100AH X 0.05 = 5A)
Coulumbic Efficiency / Battery Status Meter Efficiency for LFP = 99%.

There are TWO Voltage Ranges for LFP (just like all other battery chemistries):
The Allowable Voltage Range that does not harm the cells, is from 2.500-3.650 volts per cell. This is the "gross power".
The Working Voltage Range which is where the Deliverable AH comes from. This range is from 3.000-3.400, with Nominal Voltage being 3.200Vpc (50%SOC).
From 2.500-3.000 _and_ 3.400-3.650 only represent about 10% of GROSS CAPACITY of the battery pack at MOST ! and when you look at the Voltage Curves from Charging & Discharging tests this is exactly where the Cliff Climb & Cliff Fall are on the graph-chart...

As you Charge LFP the cells will remain pretty close together through the "Working Range" but they will deviate quickly once outside of that range. During discharge, some cells will drop voltage faster than others once below 2.950, just the same as some cells will rapidly increase their voltage after 3.400 and "run" to 3.650 far ahead of the other cells. You can a battery pack to 3.650Vpc till Amps Taken drops to 0, disconnect charger and they will immediately start to settle and within an hour or so the cells will be resting at 3.450 +/- a bit pending on cell grade, temps etc.

Hope it helps, good luck.