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Old 10-23-2019, 04:05 PM   #21
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Hello All
Gus' question got me investigating and here is some more info from Battleborn's web site. The question was about high temperature charging of Battleborn LiFePO4 batteries
"Here are some temperature parameters for our batteries that should help with your question:
High temperature: > 135F The BMS will not allow a charging or discharging current.
Low temperature: < 25F The BMS will not allow a charging current. Charging current will be allowed again at 32F. We recommend not to use the batteries in temperatures under -4F Cold weather storage The storage temperature range is -10F to 140F. We recommend bringing the battle born batteries to a 100% charge and then disconnecting them completely for storage. After 6 months in storage you should still have 75-80% charged batteries. Storing batteries in sub zero weather(-15 or more) has the potential to crack the abs and more importantly could causes a faster loss of capacity, in some cases drastically more than the typical 2-4% per month loss. Charging our lithium batteries in cold weather We have an adhesive backed heating wrap that runs off of a 12 v source and works very well. It has a temperature sensor that allows it to turn on at 34F and stays on until the temperature rises above 45F. Heating wrap draws 30 watts/2.5-3 amps and is 3/16 of an inch thick. Hope this helps, thank you. "

We did not buy the heating wrap and will take our batteries out and store them over the winter.
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Old 10-23-2019, 04:06 PM   #22
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The Battle Born logic in that description is very simplistic, with no consideration of an appropriate current for a given temperature: it has no way to control current so it just disconnects entirely at set low and high temperatures. It handles the completion of charging similarly. I haven't seen any indication that this BMS monitors current at all.
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Old 10-23-2019, 04:26 PM   #23
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Quote:
Originally Posted by Brian B-P View Post
The Battle Born logic in that description is very simplistic, with no consideration of an appropriate current for a given temperature: it has no way to control current so it just disconnects entirely at set low and high temperatures. It handles the completion of charging similarly. I haven't seen any indication that this BMS monitors current at all.
Perhaps it is Brian
I am not an expert on LiFePO4 batteries but, from what I have read from battleborn, the BMS is there to protect the battery and to monitor individual cells so that the battery is charged appropriately sending current only to those cells that need charging. I interpret this to mean (and battleborn states) I do not need a temperature controlled charger but I did change the charger in our 19 to one that provides the appropriate output for LIFePO4 batteries to ensure they can be fully charged. I am considering adding the Victron BMV-712 monitoring system and perhaps a temperature monitor but that would just be to keep an eye on how the battery performs.
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Old 10-24-2019, 12:33 AM   #24
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Originally Posted by Bear101 View Post
I am not an expert on LiFePO4 batteries but, from what I have read from battleborn, the BMS is there to protect the battery and to monitor individual cells so that the battery is charged appropriately sending current only to those cells that need charging.
That seems like a reasonable guess, but they don't actually work that way. It's not practical to turn charging current on and off to each cell individually, so they just monitor (not control) cell-level voltages, and turn off charging when the most-charged cell hits a limit, and shut off discharge when the least-charged cell is too low. A BMS in an electric car will monitor temperature and likely tell the charger what current is safe (based on cell temperatures and voltages), but the Battle Born BMS is not in communication with the charger, so even if it measured current (which I'm pretty sure it doesn't) it would have no way to regulate the charging current.

What fully-functional lithium battery management systems do to keep the cell charges even is to tweak them after charging or discharging, by draining the most-charged cells through a resistor until they are closer to the rest. This is balancing; if done after charging it's called "top balancing", and if done after discharging it's called "bottom balancing". I don't know if the Battle Born BMS balances at all.

Quote:
Originally Posted by Bear101 View Post
I interpret this to mean (and battleborn states) I do not need a temperature controlled charger but I did change the charger in our 19 to one that provides the appropriate output for LIFePO4 batteries to ensure they can be fully charged.
The chart from Trojan posted earlier shows that the charging current should be limited based on temperature, but the Battle Born system only shuts the battery off entirely when the extremes of temperature are reached. I think they're counting on the charging sources in the applications where their products are used to just not have enough current capacity to hurt the cells, regardless of temperature. RV currents are pretty low compared to electric vehicles.

The charger change is just a higher (and single, rather than staged) charging voltage. That's necessary to get full battery capacity, but doesn't address temperature at all. That's not unreasonable: charging voltage and current limits for lead-acid batteries should depend on temperature, too, and almost no one uses temperature-compensated charging systems for them.
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Old 10-24-2019, 04:33 AM   #25
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More on temperature and charging

Quote:
Originally Posted by Brian B-P View Post
The chart from Trojan posted earlier shows that the charging current should be limited based on temperature, but the Battle Born system only shuts the battery off entirely when the extremes of temperature are reached. I think they're counting on the charging sources in the applications where their products are used to just not have enough current capacity to hurt the cells, regardless of temperature. RV currents are pretty low compared to electric vehicles. The charger change is just a higher (and single, rather than staged) charging voltage. That's necessary to get full battery capacity, but doesn't address temperature at all. That's not unreasonable: charging voltage and current limits for lead-acid batteries should depend on temperature, too, and almost no one uses temperature-compensated charging systems for them.
The Trilliums have the simple on-off, high-low BMS temp protections. This is a risk should you have trailer separation and rely on the battery for the breakaway switch braking. Seems most all LiFePO4 battery BMS have this feature.

We are using the Sterling PCU1240 charger. Its manual says "Battery Temperature sensor: When the temp. drops the charging voltage goes up incrementally. When the temp. increases the charging voltage goes down incrementally." Need to monitor and learn more.

The Sterling also has the ability to control the charging current, allowing you to manually compensate with 100, 75, 50, or 25% output. With the 40A charging size, we are good on the Trojans down to 41° F (5° C). When we expect lower temps, I can use the 25% setting which is OK down to 32° F (0° C).

Our RV plans try to keep us away from sub 32 temps. :-)

Our MorningStar ProStar 40A MPPT solar charger also temperature compensates using a fixed temperature compensation coefficient - 30 millivolts / °C / 12V. This is customizable. You can also set a low temp charger cutoff temp, which I need to investigate further.

To get sophisticated, I could talk to the MorningStar via MODBUS and Trillium via CAN bus. So many options... and sounds like a Raspberry Pi project ahead.

Also need to control charging from the tow vehicle. We switched that to a Sterling BBC1230, which is also good to 40 °F with Trillium. The Sterling battery-to-battery charger has the same compensation as the shore power charger. We mainly got this to protect the batteries from the car's alternator voltage profile by poroviding a managed charging profile as when on shore or solar charger.

As an Engineer, this is interesting, and I hope I can pretty much set and forget.

73/gus
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Old 10-24-2019, 06:23 AM   #26
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Originally Posted by rbryan4 View Post
On our 19, there's a plywood panel glassed in to the box for the batteries. Since the bottom of the box is rounded and tapered, the box bottom is raised in the middle to allow for a flat spot for the plywood platform.
Yes, this is as ours is constructed. In preparing for more batteries, I added an additional 3/4" plywood over the glassed in 1/2" plywood panel. Both span the A-frame.

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Old 10-24-2019, 08:10 AM   #27
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Quote:
Originally Posted by Brian B-P View Post

The chart from Trojan posted earlier shows that the charging current should be limited based on temperature, but the Battle Born system only shuts the battery off entirely when the extremes of temperature are reached. I think they're counting on the charging sources in the applications where their products are used to just not have enough current capacity to hurt the cells, regardless of temperature. RV currents are pretty low compared to electric vehicles.

The charger change is just a higher (and single, rather than staged) charging voltage. That's necessary to get full battery capacity, but doesn't address temperature at all. That's not unreasonable: charging voltage and current limits for lead-acid batteries should depend on temperature, too, and almost no one uses temperature-compensated charging systems for them.
Thank You Brian
Another statement that I read is that the Battleborn batteries are rated for 3000 cycles wth charging at 0.5C or lower but there is no other information on the charger used.
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Old 10-24-2019, 08:33 AM   #28
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Thank You Brian
Another statement that I read is that the Battleborn batteries are rated for 3000 cycles wth charging at 0.5C or lower but there is no other information on the charger used.
0.5C would be 50A for a 100AH battery. you can charge naked Li batts at a steady current right up til you hit the maximum voltage of 4.2V per cell,then holding that 4.2V/cell voltage, the current will reduce to zero when the battery is completely topped off.

thats far simpler than the 3-stage lead acid regimen, where you'll have a constant current 'bulk' stage, then a elevated voltage 'absorption' stage, then a reduced voltage 'maintenance' stage.

a fancy Li batt like the BattleBorn has an internal charge controller that accepts lead-acid style charging current/voltages, and keeps the Li batts happy.
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Old 10-24-2019, 08:38 AM   #29
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As long as we are discussing temperatures & lithium, it should be noted that most temperature probes associated with solar controllers or converters raise the voltages as the temperatures go down. This follows the charging characteristics of lead acid batteries.

Lithium batteries do not have the same charging characteristics as lead acid, and increased voltage (over 14.8V or so for a 12V system) will engage the battery management system over voltage protection. This is why Battleborn, as well as some other manufacturers suggest shutting off temperature compensation. Of course what ever temperature compensation built into the BMS still functions.
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Old 10-24-2019, 08:53 AM   #30
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To get sophisticated, I could talk to the MorningStar via MODBUS and Trillium via CAN bus. So many options... and sounds like a Raspberry Pi project ahead.

73/gus
Interfacing a Raspberry Pi to a CANbus seems like a cool project.

Even to just check on the tow vehicle transmission temperature
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Old 10-24-2019, 10:28 AM   #31
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Still about 1.5 years away on our 19 Lithium conversion, but I’ve already started preparations for the conversion. I have the U dinette and will be bringing the batteries inside the trailer in the front of the U where the power center is. This will bring them inside in heated space like the big rigs and the folks with the 21 and 5.0.
There is a support in the center front and perfect space on each side for a battleborn 100ah which also balances the weight across the width of the trailer. If a third battery is desired later it can easily go in front of the support between the other two maintaining weight distribution.
The wiring will be simple since on the 19 since this is where the battery lines come in from the current battery location on the tongue. I’m upgrading the battery disconnect switch now, then will change the solar controller out to the Victron MPPT. Next will be to add the Victron battery monitor and charge module upgrade. Trying to take the $$$ hits in increments so I don’t have to buy everything at one time and everything is in place to just drop in the batteries when it’s time.
This also will clear the tongue to add an aluminum truck box and not have the box space taken up by batteries.
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Old 10-24-2019, 10:56 AM   #32
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I have the U dinette and will be bringing the batteries inside the trailer in the front of the U where the power center is. This will bring them inside in heated space like the big rigs and the folks with the 21 and 5.0.
There is a support in the center front and perfect space on each side for a battleborn 100ah which also balances the weight across the width of the trailer.
This is exactly why I started this thread. This is my alternative too, given our u-shaped dinette. I will have room, and have all the chargers mounted in the front-u-section. Wanted to achieve 350-400 Ah capacity eventually. Was looking for LiFePO4 exterior mounting experiences.

Have a Lithionics OPE-Li3 220Ah battery in our other trailer. It works well inside.

Yet this is also valuable inside storage space that I hate to loose. Tradeoffs...

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Old 10-24-2019, 11:17 AM   #33
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This also will clear the tongue to add an aluminum truck box...
Darn Greg. Here I thought you might say for your mini-split condenser! Still waiting to see if Ron in BC takes the A/C mod on.
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Old 10-24-2019, 11:58 AM   #34
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Dave,
You know you have me intrigued with the mini split.
Hmmm, tongue box or condenser/tongue box or condenser? Well, I’ve still got some time to chew on that.
With everything Ron is having to do to remake his 21 in the image of his 19, budget would be getting tight with me at this point, but we’ll see if he jumps in for the split.
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Old 10-24-2019, 12:05 PM   #35
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0.5C would be 50A for a 100AH battery. you can charge naked Li batts at a steady current right up til you hit the maximum voltage of 4.2V per cell,then holding that 4.2V/cell voltage, the current will reduce to zero when the battery is completely topped off.

thats far simpler than the 3-stage lead acid regimen, where you'll have a constant current 'bulk' stage, then a elevated voltage 'absorption' stage, then a reduced voltage 'maintenance' stage.
I think this is important to understand: most of these lithium conversion schemes are much simpler in charging control than modern lead-acid charger logic.

Quote:
Originally Posted by John in Santa Cruz View Post
a fancy Li batt like the BattleBorn has an internal charge controller that accepts lead-acid style charging current/voltages, and keeps the Li batts happy.
I don't think the Battle Born has any charging control other than shut-off. The price might make you expect something more than four cells and a voltage-controlled and temperature-controlled relay, but I've never seen any indication in information from Battle Born or users that there is any control of current... and that's probably okay because the charger will just run at its current limit until the battery is charged.
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Old 10-24-2019, 12:19 PM   #36
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I don't think the Battle Born has any charging control other than shut-off. The price might make you expect something more than four cells and a voltage-controlled and temperature-controlled relay, but I've never seen any indication in information from Battle Born or users that there is any control of current... and that's probably okay because the charger will just run at its current limit until the battery is charged.
a 4 cell 'naked' LiFePo4 is around 16.8V fully charged, and 11.6V 80% discharged.... And you need a charging voltage of 16.8V to fully charge them. I assumed they had a boost-buck voltage regulator to achieve this charging voltage, and another one to not output such a high voltage to a system that typically doesn't want to see more than 14V
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Old 10-24-2019, 01:02 PM   #37
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a 4 cell 'naked' LiFePo4 is around 16.8V fully charged, and 11.6V 80% discharged.... And you need a charging voltage of 16.8V to fully charge them. I assumed they had a boost-buck voltage regulator to achieve this charging voltage, and another one to not output such a high voltage to a system that typically doesn't want to see more than 14V
I think you're expecting a lot from the Battle Born product. It seems far more likely to me that these cells are just not getting fully charged, which is not a problem and is a good conservative management solution. I doubt that a BMS with balancing, disconnect, and two DC-to-DC converters (or more likely a single bidirectional converter) with 100 amp (200 amp surge) capacity would leave room in the battery for the cells, or room in the pricing to buy them. Leave out the converter(s), run the cells under 4 volts all of the time, and you have a viable drop-in "12 V" battery replacement product.

I've seen other brands of drop-in batteries, and they had no power electronics inside.

The Battle Born FAQ include this, for the question "Do I have to buy a special charger for LiFePO4 batteries?":
Quote:
You do not need a special charger to charge your LFP deep cycle battery. As I mentioned above the battery prefers to bulk charge at 14.4 volts and float at 13.6 volts. Most standard chargers can handle these settings. There are some made for lithium chargers available on our store page and they will charge faster than a regular charger in most cases.
This implies that charge rate is limited by externally applied charging voltage, because there is no internal controller. Battle Born sells "lithium" chargers, including the lithium series from Progressive Dynamics, which are just the normal PD chargers with the charging profile simplified to a fixed and higher voltage.

I may be mistaken about the Battle Born units, but I'll be surprised if I am. Has anyone ever seen inside the case?
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Old 10-24-2019, 02:03 PM   #38
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I realize that the original post proposes Trojan lithium batteries, not Battle Born, but all this discussion of Battle Born probably still helps understanding of these drop-in products...

Quote:
Originally Posted by John in Santa Cruz View Post
a 4 cell 'naked' LiFePo4 is around 16.8V fully charged, and 11.6V 80% discharged.... And you need a charging voltage of 16.8V to fully charge them. I assumed they had a boost-buck voltage regulator to achieve this charging voltage and another one to not output such a high voltage to a system that typically doesn't want to see more than 14V
The Battle Born manual implies what the unit's controls actually do...
Quote:
High voltage: > 14.7V
If an individual cell voltage exceeds a prescribed threshold during charging, the BMS will prevent a charge current from continuing. Discharge is always allowed under this condition.
Low voltage: < 10V
If an individual cell falls below a prescribed threshold during discharge, the BMS will prevent further discharge. Although the battery is in “low-voltage disconnect” mode, it will still allow a charging current. (Note: many chargers must detect a voltage over 10v to send a charge to the battery).
The BMS is cutting off charging at 14.7 V, or 3.675 V/cell, and cutting off discharge at 10.0 V, or 2.50 V/cell; hopefully both of those are based on the highest cell voltage, not just the overall. These match the specs for LiFePO4 cells from a common supplier (CALB) well. 16.8 V (4.2 V/cell) and 11.6 V (2.9 V/cell) are typical of other lithium-ion chemistries used in EVs, not LiFePO4.

A Trojan Trillium data sheet shows a charging voltage of 14.4 - 14.8V and almost all of the working range of a 4-cell stack is between 12.5 and 13.2 volts. Trojan's sheet shows these cutoffs:
Quote:
Discharge Voltage Cutoff 10.0V ± 5%
Charge Voltage Cutoff 15.6V ± 5%
... which are not far off of Battle Born's, and again look reasonable for four LiFePO4 cells in series. The description in section 6.1 of the Trillium Users Guide clearly implies that their drop-in replacements with BMS do not include any regulation of charging, other than the protective cut-offs at the extremes. That guide also provides a nice explanation of the balancing method.

If the unit had an output voltage converter, the cell voltage would never be seen externally, and the manual's sections for low and high voltage wouldn't make much sense.

As we have seen in various discussions, even lead-acid chargers are producing voltages which are causing problems for some equipment in the trailer. With a drop-in unit like this, the rest of the RV's electrical system is unchanged, so the output voltage of the converter/charger is seen by all loads; even if there were an internal voltage regulator, it would not protect the trailer's devices from the high charging voltage, which gets higher than the battery's output could ever be (with any battery).

Shifting charging voltage up to get full rated capacity from a lithium battery makes this worse. I would be hesitant to convert to a lithium setup (typically 4 LiFePO4 cells in series) without adding a regulator inline between the battery/converter/charger and the loads, or at least the voltage-sensitive loads. That's one more component to fail, so it should be two of them in parallel, or installed with a bypass switch, or both. The alternative is to just stay with the lower charging voltage limit which is typical for lead-acid (without equalization, and with bulk and absorption stages set to the same voltage), and live with less battery capacity.
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Old 10-24-2019, 04:14 PM   #39
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BMS cell versus battery level logic

Quote:
Originally Posted by Brian B-P View Post
The BMS is cutting off charging at 14.7 V, or 3.675 V/cell, and cutting off discharge at 10.0 V, or 2.50 V/cell; hopefully both of those are based on the highest cell voltage, not just the overall.
Of course I should have said "more extreme" cell voltage, not "highest", because both high and low limits are being discussed.
Quote:
Originally Posted by gklott View Post
Have a Lithionics OPE-Li3 220Ah battery in our other trailer.
My note above was about the Battle Born BMS cutoffs, but I note that in the Lithionics BMS user guide they have both cell-level and battery-level voltages to trigger cutoff:
Quote:
Pack level triggers are more conservative than cell level triggers to allow for some natural imbalance in cell voltages at the top and the bottom of the charge/discharge cycle. BMS events are triggered on both cell level and pack level, whichever happens first.

In a 12V battery, for example, pack level and cell level triggers are:
HVC Pack Level = 14.80 V
HVC Cell Level = 3.75 VPC
LVC Pack Level = 11.60 V
LVC Cell Level = 2.50 VPC
("VPC" is volts per cell)
This manual provides a good description of the Lithionics approach to battery management. Both the detailed level of documentation and the information which they present suggest to me that this is a competent company with a sound product.
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Old 10-31-2019, 03:18 AM   #40
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4.2V per cell seems a bit high for LiFePo4. That sounds more like the max charging voltage of NMC or something. Even if it's a max charging voltage for LiFePo4 as well, it'll still eventually get just as charged with any voltage much above the cell's fully-charged voltage. It'll just take longer to get the last bit in there. Luckily with Lithium batteries that "last bit" tends to be very small - voltage stays steady for most of the range then spikes rapidly for the last couple percentage of charge, so a relatively wide range of voltages only makes a 1-2% difference in total charge stored. Definitely no need for a boost converter at 14.4V.

Interestingly, apparently a multi-stage charge profile actually is optimal for lithium batteries. Constant current up to a certain point then constant voltage, and higher current for the bottom half of the capacity (charge <50%). That's only if you're trying to really optimize charge rate, though. Simple bulk+float is "good enough", especially compared to the lower charge rates that lead-acid batteries will tolerate.

The charge rate vs temperature chart is really interesting. Temperature compensation on the high end isn't really needed for LiFePo4 since they have high charge efficiency and don't really heat up, but it'd be neat if someone like Victron set up a charge profile with low-end temperature compensation.

Looking through Battleborn's manual, the BMS does seem to top-balance above 14V.
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