LiFePO4 with cold temperature protection (lithium)

[markopolo]

Trojan's Trillium batteries low temperature shutoff occurs at < -13°F (-25°C) and reconnects at > -4°F (-20°C)

Trillium 110Ah battery
Maximum Charging Current @ Temperature
>73°F (>23°C) 110 A
41° to 73°F (5° to 23°C) 56A
32° to 41°F (0° to 5°C) 15A
14° to 32°F (-10° to 0°C) 6A

They do have a switch that shuts off the battery but:

Note: If the Battery is Attached to a Charger When It is Shut Down, It May Turn Back On.

Trojan's balancing:

Balancing is performed when a parallel group of cells reaches a specified threshold voltage corresponding to almost 100% state-of-charge (SOC). At that point, the highest-charged cells “bleed down” a small amount to enable the remaining groups of cells to “catch up.”

and

Note: Once a set of batteries have achieved a balanced condition, they should remain balanced through normal use and charging. In order to keep batteries in balance and avoid over-discharge, ensure that batteries not in storage receive a full charge weekly.

[markopolo]

Originally Posted by Boxster1971

Lithonics offers an internal heater as an optional accessory for their batteries.

https://lithionicsbattery.com/produc...al-heater-kit/

They also have Temperature Based Cutoff:

Temperature Based Cutoff – when temperature inside the battery goes below or above preset safe limits BMS will open the contactor to prevent further use of the battery until temperature returns under safe limits. Different temperature limits are enforced for charging and discharging due to nature of Lithium chemistry.

I haven't found specific the specific cutoff temperatures. I wonder if it's programmable?

Type 1 & Type 2 heater kits: https://lithionicsbattery.com/wp-con...-Vs-Type-2.pdf

It's implied that there will be a delay before the battery is usable after a cold soak. That's expected.

The Type 1 heater kit is best for users who will continuously use the battery and has availability for shore power to maintain the battery temperature for immediate use.

Balancing:

Our BMS also works to minimize those voltage differences in a process called “balancing”, which occurs at the end of each full charge cycle. 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

[markopolo]

Easy to follow White paper showing before and after balancing results on a 12S3P LFP pack:

https://www.eaton.com/content/dam/ea...WP162003EN.pdf

[Winston]

Originally Posted by booster

But what happens when you have a series/parallel setup, as the current could be different to each string?

Yes, but . . .

Yes, the current will be different in each of the strings . . .

But all of the strings are tied to the same 'parallel' source - - for balancing, in the case of the Elite system, 14.2 volts. And each of the strings is independently 'resolving its differences' so that in the end all cells are 'settling' at 3.55 volts.

It would seem that this parallel combination of series strings would provide reasonable balancing.

[booster]

Originally Posted by markopolo

Easy to follow White paper showing before and after balancing results on a 12S3P LFP pack:

https://www.eaton.com/content/dam/ea...WP162003EN.pdf

Very interesting and certainly points out the idea of why balancing needed. It would have been nice if they had detailed the balancing cycle and how often it was done. If the balanced every cycle as part of the recharge cycle.


I also think I may have been misinterpreting how all these articles are actually connecting the cells. When I read a pack is wired with 12 cells in series and 3 parallel, I think they make 3 strings of 12 in series and connect them at one place. The article show only 12 cell voltages in each graph, when there are 36 cells in the packs. This would indicate they are making 12 packs of 3 in parallel and then connecting those packs in series. That is the only way I can figure they would only have 12 cell voltages as each group of 3 would have a single voltage which would be the average of the 3 cells right after charging or discharging but likely self equalize after a hold time, if they did a hold time. I would term the pack 3P/12S I think. I wonder if the tie it all together in the actual wiring as in all 3 parallel batteries connected individually to the next set of 3?


I think it would be very interesting to see the results of no balancing during the test, but building the pack with 36 batteries that were individually balanced first, to see if, and/or how long they stayed in balance.


I am starting to believe that maybe a large part of the shortened life from full charges and deep discharges is from the balance and not necessarily all from the cell basic characteristics. The poorer the balance, the narrower the usable range of SOC would need to be, and thus the very narrow range like the one stated in the video posted recently.


I guess we could liken this to the kind of issues we see with lead acid batteries like capacity walk down from undercharging and life shortening by overcharging where the better they are addressed, the longer the battery life.

[Davydd]

I went out yesterday and checked my batteries out of curiosity of this discussion. The outside air temperature was 28 deg. F. Inside the garage I set my thermostat to maintain a minimum temperature of 45 deg. It was 52 deg. inside as evidently the surrounding garages are maintaining a higher temperature. I had the van plugged into shore power at 15a with a 30a to 15a converter plug. The batteries were at 95% SOC and were not being charged. They read 13.3V with a fluctuating -3A to -4A draw. The read outs are in full amps. This means the batteries are discharging and going down to 90% SOC before charging again on low power at around 40 amps per hour. The charger can be disabled, or set on low power or high power. ARV recommends setting on low power in storage. The individual cells ranged from 3.35V to 3.39V and the cell temperatures were reported at 53 to 55 deg. which was just slightly above the room temperature.

The batteries of course were not disconnected for storage or how else would I be able to monitor. So what little draw is from active monitoring, standby of the charger, a Trik-L-Start on the chassis battery, wired alarms, wifi, microwave readout with the digital clock and other monitoring devices and I as I said before, what not. I can use my van while in storage with light, water pump, etc. It is part of my man cave use to have it functioning. if I didn't plug in the batteries would last about a week with that 4a draw before AutoGen started up in a garage. Not good. BTW, I have AutoGen turned off in case of a power outage.

While in storage mode ARV set the system to charge batteries full to 100% and then turn charging off to drop to 90% and then cycle charging on again. When I looked yesterday it was 95% with no charge and dropping to 90%. That represents about a daily cycle of only a 10% range and not a full discharge. I've experienced no perceptible drop off in batteries over 5 years maintaining them this way. The first 3 years I maintained variable heat from electric heating pads on the batteries when stored outside in the Minnesota winter.

BTW, I said about 20 hours on AutoGen over 5 years and 85,000 miles on the road of at least 500 days and estimated 80% boondocked. It actually was 17.22 hours. As I mentioned, idling to charge batteries practically never takes place despite having no propane or Onan generator.

[booster]

Davydd, I seem to remember that ARV early on changed you charge cycle to give some space at the top of the actual battery capacity as being discussed in this thread. The 13.3v would likely support that.

Is your 100% setting now the top of the actual usable range or still tied to the actual cell capacity? My guess from your numbers is that it is usable range. Do you know what the actual AH usable range is now for the 800ah bank?

[markopolo]

Originally Posted by Winston

Yes, but . . .

Yes, the current will be different in each of the strings . . .

But all of the strings are tied to the same 'parallel' source - - for balancing, in the case of the Elite system, 14.2 volts. And each of the strings is independently 'resolving its differences' so that in the end all cells are 'settling' at 3.55 volts.

It would seem that this parallel combination of series strings would provide reasonable balancing.

I think that you could have paralleled weak cells, even dead cells in the mix and still see expected pack and string voltages. Weak / dead cells would reduce the bank capacity.

[Davydd]

The 100% is at the top. The useable range of the 800ah battery bank is 80% or 640ah. Various manufacturer's claim you can discharge lithium batteries down to 10% or even close to 0%. ARV arbitrarily sets it at 20% SOC with the batteries totally disconnecting at that point. If that happens then you have to start the engine and physically hold down a button for at least a minute so the engine can raise the charge to come back online. The AutoGen would normally prevent this. I have my AutoGen set for 40% but have never invoked it other than a test. So my arbitrary operating range is 480ah. The theory of lithium batteries happy at a narrow range of various reports at 60% SOC or 85% SOC is probably lab testing and not reality in RV use. When you can charge batteries to 100% with a second alternator in less than an hour from a days electrical use of over 200ah in my case, I think it would be futile. Charging underway from the engine goes to 100% and quickly drops down to a 99% readout. There is a braking effect somewhere over 90% with lower and lower amp rate down to 0 when it hits 100%. Then when you drive for more than an hour it steadily maintains to 99-100% SOC.

This is from the ARV white paper on their lithium battery systems:

Since the actual capacity of the battery is changing over life, there needs to be a way to assure the actual state of charge does not fall too low. This is handled by the Volta and Valence BMS systems automatically because they estimate the actual battery capacity at any point in its life and report the percent state of charge accordingly. The Elite system does not have this capability. So Advanced RV sets the capacity in the BMS at 80% of the actual. Therefore, our 800 amp hr system is programmed to be limited to 640 amp hours. This way, the batteries will always provide that capacity.

[Winston]

Originally Posted by Davydd

This is from the ARV white paper on their lithium battery systems:

Since the actual capacity of the battery is changing over life, there needs to be a way to assure the actual state of charge does not fall too low. This is handled by the Volta and Valence BMS systems automatically because they estimate the actual battery capacity at any point in its life and report the percent state of charge accordingly. The Elite system does not have this capability. So Advanced RV sets the capacity in the BMS at 80% of the actual. Therefore, our 800 amp hr system is programmed to be limited to 640 amp hours. This way, the batteries will always provide that capacity.

We understand ARV to be saying: "Our SoC will register 100% when the pack is fully charged and 0% after you've drawn it down by 640ah. While you will still have 160 (unusable) amp-hours in the batteries on Day-One, when your batteries are new - - in future years the capacity of your battery bank will decrease. We have set the maximum discharge to 640ahs to allow for the future when you're total pack capacity may have dropped substantially, by as much as 160ahs".

We don't have that 'protective buffer' built into our Elite system. The advantage of not having the buffer is that we can use the full battery capacity in the early years. The disadvantage being - - we'll have to watch our actual pack/cell voltages in subsequent years and rely somewhat less on the SoC display.

It would be our expectation, therefore, that ARV is not backing down from full charging - - rather, this cushion is provided, not as protection against frequent 100% charge cycles, but as means of assuring that in future years, when your SoC says 0%, you are still safely above pack-destroying low voltage levels.

[Davydd]

As I mentioned, I set my batteries up for an arbitrary range of 480 amp hours available and don't use that as we mostly travel and quickly charge every day and will never as long as I own the van will achieve full discharge of 2,000 cycles, or 2,800 or 5,000 or whatever a lab wants to report. The batteries have never gone below freezing and never above the high end range to my knowledge except the one time I observed balancing and as I stated got alarmed. I think, knock on wood, I'm fairly comfortable with my lithium batteries. I can't say the same with my prior two B's with wet cell lead-acid and AGMs.

[markopolo]

I posted this in the "Lithium battery warming idea" but think that it's also useful info for this topic.

Originally Posted by markopolo

No charging at 32F or lower is often cited. It's stated on many LFP battery spec sheets.

From all the stuff I've read so far, I think that it's a combination of charge rate and temperature that we need to be concerned about starting at around 40F.

For Trojan Trillium batteries (5000 cycle rating): (rates approximated for this post)
>73F 1C charge rate permitted
41° to 73°F (5° to 23°C) 0.5C charge rate permitted
32° to 41°F (0° to 5°C) 0.13C charge rate permitted
14° to 32°F (-10° to 0°C) 0.05C charge rate permitted

Relion also states to limit the charge rate if the batteries are cold. It's very similar to what Trojan recommends. From Relion:

In their low temperature battery, it looks like the heating element comes on at 41F. No coincidence there I bet.

Battle Born's BMS prevents charging when the temperature drops to 24F. I doubt that charging at a 1C rate at 25F is a good idea though! They suggest to "keep the temperature up" but don't seem to provide specifics.

You could keep it simple:
Keep the batteries at 40F or higher & limit the charge rate to 0.5C. An additional benefit is that the discharge performance will also be better with the battery above 40F.

Looks like Victron makes it easy to prevent charging below 5 Celsius / 41 Fahrenheit:

https://www.victronenergy.com/blog/2...ithium-update/

Quote from the blog post:

Disabling charging is done because Victron Energy tests and research have shown that lithium iron phosphate batteries charged below +5°C will start to damage the cells.

[IdleUp]

For the most part - its not in lithium batteries best interest to be installed and stored outside an RV. While on many B / B+ coaches this is the easiest option, it not best for the longevity, conditioning or performance of lithium batteries. Aside from temperature extremes, there is another enemy which no one is really talking about, which is condensation.

Being exposed to the elements to include major temperature changes and driving in wet weather, allow a fair amount of moisture to be accumulated throughout the entire pack and circuitry. On our larger drones, where the lithium is housed in a composite case, we’ve actually seen cases where we had standing water in the sealed case.

For this reason, its well worth the effort to install lithium cells in the coach where temperatures are more stable and moisture is less of a problem. Mounting a pack inside the RV avoids un-need heating, as well as preserves the batteries condition.
Keep in mind not every China pack is BMS thermal protected, in addition unlike a higher quality lithium pack which monitors temperature of every cell, these packs use only one temperature sensor, so its conceivable it does not represent the true temperature of all the cells.

Lithium installations inside the coach offers the opportunity to use a space heater which serves two purposes; one to maintain the lithium performance, and to provide important needed ambient heat for the coach to prevent temperatures from freezing the RV’s interior components.

For years, even though my coach was winterized, I always used a certified marine space heater. These heaters are fully automatic they kick on at around 36 degrees and kick off at 40. By using one in either a underbelly compartment or the interior it keeps the coach from freezing and maintains safe temperatures.

On my Sprinter I protected my lithium batteries by mounting a 300 watt heater under the rear lounge. This protected the lithium and safely maintained the coach around 35-40 degrees.

The primary use of a space heater for me is when I’m plugged in, since I don’t camp in freezing weather. Since I use both my Sprinter and Transit as 2nd vehicles, these same heaters are used when underway as the stock alternator provides ample amperage to power the unit. On my Transit installation my lithium compartment is vented to the interior so the same 300 watt heater in the compartment keeps the coach at a safe above freezing temperature. Below is a snip from one of my winterizing articles showing a 600 space heater in the belly. This heated all the compartments as well as the sub floor where water lines are routed. This same heater heated the tile floors to help keep the interior warmer.



Keep in mind - Optimum performance for lithium is 68 degrees, so the closer you keep the pack to that temperature the more longevity you’ll get from a charge.

Aside from just the possibility of of BMS shut-down, lower temperatures seriously compromise the performance of lithium batteries. Our Cadillac ELR, Chevy Volt and BMW I-3 all have less range during colder weather. Tesla publishes loses of 20-40% of their range in cold weather due to inefficiencies. Even you iPhone can loose 30% of it running time in cold weather, so the moral of this story is the warmer you can keep your lithium, the more performance you’ll get. Contrary to what most hear on the internet and forums, the objective of maintaining lithium temperature is not just keeping it above BMS cutoff.

While I don’t have this data on my home computer - there is a lithium / temperature curve where you can self-power a heater and yet not lose any charge when compared to not heating the same pack. The chart below helps to understand how cold weather diminishes lithium abilities. This pack is discharged at 3 amps though at different temperatures to show how cold weather affects lithium performance.

Enjoy - Mike

[nebulight]

If you live somewhere where freezing temps don't happen often, it's my opinion that you shouldn't bother heating the batteries, rather stop charging until they come to temp (if the batteries are inside the van). I've redid my electrical system last year, and the main component for stopping charge below freezing is my Victron Battery Monitor BMV712 as it has a built in relay that can be triggered by a number of conditions (temp being the one I'm using). This works because I have an DIY pack with an external BMS. The BMV shuts off a victron battery protect which I'm using to stop the current from my DC-DC converter as well as my MPPT controller:



Anyone else could do the same with a simple wire loop going to the BMV and the battery protect. However it wouldn't address charging from shorepower without some additional work arounds, but this can be done. You also need a DC-DC charger rather than a simply solenoid linking your starter battery to your house as the Battery protect can only have current flowing in one direction. You will destroy the battery protect if you have current going in both directions. You also can't hook up an inverter to the battery protect as the inrush current will damage the battery protect.

[avanti]

Originally Posted by IdleUp

Being exposed to the elements to include major temperature changes and driving in wet weather, allow a fair amount of moisture to be accumulated throughout the entire pack and circuitry. On our larger drones, where the lithium is housed in a composite case, we’ve actually seen cases where we had standing water in the sealed case.

If your case is experiencing condensation on its interior, it is most certainly NOT "sealed".

[hbn7hj]

I am amazed at the complexity and number of components in these systems. Up to four battery switches and numerous other components. I suppose it is necessary but I don’t understand why.

Grandma isn’t running any of these.

[IdleUp]

Originally Posted by avanti

If your case is experiencing condensation on its interior, it is most certainly NOT "sealed".

Fuel tanks, headlight assemblies, batteries, phones, etc. are sealed units yet produce condensation. Certainly I don't know of any lithium RV batteries that are sealed in a gas to avoid condensation. The only exception is Lithionics seals its BMS mechanical contacts in a gas chamber to prevent moisture and arcing.

If you put your warm phone out in a cold rain and within just minutes the phone quits from excessive moisture. (ask me) Fuel tanks on many vehicles (especially electric / gas vehicles) are totally sealed yet they still produce condensation. This is why its recommended to store vehicles with full tank, to reduce air and condensation.

Mike

[avanti]

Originally Posted by IdleUp

Fuel tanks, headlight assemblies, batteries, phones, etc. are sealed units yet produce condensation. Certainly I don't know of any lithium RV batteries that are sealed in a gas to avoid condensation. The only exception is Lithionics seals its BMS mechanical contacts in a gas chamber to prevent moisture and arcing.

If you put your warm phone out in a cold rain and within just minutes the phone quits from excessive moisture. (ask me) Fuel tanks on many vehicles (especially electric / gas vehicles) are totally sealed yet they still produce condensation. This is why its recommended to store vehicles with full tank, to reduce air and condensation.

Mike

Total nonsense.

[SteveJ]

Originally Posted by IdleUp

Fuel tanks, headlight assemblies, batteries, phones, etc. are sealed units yet produce condensation. Certainly I don't know of any lithium RV batteries that are sealed in a gas to avoid condensation. The only exception is Lithionics seals its BMS mechanical contacts in a gas chamber to prevent moisture and arcing.

If you put your warm phone out in a cold rain and within just minutes the phone quits from excessive moisture. (ask me) Fuel tanks on many vehicles (especially electric / gas vehicles) are totally sealed yet they still produce condensation. This is why its recommended to store vehicles with full tank, to reduce air and condensation.



Mike

How would a fuel tank not let in atmospheric air as the level draws down? It would either collapse from the vacuum if the pump could pull it or would have to have a pressurized bladder system, similar to a water pressure tank.

Pretty much the only time one would see condensation in a modern headlight assembly is if it's damaged or defective.

Most phones are not sealed.

[booster]

Originally Posted by SteveJ

How would a fuel tank not let in atmospheric air as the level draws down? It would either collapse from the vacuum if the pump could pull it or would have to have a pressurized bladder system, similar to a water pressure tank.

Pretty much the only time one would see condensation in a modern headlight assembly is if it's damaged or defective.

Most phones are not sealed.

Unless they have changed them headlights are also vented to prevent pressure build up from heat. The van and my Buick have a small rubber elbow on the back of the lamp.