Lithium Batteries: Cold Weather Question

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Good info about the BMS not allowing charging below 25*. 

I would be curious to know how they internally stop the charging, but yet allow the battery cells to supply power to the RV. 

The BMS I am familiar with has a solenoid on the negative side and one on the positive side.  Drop either solenoid and all 12V to the RV is gone.
 
AStravelers said:
Good info about the BMS not allowing charging below 25*. 

I would be curious to know how they internally stop the charging, but yet allow the battery cells to supply power to the RV. 

The BMS I am familiar with has a solenoid on the negative side and one on the positive side.  Drop either solenoid and all 12V to the RV is gone.
Click to expand...

A good question, my uneducated guess is the BMS is able to cut the charging side circuitry but not the output.  Perhaps someone more informed here will chime in on your question, but I am expecting to hear back from Shawn at Battle Born on another question and when I do, I will pose your question.
 
Gizmo said:
I have recently completed the solar install on our new truck camper and it is performing very well, even with the minimal battery capability that came with our TC.  I will be installing the inverter soon.  After I am finished with all the installs and I am satisfied with the performance of everything, I will be replacing the original batteries with lithium.  In my research on these batteries, I have learned they should/must not be charged when temps drop to and below 32 degrees.  Our fulltime plans are not to be in cold weather very long if at all except maybe the first winter where my wife may take a job for a year and the occasional unexpected drop in temperature, after that we plan to follow the weather to avoid the extremes.  My only option to place the batteries is in the battery box because of space constraints and personal needs.  While we will be mostly boondocking, our plan when faced with cold weather is to stay in a CG/RV park with electric hook-up.  So, I would like to hear what suggestions you'all may have regarding heating the battery box to above the freezing point at least, considering we plan to have electrical hook-up available.  Ideas I have come up with so far is to place a work light with an incandescent bulb or perhaps a heat lamp in the box.  Another idea I am wondering about is locating a suitable heating pad of some sort.  I will be interested to hear ideas, suggestions and any product recommendations. Thanks.
Click to expand...

I'm a sailor, not an RVer, but our needs are much the same. LiFePO4 batteries should not be charged below 32 F. However, you can discharge the batteries down to -4 F (some manufacture's have slightly different specs.) You will get 40 to 60% of the rated capacity at such low temps. What I've done is install a low temperature cut-off relay that opens at 35 F, but with the contacts bypassed with a 200 amp schottky diode to allow discharge current to bypass the contacts. Once the cabin is warmed up, the relay contacts close and charge current can flow.  I am running the 100 AH lithium battery in parallel with a 100 AH AGM, so the charging circuit is not running open-load when the relay is open. The lithium battery does nearly all the work, the AGM is just there to take up the slack when the lithium is off line. My low voltage disconnect is set at 12.8 volts, and charge cutoff is set at 14.0 volts, with a restore-to-load voltage of 13.1 volts measured at the AGM. This is a very gentle cycle-range for the lithium.

There is a lot to learn when considering lithium batteries. The most important points are: 1) Getting maximum storage life requires the opposite storage-charge treatment. Lithiums last longest when stored nearly empty - while lead-acids need to be stored fully charged to prevent sulfation. 2) Because of item 1 above, trickle charging lithium batteries while in storage is a very bad idea. 3) BMS systems integrated into lithium drop-in batteries are set up to use 90% of the storage capacity. If you use external controls, like I've described, that are more conservative, you will get much more life out of the lithium battery while not sacrificing much capacity. I use 80% of capacity, and expect to double the cycle-life of the battery. 4) If conditions become extreme, your lithium battery will drop off line, potentially leaving you in the dark, or worse, causing transients from your suddenly-unloaded alternator. I suggest having at least a small AGM battery upstream and in parallel.
 
Thanks Cpt Pat for the detailed & helpful reply, looks like an eloquent solution you have.  In speaking with one of Battle Born's founders, the manufacturer of my batteries, he said that the internal BMS simply will not allow a charge when the internal core temp drops below 32 degrees.  So if the charging system is in place and operating when the temp drops below 32 degrees, no damage to the batteries as the BMS protects itself.  Obviously the batteries will need to be charged and what he recommended for me when faced with below 32 degree temps, is to line the battery box with and insulating material, which I have done and to set-up a light bulb in the box.  I believe you are correct on the storing aspect of LI vs lead acid, though since we are full timing this will not be a problem for us.
 
Cpt Pat said:
I'm a sailor, not an RVer, but our needs are much the same. LiFePO4 batteries should not be charged below 32 F. However, you can discharge the batteries down to -4 F (some manufacture's have slightly different specs.) You will get 40 to 60% of the rated capacity at such low temps. What I've done is install a low temperature cut-off relay that opens at 35 F, but with the contacts bypassed with a 200 amp schottky diode to allow discharge current to bypass the contacts. Once the cabin is warmed up, the relay contacts close and charge current can flow.  I am running the 100 AH lithium battery in parallel with a 100 AH AGM, so the charging circuit is not running open-load when the relay is open. The lithium battery does nearly all the work, the AGM is just there to take up the slack when the lithium is off line. My low voltage disconnect is set at 12.8 volts, and charge cutoff is set at 14.0 volts, with a restore-to-load voltage of 13.1 volts measured at the AGM. This is a very gentle cycle-range for the lithium.

There is a lot to learn when considering lithium batteries. The most important points are: 1) Getting maximum storage life requires the opposite storage-charge treatment. Lithiums last longest when stored nearly empty - while lead-acids need to be stored fully charged to prevent sulfation. 2) Because of item 1 above, trickle charging lithium batteries while in storage is a very bad idea. 3) BMS systems integrated into lithium drop-in batteries are set up to use 90% of the storage capacity. If you use external controls, like I've described, that are more conservative, you will get much more life out of the lithium battery while not sacrificing much capacity. I use 80% of capacity, and expect to double the cycle-life of the battery. 4) If conditions become extreme, your lithium battery will drop off line, potentially leaving you in the dark, or worse, causing transients from your suddenly-unloaded alternator. I suggest having at least a small AGM battery upstream and in parallel.
Click to expand...

There are not many low temp cut offs on the market what are you using?


 
Gizmo:


Excellent thread! I'll be watching this one closely. Please do keep reporting how things work out for you.


Frank.
 
Thanks Frank.  Funny you should ask for continued reporting, as when I first posted this thread I had just purchased and installed them but had not had a chance to use them in real life.  We are now into our first month and a half of full timing, so I am gaining some experience.  The big thing I have noticed is how much faster they charge than the AGM's that came with our rig and the lead acid batteries we had in our previous rig.  I have yet to go below 75% capacity over night, but it has been reassuring to know we can go down to somewhere between 10 & 20%.  In programming the charge controller and Trimetric battery monitor I have learned from the company (Battle Born) as well as other reliable sources that these batteries charge at close to 100% (98%) efficiency, where as on the other end of the spectrum lead acid are some where between 85 & 90%, with AGM somewhere in between.  So far considering we are full timing, with plans to mostly boondock, these lithium batteries are proving to be a good decision.  I have to say however, as good an experience as we have had so far, if we were not full timing or significant boondock stays, I could not justify the cost of these batteries.  For those who stay mostly at campgrounds with little or no boondocking, either lead acid or AGM batteries would be the more cost effective choice. I hope this helps so far and I will report back as we gain more experience.
 
Yes, please do!


We Boondock as much as we possibly can with a big solar array, Outback FM80 controller (major overkill) and 6 Interstste (Costco) GC-2's. Our solar array is also overkill for a unit our size, but that also means that I get a full charge in the early afternoon even on cloudy days. This is why I am going back and forth on the value of lithium for us.


I would love to haul less weight, and be able to put the batteries indoors to improve weight distribution, but our system works very well with the limitations of lead-acid even now. Therefore, how much do I want to pay for the benefits _I_ would receive? Yeah, I don't know. However, real-time experiences like yours are VERY helpful.


One thing that lithium would allow me to do is to run the air conditioner off the solar. Can't quite do that with the lead-acid battery bank that I have now, and adding more batteries is not reasonable from a weight standpoint in our unit.  However, we mostly travel down south during the winter months, and it never really gets that hot where we go in Canada during the summer that we need the AC.


So, it is a needs / wants decision that I have to make.  ;D


Frank.
 
Gizmo said:
Thanks Cpt Pat for the detailed & helpful reply, looks like an eloquent solution you have.  In speaking with one of Battle Born's founders, the manufacturer of my batteries, he said that the internal BMS simply will not allow a charge when the internal core temp drops below 32 degrees.  So if the charging system is in place and operating when the temp drops below 32 degrees, no damage to the batteries as the BMS protects itself.  Obviously the batteries will need to be charged and what he recommended for me when faced with below 32 degree temps, is to line the battery box with and insulating material, which I have done and to set-up a light bulb in the box.  I believe you are correct on the storing aspect of LI vs lead acid, though since we are full timing this will not be a problem for us.
Click to expand...

I've been flipping around ideas on how to keep Lithium above 40F.

Lithium has no liquid to circulate that will maintain an even battery temperature which makes heating from the top problematic. 

ideas.....
- using insulation with groves so warm air can circulate on on all sides of the batteries.
- place a thermometer (with alarm) that has wired sensor(s) on the cold side(s) of the battery to monitor the temp
- 12V heat tape (inefficient) under the batteries with a temperature controller
- modify the furnace heating ducts
- hot water circulation pump off the HW tank
- place the batteries inside the heated space of the trailer.
- a small propane heater just for batteries.

To start I've decided to install a thermometer to monitor the temperate in the battery box so I've an idea of how cold the battery box will get in the winter.

 
Unfortunately that is not an option for us because of layout and limited space in our rig, otherwise that is the best solution.  As I mentioned before, the folks at Battle Born said when I posed the problem and question to them, all that is really needed is to insulate the box and place an incandescent lamp.  I have insulated the box and have a weather station with a remote sensor in the battery box and in my basement/storage area where the tanks are located.  So far, although I have not been faced with freezing temperatures, the temp in the box has been very close to that of the basement area, so I suspect because the battery box is surrounded on 2-sides by a heated space that may have a positive effect.  I will be putting all this to the test in April when we leave Phoenix for the Black Hills of S.D. where I anticipate temps at or below the freezing mark.  Before we leave I will install an incandescent lamp, so will see and will be sure to report back how it all works out.
 
Just starting my build on a Sprinter van. I'd like to use Lithium batteries and realize I need to keep them warmer. What are others successfully doing to maintain temps above 32F? Thanks!
 
Back again on my experience.  When I originally posted I indicated we purchased 3-100Ah Battle Born batteries for our truck camper and they worked quite well for us over the course of a year and a half.  We had a few days where over night temps dropped below 32 degrees.  As mentioned earlier in the thread I followed Battle Born's suggestion of insulating the battery box, I used Reflectix and I placed a work light with a 60 watt bulb in the battery box which kept inside temp above 45 degrees.  Since then we traded in the truck camper for a 5th wheel and kept the 3-Battle Born Batteries to which I added 4-additional Battle Born 100Ah batteries, so  I now have a 700 Ah battery bank.  My cold weather set-up I now use is for boondocking, the same work light with a 60 watt incandescent bulb and when connected to city power I have a Broan electric portable heater and I have a weather station with 3- sensors one for outdoor, one for my basement and one for the forward compartment where the batteries live . Since purchasing the 5th wheel and installing the batteries and new solar system, we have only had 2-sub 32 degree F overnight temps, as we were in an RV park I employed the Broan portable heater on the lowest setting which kept the front compartment where my batteries and solar equipment live at plus 50 degrees.  We will be in our current location until at least end of December and expect to have some sub 32 degree temps so I should get more experience with my two heating systems.  It appears the forward compartment backing up to the basement is kept warmer than the outside temps, so I will hopefully have time to verify this.
 
They actually make a battery warmer.. But I'm not sure you need to keep 'em that warm

That is one thing I wondered about.. Recently my phone (LI battery) locked up. I could not do squat with it not even turn it off.. So I froze it.  that stopped the battery from working and then once it warmed back up again.. Back in service.
 
This thing is so good. There was a slight problem with delivery (one day late) and they were so kind and supportive.
Look no further, buy this item. It was going to be $400 for two AGM or gel batteries, which this replaces with ease as I said. My ageing conventional batteries were making me crazy - instant relief and I got $10 bucks apiece for the old ones at O'Reillys.
 
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