My Lithium Upgrade

[avanti]

Originally Posted by avanti

--When I build a battery disconnect, it is absolute. There is NO LOAD, therefore all we are talking about is self-discharge.

Before I get too cavalier about self-discharge, there is another issue I just thought of:

It concerns batteries with built-in BMS. How do these behave during storage? Do the little BMS boards in the batteries consume power when the battery is disconnected? If so, how much? If not, how do they know? Does it matter whether they have WiFi or some other communications port?

Hard to believe that there isn't some provision to turn the battery completely "off", but I realized that I don't understand what is going on here.

[GeorgeRa]

Originally Posted by avanti

...........................

An then there's the issue that @booster mentioned: Having to go down to 50% is counter to the goal of saving power to run the heaters when weathering a frigid spell during storage. No obvious way around this, beyond giving up storage at the optimal SOC. Going down 10% is one thing--50% is kind of painful.

Now I remember why I have been lukewarm to lithium.

Lukewarm is better than my cold.

In line of home automation we installed Rachio sprinkler system a few years ago, it adjust watering cycle lenght based on the weather forcast. Having system like that could charge Li batteries to 100% SOC with solar just before cold spell and drain it to 50% SOC after.

[MobileCabin]

Originally Posted by GeorgeRa

Lukewarm is better than my cold.



In line of home automation we installed Rachio sprinkler system a few years ago, it adjust watering cycle lenght based on the weather forcast. Having system like that could charge Li batteries to 100% SOC with solar just before cold spell and drain it to 50% SOC after.

I like that model. We need to start looking for not just a smart charger, but a very smart charger!

But really, such a system to predict future need and for ex, discharge the battery to 50% before storing is asking a lot from an RV upfitter or even a general purpose battery provider. Where would they like to dump that excess current, into a hot water heater in a RV that is going into storage? This is the level of automation we should expect to exist in the near future when the big automotive companies start making all electric platforms for RVs. Most likely the battery chemistry will improve or the very smart chargers will dump the excess current to the grid and move your electric meter backwards or store it in your whole house battery system for reuse. Until then, I find that these problematic aspects of our battery systems just adds to the long list of things to keep in mind when owning an RV.

My current B is no issue with the AGM, Magnum and access to power. My upcoming will will require a little muscle to move the Li battery to the basement when stored.

[booster]

I am not certain as I would have to dig out the manual for the ARC50 remote, but I think that you can set the Magnum on charge/cutoff/recharge cycle, which takes care of part of it automatically if you have shore power. You can also set either amps or SOC, I think, for final recharge and would have to reset that manually on the remote which is not hard to do and also reduce the rebulk setting. Put a load on it with enough draw to pull down the SOC in given amount of time to under the 50% and have the load time out. The charger would go up to 50% and sit there is there was no real load. It wouldn't be come home and drive right to storage with no shore power though because the routine would take some time. Some variation of that kind of scheme may be pretty easy to duplicate and automate.

[MsNomer]

I put a switch on the dash for the B2B. I turn the B2B off on the way home. "The way home" for us is usually a day's drive, so I can choose my end point, usually about 80%.

[avanti]

I just noticed that Victron is now specifying their LiFePO4 batteries' minimum storage temperature at -45°C which is -49°F. If this can be believed, maybe I will stop thinking about this.

https://www.victronenergy.com/upload...s-Smart-EN.pdf

[booster]

Originally Posted by avanti

I just noticed that Victron is now specifying their LiFePO4 batteries' minimum storage temperature at -45°C which is -49°F. If this can be believed, maybe I will stop thinking about this.

https://www.victronenergy.com/upload...s-Smart-EN.pdf

That is very interesting and so very much different from the way things have been heading toward warmer storage of late. I see they do have the minimum charge temp at +5C though.



It may be incomplete specs but for the little blurb on the BMS that say does cut off on low voltage and high and high temp, but nothing on low temp cutoff. Need to look at the BMS spec sheet I think to find that out. The wiring diagram doesn't appear to show the monitor connected to the VE Buss the way the charger and battery protector are in their drawing, so it may be just for monitoring? It would be nice if it could set the charge parameters and such, I think. Same would be true for the Victron solar controller was in the mix.

[jakegw2]

Regarding storage at 50%...

I think most of the heartburn that this issue creates is related to the unspoken design assumption that you want your LiFePo4 system to last the full 10+ years that it can last for if properly used. In my opinion this is a terrible design criteria and is the key driver for most of the complexity that gets discussed on this forum.

Change your design criteria to "The LiFePo4 system should have at least 75% of its original capacity at year 5" and most of this complexity goes away. You can keep it at 100% whenever you store it and still meet this criteria. You can charge it directly from the alternator and still meet this criteria. In fact, you can pretty much not think about your batteries at all and still meet this criteria.

The real question is how likely is it you will want the system you build to last longer than 5 years? If you build a simple system I think the answer will almost certainly be "not very." I started my system about two years ago and finished it earlier this year (with the addition of the battery heater system). I can already see that I am unlikely to make it the full five years before I will want to make significant upgrades. The cost of LiFePo4 batteries has dropped so much that a full rip and replace of my existing batteries would cost less then a modest increase in capability would have cost two years ago. There is almost no chance that keeping them for five years will make sense.

There are some system requirements for edge cases where the extra complexity will make sense, but for most RVers simpler will be better.

Avanti - My recommendation:

Upsize you solar. Park in a sunny area. Remote monitor your SOC, Let your batteries float at 100% whenever there is sufficient solar to do so. Have the heater kick on at the minimum charging temperature of the cells you use.

In most of the US this will be fully protective for 4 out of 5 years. As a final safety measure find a friend or neighbor you have a modest amount of trust in and leave them a set of keys. On the off chance you get an extended cold snap after a long bout of cloudy weather you can call them and ask that they start and run your van for 2 hours or so. A single run session should be enough to cover anything outside of a once in 20 years scenario (where you might need a second run session).

You might even choose to skip the remote monitoring and just set a Google Alert for weather forecasts below -4 degrees F for your area.

Enjoy your month-long winter vacation with minimal worry about your RV.

[avanti]

Originally Posted by jakegw2

Regarding storage at 50%...

I think most of the heartburn that this issue creates is related to the unspoken design assumption that you want your LiFePo4 system to last the full 10+ years that it can last for if properly used. In my opinion this is a terrible design criteria and is the key driver for most of the complexity that gets discussed on this forum.

Change your design criteria to "The LiFePo4 system should have at least 75% of its original capacity at year 5" and most of this complexity goes away. You can keep it at 100% whenever you store it and still meet this criteria. You can charge it directly from the alternator and still meet this criteria. In fact, you can pretty much not think about your batteries at all and still meet this criteria.

The real question is how likely is it you will want the system you build to last longer than 5 years? If you build a simple system I think the answer will almost certainly be "not very." I started my system about two years ago and finished it earlier this year (with the addition of the battery heater system). I can already see that I am unlikely to make it the full five years before I will want to make significant upgrades. The cost of LiFePo4 batteries has dropped so much that a full rip and replace of my existing batteries would cost less then a modest increase in capability would have cost two years ago. There is almost no chance that keeping them for five years will make sense.

There are some system requirements for edge cases where the extra complexity will make sense, but for most RVers simpler will be better.

Avanti - My recommendation:

Upsize you solar. Park in a sunny area. Remote monitor your SOC, Let your batteries float at 100% whenever there is sufficient solar to do so. Have the heater kick on at the minimum charging temperature of the cells you use.

In most of the US this will be fully protective for 4 out of 5 years. As a final safety measure find a friend or neighbor you have a modest amount of trust in and leave them a set of keys. On the off chance you get an extended cold snap after a long bout of cloudy weather you can call them and ask that they start and run your van for 2 hours or so. A single run session should be enough to cover anything outside of a once in 20 years scenario (where you might need a second run session).

You might even choose to skip the remote monitoring and just set a Google Alert for weather forecasts below -4 degrees F for your area.

Enjoy your month-long winter vacation with minimal worry about your RV.

Good post.

The point that there is a risk in optimizing for issues that don't matter is well-taken. I'm not sure that everyone around here would agree with your "5-years" target, though. I am going strong on year 8 of my current large AGM setup, and I don't think I would have been happy otherwise. But, that is a cost-effectiveness judgment--we can apply your advice without agreeing on your parameter.

My biggest modification to your point is simply to put an asterisk on several items that go beyond minor effects on lifetime cycle count. The obvious example is attempts to freeze below charging. I realize your "directly from the alternator" comment was rhetorical, but a single attempt to do so below freezing could be fatal. Another example is the memory effect issue (assuming you believe in it). If you believe the recently-referenced article, certain usage patterns could rapidly lead to a death spiral of lost capacity. The point is that not all risks are equal. But, I agree that jumping through hoops to stay at 50% during storage may not be cost-effective.

As for your specific advice to me, two comments:
1) I don't see where your "get more solar" advice comes from. DavyDD likes to tell us that solar becomes largely irrelevant with a large battery and robust charging. I tend to agree with him for the most part. Solar CAN serve to provide for a nice terminal charge profile (as it can with FLA & AGM), assuming the charge controller is so capable. But it seems to me that modest solar is adequate for this. Beyond that, a battery disconnect is nearly as effective during storage, and much simpler. I may just skip solar, or else just do a modest setup, especially since I have no desire to park in the sun when I can avoid it.

2) I guess I trust technology more than friends. Remote monitoring plus remote start serves the same function as "call a friend", and works in a greater number of storage sites (and we have several). The weather service observation is valid, but doesn't provide knowledge of the current state of the vehicle.

Thanks for the thoughtful contribution.

[jakegw2]

1) I actually agree with DavyDD on solar for camping, it has been only marginally helpful because I prefer to park in the shade when camping and the alternator charges the batteries so much faster that the solar contribution is minimal.

Storage changes things. During the summer minimal solar is sufficient to keep the batteries charged and ready to go. With my heated batteries the larger array that I already have has been more valuable. On second thought I don't know if it would be cost effective for just this use case, but I am pretty confident if I had a non-shaded parking area it would easily keep up with the heater power drain for most winter conditions that I face.

For research purposes I have left my camper unplugged and though the temperatures have been fairly mild (never below 19 degrees) the battery bank has stayed above 70% with the heater on for the past month. Of course my monthly generator exercise and Thanskgiving travel topped it off on different occasions, so it wasn't just solar to that has kept it charged. I have an outdoor plug right next to where I park it so this is a low-stakes trial of my system.

Turns out this is mostly moot for me anyway. We got a taste of the snowbirding lifestyle last year and will likely end up repeating this for the foreseeable future. One way to guarantee the -4 degree limit isn't an issue is to simply not be home during the time of year when it would come!

[avanti]

Originally Posted by jakegw2

For research purposes I have left my camper unplugged and though the temperatures have been fairly mild (never below 19 degrees) the battery bank has stayed above 70% with the heater on for the past month.

Good data. However, I don't see any reason to keep the heater on during down times. No harm letting the batteries get below freezing if they are not being used. My obsession has been with the rare truly-frigid event (and I agree with you that that will be rare, even up north). By my way of thinking, the only imperative is to keep enough power in the batteries to keep them above the "damage" threshold. Full disconnection will do that just fine. Moreover, as I said, if I can really find batteries with -50F storage temperatures, I am prepared to forget about the whole issue.

[Davydd]

This is interesting discussion but don’t take my advice with 7 years of practical use and observation of lithium ion high capacity battery banks of at least over 400ah or you probably should be sticking with AGMs if under 400ah. I had 800ah since 2014 in Alvar, my extended body 3500 ARV Sprinter van and now have 576ah in my 2020 Mies 144WB 2500 ARV Sprinter van.

Alvar had Elite Power Solutions lithium ion batteries built up in a block of 16 modules and placed under the van. My van was the first build by ARV with these batteries. They would not be removable unless you had a lift and lowering jack of some way to drop 500 total pounds of batteries and protective steel cage. Obviously they stayed in place stored outside in the first two years of Minnesota winters. They were LiFePO4 batteries. Elite Power Solutions said they could be permanently damaged if they got below -4F. Charging below freezing could affect life cycle. ARV prevented charging below freezing. These were early on RV batteries and the assumption was 2,000 cycles down to discharge of 20%. Whether that was accurate or not could be debatable but the batteries didn’t have any apparent loss in capacity in my 6 years.

When outdoors they were heated by two 12v 5a electric heating pads sandwich between the modules. On the road boodocking they would cycle on about a 1/3rd of the time so consume maybe 80ah in 24 hours and we would be recharging and driving about every day powered off the batteries and the batteries were recharged in storage by shore power. Since I stored the van in a heated garage at a minimum of 50F.

Mies, my new shorty van, I opted for U27-12XP Valence batteries. These have a drop in battery profile 27. They are 12v batteries. Since I wanted to stick with a 2500 chassis and had to fight weight restrictions I dropped to 4 batteries with a 576ah capacity. Historical experience and travel preferences and the ability of staying in place boondocking for three days easily dictated that would be all I would need. I couldn’t get half that capacity with AGM batteries with weight restrictions to stay at 2500.

Mies batteries are stored inside the van but not very easy to get to under my lower bunk bed. Heating is not a problem in storage and on the road when I keep the cabin heated in winter travel. I have a heating pad as I do with all my tanks but I doubt it would ever come on for the batteries but I haven’t winter traveled yet in Mies.

What about that 50% SOC being bandied about in this thread. You do realize that is a lab test to determine the optimum and maximum and has no real life practicality. ARV shuts down the batteries at Valence recommended and industry 20% SOC so keeping them at a theoretical 50% would give you a 30% range. That is simply put, dumb. My Valence batteries specify 4,000 cycles down to 20% SOC. that means in practical terms about 6-7 days in storage on shore power and batteries connected and 3 days on the road using the van for everyday tasks of refrigerator on, lights, and cooking in an all electric van. That means about 33 years with my battery bank or if you want to use the universally assumed 2,000 cycles over 16 years. Not worth discussing, or trying to achieve that 50%.

Solar charging? Don’t you have to have your batteries connected for your BMS to be functional and reporting? My short van I could get at most about 100w. On my extended 24 ft. van I maxed out at 460w. With high battery power capacity over 400ah the percentage of contribution goes down significantly especially in the north cloudy days, short days with low sun angles and blocking shade from houses. For the cost, roof real estate for other roof amenities and second alternator which I deem a must it makes solar almost nil or a feel good if you had it. You so the math contribution for solar.

Self discharge of my Valence batteries specify <2% per month. That’s about 70ah over winter storage with totally disconnected batteries on my 576ah battery pack. I want to keep my batteries connected and observe up to about a 3ah use or 70ah in a day with connected batteries so I can turn on the lights, the water pump, display all the readout on my Silverleaf touch screen monitor, have the internal wifi on so I can display info remotely the battery status and everything else home assist features allowed with an app, various idiot lights, the mult-plex lighting system, the battery BMS, the hot wired CO2 monitor, Trik-L-Start charging for my chassis battery, battery heat internal or external and who knows what else? My batteries are programmed to hover at 99% turn off charging until I think 88% and start recharging again, i.e. roughly 6-7 days per cycle. I probably have a more sophisticated system than most. It’s a convenience. Take your choice, shore power or live in a place that can’t possibly go below -4F for LiFePO4 Lithium Iron battery chemistry which about everyone uses currently.

Valence once had, no longer, a LiFeMgPO4 Lithium Manganese battery they once claimed to go down to -40F same as AGMs. That’s where the -40F came in to the discussion. Valence was once its own company started in 1988. Then Lithiumwerks took it over and now it is by Lithion and I don’t know all the details.