Solar, big alternator. lithium combo misunderstood?

[booster]

The world of lithium batteries has evolved a lot over the years since it showed up in RVs. The starkest changes hit the huge advantages that were originally claimed to justify pricing. Charging speeds, cycle life, usable capacity are in major change rate now, it appears.

I am still in the early stages of shoulder and bicep surgery, so can't really do much of anything. Sling comes off in 9 days finally after 6 weeks of 27/7 use. With extra time, I revisited most all of the stuff we all look at in system design and selection of components, plus a more detailed look at what use pattern might be be better or worse. Basically a process like would be used by a product development team.

I included lithium, big alternators, and solar only. No generators or shore power.

I took my best guess based on found reference information on what would be best to get good life from lithium systems without ruining usability.

It became very obvious that what I found could not be done on very many existing systems because of how they need to be used, so that part is for other times. Those would be high power use systems that need to use all the capacity and still charge often.

We don't fall into that category so what we have seen in a couple of years of us should apply, I think.

 

[booster]

The start point is about lithium charging and by many current, but changing, practices is overly conservative. My opinion is that it is not if you are looking for best life of the batteries and can do the practices easily with no inconvenience. Choosing other methods is not wrong as all it does swap priorities life vs use vs cost just like we all have done with the other battery types over the years.

* For charging and use try to stay within the range of 35% to 85% SOC all the time, unless you need to balance cells at some other voltage.

* Charge at what are very low rates compared to the older claimed rates. .2C to .4C allowed but lower and even under .2 best.

* Charge often with whatever amount of recovery you can get to easily stay in range with good reserve capacity.

* Charge at the lowest voltage you can and still charge fast enough for your needs 13.4v might even be enough for small solar systems and under 50% SOC. Alternators on big banks probably will need higher like 13.7v, but you have to sure to stop charging at the top of your range before the voltage levels out at setpoint.

When I look at all charging parameters drifting to less aggressive it appears they may be all to address the most often stated lithium failure mode, which is lithium plating. It appears you need to prevent a buildup of ion on the cathode to prevent it. The indication seems to be that the voltage needs to not be high enough to force more ions onto the cathode than can be carried off to store. For instance, if you have your solar that is only putting out 10 amps to a 50% SOC bank of 600ah set at 13.5v, it is highly unlikely that it will ever be able to charge enough in a day to get to the 13.5v setpoint and would should be a very easy and also good for the batteries way to recover some capacity. On a good solar day we can recover 100+ah in high sun angle times. That is enough to give us over a day more without needing to alternator charge. It is also probably doing a really good job of preserving the batteries.

Along the same lines would be to have the alternator setup so you could charge faster by holding it in absorption or slow by holding it in float. How much you need to recover and how long the day's drive is going to be would make that easy to know.

Of course all of this may be of little use to many because basic equipment and use are cheap and lithium batteries are so low cost preserving them may be but worth it, as we saw most do with AGM users.

The solar may be the exception if it is already there and all you need is to reset the parameters. Probably not worth the cost to install unless you DIY it. Definitely not on the new vans from the factory.

 

[phantomjock]

booster...For instance, if you have your solar that is only putting out 10 amps to a 50% SOC bank of 600ah set at 13.5v, it is highly unlikely that it will ever be able to charge enough in a day to get to the 13.5v setpoint and would should be a very easy and also good for the batteries way to recover some capacity. On a good solar day we can recover 100+ah in high sun angle times. That is enough to give us over a day more without needing to alternator charge. It is also probably doing a really good job of preserving the batteries.

I'll add to that; the very likelihood you'd rather camp in shade than in full sun make solar panels less than worthwhile. Underway the alternator(s) ought to replenish. We used a full solar array and wind generator on the sailboat. Naturally, we were not in the shade. And it served it purpose.

Thanks for the good analysis. Pair this with fuel cell technology... Free lunch? No, ya still gotta' pay-to-play!

Cheers - Jim

 

[SteveJ-ClassB]

I'll add to that; the very likelihood you'd rather camp in shade than in full sun make solar panels less than worthwhile. Underway the alternator(s) ought to replenish. We used a full solar array and wind generator on the sailboat. Naturally, we were not in the shade. And it served it purpose.

Thanks for the good analysis. Pair this with fuel cell technology... Free lunch? No, ya still gotta' pay-to-play!

Cheers - Jim

The above illustrates my decision to go with portable solar. Using an extension cable the panels can be up to 75' from the plug in port on the RV. Our camping style is principally dry/dispersed for up to 2-3 weeks at one location.

300 A/H lifepo with 360 watts of solar.

Booster, get gooder.

 

[booster]

The above illustrates my decision to go with portable solar. Using an extension cable the panels can be up to 75' from the plug in port on the RV. Our camping style is principally dry/dispersed for up to 2-3 weeks at one location.

300 A/H lifepo with 360 watts of solar.

Booster, get gooder.

Portable is fine for some , but would not work for us because of how we camp.

We generally are in campgrounds and the things we do are in the area, but not within walking distance. For instance, we stay 14 days in Custer State, Stockade south campground we hike most days at drive to trail heads. We also take cave tours etc, Typically we would be away from the campsite part or all of 10-12 of the days, so would either need a good lockup system or put it all away nearly every day. Either way we wouldn't get any charging in the van. We get more charging time, on average, with it on the van roof.

That said, it is a valid question as to if it would be worth the cost for solar with the van equipped as it is now with extra alternator and 600+ah of lithium. We did not have to make that choice because the solar has been there since we had wet cells, so as long as it there we will get the benefits for free. I think the solar is on lots of new vans with big power systems as it sounds more useful than it is to new buyers, and it is a high margin thing for the manufacturers to sell.

Getting closer to useful (if I have ever been). 1 week left of 24/7 sling, 4 weeks range of motion PT, then strength training. Should be able to finish up the alignment mods on the van by June so we can get out.