Upgrading House Batteries to Lithium

[Wyatt]

Originally Posted by caoqiang1

The battery I just bought has a 100A BMS, would that avoid alternator issue?

Another way to avoid overtaxing your alternator, is to run the generator when driving if you're leaving a campsite where you drained a significant mount of energy from your Lithium batteries.

Interesting that Ford's new F53 V8 Comes with a more robust alternator, and an option for a 240 amp one as well.

[creativepart]

Originally Posted by caoqiang1

The battery I just bought has a 100A BMS, would that avoid alternator issue?

No, that wouldn't avoid any alternator issues.

In a Lead Acid battery as the battery charge increases so does the internal electrical resistance inside the battery. This resistance is significant enough to reduce the output of the alternator trying to charge the battery.

The Lithium battery does not increase the internal resistance as it charges. This lack of internal resistance causes the alternator to work harder and harder in an effort to fully charge the battery and as a result it can overheat.

While the BMS can limit charging to no more than 100amps into the battery, the alternator can still overheat while putting out less than 100 amps.

https://www.youtube.com/watch?v=jgoIocPgOug

[AJMike]

Originally Posted by caoqiang1

The battery I just bought has a 100A BMS, would that avoid alternator issue?

No. That is not what the BMS is for.

The problem here is that apparently some alternators are capable of dealing with Lithium batteries and some are not, and it does not have anything to do with the alternator output. And I don't know which ones quality and which do not.

When I switched to Lithium batteries in our RV I tried to avoid the extra charge for the limiting device but in the end just sighed and paid it. I went for a DC-DC charger and fortunately there are some that are not terribly expensive.

I initially bought the Renogy 40 amp initially and had problems with it, probably due to the installation job that the tech did as he did not put any ventilation holes in the small space where he placed it and it overheated enough to stop working. The charger worked fine as long as the storage enclosure was open and there was moving air, but failed when the enclosure was closed. Still, the point is that Renogy makes 20 amp, 40 amp and 60 amp models, all relatively inexpensive as these things go, and Victron and others make more expensive models.

Amazon sells the Renogy devices and the 20 amp model is about $170. If you go that route consider how much you will need to charge and how long it will take. Obviously the 40 amp will charge your batteries in much less time than the 20 amp, but costs more and runs a bit hotter.

All DC-DC chargers work by limiting the charging current that flows to the batteries and thus protects your alternator by limiting the current the charger draws from it.

The BIM works by allowing full current to the batteries from the alternator, but switching it (the alternator output) off after a specific length of time, thus allowing the alternator to cool down. Then it switches back in.

In the end it is your choice. As for Lithium batteries, if you dry camp a lot you will love them. If you mainly use shore power at campgrounds you probably don't need them.

Good luck.

[DavidM]

Anyone contemplating a switch to Li batteries should read Creativepart's post above and watch the video he attached.

Mercedes, the maker of the Sprinter chassis used on many Class C diesels recommends keeping the external charge rate from its chassis alternator below 40 amps. A single 100 Ah lithium battery can easily draw that much current from the chassis alternator if the batteries are well discharged.

As you add more lithium batteries the maximum current that can be pulled from the alternator goes up. One person reported 100A into a 300 Ah lithium bank which sound reasonable to me. Even with a 200 amp rated alternator I would be leery of that much current continuously.

The Li-BIM 225 turns off and on the charging current every 15 minutes which should help. But as you can see from the video it doesn't take long. With 300 Ahs of battery capacity I would seriously consider a 40 amp DC to DC charger to limit the current.

Either measure the current or measure the alternator case temperature while idling with well discharged batteries. Anything more than 50 amps or 200 deg case temperature would be cause to worry.

In my boat cruising days I had a high output alternator on my engine with an external Balmar regulator feeding a 440 Ah lead acid battery bank. When the batteries were well discharged the external regulator would cut back charging current to 50A from 100A when its alternator case temperature probe got up to 200+. When the charging current dropped back to 50A the case temp would drop to the 180s. That is the basis for my 50A and 200F limits.

David

[Pianotuna]

folks,


Li don't wished to be charged to 100%. I would do it no more than once per month--and that would be to "reset" the battery management system.


I would not take them below 40%.


I would charge at 0.2 C (and at no more than 0.5 c)

[BobC]

Originally Posted by Pianotuna

folks,


Li don't wished to be charged to 100%. I would do it no more than once per month--and that would be to "reset" the battery management system.


I would not take them below 40%.


I would charge at 0.2 C (and at no more than 0.5 c)

This is news to me, where does all this come from? I checked a few LiFePO4 manufacturers' sites (Battle Born, etc.) and can't find any confirmation for your recommendations.

[Wyatt]

Originally Posted by BobC

This is news to me, where does all this come from? I checked a few LiFePO4 manufacturers' sites (Battle Born, etc.) and can't find any confirmation for your recommendations.

It’s not news, it’s wrong.

[DavidM]

Originally Posted by Wyatt

It’s not news, it’s wrong.

I wouldn't say it is wrong. Exaggerated, maybe and each point has some truth behind it.

David

[creativepart]

Originally Posted by Wyatt

It’s not news, it’s wrong.

Well, the not charging to 100% all of the time is pretty much recommended, but the discharge to only 40% and the only recharge at a .2 C rate is where the advice goes awry. Those are not common recommendations.

[Pianotuna]

For all you experts: https://www.solacity.com/how-to-keep...tteries-happy/

[Pianotuna]

follow the link I posted.

[creativepart]

Read it, and your takeaways were pretty much disputed in the detailed writing in the article. The article clearly says LiPo batteries are fine when discharged much deeper than 30% and that they do fine charging at higher than .2C or even .5C rates.

There is a difference between what will help a LiPo battery last for decades in a solar powered home setting and what is typical LiPo care and feeding in a RV.

It’s a good in depth article but I would never take their bullet points at the end for a guide to how LiPo batteries in an RV must be treated.

[BobC]

Creativpart is correct. For example, here's a quote from the article:

"LFP batteries can also last a very long time. Our Battle Born LFP batteries are rated at 3000 cycles, at a full 100% charge/discharge cycle. If you did that every day it makes for over 8 years of cycling! They last even longer when used in less-than-100% cycles, in fact for simplicity you can use a linear relationship: 50% discharge cycles means twice the cycles, 33% discharge cycles and you can reasonably expect three times the cycles."


I'd venture a guess that the average discharge cycle for most RVers is going to be even less than the 33%. It's the average that counts, not the occasional 100% discharge.

People often comment that AGM and FLA batteries shouldn't ever discharge below 50%. Trojan and other manufacturers cite 80% at the level that will damage batteries. Consistently discharging below 50% will, however, result in a modest decrease in battery life but an occasional discharge below 50% won't make a noticeable difference. The difference between this and Li batteries is, at 80%, the voltage may be too low for some applications.

[DavidM]

I agree totally with BobC's analysis above.

When we first got our new Thor Axis in January of this year, I replaced the original batteries with a pair of 100 Ah AGMs. Since then we have spent 2-3 dozen nights camping all without hookups.

We typically discharge our AGMs to 75% for two nights of camping which is typical for us. Once we went on a 8-10 day camping trip and the batteries got down to 45% once overnight. Would have been better if we were in sun and could use our 100 watt solar panel, but we almost always camp in shade.

So the AGMs are doing fine and I think that with this kind of usage pattern, they should last quite a while.

David

[Wyatt]

Originally Posted by DavidM

I agree totally with BobC's analysis above.

When we first got our new Thor Axis in January of this year, I replaced the original batteries with a pair of 100 Ah AGMs. Since then we have spent 2-3 dozen nights camping all without hookups.

We typically discharge our AGMs to 75% for two nights of camping which is typical for us. Once we went on a 8-10 day camping trip and the batteries got down to 45% once overnight. Would have been better if we were in sun and could use our 100 watt solar panel, but we almost always camp in shade.

So the AGMs are doing fine and I think that with this kind of usage pattern, they should last quite a while.

David

And they will. Just not as long, had they not been taken down that far.

[Wyatt]

Long term storage of Lithium batteries at 100% is not recommended, nor necessary, but charging them when you are using them to 100% is recommended and is fine.

[BobC]

Originally Posted by Wyatt

Long term storage of Lithium batteries at 100% is not recommended, nor necessary, but charging them when you are using them to 100% is recommended and is fine.

50% is recommended for long term storage. The same goes for the lithium batteries in your phones, etc.

[Wyatt]

Originally Posted by BobC

50% is recommended for long term storage. The same goes for the lithium batteries in your phones, etc.

Now the question is, how is “long term” storage defined?

[BobC]

The mystery deepens:

Battle Born refers to the 50% storage level a minimum:

https://battlebornbatteries.com/faq-...our-batteries/

Minimum makes sense to me, but I'm not an expert.

[tim myers]

I am quite late to the party, but have read most of this thread, Based on some previous advice from @creativepart, on a different but related subject, I will lean on his tutelage. Bear in mind that I am not looking to dive into a big solar array yet, just looking for a bit more battery life than my LA AGM's give me.


Here are some takeaways I have from the discussion.


1. My existing converter should be able tol charge a pair of Lithium batteries but probably not up to 100%, maybe only 90% or so. True or false?
2. I will need to install a BIM or dc to dc charger to keep from cooking my 160Amp alternator. Question how is the dc to dc charger or the BIM sized?
3. If I want to know how much power I have left in a pair of Lithium Batteries I need to have something like a Victron Battery Monitor, as my existing battery monitor will only show remaining voltage not amperage or % of power left?


Am I understanding any of this?