Possible very flexible, accurate, and less expensive lithium system

[booster]

We are on our second generation system currently, not by choice.

The first was because I wanted to learn about lithium firsthand, but be able to go back to AGM if I wanted to. I reused most of the AGM system and left it in place for the most part. The existing parts were able to do what I wanted as they were very flexible. It worked fine so I cleaned up the wiring and removed the AGM specific stuff.

2 years into it the Magnum shore charger died and they were out of business so no parts or replacement chargers available. I found a sort of suitable Samlex that was a somewhat easy swap as I needed to get us running in time for a trip.

Ever since the beginning I kept thinking about what would I do now, with knowing more about how I want/need our system to work. I want SOC control of midrange charging, no float, and a way to charge by voltage and time to calibrate the Victron monitor that is our system reference for SOC. It would also be nice if it could do the more commonly needed charge to 14.4v hold X long to balance method all the time.

I have been messing around with sketches and looking at all the brands of equipment and decided to try to use a plain old fixed voltage converter that is adjustable voltage. The hope was that it might be able do it all so the batteries could be charged to whatever you wanted and then shutoff when on shore power but have the converter power the coach. Newer charges will shut off if you take the batteries out of the circuit so they can't do that.

The first layout uses a converter, standalone inverter with internal transfer switch, a B to B for alternator charging, a Blue Sea bistable relay, with a Victron monitor using the internal contacts to control the Blue Sea relay and maybe a second relay if you use solar. The Victron monitor controls all the charging

Any and all comments, questions, error finding, improvements, very welcome and wanted as this is still just an exercise at this point of time.

 

[GeorgeRad]

Insufficient picture resolution to decipher the writing. Without going deep into your proposal perhaps naïve question, why a homebrewed system. With advances in Lithium in the RV world it seems turnkey solutions should exist, perhaps I am wrong.

 

[booster]

Insufficient picture resolution to decipher the writing. Without going deep into your proposal perhaps naïve question, why a homebrewed system. With advances in Lithium in the RV world it seems turnkey solutions should exist, perhaps I am wrong.

I actually reloaded the pic just before looking at this. Brighter and higher resolution.

I would agree that there are lots of lithium specific things available but they are not very flexible for programming and use and can't do a lot of things, like no float but keep the 12v power to the van on shore power, which is great for the smaller battery banks so aren't running on the batteries if you do no float which is getting to be more commonly recommended these days. A fully controlled and integrated system certainly could do all this, and more, but it is not redundant in most things so if it dies, you have not power, AFAIK.

The other thing is cost and repairability. This system would be quite inexpensive compared to many, I think, unless you went all not very good premade stuff. Most prebuilts can't do storage that is plugged in all the time but only charges when the SOC or Voltage low setting is hit, then it charges to setpoint and shuts off again. Most low end stuff won't do charge/off/rebulk changing, especially with full adjustabiltiy like expensive stuff does. Both the old Magnum and the new Samlex can do it and I use when stored so I don't have even look at it.

This system has built in ability to recover a lithium BMS shutdown if you have shore power. All the equipment is still standalone so if it fails the others are still working and only the one component needs replacing.

I am super picky on the charging as everyone knows, and this system would satisfy our needs at a much lower cost than what we have, plus it will do the basic charge full/balance, stuff if you want to.

An unseen option, which I think would work is if you want solar to do whatever it can all the time like would be with a small solar panel capacity and larger battery bank, you would just connect it differently. What is shown would probably be better for a small battery bank, especially if you leave home on a trip and don't want the solar charging the already full batteries.

 

[@Michael]

Victrons chargers can act as power supplies (I.E. their IP22 model).

I suspect that they can be configured as 'no float' by simply lowering the float voltage. Re-bulk is also configurable, but I'm not sure if it's flexible enough for your requirements.

 

[booster]

Victrons chargers can act as power supplies (I.E. their IP22 model).

I suspect that they can be configured as 'no float' by simply lowering the float voltage. Re-bulk is also configurable, but I'm not sure if it's flexible enough for your requirements.

I have still not been able find any real backup information for low voltage float being better, worse, or the same for lithium and particularly when stored. Some say that any voltage is too high once the battery is at that voltage because of the infamous anode plating. They do say higher voltages are worse than lower holding. Others want not input at all over storage time. But like I said, no data yet.

Having a low float voltage that the batteries will never get to while camping is likely not an issue as the battery and charge aren't equal but eventually in storage they will be. That is why the shut off no float and then rebulk as soon as the batteries get to whatever setpoint you chose seems so desirable. It covers all issues so question of OK, I think.

If a charger is operating as a pure power supply you can just put a relay on the output also as the charger will keep running at set voltage with no output, but not quite as efficient as shutting it off. Many of the "power supply" modes touted may just be fixed voltage settings that still need a battery to stay active.

I have been looking at the discharge side of the drawing and I think a 3 pole relay or 3 relays may be better to control the output of each of the sources separately.

 

[GeorgeRad]

It seems as decent papers regarding over/under charging of lithium batteries. Setting the Right Float Voltage for Lithium Battery Longevity — Large Battery by Dr. Lee Pan - AI summary: "Dr. Lee Pan is a scientist from Hubei University with a focus on high-performance battery materials, holding a Doctor of Science degree. He is also a postdoctoral fellow at Central South University, specializing in materials science and engineering. His research includes areas like explosion-proof and low-temperature batteries, with a significant amount of practical experience in the field. "

 

[booster]

Personally, I would disagree with just about everything in that link. It appears to be for lithium ion, but from what I have seen best practices for them and lifepo4 are similar. Probably targeted at electronics that are only looking at capacity after purchase and not lifespan. I can't comment on his qualifications or intentions, but it reads like a sponsor paid article to me like way to many others out there. He is linking several times to what is probably employing him, a company call "Large Power".

I think I would point to the cell phone industry which uses the same chemistry as the article and also has a lot of battery life decisions to make. Stuff like fast or slow charging, charging to full, holding the charge at full or shutting off the charger, etc. It is likely that very few have studied battery life and charging as thoroughly as the phone manufacturers.

I think most of the cell phone manufacturers have started to suggest low rate charging over high, and not charging to full all the time unless needed for capacity.

When we got our latest phones, S24 Samsung models, I was surprised that the maximize battery life toggle setting did both low rate and charged only to 80% full and cut off charging completely at 80%. Not a problem for us as we don't use phones for lots of stuff all day, but some couldn't do that, for sure.

Time will tell on RV batteries, but the trends appear to be following the that our phones have, if you want longer life and don't need super fast charging and maximum capacity all the time when just off charge.

 

[GeorgeRad]

I am trying to understand how charger with lower voltage then battery’s voltage can damage a lithium battery. Current flow will be reversed causing discharge, but damage? I don’t understand electrochemistry of lithium battery well enough to digest this perceived problem.

 

[booster]

I am trying to understand how charger with lower voltage then battery’s voltage can damage a lithium battery. Current flow will be reversed causing discharge, but damage? I don’t understand electrochemistry of lithium battery well enough to digest this perceived problem.

Like I said previously, it likely won't damage a battery right after the charge, when the battery is slowly discharging toward the float voltage. The big unanswered question is what happens when the battery and float are the same, so you have net charge going into the battery albeit at less than full voltage to cover losses. I have seen recommendations to never hold a lithium on charge at most any voltage, including from the getting more common no float folks. No real side by side data, but if anode plating is really caused by excess ions on the cathode from being charged, I can see how it can happen, possibly. That is the unknown or documented with good research, IMO.

We are still in the toddler stage of knowing how all of it works in the real world, and by time we find out it will probably be irrelevant do to a new battery type.

 

[GeorgeRad]

Indeed – anode plating is due to overcharging when discharging lithium cations can’t be placed correctly within the anode material (likely graphite) and plate anode surface with metallic lithium, but this is due to overcharging not undercharging. So back to undercharging, what is the physicochemical problem of low voltage float besides discharging.

 

[Winston-ClassB]

We, too, could not fully decipher your diagram but it still appears that Booster and Winston are at opposite corners of the "Float Ring" - - Booster, in one corner, saying 'never', Winston, at the opposing corner, arguing "always". Until someone can explain how attaching a power supply (charger) set to precisely the same voltage as the battery itself, where - - by definition, no charge flows in either direction - - is harmful to the battery, we will look at all your relays and switches . . . smile and have another glass of vino.

 

[booster]

I can't disagree completely with any of the comments, because we really don't know for sure, I think.

I just went through the "latest" information on the topic and it is still more of an opinion for most, including me, as to the affect of float charging at lower (how low?) voltages.

A couple of things stood out in the stuff I saw, though. One is that there is pretty much consensus on not holding at full charge voltage of 14.4v. Another is that I found absolutely NO information on if there is a difference between using float when the batteries are used in daily life, like in our vans, and long term storage, like our vans also see regularly. I think it is very possible, maybe likely, that this difference is one of the reasons we see so much contrary opinion stated as fact around. A third item is that much of the information is based on user experience with off grid or grid tied solar systems, which are an somewhat unusual application because they don't charge or float for about 1/2 the time every day and charge and discharge every day.

I mentioned earlier, before the latest reading, that we have backed off of "never" float for the most part while camping, except when the batteries are what we call fully charged at 80% SOC. While we don't actually use a float setting, we do use our solar when traveling to gain some free, no plug in, charge. It is currently set at 13.4v for absorption and IIRC 13.1v for float (which it really never gets to and is also rebulk voltage). Absorption time is long and covers most of the day. We turn it on usually on about the 4th day of a trip when we get to 40-50% SOC and it bounces around after that. It is only 300 watts of solar so on good sun we gain a little every day and with bad sun we can lose some. In a month on the road we mostly broke even in fall sun with frequent clouds and didn't plug in or engine charge. We have much more testing to do to see if this is always the case. I mention this as it is how a fixed location system would also work. And it does work well for us.

A big question, still, is what happens when the system is sitting at a fixed voltage, which may be holding 50% SOC or so over a 6 month storage compared to the daily use idea.

Non research opinions that showed up now that weren't around before often drifted into cell balance under or off float, with some saying float balanced the cells with using a balancer and others saying it made balance worse. IMO, balance may be a thing that is involved in all this stuff more than we realize, but have no data or testing of it over various methods. I do, mostly, believe that balance over time, without balancing is probably an indication of charging accuracy and bank degradation, but again, no data.

So I am not in the "never float" group and locked into that. We do come off it when camping. I do think the holding at a single voltage might be more a degradation when compared to a midrange charge/off/rebulk at low charge rate, and here also no data.

Also as I mentioned earlier, I think we may never really get detailed testing data on all this because lithium is getting so inexpensive it doesn't matter from a cost/benefit point of view, and also because battery technology is move quickly toward more environmentally friendly, less expensive, battery chemistries.

My personal hope and muted guess is that fuel cell technology will jump ahead of battery storage over time as it is much better suited to storing large amounts of backup energy and for vehicles can be refueled much more quickly than batteries.

Be aware that I use "engineer instinct" when I don't have data. Sometimes it is right, sometimes not. But it does allow me to test what instinct tells me to see if it is right or wrong. There is not enough time, funds, or capability to test all the difference scenarios so all you can do is take your best shot. You win some, you lose some.

 

[Winston-ClassB]

Good morning. We’re still smiling, but have switched to coffee.

Again, we wish we could throw out all those ‘bulk’, ‘absorb’, and ‘float’ terms and just speak in terms of what charge profile we trying to achieve. Indeed, you used another term “rebulk” serveral times . . . what’s that? Do you mean: “When my batteries get low, I recharge them?”

We hesitated to use the term “float” in our last comments because, for most people, float is something that is done only after two other things have been done (i.e. bulk and absorb). For us, ‘float’ is the only thing we do - - we determine what State of Charge we seek, and set our power supply/charger to that level . . .

As we were first studying lithium and purchased our first (and current) lithium pack back in 2016 - - it was apparent, even then, that charge levels of 13.4 volts represesented a nearly fully charged pack . . . that (except for balancing) there would never be a need for charge levels above 13.6 volts. The marine guru whose well thought-out opinions we relied upon has recently updated his lithium pack report to indicate that his nearly 20 year old lithium cells have never been charged at a voltage higher than 13.6. So when the spate of ‘dropin’ lithium “lead-acid replacement” batteries hit the market - - with all the manufacturers saying “14.4 volts is great, no problem”, we cringed.

We (you and I) agree on several things. When Elite Power Systems indicated that their Chinese GBS lithium cells could be charged at 3C (or, for us, a monsterous 1,500 amperes) - - they, at the very least, overstated what we now know to be ‘best practices’ for charging. We agree that a lower charge rate results in longer battery life.

We also agree that maintaining lithium at a high State of Charge also degrades lithium faster than maintaining at a lower SoC level. It seems, in fact, that the lower the SoC maintained, the longer life. It isn’t just that 100% SoC is bad, so is 75% (as compared to, say, 50%) and 50% is bad as compared to 10%. So, if we are looking to maximize lithium longevity, shouldn’t we all be operating at 10% SoC?

But here’s where, possibly, you and I depart. Does it matter whether it’s winter or summer? Does it matter whether you’re motoring down the highway enroute to Custer State Park or parked, in January, in your yard? Why draw a distinction between ‘use’ and ‘storage’. Isn’t it likely that the operative is simply “What SoC are you maintaining?” Again, whether your using or merely storing the batteries is likely irrelevant. Yes, we understand that while a 10% SoC might be best for the batteries, it’s kinda impractical when ‘on-the-road’, yet, during a prolonged storage event, you could take your cells down to 10%.

The point is . . . at some point we must determine what SoC we can live with. You’ve chosen 80% (mostly). But why not 100% to get all the capacity of your system? Or, 50% to get longer life? The answer is obvious - - it’s a trade-off between more capacity or more battery life.

But here’s where our “engineering instinct” kicks in - - we think all this clap-trap about “floating” isn’t really about floating - - it’s about what voltage/SoC one chooses to maintain their pack. You mentioned that possibly one could float their pack at a lower voltage, although you understandingly were unsure what that “low voltage” should be. So you don’t want to float you batteries at 13.4 volts (~80% SoC), but possibly at 13.1 volts? Are you saying ‘floating’ is bad? Or, aren’t you really saying that maintaining a constant 80% SoC isn’t good? But you’ve already chosen 80% SoC as the ‘compromise’ setting between “longevity” and “capacity” - - so why not just accept that at 80% SoC, you’re going to lose a little longevity over the ‘average’ 60% that your current on/off system might provide?

We know you are concerned about ‘plating your anodes’ - - but still hoping someone will verify how it is possible to place ions or plating on an anode where absolutely no charget is flowing. We continue to argue that whatever loss in longevity occurs at 80% SoC, it’s going to occur whether your batteries are just sitting there at 80% or are sitting there with a power supply connected.

 

[GeorgeRad]

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

My personal hope and muted guess is that fuel cell technology will jump ahead of battery storage over time as it is much better suited to storing large amounts of backup energy and for vehicles can be refueled much more quickly than batteries.

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

Fuel cells have been maturing for more than 20 years but are based on hydrogen and a few on methanol. Unfortunately, LPG based fuel cells had a very limited success, like “The bugler Who Wouldn’t Die”

LPG needs to be desulfurized and reformed to hydrogen gas which then can be fed to fuel cell, this process is expensive and difficult (C3H8 + 3H2O = 3CO + 7H2 and CO+H2O = CO2 + H2). Hydrogen gas is by far best fuel for fuel cells but its distribution of it is difficult (-253C) and that is why we still don’t have broadly available fuel cell cars. From my perspective LPG fuel cel is just like Wunderwaffe, an "almost here" dream.

 

[booster]

Fuel cells have been maturing for more than 20 years but are based on hydrogen and a few on methanol. Unfortunately, LPG based fuel cells had a very limited success, like “The bugler Who Wouldn’t Die”

LPG needs to be desulfurized and reformed to hydrogen gas which then can be fed to fuel cell, this process is expensive and difficult (C3H8 + 3H2O = 3CO + 7H2 and CO+H2O = CO2 + H2). Hydrogen gas is by far best fuel for fuel cells but its distribution of it is difficult (-253C) and that is why we still don’t have broadly available fuel cell cars. From my perspective LPG fuel cel is just like Wunderwaffe, an "almost here" dream.

I agree that lpg fuel cells are not a good deal, but there are still opportunities with liguid hydrogen. How to store in on vehicle has long been an issue and still is. I saw and article lately that they are looking a compressed gas, not liquid wiht high pressure composite material tanks in the vehicles. The aim was 300 mile range.

By coincidence there was an article in Minnesota Star Tribune today on hydrogen mining that might be possible in northern Minnesota, kind of like natural gas is.

 

[otr]

It might be worth checking out the Facebook roadtrek zion & Simplicity Owners Group, lots of lithium battery conversation there

 

[beauregaard]

This is a great topic, and though most of it is over my head, I think I've learned something.
Thanks to y'all!
My take on hydrogen is that unless it's made from water on board, the nationwide infrastructure for it isn't there, and probably never will be.
{P.S.>I *love* Peter Sellars}

 

[booster]

This is a great topic, and though most of it is over my head, I think I've learned something.
Thanks to y'all!
My take on hydrogen is that unless it's made from water on board, the nationwide infrastructure for it isn't there, and probably never will be.
{P.S.>I *love* Peter Sellars}

Yep, the infrastructure isn't there, currently. Analogy would be how many charging stations were available before electric cars showed up, or gas stations before cars and trucks showed up. I think. And yes, would use water.

I don't think you can get enough solar on any vehicle to make enough hydrogen to use for propulsion.

You can make plenty with electricity at the hydrogen fill points, or at a nearby bulk storage location.

 

[Winterjack]

Good conversation. From what I am reading it seems you want a SoC of say 50% when not using the rv and then 80 or above when using the rv. Is that correct? Then what would be nice would be a button to select between the two for when using and not, correct?

 

[booster]

Good conversation. From what I am reading it seems you want a SoC of say 50% when not using the rv and then 80 or above when using the rv. Is that correct? Then what would be nice would be a button to select between the two for when using and not, correct?

No, that is not how it is used. We are doing what is referred to commonly as "midrange charging", which is just what it sounds like it is. The low end SOC is 35% and when we get that low in use, we charge to 80% SOC and stop charging. We cycle only between 35 and 80% in use and when stored.

There are quite a lot of claims that midrange use is much easier on lithium batteries and preserves capacity longer. But, now there is getting to be a bunch of information coming out that says that aging is more of an issue for lithium than many of the things that are said to be best for long life. One of the sources I saw said that lithium life (down to 80% total capacity test) is roughly 7-9 years unless they are abused. I think that means you should get around 9 years if you take good care of them and 7 with moderate care. For most of us they will age out long before we hit the cycle life of them, but in applications that may charge like 3-5 times a day then preserving life carefully to last longer might make a time difference also.