Drop in LiFePO4 batt

[Delfin]

Using them with charge sources designed for lead will definitely reduce their lifespan.

When you say "designed for lead", I presume you are referring to a charger with no ability to have charge parameters adjusted because otherwise this statement is false. My Trace charger and Balmar alternator/regulator are "designed for lead" I suppose, since they can certainly charge lead batteries, but since they both allow changes in charging parameters they are also quite usable for Li batteries.

 

[john61ct]

Yes. The critical bit is being able to customize the Volts setpoints, to 3.45Vpc (13.8V for 12V nominal) for charging, and 13.2V for float.

Ending charging based on endAmps of .02C being accepted by the bank would be nice, but since LFP has no need to get to Full, just stopping based on hitting the target voltage is fine.

A large minimum absorb time would not be healthy.

Actually just stopping charge current completely would be ideal, but most still force a Float instead.

 

[Delfin]

Final report (unless something unexpected occurs).....

The characteristics of this battery chemistry are pretty interesting. After a day and a half on the hook, we'd used up 345 Ah. Heading for Nanaimo, I recharged the LiFe batteries just with the large frame alternator on the CAT. I've throttled the output of the alternator to keep it at around 180 degrees nearest the engine and with the other loads being drawn while underway, the alternator was pushing 93 amps to the batteries. Over a 5 minute period, the amp counter on the Link 20 indicated an acceptance rate by the batteries at a rate of 90 Ah. Unless I am making a mistake, that means that the batteries are 97% efficient in storing energy directed their way.

What is really impressive is that the 90 Ah acceptance rate continues until 6 minutes before it suddenly falls off a cliff as the batteries reach the full mark. Within that 6 minutes the acceptance falls to 25 Ah, at which time I disconnect them from the charging source and run off the lead acid starter batteries while underway. Once at anchorage in Nanaimo, I'll turn the LiFe back on and we'll run off that for a couple of days.

What I still don't understand, and Lithionics hasn't been able to give me an answer, is why peak voltage of only 27.3 volts is reached at the point when the batteries won't accept any more current. The regulator is set to 28 volts peak, but I never get there. Not sure it makes any difference since when the battery is full, it's full and the resting voltage of 26.8 volts is what Lithionics says the batteries will resolve to after they are fully charged.

The other thing that is remarkable about the LiFe is that as you discharge them, the voltage drops only about .1 of a volt per 50 Ah removed, no matter the rate at which that 50 Ah is consumed (within reason). At 80% discharge, you are still getting around 25.8 volts. Amazing.

 

[Art]

Final report (unless something unexpected occurs).....

The characteristics of this battery chemistry are pretty interesting. After a day and a half on the hook, we'd used up 345 Ah. Heading for Nanaimo, I recharged the LiFe batteries just with the large frame alternator on the CAT. I've throttled the output of the alternator to keep it at around 180 degrees nearest the engine and with the other loads being drawn while underway, the alternator was pushing 93 amps to the batteries. Over a 5 minute period, the amp counter on the Link 20 indicated an acceptance rate by the batteries at a rate of 90 Ah. Unless I am making a mistake, that means that the batteries are 97% efficient in storing energy directed their way.

What is really impressive is that the 90 Ah acceptance rate continues until 6 minutes before it suddenly falls off a cliff as the batteries reach the full mark. Within that 6 minutes the acceptance falls to 25 Ah, at which time I disconnect them from the charging source and run off the lead acid starter batteries while underway. Once at anchorage in Nanaimo, I'll turn the LiFe back on and we'll run off that for a couple of days.

What I still don't understand, and Lithionics hasn't been able to give me an answer, is why peak voltage of only 27.3 volts is reached at the point when the batteries won't accept any more current. The regulator is set to 28 volts peak, but I never get there. Not sure it makes any difference since when the battery is full, it's full and the resting voltage of 26.8 volts is what Lithionics says the batteries will resolve to after they are fully charged.

The other thing that is remarkable about the LiFe is that as you discharge them, the voltage drops only about .1 of a volt per 50 Ah removed, no matter the rate at which that 50 Ah is consumed (within reason). At 80% discharge, you are still getting around 25.8 volts. Amazing.

Delfin - I can tell you are a happy boater with happy Batt banks! Congrats!! And, thanks for all the batt input you've been sharing... I thank all the other batt posters too; I've been listening and learning. - Art

 

[john61ct]

Yes you're describing exactly the advantages that LFP is supposed to deliver

What I still don't understand, and Lithionics hasn't been able to give me an answer, is why peak voltage of only 27.3 volts is reached at the point when the batteries won't accept any more current.

You mention acceptance at 90A, which is due to the charge source's limited current output, so would be much higher, shorter runtime with a bigger alt.

Then a sudden drop to 25A. Is that at 27.3V?

If you were charging at a lower current rate and/or charging voltage, you would likely hit the shoulder at a slightly higher voltage.

At 600AH in theory you could go until it drops to 6-10A without hurting longevity. But remember, the goal is **not** to get every AH of capacity, it is to avoid climbing that shoulder.

Are you standing there watching every charge cycle?

I would strive for a setup you can trust to walk away and do other things; set all your sources to 3.45Vpc, IOW 27.6, or even a notch or two lower, better to err on the low side than high.

 

[john61ct]

wrong thread

 

[Delfin]

Did I say final report? Well, maybe this one....

After spending a couple of weeks at anchor (mostly) I think I've reached some conclusions on managing an LiFePO4 bank that may be incorrect and if so, I'd love to be corrected. If not, I don't think I have heard anyone else make the same observations so with the caveat that I may be wrong, here goes:

1. The concern over balancing cells within a Li bank are overblown. As CMS/Maine Sail has observed on his blog, if you don't exceed about 28 volts charging the cells pretty much stay balanced by themselves. I think this makes sense because if, say one cell is at 28.5 v and the other 7 in my bank are at 27.9 v, then as soon as you shut off charging the higher voltage cell will flow into the other cells until they all settle down to 28 volts, or thereabouts. Conclusion: Maybe trigger cell balancing very occasionally, just in case but I doubt it will need to be done more than a few times a year, if that.

2. The concern about trying to set up traditional charging sources to accommodate Li chemistry is also overblown if you use the most intelligent charging regulator around, which would be a human being. Automated charging management is important for lead acid batteries because the process never really ends since they require floating to keep from self-discharging, as well as a very extended charging cycle to get them full enough after a discharge that you don't diminish their durability through undercharging. That is very different from Li batteries since they don't need fancy 3 step regulation and would be completely happy will a managed bulk charge phase that ends when the acceptance rate drops to the point that they are "full enough". Consequently, in my case I doubt I will ever put a charging current to this Li bank without monitoring the voltage and acceptance rate and turning it off manually when I'm happy with the charge.

3. The concern about having massive charging sources to take advantage of the Li battery's ability to absorb a whole lot of charging current is also somewhat overblown, depending on a few other factors. In our case, it looks like we can go close to 2 days on a single Li charge, using up around 450 Ah. At that point, the genset goes on, and I start the CAT. This gives me 200 Amps charging current and with the genset on we make water, do laundry etc. I'm not worried about running the CAT without much of a load for a couple of hours since this engine was designed to idle half the time while running gensets and other equipment on the North Slope project. The time we want the genset to run is determined by the activity that needs ac voltage the longest, and that is water making, not battery charging. The result of all of this is that my original plan of adding another high output charge source to the genset to reduce charge time to 90 minutes or so is pointless, since I'll have to run the water maker for longer than that anyway.

Bottom line - while I have the charge sources all programmed so I could walk away and the Li batteries would be charged appropriately, since this is a once in every couple of days activity and I know that it will take almost precisely 2.25 hours to recharge the bank, I am fine being a human voltage regulator and managing the batteries manually, and I'm not gong to worry about cell balancing because it looks like a non problem. In other words, these batteries look, at least to me, to be easier and not harder to manage than the AGM batteries they replaced.

 

[john61ct]

Yes and yes.

BMS that automate balancing add more risk and complexity than the "problem" they're trying to solve.

EV tech is the 800lb gorilla here, and their needs are far different from gentler Hose power storage.

And of course there is a diminishing return on taking advantage of LFP's high CAR, especially when already burning fuel for other reasons.

200A is heaps anyway, I sometimes have a hard time convincing people it's worth going over 40. . .

I'm fine with manually supervising charging, as long as you're comfortable with *having* to do so.

Me, I don't trust myself more than hardware, and getting more forgetful and prone to nodding off every year, so continue to strive for "flip a switch and walk away" as much as possible.

 

[Delfin]

Yes and yes.

BMS that automate balancing add more risk and complexity than the "problem" they're trying to solve.

EV tech is the 800lb gorilla here, and their needs are far different from gentler Hose power storage.

And of course there is a diminishing return on taking advantage of LFP's high CAR, especially when already burning fuel for other reasons.

200A is heaps anyway, I sometimes have a hard time convincing people it's worth going over 40. . .

I'm fine with manually supervising charging, as long as you're comfortable with *having* to do so.

Me, I don't trust myself more than hardware, and getting more forgetful and prone to nodding off every year, so continue to strive for "flip a switch and walk away" as much as possible.

I guess what I am suggesting is that to get maximum performance from these batteries at the lowest risk to your investment, manually supervise charging, but set everything up so that if you do nod off, you're covered.

 

[twistedtree]

I guess what I am suggesting is that to get maximum performance from these batteries at the lowest risk to your investment, manually supervise charging, but set everything up so that if you do nod off, you're covered.

That could work. For me it's important that any system be able to pass the Wife and Kids Test. If they can't do it, it's too complicated.

 

[Delfin]

That could work. For me it's important that any system be able to pass the Wife and Kids Test. If they can't do it, it's too complicated.

I just observe the Link 20 voltage and charge acceptance rate of the batteries, knowing that if I am out 200 amps, one hour later the battery will be nearly full. The drop off of acceptance happens quickly, so the only skills necessary are being able to read that amperage reading and turn off the charging at an acceptance rate of around 30 amps. If you forget, not to worry, the regulation settings will manage it, if a bit less optimally than a human would.

 

[twistedtree]

I just observe the Link 20 voltage and charge acceptance rate of the batteries, knowing that if I am out 200 amps, one hour later the battery will be nearly full. The drop off of acceptance happens quickly, so the only skills necessary are being able to read that amperage reading and turn off the charging at an acceptance rate of around 30 amps. If you forget, not to worry, the regulation settings will manage it, if a bit less optimally than a human would.

So when operating "manually", you stop charging based on acceptance current. But most chargers stop based on voltage for bulk, and usually time for absorb, but sometimes also acceptance current. How do you find things work with voltage-based end of charge?

The integrated Li battery & charge systems I've looked at all monitor voltage and acceptance current at the battery, and control charge sources based on that, just like you are doing manually. It's the way we should have all been doing charging for the past century, but habit is hard to break. This seems to be the big difference, between integrated li systems and drop in replacements like you have done with traditional chargers, and the challenge in doing such a drop in replacement.

 

[john61ct]

Big difference with LFP is, there's no need to get right up to Full.

So ending charge based on Voltage is fine, as long as the setpoint is well below 3.5Vpc.

Doing it this way, different charge current rates will mean different resulting SoC levels, but as long as you're not hitting the shoulder, no problem.

Now **staying** at say 3.45Vpc (call it Absorb if you like) until amps drop to say .025C, will indeed push a little more AHage into the bank.

That level of precision's only point is say resetting the "Full" level for the SoC monitor.

But if doing that in daily use, is in any way a challenge for your setup, then why bother? Holdover from lead thinking IMO.

 

[Delfin]

So when operating "manually", you stop charging based on acceptance current. But most chargers stop based on voltage for bulk, and usually time for absorb, but sometimes also acceptance current. How do you find things work with voltage-based end of charge?

The integrated Li battery & charge systems I've looked at all monitor voltage and acceptance current at the battery, and control charge sources based on that, just like you are doing manually. It's the way we should have all been doing charging for the past century, but habit is hard to break. This seems to be the big difference, between integrated li systems and drop in replacements like you have done with traditional chargers, and the challenge in doing such a drop in replacement.

TT, I am not that convinced that the Lithionics BMS is as sophisticated as it might be, but hope they know what they are doing. They are the choice for a number of folks who seem to know what they talking about, but I guess I'll find out. Their BMS does not control charge voltage or current. Their functionality is low voltage cut out, high voltage cut out, balancing of cells once you hit 29 volts and a field control circuit cut out when the BMS isolates the batteries from a charge source.

What I observe is that with target voltage set to 28 volts, acceptance is pretty much whatever you throw at the batteries at a voltage of 27 volts +, with about 7 minutes between when current acceptance just begins to taper off from 200 amps and when acceptance reaches 2% of capacity or 12 Ah. So, if I understand your question, the answer is I only get close to 28 volts before I get to an acceptance rate that isn't going to add much more juice. And, after removing 400 amps, I still see 26.1 volts at rest, so I am pretty sure I am getting full capacity on the charge cycle.

 

[Delfin]

Big difference with LFP is, there's no need to get right up to Full.

So ending charge based on Voltage is fine, as long as the setpoint is well below 3.5Vpc.

Doing it this way, different charge current rates will mean different resulting SoC levels, but as long as you're not hitting the shoulder, no problem.

Now **staying** at say 3.45Vpc (call it Absorb if you like) until amps drop to say .025C, will indeed push a little more AHage into the bank.

That level of precision's only point is say resetting the "Full" level for the SoC monitor.

But if doing that in daily use, is in any way a challenge for your setup, then why bother? Holdover from lead thinking IMO.

I think that is right John. Li banks should be viewed as fuel tanks. You fill them without worrying whether you can push another quart of fuel in, then use the fuel, then refuel. Whether you refuel at an 1/8th of a tank or 1/4 of a tank; whether you refill to 100% or 95% is all pretty much immaterial. In many ways, Li banks are a lot easier to manage than lead.

 

[sunchaser]

I think that is right John. Li banks should be viewed as fuel tanks. You fill them without worrying whether you can push another quart of fuel in, then use the fuel, then refuel. Whether you refuel at an 1/8th of a tank or 1/4 of a tank; whether you refill to 100% or 95% is all pretty much immaterial. In many ways, Li banks are a lot easier to manage than lead.

Good analogy when saying they are like a fuel tank. Three questions -

First, is there a simple and automatic method to shut off charging much like a gas pump at Circle K?

Second, are solar panels and current controllers compatible with the drop in Li batteries?

Thirdly, my lead battery banks require close to 0 management, beyond knowing when to shut down the genset during charging routines. Especially with our cruising style where standard on engine alternators can push an easy 200+ ah per day into the Trojans. That said, on extended daily cruising hours would your Li setup, when batteries are "full", be able to automatically regulate on engine alternator amps?

Thanks Carl, nice to see you taking the plunge, beyond citing YouTube or Google. Real world user experience can't be beat.

 

[john61ct]

First, is there a simple and automatic method to shut off charging much like a gas pump at Circle K?

Second, are solar panels and current controllers compatible with the drop in Li batteries?

Thirdly, my lead battery banks require close to 0 management, beyond knowing when to shut down the genset during charging routines. Especially with our cruising style where standard on engine alternators can push an easy 200+ ah per day into the Trojans. That said, on extended daily cruising hours would your Li setup, when batteries are "full", be able to automatically regulate on engine alternator amps?

1. Yes, but done by the available algorithms by the charge source. Since "just stop" is not an option, workaround is a low float, say 13.2V (3.3Vpc). Adjustable user-set voltage is critical for longevity.

2. Yes, as with #1.

3. Yes, but need a lead batt to be always in the loop there as a load dump, since LFP internal BMS can cut themselves out and you don't want to fry diodes. For bank longevity a **voltage-adjustable** alt regulator, or large-amp B2B is required.

Not sure if Sterling has their 180A unit out in the field yet.

 

[Delfin]

Good analogy when saying they are like a fuel tank. Three questions -

First, is there a simple and automatic method to shut off charging much like a gas pump at Circle K?

Second, are solar panels and current controllers compatible with the drop in Li batteries?

Thirdly, my lead battery banks require close to 0 management, beyond knowing when to shut down the genset during charging routines. Especially with our cruising style where standard on engine alternators can push an easy 200+ ah per day into the Trojans. That said, on extended daily cruising hours would your Li setup, when batteries are "full", be able to automatically regulate on engine alternator amps?

Thanks Carl, nice to see you taking the plunge, beyond citing YouTube or Google. Real world user experience can't be beat.

Hi Tom,

To your first, the simple way to shut off charging is to isolate the batteries from the charge buss by turning off the BMS. But you asked about automatic and AFAIK only through proper set up of the regulators can you automate the process, or at least provide a working facsimile of "shutting them off." I have my regulators set for 28 v bulk, 27.8 absorption , and 26.6 float. You don't want to float them, apparently, so the 26.6 float basically means they are kept at around 85% SoC, or thereabouts, which avoids dumping current into a full battery and just generating heat. All the other automatic shutoffs are for when things fail, so you have high and low voltage cut outs managed by the BMS, as well as a field control circuit that can kill the alternator output if the BMS goes off line. So, I think it is easy enough with a programmable alternator like the Balmar MC 6xx to automate the process quite safely, but I just find it easy to manually manage so I'll rely on the automatic back up of the regulator program only when I forget to turn off the charging when the Li bank is full.

To your second, I have zero experience with solar so can't comment directly but from what I have read, the high voltage potentials of solar create special opportunities to screw up a Li bank so good controllers appear a must.

To your final, sure, you can run these just like you would a lead bank, IF the charging voltages are managed through programmable regulators. The one concern I have, and one reason I am managing these as I am, goes to one of John's points, and that is it is very nice to have an alternate end point for charge current if for some reason the BMS isolates the Li bank from the charge source. This avoids isolating the alternator from any end point for its output and possibly frying it. For me, and most of us, that is just the lead starting bank, so if I am charging the Li bank underway, once that bank is "full", I manually combine the lead and Li banks and turn off the BMS. Now the Li bank is slumbering in the corner while the alternator output is floating the lead bank. When we get to our anchoring destination, turn off the engine, turn on the BMS and auto combine the two banks, which as a practical matter leaves the engine bank isolated from house current draws and prevents it from scavenging juice from the Li bank.

Sitting at the dock on shore power is just the opposite. Turn off the BMS so the Li bank is off line (and preferably sitting around 60% SoC), and now shore charge current is directed towards the starter bank. It really is more like managing fuel tanks than batteries. Switch to this tank, then to another.

The one thing that is more of a burden in all of this for me is that I do have to think proactively about battery management, where with lead batteries you pretty much set the system up and ignore it other than topping up wet cells. However, the trade off is much stabler and higher voltages over their complete discharge cycle that is better for electronics and motors, much shorter generator run times, and very, very long cycle life. Fiddling with stuff on a cruising boat is part of its allure, at least for me, so I don't mind the management burden while I certainly understand why others might feel differently.

It's a lot harder to write a description on how to manage these than it is to do it....

 

[sunchaser]

Good points Carl. Especially the one about the allure of fiddling with things. Each cruising style is different and ease of system operation and reliability is my mantra.

We have found that dinner time and laundry time are our big house bank and/or electric draw times. To that end, we run the genset during these periods, which pretty well keeps the house bank charged up. A Li bank used similarly to what you are finding, may indeed be in our future. If nothing else just to have a higher house bank charge rate utilizing existing equipment.

Here is the $64 question. For blue water travel and long periods away from dock, what redundancies would you foresee? Both a LFP and lead largely independent battery banks or --?

 

[Delfin]

Good points Carl. Especially the one about the allure of fiddling with things. Each cruising style is different and ease of system operation and reliability is my mantra.

We have found that dinner time and laundry time are our big house bank and/or electric draw times. To that end, we run the genset during these periods, which pretty well keeps the house bank charged up. A Li bank used similarly to what you are finding, may indeed be in our future. If nothing else just to have a higher house bank charge rate utilizing existing equipment.

Here is the $64 question. For blue water travel and long periods away from dock, what redundancies would you foresee? Both a LFP and lead largely independent battery banks or --?

I don't think I would change much of anything. If traveling long distances, while underway the lead acid starter bank is online and the Li bank off. At distant anchorages Li on and Pb off. I guess I am comfortable enough with the LiFePO4 chemistry that I feel that if they aren't over charged there doesn't seem to be anything more to go wrong with them than with the AGMs they replaced. All the horror stories I have read involve not paying attention to the charging, surge voltages from solar, or installations that are heavily dependent on the skill of the DIY person whose project it is. I could be caught short if Lithionics knows less about this technology than they seem to, but I don't think that will be the case.

 

[john61ct]

Yes, buying from a top-shelf vendor like Ocean Planet and letting them install/integrate with all the boat's electrics should buy a lot of peace of mind.

But LFP still isn't for someone who doesn't want to have to know or think about their system, Maine Sail says he turns down a lot of customers like that, should stick with lead.