So, I have an AC-34 HPEVS motor and a Curtis F6a controller. 48 volts. Eve LiFePo4 batteries. 3.2v and 280ah each. 16 of them. Have had them for three years in storage at 55-65 degrees. They were all 3.2v when I got them three years ago and 3.2 when I put them in the boat this spring. I have a JK BMS. Yesterday, for the first time, I put the boat in the water and they got their first true loads. ?The power is crazy and I have a 28000 lb ketch sailboat with a full keel. Had really good power, which made controlling the boat so much better. However, after 1/2 an hour tooling around at fairly low rpms the app on the JK BMS said cell/module #6 voltage was dying and after another 10 minutes it was down to nothing/zero volts. Still had enough to motor. Docked the boat and tied it up for the night. Went back the next morning, with a spare cell/module I had, and measured the voltage on #6. Had no volts. Nothing. Took it out and replaced it with a spare, which was reading 3.2v.? We were all set. Headed back out to the mouth of the harbor humming along at about 1500 rpms. After 20 minutes the motor sounded like it was losing power and sure enough it was. Opened the App and now two more cells were down to zero on the app and the Curtis display said Fault Code L23 - low battery voltage. Battery bank was down to 36v total. A slight caveat. I have a Honda 2200eu generator for when the battery runs down and I'm motoring and the batteries needs additional juice. Plugged the generator into the shore power outlet fired it up - and noticed that when I did that the motor actually lost a little power. At least that's what it seemed like to us. ?So, anyone have any experience losing cells/modules after they get put under loads and which showed 3.2v before.? Is it possible/likely that they simply are bad cells/modules? I originally bought 32 of them and it seems to me that losing 3 of them, when they've been in dry climate controlled storage, is not a good percentage of bad cells/modules. I have three more spares and will replace the ones that are reading zero voltage and see what happens. But I am, also, wondering if there is something I am doing, or not doing, to cause this? As I am new to this that is definitely a possibility but I don't know what I did, or didn't do to cause it. Seems like all the cells would be affected if I did something. Another thing to note is that I have a 24v battery bank for the house electronics that get their charge from the 48 volt bank, and I have a 12 volt battery bank that I use for the electric trolling motor for the dingy. All of theses cells/modules are, also, the same Eve cells that were bought at the same time as part of the same order.? I have used the 24 volt bank a little and used the trolling motor a few times. All of these cells are reading decent voltage and no cells/modules appear to be tanking in the 24v bank or the 12 volt bank. Any ideas would be greatly appreciated. My first time doing this so I am trying to figure this stuff out as I go along.

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Peter Knowlton

South Dartmouth MA

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Sounds like you didn’t balance them or charge them after you received them? Voltage is almost meaningless with LFP. You can have one cell at 25% SOC and another at 85% and they with both read 3.2 volts.?

The cells were probably fine. The ones that hit 0 volts may now be toast.?

I will try to bring them back. I had thought from what I read, and what some have told me, that since the voltage for each battery was nearly identical there was no need to balance them. Looks like that was bad advice. I am going to try and bring the zero's back and will be balancing the bank. Thanks for that.

Thanks Jerry, Gives me hope. I just might try that. I have a couple that are below 2, as well. First it was the #6 module, then #5 went, and #12 went about the same time as #5. Do you have the link for that DC power supply you got?

Peter,
Another possible failure point (there are many different types of failure points): each battery connection. Make sure each connection to each post of each battery has the same high amperage surface contact area, the same cleanliness, the same torque value on the nuts or bolts, the same operating temperature, the same washers, the same lug count, etc. The basic concept is that you are trying to drain and charge each battery identically. If one of the posts has a higher resistance to electricity flow (dirty, loose, wavy washer, different size washer, wavy lug, worse crimping of the battery cable to the lug...) that post will run hot, which changes the internal resistance of the battery, which further exacerbates the imbalance, which further drains that battery, which can quickly and permanently change the internal chemistry of the battery.
Most of the time, these slight imbalances amount to a hill of dry beans (dry beans self-level pretty well). But if you cook the beans, the hill of beans can be significant.
The BMS was telling you to stop, in a language that assumed you were an electrical engineer with deep knowledge of LiFePO4 battery chemistry. Sometimes safety requires us to kill the batteries to save the boat, so the nice thing about your BMS is that it let you kill some batteries to save yourselves.
One really helpful simple tool is a $30 temperature gun. A more expensive but automated option is to install calibrated temperature probes on each battery terminal, and feeding that information to a BMS that would alert you to temperature imbalances.
One gallon of diesel compares to roughly 40 kWh of energy. You have roughly 4 kWh in your fully charged healthy 16 battery pack (4,480 under perfect conditions, which they never are). But your e-propulsion is ideally about 5 times more efficient than diesel. This means your 4 kWh pack, times 5 for efficiency, equals 20 kWh diesel power equivalent. So going out with your (16) 280Ahr batteries fully charged is like leaving the dock with 1/2 gallon of diesel fuel. You could go really slow (~1 knot) for ~10 hours, or really fast for ~10 minutes, but then the batteries need charging. Your 2200EU generator allows you to travel at ~1 knot continuously if the generator is running continuously. These are very approximate water speed estimates, not GPS speeds, and are influenced by literally hundreds of variables about your sailboat, the sea state, the weather, people moving around on your boat, etc.
This is the ballpark you are playing in. It is not an argument for or against e-propulsion, just the current state of electricity storage and creation.
My arguments for e-propulsion are:
low operating cost
low maintenance
low stink
low sound
low space requirements
low emissions
high reliability
high precision of thrust
high thrust available

high longevity
high tech
high investment in a better tomorrow
The hard part: e-propulsion often comes with a high learning curve. Many of our ancestors died during the learning curve of gasoline, but they gifted us cultural wisdom about the dangers of gasoline. We are gifting our progeny with the cultural wisdom of clean energy use. Don't kill yourself in the process: each battery can be lethal.

Thanks for all your suggestions and comments. I am following through with them all. However, I do have one fine question before I begin the balance. The specs on the Eve 280ah cells says nominal voltage 3.2v. However, I have seen others, Will Prowse among them and he seems like a reputable person, balance theirs at 3.6. Since I’ve never seen any of my batteries register more than 3.30 and ALL of them from the day I got them in the 3.28 to 3.29 range I am reluctant to put the current for balancing up to 3.6. I cannot find any other specs for these batteries other that that nominal 3.2v. Should I just balance at 3.2 or should I go higher? Since I screwed them up the first time I am being very cautious and before I plug anything in or hook anything on I’m making sure to know just what I need to do and what settings need to be to do a successful balance. Thanks so much.

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peter

3.65V is 'full' for LFP cells.? By bringing all your cells to that voltage (usually in parallel), you're more sure they are at the same energy level (assuming capacity-balanced cells).? This approach is referred to as 'top-balancing'.

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The problem with 3.2V is that's on the very flat part of the charge/discharge curve for LFP chemistry.? You could be at 20% SOC or 40% SOC, depending on very small voltage differences that would all read as 3.2V on a not-very-precise-or-accurate meter.

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There is also an approach called bottom-balancing, which I've never used, that tries to achieve the same result by starting at 0% SOC (or some other very low number).? I don't like bringing cells down that low (it can be hard on them), and it's not as well-defined of a voltage (2.5V, 2.75V, ...?).? 100% SOC is easy to know you're at, based on the cells not accepting further charge beyond just a trickle (C/100 say).

On Mon, Sep 30, 2024 at 06:17 PM, shredderf16 wrote:

The top balance works. About 3.6v in parallel with small DC power supply. Might take a week to 10 days.

I use this current-controlled power supply to speed up top balances (over 100 amps at 3.65V (voltage adjustable)):

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Peter

OK, first, your BMS is not doing its job.

The primary job of a BMS is to disconnect the battery if any of the individual cells go lower or higher than what the settings are, and / or the cells get too cold or too hot (heat not usually an issue for LFP / LiFeO4). So if one of your cells went below 2.5V it should have disconnected the whole pack, and then none of your cells should have went to 0V.

There is a unique problem with a BMS that disconnects the propulsion battery on a boat, it isn’t hard to figure out. It is for this reason that I do not have a BMS on my boat. I have a settable low voltage relay that controls a big 300 amp relay to disconnect the batteries when pack voltage gets too low, along with a 300 amp circuit breaker to bypass this relay in emergency situations. My solar chargers and shore power chargers are set to stop charging when voltage gets too high, and I don’t do regen, yet. And I don’t have any temperature protection.

There are 2 main types of BMS; 2 port and 3 port. The 2 port one only has two big connections (one to battery, the other to the load), the 3 port one has three big connedtions (one to battery, one to the load, the third one to the charger). The 3 port one with the separate charger lead should keep the load connected while disconnecting the charger when fully charged. If you have a 3 port BMS you should make sure that you don’t have the charge and load ports swapped.

Some BMS’s also balance charge the cells. This usually happens by sending current from the highest voltage to the lowest voltage cell. Most BMS’s balance charge current is very small and most of them try to balance all the time. Balancing all the time can be a problem, if your battery gets low then it will drain itself and should cut off.

LFP batteries do not usually need to be balanced while being used because the voltage variance should be very small. Other Lithium Ion batteries (not LiFeO4) do need to be balanced while being used because they can have larger voltage variance and can potentially shut down prematurely if one cell drops below settings due to voltage sag while being used.

I think a lot of people now think that “top balancing” is the best way to go with LFP batteries (check out “off grid garage” on youtube), but to do this you need a BMS that can be programmed to only balance when the voltage gets up to a certain voltage. Most BMS’s don’t have this programing capability, but most have the capability for the balancing to be turned off and on with an accessory switch.

?This start balancing voltage will vary according to who or what you believe but should be above 3.2V (working voltage) and obviously below 3.65V (max voltage). I use 3.4V start balancing and only charge to 3.6V my two 48V -100Ah packs.

In my opinion, the balance charging current for a BMS that has balance charging is usually only good for small Ah batteries (like 50Ah or less). Some people use a separate piece of equipment to balance charge, this is what I do. I used to have a 5 amp passive ?balance charger and I had to install a switch to turn it on and off, or it would just drain the battery. Now I have a 1 amp active balancer (made by Daly) on each battery pack. I am not a Daly fanboy at all (most of their stuff fails more or at least as much as anything else) but I tried one of their 16s 1 amp Smart Equalizers because I saw a few reviews that people were happy with them on their 48V-300Ah battery packs. The “Smart” ones have Bluetooth. The first one worked well enough that I bought another one. That was a year ago and I am still happy with them.

When you start fooling around with low voltage (3-4V) batteries you HAVE to get a meter that reads out to 2 decimal places. 3.2 volts is not good enough, 3.24 volts IS good enough, 3.249 volts is even better (but a 3 decimal place meter is quite pricey).

I agree with your general opinion of Daly products, and I usually avoid them like the plague.

But I did find a few reviews that said the smart balancer worked on the larger cells.?

I was skeptical, especially of the 1 amp balance charge being able to balance my 100 Ah pack, but I wasn't happy with the "always on" 5amp balancers that I had.

The Daly one did intrigue me with the bluetooth option (with a dongle) and it had the changeable settings, and it was the cheapest one that did what I wanted.

I am a cheapskate so I got it on Amazon so I could send it back if it didn't work for me.

However, it did work for me, so I bought another one and both have been flawless for about 11 1/2 months, and they do balance my cells.

I have a JK BMS on the 48v motor bank, 24v house bank, and 12v outboard electric motor bank. Both the 12v and 24v work fine and I don't use them for balancing. I inadvertently killed the JK BMS on the 48v bank so have gone back to what I originally had, a Dilithium Designs BMS. We'll see how that pans out. Doesn't balance the bank, which is ok with me. I just want to keep an eye on each cell.?

Thanks for this. After my initial post and comments from members I decided to break down the 16 cells into groups of 4, charge them with a Victron 12v charger to 3.5 volts and then put them all back together and balance them to 3.642 with a low amp power source that I got from Amazon at a members suggestion. (Balancer wouldn't charge them higher than that that but figured .008 from 6.5 was fine.)? Put them back on the boat a couple weeks ago and so far so good. I think I am getting the hang of it now, thanks to this group of wonderful advisers and experts. My learning curve is slow but steady. ;)

As mentioned above, your BMS is not functioning properly if it let you drive any cells lower than 2.5v.?
also, and sorry if this is dumb, but you never mention charging voltages. It almost sounds like you noted the batteries at 3.2v per cell and called them charged. Generally when sold, these cells will have 50% charge or less, at higher states of charge (and temperature) ?they lose life faster.
They will not be close to fully charged unless you get them up to at least 3.45-3.5v per cell. ?After that, they will come back down to a resting voltage of about 3.2-3.3, depending on several factors including temperature and condition. Going to 3.65 regularly is hard on them, I go to about 3.55, which does not fully charge them unless I do it at low amperage, but that is an open debate with a lot of detail and opinion. 3.4-3.6 is reasonable. Make sure your solar charging doesn’t raise it to 3.6 and hold it there indefinitely, that will kill them too.?
there are BMS that you can adjust parameters like max voltage, min voltage, balance voltage, etc.?

I have used active balancers to get all

cells more or less balanced and had good luck.?

anton

Nominal is a funny word. The relevant definition for batteries is, "Existing in name only; not real." For instance a "12 volt" lead acid battery is the name, but the voltage should be 12.5v or 13.7 or 14.4 when fully charged or when on life support or when charging (respectively). These voltage values change by manufacturer, by sealed or flooded, lithium or lead, by intended use case, by longevity requirements... the list really does go on and on. So point 1 is to start with the particular recommendations of the manufacturer for fully charged voltages and for storage voltages and for charging voltages.
Point 2: the idea of rust, deterioration. Humans deteriorate; metals deteriorate, some faster or slower than others. For every battery chemistry, there is a slowest-deterioration temperature and voltage. That voltage is chosen for how lithium chemistry batteries are shipped and stored. If the shipping voltage was any higher or lower, the batteries would degrade internally faster. So when you fully charge the batteries, use them quickly in hours or days, not slowly in weeks or months. The same use-it-or-lose-it idea also applies to batteries below their shipping voltage. In other words, for optimal longevity, minimize time spent above or below the shipping voltage. The bigger the deviation from the shipping voltage, higher or lower, the shorter the overall lifespan of the battery. That is why many people normally only charge to 70% or 80% of full, and then only right before they are going to use that particular electric vehicle or device. After use, leave at or very near shipping charge voltage. If you need a 100% charge every once in a while for maximum range, all the better (because it helps the BMS stay calibrated).
Question: while a lithium chemistry battery is being drained or charged, does it also degrade, or does it only degrade while sitting idle? I assume the active chemical reactions of charging or discharging take precedence over ambient degradation, so I'm guessing lithium batteries only degrade while sitting idle. Any chemists?

If you read too much about lithium batteries it just makes you paranoid!

I am not a chemist, so take this with a grain bag of salt, but from what I read I understand that lifepo4 and NMC batteries have a calendar life, which is negatively affected by storage at higher states of charge and higher temperatures but also a cycle life which is negatively affected by charging to higher voltage and discharging to lower voltage. and of course number of charge cycles. What constitutes a charge cycle is hard to pin down. 100% to 0 would definitely be one, but 70-30, then 90-50, then 65-36, etc.? I imagine 100%-0% counts as 1, but does 70-30 counts as .4 of a cycle? I doubt it’s linear and likely only quantifiable by extensive testing and only valid for that battery types size etc.?
The thing that makes me paranoid is that I read somewhere that if current is pushed into a lithium battery, even a tiny current, even if the voltage doesn’t go very high, if done long enough, ?it will overcharge and ruin the battery. ?That is to say there is no safe “float” voltage. Once charged, stop charging until some energy has been used. So it seems to me that traction use, where the battery is charged then disconnected and used, is a simpler situation, but solar charging must be setup carefully so as to not hold the batteries at a high state of charge.?
I have decided that the best policy is to avoid holding at high voltage ever, but just use as necessary and convenient and not worry too much. Have a large enough battery that you don’t have to use 100% of its capacity every day.?
With lifepo4, if not held at high voltage with solar, service life should be decades if rarely drawn down below 20%.?
anton