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

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. ;)

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.?

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.

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).

First, do not charge the cells to 3.7, especially at that low rate. Stop at 3.55 or 3.6 at most.?
Second, the math is the math. As others have pointed out, if you parallel all the cells, ?280ahx16=4.480ah at 3.2v nominal. If they were completely discharged, it would take 1,280 hours to recharge at 3.5a. Figure they were at 50%, it would take half that many hours, 640hrs.?
When I was doing this, I took a 30a, 12v charger and brought 12v nominal, 4 series, 4 parallel ? to 3.45v (roughly) per cell for a total of 13.8v, then paralleled them all and charged to 3.55. I hooked up the 12v charger without a BMS and let it go but had a timer on my phone to check it every hour or so and did not let it run overnight. ?Don’t do that, it’s risky!
Even doing it that way was 280ahX4=720/30=24hrs, though I think it only took about 12hrs, so presumably the cells were at about 50%.

No need to let them sit paralleled of you’re going to charge them, that’s just a waste of time unless that’s your only balancing strategy.?
I have also built some packs from used cells and just stuck them together at whatever state of charge they were at, but used a 4a active balancer and let it balance over time while using it.?

anton

there is a relatively new youtube channel called Fantasia Sailing (from Australia) that shows him running and comparing his cat with one diesel and one electric motor. He does speed and power tests each by itself. I know your cat is probably much heavier than his but still the best comparison around in my opinion.

?

Indigo Lady is a sailing cat converted to an all electric power cat that should be somewhere around the Caribbean. It doesn't seem like their cat is very efficient to me. they have a huge solar array and huge battery packs and seems like they only do around 60-70 miles a day. I think they need a prop change

Peter

By now I’m sure you have got your batteries charged but I will try to explain for others to maybe learn from.

For a battery to charge, the charger voltage must be higher than the battery voltage so that current will flow into the battery.

Usually, the larger the voltage difference, the larger the charging current. This is why most chargers that are set on 3.6 volts are connected to a battery that has 3.2 volts will only show enough voltage to reach the maximum current the charger can deliver at the immediate resistance of the battery (I wanted to say “current” instead of “immediate” but it would be confusing). This resistance in LFP batteries changes as the battery charge changes (and can be different between batteries). This is why we have to have smart battery chargers to keep changing the charge voltage as the battery voltage increases.

If the actual battery voltage while being charged is 3.20 the charger and or display might only show 3.30 (or similar), but as soon as you turn off the charger the battery voltage will drop back down to near actual voltage then after about an hour it should be actual “resting” voltage.

As the battery voltage goes up while charging, so does the charge voltage but the charge amps stays the same. Then when the actual battery is close enough to 3.6 volts, the charger display should stop on 3.6 volts and then as the battery is charged more, the charger lowers the charge amps, and when it gets down to 0.1 or 0.2 amps the battery is fully charged.

When charging a LFP battery from discharged, the charge voltage will be between 3.1 and 3.35 for a long, long time compared to before and after these voltages.

Riding style will depend on who’s riding. ?Older people will most likely be more steady. ?Younger will be more erratic I would guess. ?Not going to let anyone be wild though! ?I will assume a mix to calculate power requirements once I figure out how to do it.

LiFePO4 (Lithium Iron Phosphate) is the same as LFP (Lithium Ferrophosphate):

?

?

I'm using 180Wh/Kg to arrive at ~250lbs.? That's the best gravimetric energy density for LFP that's widely available.

?

And yes, dropping your runtime requirement to half will reduce the battery weight by half.

?

There are more energy-dense battery chemistries available, but as you point out, those will not be as safe as LFP.

Thanks. ?Have seen that video and you are correct, would be way underpowered (is also very nice but very expensive).

Was planning on using LiFePO4 (assume same as LFP?) as I am reading they are supposed to be the safest. ?By eliminating the gas power head and gas tank I save maybe 112lbs. ?With the new motor, etc. that’d be almost a 200lb increase in weight which probably is not a great idea for this small boat. ?How are you figuring battery weight? ?Would 30 minutes halve the weight? ?You are not dealing with an engineer here and I am just beginning to educate myself on this stuff! ?Thanks.