Sail Life has a discussion of one option to solve some of your concerns. It’s a little mor DIY than drop-in batteries, but the BMS and external alternator regulator help solve the charging disconnect anyway -
Great, thanks.Sail Life has a discussion of one option to solve some of your concerns. It’s a little mor DIY than drop-in batteries, but the BMS and external alternator regulator help solve the charging disconnect anyway -
Thanks for the video. This guy mumbles and speaks too quickly for me, and he's a bit scattered. Also, his battery compartment looks like a bowl of spaghetti. But, there's some good info in there. I have to back up and replay several times to get what products he's mentioning.Great, thanks.
I watch him every week so maybe I’ve gotten accustomed to his patterns. The battery system was also very much a work in progress at that point, thus the spaghetti. His finished work is much cleaner.Thanks for the video. This guy mumbles and speaks too quickly for me, and he's a bit scattered. Also, his battery compartment looks like a bowl of spaghetti. But, there's some good info in there. I have to back up and replay several times to get what products he's mentioning.
REC and Battery Ballance X2 are two that I know of. I also understand that you can also get the control interface from most any BMS that has a RS485 port with some additional hardware, but I do not know how to do it.That's good to know. Now if I could only find them!
Whoever came up with the term "Battery Management System" to describe the actual purpose of the device is responsible for a lot of the confusion here IMHO. The typical BMS is really just a CPS (Cell Protection System). It doesn't manage anything, it just keeps the cells from being put in a dangerous state. You could argue that balancing is management... maybe.I'm gradually absorbing knowledge about LFPs and BMSs. It's funny, some things that are probably common knowledge just dawn on me and I say, "Oh, yea, that's how it works, or that's how it's going to happen."
Maybe I'm wrong, but it occurs to me that a couple of aspects of BMSs aren't very desirable. One, in particular, is that the BMS will disconnect the battery in an overcharge condition. That means the alternator will be open, and without a zap protector or having a lead acid batter connected to the alternator you will zap the alternator. And, you will lose house power! Everything will go dark.
Second, there's no feature of a BMS I've been able to find that allows one to specify the desired state of charge in and the BMS will target that, including discharging the battery. You would need a load, of course, but none I've found can do this.
I guess I want a BMS that also manages the alternator and can control the application of an external load, like the AC water heater, for example, through an inverter.
Does anyone make a complete power management system for LFPs on yachts?
Still a bit naive here.
Thanks
Not allowed under either ISO or ABYC...I watch him every week so maybe I’ve gotten accustomed to his patterns. The battery system was also very much a work in progress at that point, thus the spaghetti. His finished work is much cleaner.
Here’s another perspective on blending lead acid with Lithium -
Your case of wanting to keep the Lithium bank at a partial SOC for extended periods makes blending with lead acid a little more troublesome. If you keep the lithium at a partial SOC the lead might be below full too, which would kill it pretty quickly. I guess you could look at the discharge curves and try to see if 80% on Lithium is acceptably close voltage to 100% on lead acid. If not you could treat the lead acid side as sacrificial, just there to protect the lithium, but that doesn’t seem very elegant.
You may have trouble getting the discharge current you need for starting from a Lithium bank that size. LiFePO4 is not especially well suited for high discharge current. For example even to 400AH bank suggested earlier says in the spec sheet it has a maximum output current of 300A for 3 seconds (200A continuous). Using that same ratio a 40 aH LFP bank will not come close to what you need for starting.a fairly small LFP bank, maybe 40Ah, that's always kept at 80%, charged from the house bank, and used for starting.
I think it depends on your usage and how long you’re comfortable running the engine to charge. Between refrigeration and electronics burning 100 AH per day is pretty achievable. That’s an hour of engine running per day to recharge. A bigger bank gives you more days before recharge is needed, but eventually you still have to make up the hours. Spend a few months on the boat and those engine hours add up. If you’re motoring between places anyway or you don’t mind the engine or generator hours then no big deal. But some choose to offset those hours with solar instead.I was also thinking, with the quick charging of an LFP bank, and the capacity increase compared to FLA, who needs solar?
I highly doubt that is the case! I'm going to do some research, but it strains credulity that a 40Ah LFP bank won't start a garden tractor diesel! I have a hand-held LiOn pack that will start my diesel!You may have trouble getting the discharge current you need for starting from a Lithium bank that size. LiFePO4 is not especially well suited for high discharge current. For example even to 400AH bank suggested earlier says in the spec sheet it has a maximum output current of 300A for 3 seconds (200A continuous). Using that same ratio a 40 aH LFP bank will not come close to what you need for starting.
As another data point, a BattleBorn 50 aH battery has these specs:I highly date that is the case! I'm going to do some research, but it strains credulity that a 40Ah LFP bank won't start a garden tractor diesel! I have a hand-held LiOn pack that will start my diesel!
It’s not an LFP limitation, it’s the BMS. Here’s a 60ah start battery:You may have trouble getting the discharge current you need for starting from a Lithium bank that size. LiFePO4 is not especially well suited for high discharge current. For example even to 400AH bank suggested earlier says in the spec sheet it has a maximum output current of 300A for 3 seconds (200A continuous). Using that same ratio a 40 aH LFP bank will not come close to what you need for starting.
Interesting. Unless you have external regulation I think typically you charge the AGMs with the alternator and use the B2B for the LFP (mine is set up that way). The APD should protect against a BMS disconnect, but won’t protect against overheating the Alternator or overcharging the LFP.I’ve added a B2B and an alternator protection device on the LFP I’m currently installing. The B2B will charge the other AGM’s I have in the boat. The alternator protection should keep the diodes happy.
Interesting, indeed. I'm new to the topic of LFPs, but I have some thoughts. I thought one of the great benefits of LFP was that it could take advantage of all of the output of high-output alternators, and in so doing charge up very quickly, reducing engine run time for charging. If you're charging the AGMs with the alternator you lose this advantage. If you're charging LFPs with AGMs, what advantage is there at all? You're just shuffling energy from one store to another with the consequent transfer inefficiency.Interesting. Unless you have external regulation I think typically you charge the AGMs with the alternator and use the B2B for the LFP (mine is set up that way).
Well, the system should be designed to protect against alternator overheating, especially with a high-output alternator; the smart regulator should do this; and, the BMS will protect against LFP overcharging, which is where the BMS disconnect comes from, no? In fact, I'm told some BMS's, or systems built with them, can avoid the disconnect by reducing or ending the alternator output (via field current control, presumably).The APD should protect against a BMS disconnect, but won’t protect against overheating the Alternator or overcharging the LFP.