To piggy back on what Tom said,
Its best practice to have two means of protecting batteries. On the charge side, the charger have the correct charge profile and the BMS is secondary and should only be used as back up in case the charger fails. On the discharge side, the motor controller/inverter should be programmed with the correct voltage settings and the BMS is the failsafe.
Unless you are charging at a high C rate (most of us in DIY electric boats are not) you do not need to worry about CVCC. You can just charge with CV and stop. Unlike lead acid, which prefer to be fully charged and even over charged occasionally, lithium prefers to be less than fully charged. They would be perfectly happy sitting at 50% SOC for years. If using a lead acid charger, turn off the float charge or make it as low as possible. Be certain it does not have an equalization charge. Overcharging lithium just once can and most likely will ruin them, sometimes in a dramatic way.
For lifepo4 I stop charging at 3.5 VPC. There is almost no capacity above that voltage. If you look at a discharge chart you will see what I mean. Lifpo4 voltages should not be confused with lithium chemistries with a 4.2 VPC cutoff
I typically use 90% as upper limit and 10% on the low end.
Matt Foley
Sunlight Conversions
Perpetual Energy, LLC
201-914-0466
On Tuesday, April 28, 2020, 09:40:12 AM EDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:
MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature. The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack. The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature. The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack. The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.
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