As with you my traction battery and house battery are the same system. My Victron Quattro charger is set to Change "bulk" to 56 volts and "float" at 53.4 volts. This is with a pack built from 16 LiFePO4 cells in series. At 53.4 volts. The voltage each cell sees is 3.33 volts that is also the resting voltage of a charged LiFePO4 cells. And is a safe float voltage for this type of lithium chemistry. The charger controls voltage to protect your battery at the pack level. The inverter and none critical systems would stop using power at 42 volts.
The BMS exist to protect the CELLS should one get out of balance or fail. For mine: If a single cell should drop below the Low Voltage Cutoff it is set to 2.5V at 0C temp, 2.6V at 25C temp and 2.7V at 50C temp, linearly adjusting itself across the entire temp range. Should this be breached it alarms and signals my inverter that it should stop drawing power from the pack. I don't believe the traction pack should disconnect for safety reasons so I as a human need to head the alarm. I would risk my battery over my Boat's remover-ability. The High voltage cut off per cell I have set well above what my charger would ever send at 3.56 volts.
So to summarize my charger is in charge of protecting the battery at the pack level, and does most of the hard work. My BMS is in charge of protecting the battery at the cell level. They rarely disagree with each other but if they do the BMS would trump the charger. This works because my charger has intelligent dry contacts.
A cycle is an abstract thing. It would take a large amount of shallow cycling to equal one battery cycle with lead or lithium. There are some who think ripple in the current supplied to LiFePO4 cells via floating could be harmful over time. I regularly cycle my pack from 1/3 empty and full, and also float them for months on end. I still have nearly 100% full capacity after 7-8 years of heavy use. On cells with a calendar life of a decade. One of the reason I got such a great deal was my cells where stored for two years at half voltage before I got them. They truly do tolerate a ton of abuse.
Hopefully this is helpful
James Sizemore
On Sep 20, 2018, at 3:31 PM, clh5_98@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:
James and all,I'm struggling to see how the charger works with a BMS in the mix. I understand the BMS sends a signal to the charger to "turn on" when the bank voltage, or SOC drops below a configured level. I can understand if one just uses the drive system to get out and back and then hooks back up to shore power to charge the bank back up. My system is more complex than that, though. I have 3X48V to 12 V DC/DC converters. I have 2X12 VDC refrigerators, and all the other 12 volt stuff that a boat has. Because of this, I'm constantly consuming from the batteries and/or the charger regardless if I'm using the drive system, or not. It seems to me that with a BMS and LiFePO4 cells my batteries would be constantly cycling between fully charged, to somewhat discharged, back to fully charged. Is this OK, or does it count as battery cycles and lead to early demise of the cells? Right now with my FLA bank spending most of the time floating on the charger, all DC loads are just picked up by the charger.Chris
__._,_.___
Posted by: "james@deny.org" <james@deny.org>
| Reply via web post | • | Reply to sender | • | Reply to group | • | Start a New Topic | • | Messages in this topic (70) |
Have you tried the highest rated email app?
With 4.5 stars in iTunes, the Yahoo Mail app is the highest rated email app on the market. What are you waiting for? Now you can access all your inboxes (Gmail, Outlook, AOL and more) in one place. Never delete an email again with 1000GB of free cloud storage.
SPONSORED LINKS
.
__,_._,___
No comments:
Post a Comment