LiFePo4 for DUMMIES

[deckofficer]

Originally Posted by Maine Sail

If anyone knows a way to correct this drift in my Cell Log8S PLEASE let me know....

Is there any chance this drift could be temperature related? I know on my cells, they do give off some heat (not much, about 100* when ambient is 75*), and those small voltage sense wires for the Junsi could heat up and slightly change resistance.

[Maine Sail]

Originally Posted by deckofficer

Is there any chance this drift could be temperature related? I know on my cells, they do give off some heat (not much, about 100* when ambient is 75*), and those small voltage sense wires for the Junsi could heat up and slightly change resistance.

This is drift directly compared to a known calibrated instrument taken via A/B readings....

[folivier]

I thought the HP BMS alarmed at 14.2 and cut out at 15.0
It cuts out at 14.2 also? I have the Victron BMV 600 alarm set at 14.2 and the BMS alarms a few seconds later.
I may rethink using the cell logger as an alarm and just use it for information. I'm really interested in how fully charged I'm getting the battery shutting the charger down (I think) early.

[deckofficer]

I understand it was an A/B reading, but just for grins and giggles since you have noted these voltages under discharging conditions (warm), let all that battery mass go to ambient temps by letting it sit without charging or discharging for awhile and see if the drift is the same.

[Maine Sail]

Originally Posted by folivier

I thought the HP BMS alarmed at 14.2 and cut out at 15.0
It cuts out at 14.2 also? I have the Victron BMV 600 alarm set at 14.2 and the BMS alarms a few seconds later.
I may rethink using the cell logger as an alarm and just use it for information. I'm really interested in how fully charged I'm getting the battery shutting the charger down (I think) early.

High & Low Voltage Disconnect Levels
HVC = 14.2V
LVC = 11.6V

EMERGENCY Bank Disconnect
High = 15V / 3.75VPC
Low = 10.4 / 2.6VPC

[deckofficer]

Originally Posted by folivier

I thought the HP BMS alarmed at 14.2 and cut out at 15.0
It cuts out at 14.2 also? I have the Victron BMV 600 alarm set at 14.2 and the BMS alarms a few seconds later.
I may rethink using the cell logger as an alarm and just use it for information. I'm really interested in how fully charged I'm getting the battery shutting the charger down (I think) early.

What is the cell's resting voltages after you terminate charging early? If it was during the taper, you might have more in than you think. I'm charging at 14.6 volts and at the first sign of current taper the cells are better than 95% filled. I'm used to LA and when the charger started to taper on them they were still a long time from being filled.

[CharlieJ]

deckofficer Post #120-
I have found that the Victron Quattro and Phoenix Multi-Plus families of inverter/chargers provide the most flexibility in programming by computer including a LFP "Assistant" for integration with a BMS.

Their Phoenix Inverter is also programmable by computer and I have one in my shop but have not programmed it yet.

[folivier]

I think I may be confused on the charging requirements. Balqon recommended to set the charging at 14.0 volts and that is what I've tried to set on my inverter. But at the end of the charge the voltage goes over 14.2.
Please correct me on my thinking: If I want a target voltage of 13.8 (or whatever) then at the bulk phase what should the voltage be? Is the voltage important here?

Then in absorb phase the current will slowly reduce as the battery approaches full charge and the voltage will rise. But should the voltage be 13.8 the entire time? Or is it ok for the voltage to be about 13.5 then reach 13.8 at the end of the charge?

Thanks for setting me straight!

[folivier]

Here is a rundown on how I'm charging now, started at 75% SOC:
13.66V @ 98amps bulk charge for 45 minutes
13.70v @ 83amps absorb
13.80v @ 100amps
13.87v @ 80amps
14.02v @ 77amps
14.11v @ 52amps
14.21v @ 38amps absorb for 2-1/2 hours
14.24v # 30amps BMS alarm, shut off charger before going into float
Resting voltage after 15 minutes: 13.6

[deckofficer]

Originally Posted by folivier

Here is a rundown on how I'm charging now, started at 75% SOC:
13.66V @ 98amps bulk charge for 45 minutes
13.70v @ 83amps absorb
13.80v @ 100amps
13.87v @ 80amps
14.02v @ 77amps
14.11v @ 52amps
14.21v @ 38amps absorb for 2-1/2 hours
14.24v # 30amps BMS alarm, shut off charger before going into float
Resting voltage after 15 minutes: 13.6

For what I can gather from the above, your inverter/charger is capable of 100 amps charge current. I sure don't know why at 13.8 volts it returned to 100 amps, but I'm fairly certain that the resting voltage of 13.6 volts, which is 3.4 volts per cell represents 100% SOC.

When my 50 amp charger tapers to a 5 amp rate, my cell voltages with charger still on is around 3.55 or 14.2 pack voltage.

My resting voltage after a full charge is 13.52 volts or 3.38 volts per cell. It took awhile to dig this up, so I'll repeat, if your resting voltage is 13.6 volts, your bank is in fact fully charged.

If you want to do a capacity test to confirm your state of charge, pull 800 a-hr from the bank and then check resting voltage with no loads. Pack voltage should be close to 12.88 volts. Since you have such a large bank, if your inverter can handle (2) 1500 watt space heaters, that would be a good load. Check the amp draw and divide into 800 for the amount of hours you need to run the load to get to 80% DOD. With two heaters you should be able to complete the test in just under 4 hours. Does your inverter display battery input amps? If not, do you have a Amprobe to check amps?

[deckofficer]

folivier,

Of course if your inverter is only rated at 3000 watts, or your battery cable run is long or not 4/0 gauge, just run a single heater, it will be easier on the inverter and cable run. It will take twice as long, but your battery bank doesn't have the limiting factors of the inverter and cables. Your bank would have no issue producing 3000 amps, can't say the same for the inverter and cables.

[rjdives]

I have been talking with a guy here in Florida that is a dealer for lithium batteries. They have been using them for a couple of years on charter cats in panama. They come in 12, 24 and 48 volt. Here is the 12 volt 400ah spec sheet. The batteries come with built in Individual cell temp and voltage monitoring, active shunt cell monitoring, charge enable(12.5v), over discharge protection (10v), over temp protection (enabled 140f) SOC & DOD monitoring and short circuit protection.

Here is Alan's contact info



Simplicity Marine Products, Inc
635 43rd St, Blvd. West
Palmetto, FL 34221 USA
Phone941) 722-8475
Fax727) 499-7457
Email: Simplicity@Simplicity-Marine.com

[Blue Skye]

Mainsail, I hope you know 99% of us that have read your many posts on LiFePO greatly appreciate it Keep up the great work!

[CAELESTIS]

Perhaps a new battery source??

Tesla Plans to Build World

[deckofficer]

Originally Posted by CAELESTIS

Perhaps a new battery source??

Tesla Plans to Build World

Well, maybe. If you don't mind using a couple 1000 of the 18650 cells that Tesla uses. If memory serves, the 300 mile Model S uses about 7000 cells.