Relationship between voltage of stored charge and % capacity, Lithium and Lead

[Refueler]

They do mean lithium ion. The vast majority of their products use lithium ion batteries, with the exception of one which uses LiFePo4.

It is easier to use voltage to measure state of charge with lithium ion as the charge curve is not as flat as with LiFePo4 which has vary little variation except at nearly full or nearly empty.

LiFePo4 has sufficient gradient to voltage curve to give an approximate state of charge. ..... see table I posted earlier - not my Table - thats from a Battery Business ... so maybe they might know something about it ??

 

[noelex]

If you purchase a solar generator you do need to be careful about the type of lithium chemistry used.

LiFePO4 is the better (some would say the only) choice. Some companies make different models with both LiFePO4 and other lithium chemistries (mainly NMC) so make sure you do your research before buying.

 

[Sandy]

Check the battery capacity is correctly set to 390Ahrs on the Victron monitor.

It is.

 

[Sandy]

State of charge depends on an accurate measure of capacity of the pack, an accurate enough measure of power in and out (Coulomb counting), and a monitor that has been synchronised regularly enough to 100% when the battery is fully charged (based on tail current at target voltage). LFP has a Peukert value close to 1 so It should be easier to get an accurate figure but it does require users to regularly synchronise to 100% as even the best monitor drifts over time.

Thanks. I'm going ashore next week and will have access to shore power. Over the winter I can so some resets.

 

[Refueler]

If you purchase a solar generator you do need to be careful about the type of lithium chemistry used.

LiFePO4 is the better (some would say the only) choice. Some companies make different models with both LiFePO4 and other lithium chemistries (mainly NMC) so make sure you do your research before buying.

The main difference other than the chemistry - is that each variant has a different terminal and nominal voltage., Not only do they vary between the chemistry's ... but as example LiIon can be in 3,3v .. 3,6v ... 4.2v cell form.
So check label for Chemistry AND max voltage rating.

Take note that Li cells - when reported are often stated at nominal - which is not the max figure we need to know ... example LiPo standard version is nominal 3.75v per cell - but full charge 4.2v per cell.
This does not help average punter when he's shopping for cells !!!
NOTE the word NOMINAL ... not NORMAL

 

[Supertramp]

Some time ago I found a thread on here about lead acid batteries which contained a table showing the expected voltage at different SOC and with different current loads (I guess using data from graphs). I have it laminated and next to my battery monitor as a reassurance check that the battery voltages under load and at less than 100% SOC are in line. It is at least consistent for my setup.

Presumably you can do similar for lithium?

 

[Kelpie]

Some time ago I found a thread on here about lead acid batteries which contained a table showing the expected voltage at different SOC and with different current loads (I guess using data from graphs). I have it laminated and next to my battery monitor as a reassurance check that the battery voltages under load and at less than 100% SOC are in line. It is at least consistent for my setup.

Presumably you can do similar for lithium?

Yes, bit it's far less useful.
LiFePO4 cells will sit at about 3.3v when they are between 30-70% SOC. The voltage changes a bit more noticeably outside of that range, and changes abruptly in first and last 5%.
Total cell voltage variation is about 2.5-3.7v, but you don't really want to go outside 3-3.6v in normal use.

 

[Alan S]

Yes, bit it's far less useful.
LiFePO4 cells will sit at about 3.3v when they are between 30-70% SOC. The voltage changes a bit more noticeably outside of that range, and changes abruptly in first and last 5%.
Total cell voltage variation is about 2.5-3.7v, but you don't really want to go outside 3-3.6v in normal use.

Am I correct in assuming that is 3 - 3.6V actually in use, not resting? There will be a big difference.

 

[Poey50]

Am I correct in assuming that is 3 - 3.6V actually in use, not resting? There will be a big difference.

Not as big a difference as with lead acid.

 

[Kelpie]

Am I correct in assuming that is 3 - 3.6V actually in use, not resting? There will be a big difference.

There's not much voltage sag at all in use, if measured at the battery.

 

[Refueler]

Not as big a difference as with lead acid.

Depends on load ... a high load will cause voltage sag regardless of battery chemistry. Its also depends on the discharge C rate as well ...

 

[allendick]

I have both the Heart monitor and the Smartgauge on the same 500 AH AGM battery setup.

They seem to agree pretty closely much of the time after the Smartgauge has had time to learn after installation or reset. The Heart device drifts a bit over time. Neither is perfect.

The SmartGage only measures voltage and is connected with three light wires. The Heart device has a shunt and counts the current coming and going.