Typical Volt Levels LiFePO4 battery pack from G.M

[windhfred]

Yesterday I took a longer trip with my E-bike (picture will be added later). I use the G.M 36 V battery pack. Have anybody some typical values for the voltage starting from fully loaded battery to almost empty ?
I measured a fully charged pack to 43,1 V, and after a 15 miles trip with some pedal assist I got 38 V. Are this values normal ? My charger works fine and all 12 LED:s  lit after 2- 3 hours of charging.

[Leslie]

It depends on the amp hours of the pack.  The GMV 36 is a little little pack is it not? so I think your bike is going well...

I'm no lifepo4 expert but 15 miles/24 kms isnt too bad for a little pack... not sure about start voltages for lifepo4, anything over 42+ for sla's volts sounds good.. your voltages look great after a good ride.

[Leslie]

http://visforvoltage.org/forum/3507-lifepo4-quicker-charge


  On either charger, the end voltage at full charge is 44 to 45 volts. I had read on another thread, maybe at enless sphere, that charging lifepo4 with simple sla chargers was ok, but resulted in a slight undercharge.


It seems something may be a little odd here.  Im not sure if he means during full charge or float charge here.


Ive never owned lifepo4 but with sla's Full charge with my charger is 44 volts and float sits at 42 volts and I have new SLA's so they sitting rested with no float at 40v.  Things tend to improve with SLA's when the plates gets some surface area etched into them...

Im not sure the same goes with lifepo4's but maybe take it obn a few short runs and charge em up and see if it improves..

 

[windhfred]

I am running with the small pack with 10Ah rate. What I meant when I said full charge is the voltage level (unloaded) after the charger is removed. I suppose this is what you call the "float voltage" ? And I am using the included Lithium charger as well, so I really hope this charger brings my pack up to the correct level of charge, the pack seems to work fine so far..

[Lanchon]

typically lifepo4 cells should be charged CCCV to 3.6V and then floated at 3.45V. 43.1V/12cells=3.59V/cell, so it's fine. cutoff ranges from 2.7V to 2.3V or even as low as 2V for some tough cells. (38V/12cells=3.17V)

[Leslie]

Yeah I thought as much. 43+v seemed pretty nice to me. 

Do lifepo4 improve a little on the first 3 months of use or is it a slow downhill ride?

Oh and another thing is to test each 12volt battery and see if one is dying out faster than the others. You may find a bad connection like I did once.

Some moron was kicking at my bike and one of the terminal connection got damaged.  Next thing you know I,m getting three hour charges and voltage cut outs after 15 kms.  One of the batteries was draing down to 11.7 volts while all the others were sitting on 12.6 volts.

                       <bad connection 
        T_____T--/--T______T----T_____T
 -0v   |_12.6_|      |_ 11.7_|     |_12.6_|  +36.9V
       
current flow -->

The 11. 75V battery is in SLA EV terms fully discharged...

[OneEye]

Many LiFePO₄ cells show a short period of improvement when new, then the long decline as you burn through the recharge cycles.