What voltage for a 48v LiFePO4 & SLA charged & low?

[1000watt]

For my 48v 10ah LiFePO4

I fully charged my pack and the voltage is 59.33v
What voltage would be considered LOW?

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On my SLA (12v 12ah batts) 48v pack, I follow these guidelines:

CHARGED:
While charging - Full charge should show 55v (13.75v ea) [after charging and letting them sit for a while 53v (13.25v ea) is the normal fully charged voltage for SLA]

LOW:
UNDER LOAD voltage 42.0v (10.5v ea) [STOP AND RECHARGE]
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Thanks.

 

[TMaster]

Lifepo4

3.6v or 3.65v absolute max peak voltage per cell depending on the brand or type. (16 cells = 57.6v or 58.4v)( 48V configuration)
2.0v Low voltage discharge per cell, Athough many people use 2.5v because theres hardly any capacity left after 2.5v per cell anyway. (40v for the entire pack would be safe at 2.5v per cell)

It looks like your BMS or charger is pushing the limit on your Lifepo4 battery, Although it may be fine since its so close. You may wan't to ask about that.

SLA

12.6v to 13.4v Charged voltage after sitting for a bit. (12V SLA)
1.75v per cell Low voltage discharge, there are 6 cells in a 12V SLA battery. This amounts to 10.5v (42v for the entire pack, 4 packs *12v).

Note: Just because you see a total pack voltage, that doesn't mean each cell is equal, unless your BMS is really good!

My experience with Lithium polymer batteries for RC applications, when drained down the cells are usually not equal. Thats why is always a good idea to stay just above the LVC votlage to insure the lagging cells are not below that.

After searching on this forum for a while now, I've determined I won't be using a BMS with my lifepo4's with my new setup, to save money, hassle and the quality issues. I will use my balancing charger instead to charge each pack, and solder in the balance tap connectors into each pack. Put a voltage monitor on the bike to keep an eye on the voltage. Maybe even wire in a cuttoff relay circuit.

 

[Russell]

1000watt,

I also have a 48V/10Ah LiFePO4 battery and my charger also charges to 59.3V. After sitting for 6 days now unused that voltage has fallen to 55.0V. LiFePO4 batteries have a high surface charge that doesn't amount to beans capacity-wise which means the battery is full at anything over 3.35V/cell. This is not unlike SLA batteries where a 48V pack is charged to 55.2V (13.8x4) but the extra voltage quickly dissipates and the pack is considered full at 52.0-52.8V (13.0-13.2V x 4).

The discharge curve of LiFePO4 is so flat it's difficult to go by the resting voltage of the battery to determine the SOC. I have however kept a battery log since I got my LiFePO4 in September and suggest others do the same to keep track of their investment, it's also the best way to know what is normal for your battery. From that log here are representative resting voltages after some rides with the amount of Amp-hours used;

52.8V 2.8Ah
52.7V 4.1Ah
52.4V 6.7Ah
52.2V 7.3Ah
51.8V 8.3Ah
51.5V 9.0Ah

Now that I have these values if I only had a voltmeter I could get a rough estimate of my battery's SOC however I could never have gotten the data without a wattmeter to begin with and in my opinion it's an essential piece of equipment no E-biker should be without, but then you don't need me telling you this since you indicate you have a Watts-Up meter in your signature. The best thing to do then is to monitor your WU meter and keep the discharges to less than 80% or even 70% if you want maximum longevity from your battery. By the way the minimum voltage under load I've recorded for my 48V/10Ah battery is 42.90V and the maximum I've discharged it is 9.3Ah and neither the BMS or the controller cut-out. All of the data I have collected so far gives me confidence my battery is operating within spec.

-R