watchdogtimer
New Member
- Joined
- May 25, 2021
- Messages
- 5
I have a 12V 10AH Dakota Lithium LiFePO4 I have been using for the last 5 years to regulate the voltage in my pedal-powered home office. The battery charges at ~1.5-2A when I'm working on my computer and pedaling my generator. When I am not pedaling, it discharges at ~0.5A to supply power for our modem/router and small web server 24/7.
The battery charges mostly using constant current. When the battery voltage rises to ~14.4 V, a relay between the generator and battery will trip open, disconnecting the generator to prevent overcharging the battery.
A few months ago, I added a beverage cup heater controlled by PWM as a sink load to allow constant-voltage charging when the battery voltage approaches the relay trip voltage.
I normally pedal ~2 hours before breakfast each morning and 1-1.5 hrs before noon, which usually tops off the battery. I pedal another 1-1.5 hrs each evening to partially recharge it. I seldom use more than 50-60% of the battery's rated capacity.
I estimate battery state-of-charge in my system using a mix of battery voltage and coulomb counting. The SOC is reset every hour of non-pedaling by measuring the battery voltage. Between those periods, or while I am pedaling, I add or subtract the accumulated amp-hours of the current flowing into or out of the battery.
I have noticed recently that the battery voltage declines more rapidly after top-off than it used to. It used to hold 13.0-13.2 V when discharging; now, it's around 12.5-12.7 V. In other words, the flat portion of the battery's voltage-SOC discharge curve has shifted downwards.
Is this simply normal SOC degradation of an aged LiFePO4 battery, or a sign it needs rebalancing? If the former, how much lower should I expect the steady-state voltage to fall? If the latter, how would I go about doing that on a sealed 12 V battery, given my system? I always assumed the battery's onboard BMS handled rebalancing...
Thanks!
The battery charges mostly using constant current. When the battery voltage rises to ~14.4 V, a relay between the generator and battery will trip open, disconnecting the generator to prevent overcharging the battery.
A few months ago, I added a beverage cup heater controlled by PWM as a sink load to allow constant-voltage charging when the battery voltage approaches the relay trip voltage.
I normally pedal ~2 hours before breakfast each morning and 1-1.5 hrs before noon, which usually tops off the battery. I pedal another 1-1.5 hrs each evening to partially recharge it. I seldom use more than 50-60% of the battery's rated capacity.
I estimate battery state-of-charge in my system using a mix of battery voltage and coulomb counting. The SOC is reset every hour of non-pedaling by measuring the battery voltage. Between those periods, or while I am pedaling, I add or subtract the accumulated amp-hours of the current flowing into or out of the battery.
I have noticed recently that the battery voltage declines more rapidly after top-off than it used to. It used to hold 13.0-13.2 V when discharging; now, it's around 12.5-12.7 V. In other words, the flat portion of the battery's voltage-SOC discharge curve has shifted downwards.
Is this simply normal SOC degradation of an aged LiFePO4 battery, or a sign it needs rebalancing? If the former, how much lower should I expect the steady-state voltage to fall? If the latter, how would I go about doing that on a sealed 12 V battery, given my system? I always assumed the battery's onboard BMS handled rebalancing...
Thanks!