Charging a 4S LifePo4 pack in a vehicle
- Thread starter lvlaaron
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jonyjoe505
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- Feb 28, 2018
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you would need an overvoltage relay to disconnect battery when its full. Also since you will be charging at high amps, you willneed active balancers, all the lifepo4 I built go out of balance near the top end, active balancers are the only ones that can keep up when fast charging.
My lifepo4, its connected to solar but it also applies to any other charge method. The 30amp automotive relay can be replaced with a larger 200 amp solenoid (or as they call them here contactors) . The solenoid will go in between the alternator and battery. The overvoltage relay monitors battery voltage, when it reaches 14.6 volts ( or whatever your requirements are) it will trigger the solenoid to disconnect the charging. Overvoltage relay costs 6 dollars, solenoid can be found for 30 dollars.
Here are the active balancers I use, you can buy a 4s model for about 100 dollars. They can balance at up to 10 amps per cell.Active balancers is the only thing that will allow you to charge without a balance charger and get a good charge. Without the balancers, the battery BMS will always stop the charge early as soon as the high cell reaches the cutoff voltage.
They also sell battery isolators in the 200 dollar range that can handle lifepo4, but they do the exact same thing the overvoltage relay does. And you would still need to buy active balancers. The overvoltage relays are small but extremely reliable, they are connected 24/7 on my 220ah lifepo4battery system in my van, I don't even need to monitor my battery anymore, they always work when needed, if they fail you have the battery BMS as a last defense. Its a simple system but it works excellent.
My lifepo4, its connected to solar but it also applies to any other charge method. The 30amp automotive relay can be replaced with a larger 200 amp solenoid (or as they call them here contactors) . The solenoid will go in between the alternator and battery. The overvoltage relay monitors battery voltage, when it reaches 14.6 volts ( or whatever your requirements are) it will trigger the solenoid to disconnect the charging. Overvoltage relay costs 6 dollars, solenoid can be found for 30 dollars.
Here are the active balancers I use, you can buy a 4s model for about 100 dollars. They can balance at up to 10 amps per cell.Active balancers is the only thing that will allow you to charge without a balance charger and get a good charge. Without the balancers, the battery BMS will always stop the charge early as soon as the high cell reaches the cutoff voltage.
They also sell battery isolators in the 200 dollar range that can handle lifepo4, but they do the exact same thing the overvoltage relay does. And you would still need to buy active balancers. The overvoltage relays are small but extremely reliable, they are connected 24/7 on my 220ah lifepo4battery system in my van, I don't even need to monitor my battery anymore, they always work when needed, if they fail you have the battery BMS as a last defense. Its a simple system but it works excellent.
Korishan
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Using LiFePO4 cells are basically a direct replacement for Lead Acid. So, essentially, you shouldn't have to disconnect the pack from the car alternator from charging. The Alt detects when there's needed power and delivers it.
The only thing I'd be more worried about is charging from a low voltage via the Alt. The Alt will put out 14.x Volt right off the bat. If you string is sitting at 10V, then 14V will be dumped into them. Not sure if this is bad or not with LiFePO4 cells. It is for Lithium Cobalts, tho.
The only thing I'd be more worried about is charging from a low voltage via the Alt. The Alt will put out 14.x Volt right off the bat. If you string is sitting at 10V, then 14V will be dumped into them. Not sure if this is bad or not with LiFePO4 cells. It is for Lithium Cobalts, tho.