RV and vandwellers wiki

User Tools

Site Tools

Trace:
electrical:12v:drop-in_lifepo4

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision 		Previous revision
electrical:12v:drop-in_lifepo4 [2024/02/18 14:28]
frater_secessus [Charging cut-off] belt and 		electrical:12v:drop-in_lifepo4 [2024/05/21 22:08] (current)
frater_secessus [myth: you have to charge Li to 100%]
Line 45: Line 45:
   * the flat voltage curve makes gauging SoC by voltage extremely challenging, and battery "gauges" designed for lead chemistry batteries will not work. An amp-counting [[electrical:12v:battery_monitor|battery monitor]] will be more useful with Li.    * the flat voltage curve makes gauging SoC by voltage extremely challenging, and battery "gauges" designed for lead chemistry batteries will not work. An amp-counting [[electrical:12v:battery_monitor|battery monitor]] will be more useful with Li. 
  
 +===== sizing the bank =====
  
 +Other than cost, there is little downside to having a larger LiFePO4 bank.(([[electrical:12v:directcharginglfp|direct-charging from alternator]] would require some thought))  Upsides include:
 +
 +  * greater [[opinion:solar:sizing.walkthrough#days_of_autonomy|autonomy]] when charging is absent or limited due to poor solar conditions
 +  * supporting larger discharge current - [[electrical:12v:battery_capacity|0.5C]] is a common max spec.  So a 200Ah LFP could support 100A loads((0.5 x 200Ah)) while a 100Ah could only support 50A.  
 +  * safely accepting larger charging currents when charging time is limited.  Charging specs vary between 0.2C to 0.5C;  [[electrical:12v:drop-in_lifepo4#an_example_of_long_life|0.4C]] seems to be a good balance between longevity and charging time.  200Ah could accept 80A from the alternator while 100Ah could only accept 40A.  
  
  
Line 274: Line 280:
   * to top-balance cells((to the degree this works))   * to top-balance cells((to the degree this works))
  
 +==== myth:  lithium batteries draw the full current until they are almost full ====
 +
 +
 +  * both lead and li chemistry charge acceptance [[electrical:12v:directcharginglfp#current_demands_of_dc-dc_chargers_vs_isolators|will taper]] when charged by a [[electrical:12v:alternator|relay/isolator]], and 
 +  * both will charge ~at [[electrical:12v:b2b|a DC-DC charger]]'s rated output until Absorption voltage is reached
 +
 +If we observed closely we //would// see some differences:  the LFP taper is shaped a bit differently, and that lead Absorption tends to start earlier and last longer.  
  
 ==== myth:  if you don't charge to 14.4v the cells won't balance ==== ==== myth:  if you don't charge to 14.4v the cells won't balance ====
Line 317: Line 330:
   * **Equalize duration** - zero, or as low as the controller will allow.  Will make no practical difference when Veq is set to Vabs.    * **Equalize duration** - zero, or as low as the controller will allow.  Will make no practical difference when Veq is set to Vabs. 
   * **Temperature compensation** - Lead needs different charging voltages at different temperatures but Li does not.  Change setting to **0**mV/cell.((lead defaults are something like -4mV/cell))   * **Temperature compensation** - Lead needs different charging voltages at different temperatures but Li does not.  Change setting to **0**mV/cell.((lead defaults are something like -4mV/cell))
 +
 +Note:  if you are willing to babysit, even a single-voltage power supply would work.  Stop charging when the voltage hits your desired setpoint.  
  
 ==== myth:  you shouldn't Float lithium ==== ==== myth:  you shouldn't Float lithium ====
Line 360: Line 375:
 === testing your isolator with Li === === testing your isolator with Li ===
  
-see [[electrical:12v:directcharginglfp#assessing_your_setup_for_direct_alternator_charging|this section]]+see [[electrical:12v:directcharginglfp#assessing_your_own_setup_for_direct_alternator_charging|this section]]
  
 ==== but that Victron video ==== ==== but that Victron video ====
Line 519: Line 534:
  
 >> For belt-and-suspenders you could add a $10 12v temp controller or NO thermal switch in series [with the disabling method].   Stick the probe (or switch) on the bank and only complete the [disabling ] circuit when the ignition is on **and** measured temp >0C or >2C or whatever you prefer.  >> For belt-and-suspenders you could add a $10 12v temp controller or NO thermal switch in series [with the disabling method].   Stick the probe (or switch) on the bank and only complete the [disabling ] circuit when the ignition is on **and** measured temp >0C or >2C or whatever you prefer. 
 +
 +Note that some chargers have built-in low-temp charging cutoff already.  
  
  
Line 579: Line 596:
 Some batteries have BMS with bluetooth or other forms of connectivity.  With these you would be able to see more information, like individual cell balance, statistics, setting and the status of any protections.  Some batteries have BMS with bluetooth or other forms of connectivity.  With these you would be able to see more information, like individual cell balance, statistics, setting and the status of any protections. 
  
 +Having visibility into the state of the BMS/cells might be useful for tech geeks, but often muddies the waters for non-technical customers.  Lack of BT is not a dealbreaker. 
  
  
electrical/12v/drop-in_lifepo4.1708284526.txt.gz ยท Last modified: 2024/02/18 14:28 by frater_secessus

Page Tools

Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution-Noncommercial-Share Alike 4.0 International

affilliate disclosure

CC Attribution-Noncommercial-Share Alike 4.0 International Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki