Differences

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

--- opinion:frater_secessus:lifepo4_charging_voltage [2023/06/28 23:17]
frater_secessus [the full process]
+++ opinion:frater_secessus:lifepo4_charging_voltage [2024/02/10 11:33] (current)
frater_secessus [the full process13.6v example
@@ Line 1: / Line 1: @@
 DRAFT
-====== Problems caused by excessive LiFePO4 charging voltage ======
+====== Problems caused by lithium charging profiles ======
+You'd think that a "lithium profile" would be suitable for lithium.  That may or may not be so for your particular use case.  Read on...
+===== excessive charging voltage =====
 [[https://img.mousetrap.net/misc/toohigh.jpg|{{ https://img.mousetrap.net/misc/thumbs/toohigh.jpg}}]]
@@ Line 11: / Line 14: @@
   * voltages in the system are spiking, perhaps tripping your inverter
-It's fairly common for **excessive charging voltage** to cause these symptoms.  Unfortunately it's //very// common for preconfigured Lithium profiles to charge at voltages high enough to trigger the issue.
+It's fairly common for **excessive charging voltage** to indirectly cause these symptoms.  Unfortunately it's //very// common for preconfigured Lithium profiles to charge at voltages high enough to start the problematic chain of events.
-===== TLDR =====
+==== TLDR ====
-If this is the problem then reducing the charging voltage will cause the symptoms to improve or disappear.
+If excessive charging voltage is the problem then reducing the charging voltage will cause the symptoms to improve or disappear.
 [[opinion:frater_secessus:pareto|about these summaries]]
-===== the full process =====
+==== the full process ====
-  - reduce charging voltage (aka "absorption voltage", "boost voltage") to something like 13.6v and float voltage, if used, to something like 13.4v.  You may have to use a USER profile instead of a canned LITHIUM profile.  If you choose to modify the Li profile itself take a pic or notes of the original settings so you know what they were and can return to them later if desired.
-  - observe for a few days.  Charging will be slower and may not finish by sundown((you may have to define or increase an Absorption/boost duration)), but we are most interested in whether or not the symptoms above clear up.
+  - reduce charging voltage (aka "absorption voltage", "boost voltage") to something like 13.6v.  Float if used, can be set to something like 13.3v-13.4v.  You may have to use a USER profile instead of a canned LITHIUM profile to make these changes.((note that the LITHIUM profile may have protections that others do not.  Low temp charge disconnect, for example.  Read the docs for your charger.))  If you choose to modify the Li profile itself take a pic or notes of the original settings so you know what they were and can return to them later if desired.((If a configuraable profile is not available the gentlest canned profile is often GEL, which will charge at ~14.2v.  Not great, but better than 14.4v or 14.6v.))
-  - if they do clear up you can start to raise the charging voltage back up gradually (13.65v, 13.7v, 13.74v, etc) or you can leave it low.  {note from secessus:  there is little benefit to charging LiFePO4 >13.8v.]  Float can remain at 13.4v.
+  - observe for a few days.  Charging will be slower and may not finish by sundown((you may have to define or increase an Absorption/boost duration)); we want to see if it can keep on charging rather than trigger BMS cutoff.
+  - if symptoms do clear up you can start to raise the charging voltage back up gradually (13.65v, 13.7v, 13.75v, etc) or you can leave it low if you are getting enough charge.  {note from secessus:  there is little benefit to charging LiFePO4 >13.8v.]  Float can remain low at 13.3v-13.4v.
   - if it starts acting up again drop charging voltage back down a notch or two
-==== why lower-voltage charging works ====
+=== why lower-voltage charging works ===
-LiFePO4 will fully charge at voltages as low as the mid-13s, but it will take more time at lower voltages;  that time is called "Absorption duration"(("boost duration in Renogy- and EpEver-speak)).  At the kinds of current levels we usually see in offgrid charging((~0.2C)) the duration looks like this:
+LiFePO4 will fully charge at voltages as low as the mid-13s,  but it will take more time.  That extra time is called "Absorption duration"(("boost duration in Renogy- and EpEver-speak)).  At the kinds of current levels we usually see in offgrid charging((~0.2C)) the duration looks like this:
-  *  ≥14.0v will charge to 100% SoC with zero absorption: hit the voltage setpoint and //stop//. Cell voltages tend to diverge as charging voltage increases.
+  *  ≥14.0v will charge to ~100% SoC with zero minutes of absorption durations: hit the voltage setpoint and //stop//. Cell voltages tend to diverge as charging voltage increases above 14.0v because they are further up the knee (see below)
-  * 13.8v will charge to 100% SoC with token Absorption (10-30 minutes) and cells tend to stay in balance.
+  * 13.8v will charge to ~100% SoC with a small amount of Absorption (10-30 minutes?) and cells tend to stay in balance.
-  * 13.6v will charge to 100% SoC with several hours of Absorption  <-- where we are starting
+  * 13.6v will charge to ~100% SoC with several hours of Absorption ([[https://diysolarforum.com/threads/victron-dcdc-12-12-30-charger-no-bluetooth-on-new-install.78373/post-1003471|example]] with data)  <-- where we are starting
-  * 13.4v will //eventually// fully charge the bank but it would take days.  Impractical for solar charging since the sun keeps going down...
+==== why the problem occurs ====
-===== why the problem occurs =====
 {{  https://us.v-cdn.net/6024911/uploads/editor/ty/18vvr0fd7cff.jpg?135}}
@@ Line 60: / Line 55: @@
-===== further reading =====
+==== further reading ====
   * [[electrical:12v:drop-in_lifepo4#why_are_manufacturer-recommended_charging_voltages_so_high|an approach to greater LiFePO4 longevity]]
+===== lack of pseudo-float =====
+So your charge controller isn't charging even though battery state of charge is dropping?
+This can be intentional behavior, caused by a Li profile that
+  - charges to a high voltage (see above)
+  - then allows the battery to discharge until it hits the [[electrical:solar:charge_controller_setpoints|Rebulk setpoint]]...
+  - at which point it charges to the high voltage again...
+  - rinse and repeat until the sun goes down
+During the discharge stage the controller will appear to stop working.  In reality it's waiting to hit that rebulk setpoint to start the party again.
+To avoid this problem. configure a "float" voltage of 13.3v-13.4v.  [[electrical:12v:drop-in_lifepo4#mythyou_shouldn_t_float_lithium|This will hold state of charge without overcharging]].

RV and vandwellers wiki

User Tools

Site Tools

Differences

Page Tools