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electrical:12v:drop-in_lifepo4 [2022/09/14 15:22]
frater_secessus [myth: you must use DC-DC for alternator charging Li]
electrical:12v:drop-in_lifepo4 [2024/03/20 11:51] (current)
frater_secessus [myth: you must use DC-DC for alternator charging Li] link updat
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 The other approach to lithium is **DIY**((do it yourself)), where one selects cells, BMS, and other components and builds it themselves.  That topic is beyond the scope of this article.  People interested in DIY might want to read the [[https://diysolarforum.com/forums/diy-lifepo4-battery-banks.22/|DIY LiFePO4 Battery Banks subforum]] over on DIY Solar.  You can also see the [[electrical:12v:lifepo4_batteries_thread|Lithium Battery Summary]] article for high points of a debate on lithium suitability for long term use. The other approach to lithium is **DIY**((do it yourself)), where one selects cells, BMS, and other components and builds it themselves.  That topic is beyond the scope of this article.  People interested in DIY might want to read the [[https://diysolarforum.com/forums/diy-lifepo4-battery-banks.22/|DIY LiFePO4 Battery Banks subforum]] over on DIY Solar.  You can also see the [[electrical:12v:lifepo4_batteries_thread|Lithium Battery Summary]] article for high points of a debate on lithium suitability for long term use.
  
 +Beginning in roughly 2022, the market for drop-in Lithium batteries started growing extremely quickly and prices started coming down out of the stratosphere. Knock-off branded Chinese lithium batteries have also come up in quality, with a slew of different "brands" (that are all idendical) starting to feature things like bluetooth monitoring, cold cut-off, and internal heaters.
 +
 +The [[https://diysolarforum.com/|DIY Solar Forums]] are a good place to check for updated info, as well as links to teardown reviews and disassembly videos where the internal component quality has been given a detailed review.
 ===== Drop-in lithium benefits ===== ===== Drop-in lithium benefits =====
  
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   * Drop-in batteries are typically "black boxes" with no practical way tell what is going on inside.  Some do have bluetooth or other methods to interact with the insides.    * Drop-in batteries are typically "black boxes" with no practical way tell what is going on inside.  Some do have bluetooth or other methods to interact with the insides. 
   * Drop-ins are not always repairable.  Some, like SOK metal-cased batteries are reportedly repairable.    * Drop-ins are not always repairable.  Some, like SOK metal-cased batteries are reportedly repairable. 
-  * Drop-ins are very expensive compared to DIY lithium+  * Drop-ins are very expensive compared to [[electrical:12v:lifepo4_batteries_thread|DIY lithium]]
  
  
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   * Li batteries are not vulnerable to [[electrical:12v:psoc|partial states of charge]] like Pb.  If anything they //prefer// sitting at PSoC.   * Li batteries are not vulnerable to [[electrical:12v:psoc|partial states of charge]] like Pb.  If anything they //prefer// sitting at PSoC.
   * flat voltage curve - stable voltage over much of its state of charge   * flat voltage curve - stable voltage over much of its state of charge
-  * very little Peukert effect (reduction of capacity at higher discharge rates)+  * very little reduction of capacity at higher discharge rates compared to lead((there is a non-Peukert mechanism that starts to attenuate apparent capacity at very high C rates))
   * much less voltage sag under heavy loads   * much less voltage sag under heavy loads
  
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   * Li is relatively expensive   * Li is relatively expensive
   * Li cells need a [[#bms_functions|BMS]] to protect them from damage.((some DIYers run Li "barefoot" (without a BMS) )) For example, Li can be damaged by overvoltage, undervoltage, charging below freezing (32F), etc.  Some batteries have low-temp cutoff and/or internal heating to address the cold-charging limitation.  Most Drop-in Lithium batteries will have a BMS integrated into them, but raw cells do not.   * Li cells need a [[#bms_functions|BMS]] to protect them from damage.((some DIYers run Li "barefoot" (without a BMS) )) For example, Li can be damaged by overvoltage, undervoltage, charging below freezing (32F), etc.  Some batteries have low-temp cutoff and/or internal heating to address the cold-charging limitation.  Most Drop-in Lithium batteries will have a BMS integrated into them, but raw cells do not.
-  * Li can be **damaged** by long duration at full charge or full discharge.+  * Li can be **damaged** by long duration at full charge or high voltage, or high ambient temperatures
   * 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.  
  
  
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 ==== Why are manufacturer-recommended charging voltages so high? ==== ==== Why are manufacturer-recommended charging voltages so high? ====
  
-Manufacturers need simple instructions that will still allow the batteries to meet their advertised lifetime and reduce customer support issues. In this scenario higher charging voltages have the following benefits to the seller:+{{ https://memecreator.org/static/images/memes/5578892.jpg?125}} 
 +Manufacturers need simple instructions that will still allow the batteries to meet their advertised lifetime and reduce customer support issues. In this scenario higher charging voltages have the following benefits //to the seller//:
    
   * allow use of conventional lead-chemistry battery chargers or "lithium" chargers (reduce customer confusion)   * allow use of conventional lead-chemistry battery chargers or "lithium" chargers (reduce customer confusion)
   * ensure batteries can deliver 100% of advertised capacity (reduce customer service calls)   * ensure batteries can deliver 100% of advertised capacity (reduce customer service calls)
 +  * fully charge the batteries under the most challenging scenarios (solar charging, where charging duration is constrained by sundown)
   * predictable SoC at end of charging (reduce customer service calls)   * predictable SoC at end of charging (reduce customer service calls)
   * faster charging    * faster charging 
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       * at higher charging voltages((≥14.0v)) little or no absorption time is required.  "Charge and stop." (simpler for customers)       * at higher charging voltages((≥14.0v)) little or no absorption time is required.  "Charge and stop." (simpler for customers)
   * raise cell voltage so passive top-balancing can occur (customers get to see the vaunted cell balancer feature).   * raise cell voltage so passive top-balancing can occur (customers get to see the vaunted cell balancer feature).
 +
 +But higher charging voltages are more likely to [[opinion:frater_secessus:lifepo4_charging_voltage|cause cell imbalance and behavior that worries new users]], like premature disconnect of charging and apparent battery voltage spikes.(("apparent" because the [[electrical:solar:charge_controller|controller]] and [[electrical:12v:battery_monitor|battery monitor]] will report the spike, but since the BMS is disconnected the battery cells do not experience the spike))
 +
 +To walk the battery back down from this precipice we need to lower charging voltage, at least temporarily:
 +
 +  - reduce Absorption ("boost") voltage to 13.8v((13.6v may be required over many days for particularly bad cases)), (3.45Vpc) or lower
 +  - verify that charging completes as expected.  If cell voltages are visible verify their balance is improving.  
 +  - optional:  start moving back up by 0.05v or 0.1v increments if desired, watching as in step 2 above.  Example:  13.8v, then 13.85v, then 13.9v, etc.  **There is little reason to charge >14.0v (3.5Vpc)**.  
 +
 +
  
  
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 The overall idea is to treat the bank like there is no BMS, no safety net.  Charging rates/voltages are conservative and charging takes longer.  Note this only works if one has enough //time// for gentle charging;  if you only have a 2-hour charging window hard-and-fast is the only option and we accept the shorter life trade-off.  The overall idea is to treat the bank like there is no BMS, no safety net.  Charging rates/voltages are conservative and charging takes longer.  Note this only works if one has enough //time// for gentle charging;  if you only have a 2-hour charging window hard-and-fast is the only option and we accept the shorter life trade-off. 
 +
 +=== an example of long life ===
 +
 +The longest-lived, fully documented, instrumented LFP bank in actual use appears to be [[https://www.sailnet.com/threads/happy-13th-birthday-to-my-lifepo4-battery-bank-5-10-2009.343929/|Maine Sail's 400Ah bank from 2009]]. It's still holding rated capacity. His charging regime is
 +
 +  * charge to 13.8v (3.45Vpc)
 +  * at 0.4C
 +  * with 30mins Absorption
 +  * he is charging this bank from alternator, so he stops after Absorption. In other contexts with solar charging he has used 13.4v (3.35Vpc) as a quasi-Float (voltage floor below resting voltage)
 +
 +Maine Sail's approach demonstrates several of the life-extending approaches discussed in this sub-article. 
 +
 +Note from secessus:  
 +
 +> We don't have to slavishly follow what MS and the other early-adopters are doing, but we would be wise to pay attention. I am suggesting the values above would be a better default than every Li profile I have seen so far. I'd encourage new users to start from there and adjust as needed. 
 +
 +
 +=== high SoC ===
 +
 +There is [[https://www.sciencedirect.com/science/article/pii/S2667141722000283?via%3Dihub|some evidence]] that high states of charge may worsen capacity degradation at temperatures >86F:
 +
 +>> When capacity degradation occurs in LFP cells at elevated temperatures, both temperature (30–60 ​°C) and SOC determine the degradation rate. High storage temperature, which is the most important factor, combined with high SOC result in the greatest degradation 
  
  
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   * cells more likely to stay in balance   * cells more likely to stay in balance
  
-At gentle charge rates like C/5, the following patterns emerge:+At gentle charge rates like 0.2C, the following patterns emerge:
  
-  *  ≤13.4v will not fully charge the bank in one day of charging+  *  ≤13.4v will not fully charge the bank 
 +  * 13.4v will get the bank to ~85% over a couple of days, then stabilize there
   * 13.6v will charge to 100%  SoC with several hours of Absorption   * 13.6v will charge to 100%  SoC with several hours of Absorption
-  * 13.8v will charge to 100% SoC with a shorter Absorption and cells tend to stay in balance.+  * 13.8v will charge to 100% SoC with token Absorption (10-30 minutes) and cells tend to stay in balance.
   * ≥14.0v will charge to 100% SoC with no absorption.  Cell voltages tend to diverge.   * ≥14.0v will charge to 100% SoC with no absorption.  Cell voltages tend to diverge.
  
 Some drop-in BMS only start top-balancing at 14.2v((3.55Vpc)) but increasing voltage to that level tends to //cause// imbalance. Catch-22.   Some drop-in BMS only start top-balancing at 14.2v((3.55Vpc)) but increasing voltage to that level tends to //cause// imbalance. Catch-22.  
  
-If charging at lower votlages the **initial charge** (and occasional charges thereafter) might be to mfg spec voltage.  This might allow the BMS to reset "full" and top-balance to the degree that such balancing works. +If charging at lower voltages the **initial charge** (and occasional charges thereafter) might be to mfg spec voltage.  This might allow the BMS to reset "full" and top-balance to the degree that such balancing works. 
  
 Also see:  Will Prowse' [[https://www.youtube.com/watch?v=Yf9N9zBgyB8|Lithium Battery Longevity: Double or Quadruple the Life of Your Lithium Battery]] Also see:  Will Prowse' [[https://www.youtube.com/watch?v=Yf9N9zBgyB8|Lithium Battery Longevity: Double or Quadruple the Life of Your Lithium Battery]]
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 +
 +
 +
 +=====self-heating batteries=====
 +
 +Lithium cannot be charged in freezing temps.  We can either:
 +
 +  -  cut off charging in the chargers; and/or
 +  - warm the batteries, either internally (self-heating) or externally (typically with warming mats).  
 +
 +
 +Self-heating is convenient, and does not require lithium- or temperature-aware chargers. The downsides are:
 +
 +  *  typically substantially more $$$ than warming pads
 +  *  can miss out on charging opportunities. Not a big deal with smaller solar-only setups, but can really hamper alternator or big solar.
 +
 +
 +==== how self-heating batteries work ====
 +
 +The last issue is a function of how they work.  
 +
 +  - When the BMS detects dangerously-low temps it deactivates charging to the battery cells
 +  - any charging power is sent to the internal warming pads, typically ~50w
 +  - when the BMS detects the temps are ok it turns the charging back on.  The warming may be switched off, or may continue to warm the battery further to a given temp setpoint.
 +
 +==== how this could cause a missed charging opportunity ====
 +
 +Imagine a half-hour drive on a freezing morning with a 50A [[electrical:12v:b2b|DC-DC charger]].((Doesn't have to be DC-DC but it makes the math easier because charging current is more stable.)) You could pump 25Ah((minus the energy it took to hold temp overnight)) into an externally-warmed battery, or you could use the alternator to run the 50W internal heater and get 0Ah replaced.
 +
 +With only small solar the Wh consumed overnight and Wh not produced in the morning might be a breakeven.
  
  
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 Charging Li at very high rates may also strain the [[electrical:12v:alternator|alternator]].   Charging Li at very high rates may also strain the [[electrical:12v:alternator|alternator]].  
 +
 +==== myth:  you can't use a combiner to charge batteries of different chemistries ====
 +
 +There are two different challenges here:
 +
 +  - **different resting voltages** - if the lead rests at 12.8v and LiFePO4 at 13.6v then when charging stops the lead batt could put a drain on the li batt.  The [[electrical:12v:alternator#combiners|charging relay]]((or [[electrical:12v:b2b|DC-DC]])) is primarily there to stop house loads from draining the starter battery, but this separation also means **the starter battery cannot drain the house battery**.((unless self-[[electrical:12v:self-jumpstarting|jumpstarting]])) ((note, however, [[electrical:12v:alternator#gotchas|a gotcha with VSRs]]))
 +  - **acceptable charging voltages** - the alternator voltage needs to be acceptable (not necessarily //optimal//) to both batteries.  Read on.
 +
 +=== acceptable charging voltage ranges ===
 +
 +We can assume **the alternator voltage is acceptable to the starter battery** because the manufacturer designed that system.((and we can observe that the vehicle starts on demand)).  So we only have think about whether or not the alternator voltage is acceptable to the house bank.  
 +
 +For the following thought experiment we will use some a typical alternator output voltage of 14.2v and house bank charging voltage [[electrical:solar:charge_controller_setpoints|setpoints]] ("Absorption" or "Boost" voltage, Vabs); check your vehicle's alternator voltage and  battery manufacturer charging specs to make your actual decision.
 +
 +^ Chemistry  ^ Acceptable Vabs  ^ Optimal Vabs                                                                                                        ^
 +| Gel        | 14.0v - 14.3v        | 14.2v                                                                                                               |
 +| AGM        | 14.2v - 14.5v        | 14.4v                                                                                                               |
 +| Flooded    | 14.4v - 14.8v        | 14.6v                                                                                                               |
 +| LiFePO4    | 13.6v - 14.4v        | 14.0v((this is a matter of some debate.  LFP mfg charging recommendations are often [[opinion:frater_secessus:lifepo4_charging_voltage|quite high]] - secessus))  |
 +
 +
 +Let's think about some combinations.  In all these cases [[electrical:12v:alt_and_solar#how_alternator_charging_helps|alternator charging is extremely useful]] for [[electrical:12v:charging#bulk_stage|Bulk stage charging]] but may not be sufficient on its own:
 +
 +  * **easy to meet charging requirements by alternator alone**
 +    * starter battery + LiFePO4. Charging LFP at 14.2v is a good balance between moderate voltage and charging time. Lithium is not affected by [[electrical:12v:psoc|partial states of charge]] so you can charge as little or much as you want.  Caveat:  alternator charging should be [[electrical:12v:alternator#disabling_alternator_charging|disabled]] if you drive long enough to reach your desired state of charge. Specifically, LFP should not be held at high voltage after reaching full charge.
 +  * **unlikely to meet charging requirements by alternator alone** - could theoretically meet charging by alternator alone //if// given sufficient time.  Unfortunately most people don't drive enough hours ((typically 5-6 hours from 50% SoC)) to complete Absorption;  [[electrical:12v:psoc|incomplete charging damages lead batteries]].  less one is driving for many hours each day it is unlikely that there will be sufficient time to complete Absorption. For this reason solar or other long-duration charging source is often [[electrical:12v:alt_and_solar#how_solar_helps|added to handle Float and late Absorption]].
 +    * starter battery + AGM.  14.2v from the alternator is in the acceptable range, but just barely.  Extremely long Absorption would be required and adding solar is highly recommended.  
 +    * starter battery + Gel.  The alternator is putting out the exact Vabs spec'd by the manufacturer.  Caveat:  gel can be damaged (electrolyte cavitated) by excess current. Ensure your setup charges withing the mfg current specs. 
 +  * **Useful but impossible((practically)) to meet charging requirements by alternator alone ** - cannot reach Vabs in any case.  Solar is nearly mandatory, although DC-DC charging will do it if one is driving many hours a day.
 +    * starter battery + flooded.  Alternator charging is useful for Bulk stage (shoving Ah into the bank) but it cannot meet the minimum Vabs.  
 +
 +
  
 ==== myth:  you have to charge Li to 100% ==== ==== myth:  you have to charge Li to 100% ====
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 Overcharging lithium to run the cell balancers is like driving up to every red light at 100mph in order to trigger the ABS.  It's //causing// the problem in order to //solve// the problem. Overcharging lithium to run the cell balancers is like driving up to every red light at 100mph in order to trigger the ABS.  It's //causing// the problem in order to //solve// the problem.
  
 +==== myth:  lithium doesn't need absorption ====
  
 +
 +Lithium doesn't need Absorption [[electrical:12v:charging#absorption_stage|in the way lead does]].  In some circumstances, however, an Absorption duration can help match [[electrical:solar:charge_controller_setpoints|charging setpoint]] expectations to [[electrical:depth_of_discharge|state of charge]] reality.
 +
 +Most charts and tables showing voltage v. SoC assume moderate rates of charge like 0.2[[electrical:12v:battery_capacity|C]] (20A per 100Ah of capacity).  At that rate the charts are reasonably accurate.
 +
 +**Very high charge rates**, as sometimes seen with [[electrical:12v:drop-in_lifepo4#mythyou_must_use_dc-dc_for_alternator_charging_li|alternator charging]] or large [[electrical:converter|shore power chargers]], can throw off these chart estimates. 0.8C charging might only yield 80% SoC when one expected 90%. Conversely, **very low charge rates** may result in unintentional overcharge;  98% instead of 90%.
 +
 +One rule of thumb is that the bank is fully charged when you are at your target voltage and current acceptance has decreased to ≤0.10C.  Other sources give 0.04C or other values that vary with the base charging rate.((https://diysolarforum.com/threads/tail-current-charge-table.26828/post-500852)).  One could try tail currents in this ballpark and see which gives you the SoC you expect. 
 +
 +Further reading:  [[https://www.youtube.com/results?search_query=offgrid+garage+absorption|Off-grid Garage videos]] testing various absorption approaches
 ==== myth:  you can't charge Li with a lead battery charger ==== ==== myth:  you can't charge Li with a lead battery charger ====
  
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   - decide whether the charger can charge to mfg specs   - decide whether the charger can charge to mfg specs
  
-Armed with a full understanding, here is one approach to thinking about lead battery charger setpoints:+Armed with a full understanding, here is one approach to thinking about lead battery charger setpoints for lithium banks:
  
   * **Absorption voltage** (Vabs) - whatever charging voltage your battery manufacturer recommends.((see the section on longevity in this article))   * **Absorption voltage** (Vabs) - whatever charging voltage your battery manufacturer recommends.((see the section on longevity in this article))
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   * **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 ====
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   - the self-discharge rate is so high that they lose capacity just sitting there   - the self-discharge rate is so high that they lose capacity just sitting there
  
-Neither of these is true for Li, which dislikes sitting at 100% SoC and has vanishingly-low self-discharge rates.((but see [[https://www.technomadia.com/2020/06/what-killed-our-rv-lithium-batteries-8-5-years-of-lifepo4/|this cautionary tale]] about add-on balancers depleting/killing a $4,000 bank)) So **with lithium Float is used for a different purpose**, as a **voltage floor**.  It is a voltage below which the charger shouldn't let the bank fall while charging is present.  Without no Vfloat (or a very low one) the bank would charge then fall until the next morning when charging starts again.  After initial charging loads would run off the battery instead of the charging source.  Having a sane Vfloat allows Li to "relax" after charging while retaining the desired amount of Ah/Wh capacity.+Neither of these is true for Li, which dislikes sitting at 100% SoC and has vanishingly-low self-discharge rates.((but see [[https://www.technomadia.com/2020/06/what-killed-our-rv-lithium-batteries-8-5-years-of-lifepo4/|this cautionary tale]] about add-on balancers depleting/killing a $4,000 bank)) So **with lithium Float is used for a different purpose**, as a **voltage floor**.  It is a voltage below which the charger shouldn't let the bank fall while charging is present.  Without Vfloat (or a very low one) the bank would charge then fall until reaching the "re-bulk" setpoint.((when a fresh charge cycle begins)).  After initial charging loads would run off the battery instead of the charging source.  Having a sane Vfloat allows Li to "relax" after charging while retaining the desired amount of Ah/Wh capacity.
  
 What Vfloat setpoint should actually be is a matter of some discussion and experimentation.  Each setup (and use case) is different, but in general((and using nominal 12v math)) What Vfloat setpoint should actually be is a matter of some discussion and experimentation.  Each setup (and use case) is different, but in general((and using nominal 12v math))
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 +If you cannot set a Float within the confines of the Li profile then leverage the USER or GEl profile, modifying as described in the previous section. 
 ==== myth:  you must use DC-DC for alternator charging Li ==== ==== myth:  you must use DC-DC for alternator charging Li ====
  
-Depends on the battery, the alternator, the use case, and even the [[electrical:12v:alternator|isolator]].  For example, [[https://www.youtube.com/watch?v=VY2b71zoyvg|Battle Born says]] this about isolator charging lithium:+Depends on the battery, the alternator, the use case, and even the [[electrical:12v:alternator|combiner]].  For example, [[https://www.youtube.com/watch?v=VY2b71zoyvg|Battle Born says]] this about direct-charging lithium:
  
 >> Yes, you can.  Under most circumstances you don't even need to modify your system. >> Yes, you can.  Under most circumstances you don't even need to modify your system.
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   * you already have an [[electrical:12v:alternator|isolator]] installed from a previous Pb bank.  Might as well see if it meets needs "for free".   * you already have an [[electrical:12v:alternator|isolator]] installed from a previous Pb bank.  Might as well see if it meets needs "for free".
-  * even if you have no isolator installed an isolator is much less expensive, costing as little as 1/10th the price of DC-DC. If after testing you do decide to go DC-DC you can carry the isolator as a backup. +  * even if you have no isolator installed an isolator is much less expensive, costing as little as 1/10th the price of DC-DC. If after testing you do decide to go DC-DC you can carry the isolator as a backup. Or daisy-chain the DC-DC behind it for units that use D+ rather than voltage triggering
   * an isolator is likely to charge with more current than smaller (~20A) DC-DC units during shorter drives.((On longer drives the DC-DC will be able to provide higher voltage than the alternator so its current will remain stable while isolator current drops with the voltage delta))     * an isolator is likely to charge with more current than smaller (~20A) DC-DC units during shorter drives.((On longer drives the DC-DC will be able to provide higher voltage than the alternator so its current will remain stable while isolator current drops with the voltage delta))  
   * you want to be able to [[electrical:12v:self-jumpstarting|self-jumpstart]]   * you want to be able to [[electrical:12v:self-jumpstarting|self-jumpstart]]
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 === testing your isolator with Li === === testing your isolator with Li ===
  
-Here an order of operations one might use to assess whether or not isolator charging will work in a given install:((discontinue at once if you observe unacceptable results, and consider DC-DC or increasing solar)):+see [[electrical:12v:directcharginglfp#assessing_your_own_setup_for_direct_alternator_charging|this section]]
  
-  - if the isolator is already in use with lead-chemistry banks before the upgrade, //pay attention to the voltage and current at which the existing bank is being charged// This is your baseline for alternator charging. Ah-for-Ah lithium will likely draw more current than lead, but Li banks are typically lower in Ah than the lead banks they replace as DoD can be lower.((Lithium requires about 0.62 as much Ah as lead for the same amount of //usable// capacity.)) +==== but that Victron video ====
-  - Read and understand your Li battery manufacturer's charging specs - undercharging is fine((assuming one stays above 20% State of Charge)); overcharging is less so but is relatively rare in an isolator context. +
-  - Read and understand your alternator's specs +
-  - Read and understand your isolator's specs and functionality +
-  - observe your vehicle's chassis voltage during normal operation - note that the voltage //at the battery's location// will likely be lower due to long wiring and also lower when the wiring is carrying a hefty charging current.   +
-  - make a first approximation about the ability of alternator, your isolator, and your Li battery to cooperate +
-  - install [[electrical:12v:battery_monitor|a battery monitor]] so you can observe current and voltage at the battery.  Or use the battery's own BT access. +
-  - ensure the fuse between your chassis and battery bank is sized so //you cannot draw more than the alternator and wiring can handle// +
-  - make the first test run a brief one and with the Li fairly well charged.((higher states of charge will typically lessen current demands to some degree))((if you have paralleled batteries you might want to do this step with just one in place to get a feel for the draw.))  Start the engine and see if the charging current and voltage is acceptable.  Turn off the engine. +
-  - test it with a drive. +
-  - repeat the last two steps with the Li bank at lower and lower states of charge, down to the lowest expected state of charge you expect to recharge from alternator.+
  
- +Why would a manufacturer of pricey [[electrical:12v:b2b|DC-DC chargers]] want to publish [[https://www.youtube.com/watch?v=jgoIocPgOug|a video]] of a big LFP pack destroying a low-output car alternator((2:50)) at idle speeds?  And why would they turn comments off?  Oh, right.  
-**Caveats**:   +
- +
-  * Only alternator charge while driving ([[rv:idling|no idling]] except for brief preliminary test).   +
-  * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical:depth_of_discharge|states of charge]]. +
-  * You may want a manual disconnect or [[electrical:12v:alternator_charging_hvd|HVD]] to shut off alternator charging due to excess voltage or if the bank is already charged.  These can be added on the D+ wire (ignition triggered) or electronics ground wire (VSR, solenoid, or voltage-triggered DC-DC) +
- +
-=== but that Victron video! === +
- +
-Why would a manufacturer of pricey [[electrical:12v:b2b|DC-DC chargers]] want to publish [[https://www.youtube.com/watch?v=jgoIocPgOug|a video]] of an LFP pack smoking an alternator?((7:01))  And why would they turn comments off?  Oh, right.  +
  
 The setup: The setup:
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   * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https://nomadicsupply.com/product/victron-energy-300ah-12-8v-smart-lifepo4-bluetooth-battery/|website]]).   ~50% DoD at the start of each test.     * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https://nomadicsupply.com/product/victron-energy-300ah-12-8v-smart-lifepo4-bluetooth-battery/|website]]).   ~50% DoD at the start of each test.  
   * [[https://amzn.to/3woATOe|Victron BMV 712]] to measure current into battery   * [[https://amzn.to/3woATOe|Victron BMV 712]] to measure current into battery
-  * "traditional" alternator (Expom ER-438740,((label visible at 2:51)) used in small vans and passenger cars up to 2.0 liters in Eastern Europe.  Quick googling this is somewhere between a 70A and 90A alternator.  +  * "traditional" alternator (Expom ER-438740,((label visible at 2:51)) used in small vans and passenger cars 2.0 liters in Eastern Europe.  Quick googling shows it'somewhere between a **70A and 90A** alternator.  
   * Balmar alternator ([[https://balmar.net/6-series-alternators/|six series]], with external regulator and optional temperature sensor).  This dual-fan line is available in 70A, 100A, and 120A models.  The 96A cap shown in the monitoring software rules out the 70A model.     * Balmar alternator ([[https://balmar.net/6-series-alternators/|six series]], with external regulator and optional temperature sensor).  This dual-fan line is available in 70A, 100A, and 120A models.  The 96A cap shown in the monitoring software rules out the 70A model.  
 +  * dedicated negative return ("ground") wire between house battery and charging system.  Typical relay-charging setups use the vehicle's chassis as the return leg, introducing a great deal of resistance.((the resistance of steel is ~10x that of copper))
  
 The results: The results:
 +
 +Keep in mind that alternator RPM is typically 3x engine RPM.
  
   * "traditional" alternator    * "traditional" alternator 
-    * 1.500rpm - 65.1A.  43deg C. +    * 1.500rpm((~500 engine RPM)) - 65.1A.  43deg C. 
-    * 3.000rpm - 78.9A.  43deg C.+    * 3.000rpm((~1000 engine RPM)) - 78.9A.  43deg C.
     * a 126 and 128deg C interior temps were shown but it was not clear what they they are from.       * a 126 and 128deg C interior temps were shown but it was not clear what they they are from.  
   * Balmar   * Balmar
-    * 2,100rpm - 50A, 42deg C external, 74deg C internal. +    * 2,100rpm((~700 engine RPM)) - 50A, 42deg C external, 74deg C internal. 
-    * 3,600rpm - 94.3A, unstated alt case temp, 130deg C internal.+    * 3,600rpm((~1200 engine RPM - 94.3A, unstated alt case temp, 130deg C internal.
  
 Their conclusion:((5:27)) Their conclusion:((5:27))
  
-...issues can arise when charging lithium batteries with an alternator.+> charging lithium batteries at low RPM results in the altenator overheating.((3:13))
  
-Duh.  Especially when charging a 300Ah no-BMS bank from a ≤90A alternator at idle.  +Yes, **300Ah** LFP bank //can// smoke a ≤**90A** alternator **at idle**.  Is anyone surprised?  That's why we don't don't charge at idle, and don't direct-charge big banks off small alternators. Or run big DC-DC off small alternators for that matter.   In other breaking news:  carrying 1000lbs of cement bags in the back of your Civic will cause damage, too.  
  
 They go on to list the workarounds: They go on to list the workarounds:
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   - fit an externally-regulated alternator with temp sensor, as shown in the video (~$850)   - fit an externally-regulated alternator with temp sensor, as shown in the video (~$850)
   - or (surprise!), install a Victron [[https://amzn.to/3CYTrWo|Orion Tr-Smart DC-DC charger]] (~$250)   - or (surprise!), install a Victron [[https://amzn.to/3CYTrWo|Orion Tr-Smart DC-DC charger]] (~$250)
-  - {not mentioned:  adding resistance with a shunt((see below)) (~$34).+  - {not mentioned:  adding resistance by using the chassis for negative return, or by other means((see below)) ($0 to ~$34).
  
  
-I would very much like to have seen the regular alt and all <del>three</del> four workarounds demonstrated //at the same RPM settings//.  +I would very much like to have seen the regular alt and all <del>three</del> four workarounds demonstrated //at the same RPM settings//.  -- secessus }
  
  
 +==== and that Sterling video ====
  
-=== actual reports of direct alternator charging ===+[[https://www.youtube.com/watch?v=ShtGB07fCSs|Sterling also made a video]], but left comments on.  They use a 90A Bosch alternator((0:30)) and 1 Sterling LiFePO4, presumably 100Ah.   The battery is connected to an additional load (ahem) and has a heavy dedicated NEG return.((3:25))  The alt has no cooling airflow as one would have on a moving vehicle (or even an alt behind a radiator fan).  
 + 
 +{Note from secessus:  I rather like Sterling stuff, but will call out FUD anywhere I see it} 
 + 
 +=== the video === 
 + 
 +> why do we put on our lithium batteries that you must use a battery-to-battery charger.... 
 + 
 +Because Sterling's main product line is pricey battery-to-battery (DC-DC) chargers. 
 + 
 +> what I want to show is what temperature the alternator will go to when you start putting maximum current through the alternator((0:49)) 
 + 
 +**Any alternator will overheat at continuous max current**. This is like saying "don't buy Nike shoes because if you jump off a building you'll break your legs."  Duhhh.  
 + 
 +The question is:  how much current will a LiFePO4 pull from the alternator in a normal install?  The sellers of DC-DC chargers are uninterested in showing us this.  Spoiler:  [[electrical:12v:directcharginglfp#analysis_of_van-relevant_installs|about 0.32C]], or 32A per 100Ah of capacity. 
 + 
 +> try and keep your alternator down below 80% [output](()) 
 + 
 +I'd say even lower, 50% for road vehicles with internal regulation.  
 + 
 +The testing, //using external load to drive up the current//: 
 + 
 +  * 99.9A from the 90A alt:  150C at the coils.((4:12))  Don't do that.  
 +  * 97A from the 90A alt:  165C at the coils.((5:09)).  Seriously stop doing that.   
 + 
 + 
 +Then, as with Victron, reduce alternator RPM so it struggles.((5:45))   
 + 
 +  * 92A out of the 90A alt at reduced RPM.  184C at the coils.((6:45)) You're going to wreck it 
 + 
 +At this point they disconnect the load and battery charge acceptance begins to drop.  Within 5 mins((11:07)) acceptance has dropped to 76A.   
 + 
 +At 11:45 he re-applies the artificial load "to see how much hotter it will get" ??? 
 + 
 +**DC-DC chargers are good enough technology that there is no need to trick customers into buying them. **  
 + 
 + 
 + 
 + 
 + 
 + 
 + 
 +=== the comment section === 
 + 
 + 
 +> But the variability in charge rate, alternator output voltage, battery voltage-The calculations for the majority of the period would just not be correct.((https://www.youtube.com/watch?v=ShtGB07fCSs&lc=Ugz-FcEMYLZ-G4_akot4AaABAg.9o1CQVtVEye9o2QvjBnJCp))  
 + 
 +Correct;  direct-charging does not have consistent current so cannot be precisely calculated.  
 + 
 + 
 + 
 +> we do have customers who simply use our non current limiting charge systems on lithium and rarely complain((https://www.youtube.com/watch?v=ShtGB07fCSs&lc=UgxnqrYFdIW_Yilq6yd4AaABAg.9JRqghM2DQj9JVGS8L69dL)) 
 + 
 +Seems like it's worthy of further study.  
  
-{secessus: "No armchair theorizing or hand-waving. **Only empirical reports** with bank size and current measurements.  //All// of them as I find them, good, bad, or indifferent"} 
  
  
-  * **560Ah** pulling 100A (0.18C) from 200A alternator at idle.  -- [[https://diysolarforum.com/threads/charging-lifepo4-without-charge-controller-strange-theory.16501/post-187344|source]]. 
-  * **500Ah** in trailer pulling 150A-180A (0.36C) F350 tow vehicle (!).  ~400A dual-alt setup did not behave as expected; most current was pulled from the 225A main alt and ran primary alt hotter than owner wanted before BIM cycling could start.  No temp readings given. -- [[https://www.youtube.com/watch?v=uwrG3gUdDT8|source]] 
-  * **400Ah** at 17% SoC bank pulling 75A (0.19C) from sprinter at idle. Alt temp remained normal.   -[[https://www.youtube.com/watch?v=KXG7-EegNV0|source]] 
-  * **400Ah** pulling 75A (0.19A) from 2005 Winnebago Adventurer -- [[https://www.youtube.com/watch?v=4kj8hAH_48U&lc=Ugz0JA9aySj3QBiH6ZJ4AaABAg|source - featured comment]].  Owner later installed 20A DC-DC. 
-  * **300Ah** pulling 40A-74A (0.25) at 93% SoC in Sprinter.  -- [[https://www.youtube.com/watch?v=v9O0w_jImr4|source]] 
-  * **300Ah** pulling ~103A (0.34C) from Winnebago Voyage 38J W24 Workhorse chassis after low voltage disconnect. -- [[https://www.youtube.com/watch?v=4kj8hAH_48U|source]].  Owner later installed BIM.  
-  * in the famous Victron video (see above for synopsis), **300Ah** of LFP pulled ~79A (0.26C) from a ≤90A car alternator and ~94A (0.31C) from an externally-regulated Balmar ≥100A alt.  
-  * **240Ah** bank pulling 160A (0.67C) from 220A alt at 25% SoC,   Usually 80-100A (0.42C)  User added resistance to reduce charging to 60-70A. (0.29A) -- [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/post-233088|source]] 
-  * **200Ah** pulling 54A at 81% SoC in Transit. -- [[https://www.youtube.com/watch?v=_vIdExHUDYQ|source]] 
-  * **200Ah**  pulling 80-90A (0.45C) from 180A alt at 35% SoC - [[https://www.promasterforum.com/threads/alternator-output-gauge.88467/post-682845|source]] Falling to 45A (0.23C) at 85% SoC.  
-  * **200Ah** pulling ~60A (0.3C) from 180A alt at 50% DoD - [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/post-179329|source]]  Falling to 50A (0.25C) at 80% SoC 
-  * **100Ah** pulls ~30A (0.3C) from a 180A alt at ~40% SoC, and ~15A (0.15C) when getting near full.  -- [[https://mouse.mousetrap.net/boondocking/lithium.html|source]] 
-  * **50Ah** pulling 40A (0.8C) from 110A alt near low voltage cutoff, dropping to 30A (0.6C) within a few minutes and continuing down. -- Personal observation/measurement by secessus. 
  
  
  
 === further reading === === further reading ===
 +
  
   * [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/|mega-thread]] on DIYsolarforum, including [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/post-234435|using a resistor to decrease current]].   * [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/|mega-thread]] on DIYsolarforum, including [[https://diysolarforum.com/threads/experiences-charging-lfp-from-alternator-without-a-dc-dc-charger.14884/post-234435|using a resistor to decrease current]].
   * [[https://www.youtube.com/watch?v=KXG7-EegNV0|YT vid]] where Ron tested 400Ah of LFP with an isolator on his Sprinter.   * [[https://www.youtube.com/watch?v=KXG7-EegNV0|YT vid]] where Ron tested 400Ah of LFP with an isolator on his Sprinter.
 +  * [[https://www.youtube.com/watch?v=DJrZekLjNqk|YT vid]] where both 280Ah and 100Ah LFP batts are charged with a Toyota Hilux and and RV. 
 +  * [[electrical:12v:directChargingLFP|technical info and data collected by secessus]] on direct-charging setups
  
  
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 Charging is disabled for a few different reasons:  temperature extremes, high cell voltage, overcurrent.  Charging is disabled for a few different reasons:  temperature extremes, high cell voltage, overcurrent. 
- 
-People who camp in cold weather may want to select a battery that has "low temperature cut-off", which disables charging near freezing.((Lithium is permanently damaged by charging below freezing)).  The belt-and-suspenders solution is both low temperature cutoff and a way to keep the batteries warm.  Some pricier batteries have internal heating, or you may [[https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26|DIY a heater]]. 
  
 Note that the BMS overcurrent protection kicks in only at the limit, typically 1[[electrical:12v:battery_capacity|C]] (100A for a 100Ah battery).  See the section on the [[:#an_approach_to_greater_longevity|benefits of even gentler charging]]. Note that the BMS overcurrent protection kicks in only at the limit, typically 1[[electrical:12v:battery_capacity|C]] (100A for a 100Ah battery).  See the section on the [[:#an_approach_to_greater_longevity|benefits of even gentler charging]].
 +
 +=== low temperature charging cutoff ===
 +
 +
 +People who camp in cold weather may want to select a battery that has //low temperature cutoff//, which disables charging near freezing.((Lithium is permanently damaged by charging below freezing)).  The belt-and-suspenders solution is both low temperature cutoff and a way to keep the batteries warm.  Some pricier batteries have internal heating, or you may [[https://diysolarforum.com/threads/lifepo4-heating-pad-for-cold-temperatures.5/page-26|DIY a heater]].
 +
 +It may be possible to add low temperature cutoff to a battery whose BMS lacks that feature.  It requires the charging source that can be [[electrical:12v:alternator#disabling_alternator_charging|disabled on demand]].  In this approach the we are reversing the logic so that **the default state of the charging source is disabled** and it is only **enabled when battery temps are warm enough** to safely charge.  
 +
 +>> 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. 
 +
 +
  
  
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 The low temperature discharge cut-off is typically much lower (like -20C) than for charging. The low temperature discharge cut-off is typically much lower (like -20C) than for charging.
  
 +=== wake-up ===
 +
 +After low voltage cutoff drop-ins often go into a sleep mode.  The "wake-up" procedure will be detailed in the battery manual but typically involves a "dumb" charger that does not check for battery voltage before beginning charging.  Some chargers (Victron SmartSolar for example) can emulate this dumb mode in Lithium mode in order to wake the battery.   See details in product descriptions below. 
  
 +This issue occurs because the charging and discharging channels are separately controlled.  When the battery is too low the discharge channel is disabled which means battery voltage is not exposed to the outside world.  The charging channel remains active but the charger doesn't know that. "Jumping" the battery works because the jumper cables are not looking for voltage. 
 ==== cell balancing ==== ==== cell balancing ====
  
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     * [[https://amzn.to/3udOQLK|206Ah 12v]]     * [[https://amzn.to/3udOQLK|206Ah 12v]]
  
 +[[http://support.sokbattery.com/how-to-wake-up-a-sleeping-battery/|wake-up procedure]]
 ==== Rebel Batteries ==== ==== Rebel Batteries ====
  
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 ==== Ampere Time ==== ==== Ampere Time ====
  
 +Now known as LiTime.
  
 No cold cutoff.   [[https://www.youtube.com/watch?v=FQUhjDkQY5Q|Will Prowse teardown video]] No cold cutoff.   [[https://www.youtube.com/watch?v=FQUhjDkQY5Q|Will Prowse teardown video]]
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 +==== PowerUrus  ====
 +
 +Budget PowerUrus line by RoyPow
  
 +[[https://www.youtube.com/watch?v=2KeQZrsnz-4|Will Prowse teardown]], low temp cutoff confirmed. Bluetooth.
 ==== Renogy ==== ==== Renogy ====
  
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   * [[https://amzn.to/3D37fOP|50Ah 12v]] original   * [[https://amzn.to/3D37fOP|50Ah 12v]] original
  
 +Initial activation may require a quick press-and-release of the button rather than longpress.((https://diysolarforum.com/threads/cant-get-bms-to-wake-renogy-100ah-battery-to-wake-up-from-shelf-mode.22628/post-296912))
 ==== Relion ==== ==== Relion ====
  
electrical/12v/drop-in_lifepo4.1663183371.txt.gz · Last modified: 2022/09/14 15:22 by frater_secessus