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electrical:12v:drop-in_lifepo4 [2022/10/18 12:13] frater_secessus [myth: you must use DC-DC for alternator charging Li] |
electrical:12v:drop-in_lifepo4 [2024/04/12 23:02] frater_secessus [bluetooth] |
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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. | The other approach to lithium is **DIY**((do it yourself)), where one selects cells, BMS, and other components and builds it themselves. | ||
+ | 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 " | ||
+ | |||
+ | The [[https:// | ||
===== 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. | * Drop-in batteries are typically "black boxes" with no practical way tell what is going on inside. | ||
* Drop-ins are not always repairable. | * Drop-ins are not always repairable. | ||
- | * Drop-ins are very expensive compared to DIY lithium | + | * Drop-ins are very expensive compared to [[electrical: |
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* Li batteries are not vulnerable to [[electrical: | * Li batteries are not vulnerable to [[electrical: | ||
* 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 | + | * 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 [[# | * Li cells need a [[# | ||
- | * 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, | * the flat voltage curve makes gauging SoC by voltage extremely challenging, | ||
+ | ===== sizing the bank ===== | ||
+ | |||
+ | Other than cost, there is little downside to having a larger LiFePO4 bank.(([[electrical: | ||
+ | * greater [[opinion: | ||
+ | * supporting larger discharge current - [[electrical: | ||
+ | * safely accepting larger charging currents when charging time is limited. | ||
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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:// |
+ | 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 | ||
* allow use of conventional lead-chemistry battery chargers or " | * allow use of conventional lead-chemistry battery chargers or " | ||
* 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. | * at higher charging voltages((≥14.0v)) little or no absorption time is required. | ||
* 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: | ||
+ | |||
+ | To walk the battery back down from this precipice we need to lower charging voltage, at least temporarily: | ||
+ | |||
+ | - reduce Absorption (" | ||
+ | - verify that charging completes as expected. | ||
+ | - optional: | ||
+ | |||
+ | |||
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The overall idea is to treat the bank like there is no BMS, no safety net. Charging rates/ | The overall idea is to treat the bank like there is no BMS, no safety net. Charging rates/ | ||
+ | |||
+ | === an example of long life === | ||
+ | |||
+ | The longest-lived, | ||
+ | |||
+ | * 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:// | ||
+ | |||
+ | >> When capacity degradation occurs in LFP cells at elevated temperatures, | ||
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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 | ||
* 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 | + | * 13.8v will charge to 100% SoC with token Absorption |
* ≥14.0v will charge to 100% SoC with no absorption. | * ≥14.0v will charge to 100% SoC with no absorption. | ||
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 | + | If charging at lower voltages |
Also see: Will Prowse' | Also see: Will Prowse' | ||
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+ | |||
+ | |||
+ | |||
+ | =====self-heating batteries===== | ||
+ | |||
+ | Lithium cannot be charged in freezing temps. | ||
+ | |||
+ | - 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: | ||
+ | |||
+ | 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: | Charging Li at very high rates may also strain the [[electrical: | ||
+ | |||
+ | ==== 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: | ||
+ | - **acceptable charging voltages** - the alternator voltage needs to be acceptable (not necessarily // | ||
+ | |||
+ | === 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)). | ||
+ | |||
+ | For the following thought experiment we will use some a typical alternator output voltage of 14.2v and house bank charging voltage [[electrical: | ||
+ | |||
+ | ^ Chemistry | ||
+ | | Gel | 14.0v - 14.3v | 14.2v | | ||
+ | | AGM | 14.2v - 14.5v | 14.4v | | ||
+ | | Flooded | ||
+ | | LiFePO4 | ||
+ | |||
+ | |||
+ | Let's think about some combinations. | ||
+ | |||
+ | * **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: | ||
+ | * **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; | ||
+ | * starter battery + AGM. 14.2v from the alternator is in the acceptable range, but just barely. | ||
+ | * starter battery + Gel. The alternator is putting out the exact Vabs spec'd by the manufacturer. | ||
+ | * **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. | ||
+ | |||
+ | |||
==== myth: you have to charge Li to 100% ==== | ==== myth: you have to charge Li to 100% ==== | ||
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**Very high charge rates**, as sometimes seen with [[electrical: | **Very high charge rates**, as sometimes seen with [[electrical: | ||
- | 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. | + | 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:// |
Further reading: | Further reading: | ||
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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, | + | Armed with a full understanding, |
* **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. | * **Equalize duration** - zero, or as low as the controller will allow. | ||
* **Temperature compensation** - Lead needs different charging voltages at different temperatures but Li does not. Change setting to **0**mV/ | * **Temperature compensation** - Lead needs different charging voltages at different temperatures but Li does not. Change setting to **0**mV/ | ||
+ | |||
+ | 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' | ==== myth: you shouldn' | ||
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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:// | + | Neither of these is true for Li, which dislikes sitting at 100% SoC and has vanishingly-low self-discharge rates.((but see [[https:// |
What Vfloat setpoint should actually be is a matter of some discussion and experimentation. | What Vfloat setpoint should actually be is a matter of some discussion and experimentation. | ||
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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: | + | Depends on the battery, the alternator, the use case, and even the [[electrical: |
>> 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: | * you already have an [[electrical: | ||
- | * 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: | * you want to be able to [[electrical: | ||
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=== testing your isolator with Li === | === testing your isolator with Li === | ||
- | see [[electrical: | + | see [[electrical: |
- | === but that Victron video! === | + | ==== but that Victron video ==== |
- | Why would a manufacturer of pricey [[electrical: | + | Why would a manufacturer of pricey [[electrical: |
The setup: | The setup: | ||
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* Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https:// | * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https:// | ||
* [[https:// | * [[https:// | ||
- | * " | + | * " |
* Balmar alternator ([[https:// | * Balmar alternator ([[https:// | ||
+ | * dedicated negative return (" | ||
The results: | The results: | ||
+ | |||
+ | Keep in mind that alternator RPM is typically 3x engine RPM. | ||
* " | * " | ||
- | * 1.500rpm - 65.1A. | + | * 1.500rpm((~500 engine RPM)) - 65.1A. |
- | * 3.000rpm - 78.9A. | + | * 3.000rpm((~1000 engine RPM)) - 78.9A. |
* 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: | Their conclusion: | ||
- | > ...issues can arise when charging lithium batteries | + | > charging lithium batteries |
- | Duh. Especially when charging | + | Yes, a **300Ah** LFP bank //can// smoke a ≤**90A** alternator |
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!), | - or (surprise!), | ||
- | - {not mentioned: | + | - {not mentioned: |
{ I would very much like to have seen the regular alt and all < | { I would very much like to have seen the regular alt and all < | ||
+ | |||
+ | ==== and that Sterling video ==== | ||
+ | |||
+ | [[https:// | ||
+ | |||
+ | {Note from secessus: | ||
+ | |||
+ | === the video === | ||
+ | |||
+ | > why do we put on our lithium batteries that you must use a battery-to-battery charger.... | ||
+ | |||
+ | Because Sterling' | ||
+ | |||
+ | > what I want to show is what temperature the alternator will go to when you start putting maximum current through the alternator((0: | ||
+ | |||
+ | **Any alternator will overheat at continuous max current**. This is like saying " | ||
+ | |||
+ | The question is: how much current will a LiFePO4 pull from the alternator in a normal install? | ||
+ | |||
+ | > 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: | ||
+ | * 97A from the 90A alt: 165C at the coils.((5: | ||
+ | |||
+ | |||
+ | Then, as with Victron, reduce alternator RPM so it struggles.((5: | ||
+ | |||
+ | * 92A out of the 90A alt at reduced RPM. 184C at the coils.((6: | ||
+ | |||
+ | At this point they disconnect the load and battery charge acceptance begins to drop. Within 5 mins((11: | ||
+ | |||
+ | 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:// | ||
+ | |||
+ | Correct; | ||
+ | |||
+ | |||
+ | |||
+ | > we do have customers who simply use our non current limiting charge systems on lithium and rarely complain((https:// | ||
+ | |||
+ | Seems like it's worthy of further study. | ||
- | === actual reports of direct alternator charging === | ||
- | See [[electrical: | ||
=== further reading === | === further reading === | ||
+ | |||
* [[https:// | * [[https:// | ||
* [[https:// | * [[https:// | ||
+ | * [[https:// | ||
+ | * [[electrical: | ||
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Charging is disabled for a few different reasons: | Charging is disabled for a few different reasons: | ||
- | |||
- | People who camp in cold weather may want to select a battery that has "low temperature cut-off", | ||
Note that the BMS overcurrent protection kicks in only at the limit, typically 1[[electrical: | Note that the BMS overcurrent protection kicks in only at the limit, typically 1[[electrical: | ||
+ | |||
+ | === 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)). | ||
+ | |||
+ | It may be possible to add low temperature cutoff to a battery whose BMS lacks that feature. | ||
+ | |||
+ | >> For belt-and-suspenders you could add a $10 12v temp controller or NO thermal switch in series [with the disabling method]. | ||
+ | |||
+ | Note that some chargers have built-in low-temp charging cutoff already. | ||
+ | |||
+ | |||
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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 " | ||
+ | This issue occurs because the charging and discharging channels are separately controlled. | ||
==== cell balancing ==== | ==== cell balancing ==== | ||
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Some batteries have BMS with bluetooth or other forms of connectivity. | Some batteries have BMS with bluetooth or other forms of connectivity. | ||
+ | Having visibility into the state of the BMS/cells might be useful for tech geeks, but often muddies the waters for non-technical customers. | ||
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* [[https:// | * [[https:// | ||
+ | [[http:// | ||
==== Rebel Batteries ==== | ==== Rebel Batteries ==== | ||
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==== Ampere Time ==== | ==== Ampere Time ==== | ||
+ | Now known as LiTime. | ||
No cold cutoff. | No cold cutoff. | ||
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+ | ==== PowerUrus | ||
+ | |||
+ | Budget PowerUrus line by RoyPow | ||
+ | [[https:// | ||
==== Renogy ==== | ==== Renogy ==== | ||
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* [[https:// | * [[https:// | ||
+ | Initial activation may require a quick press-and-release of the button rather than longpress.((https:// | ||
==== Relion ==== | ==== Relion ==== | ||