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electrical:12v:drop-in_lifepo4 [2022/03/16 19:13] frater_secessus [myth: you must use DC-DC for alternator charging Li] |
electrical:12v:drop-in_lifepo4 [2024/02/11 11:26] frater_secessus [myth: you can't use a combiner to charge batteries of different chemistries] |
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> [[https:// | > [[https:// | ||
- | " | + | " |
- | 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. |
- | ===== drop-in lithium benefits ===== | + | |
+ | 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-ins are ready to use. Buy it, install it. | ||
+ | |||
+ | |||
+ | ===== Drop-in lithium limitations ===== | ||
+ | |||
+ | * 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 very expensive compared to [[electrical: | ||
- | * Drop-ins are ready to use. Buy it, install it. | ||
===== overall lithium benefits ===== | ===== overall lithium benefits ===== | ||
Line 21: | Line 33: | ||
* 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 | ||
- | |||
- | |||
- | ===== drop-in lithium limitations ===== | ||
- | |||
- | * 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 very expensive compared to DIY lithium | ||
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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 durations | + | * Li can be **damaged** by long duration |
- | * the flat voltage curve makes gauging SoC by voltage extremely challenging. | + | * the flat voltage curve makes gauging SoC by voltage extremely challenging, and battery " |
Line 92: | Line 97: | ||
* **charging to 3.4vpc** (13.6v for a 4S pack) **and holding voltage** for 4+ hours yielded 98.2% SoC. | * **charging to 3.4vpc** (13.6v for a 4S pack) **and holding voltage** for 4+ hours yielded 98.2% SoC. | ||
- | === 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 | + | ==== Why are manufacturer-recommended charging voltages so high? ==== |
+ | |||
+ | {{ https:// | ||
+ | Manufacturers need simple instructions that will still allow the batteries to meet their advertised lifetime and reduce customer support issues. In this scenario | ||
* 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) | ||
* faster charging | * faster charging | ||
- | * higher charging **rate** - bigger differences between charger and battery voltage mean more current. | + | * higher charging **rate** - bigger differences between charger and battery voltage mean more current |
- | * 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 | + | * 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: | ||
+ | |||
+ | |||
==== an approach to greater longevity ==== | ==== an approach to greater longevity ==== | ||
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* charge/ | * charge/ | ||
* at human-comfortable temperatures. | * at human-comfortable temperatures. | ||
+ | * not held at high states of charge (see below) | ||
* discharged no lower than 20% State of Charge | * discharged no lower than 20% State of Charge | ||
* generally operated " | * generally operated " | ||
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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==== myth: you can charge Li as fast as you want ==== | ==== myth: you can charge Li as fast as you want ==== | ||
- | BMS are often configured to limit charging to 1C (100A for a 100Ah battery) as an absolute maximum. | + | BMS are often configured to limit charging to 1C (100A for a 100Ah battery) as an absolute maximum. |
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 typical charging voltage setpoints (" | ||
+ | |||
+ | ^ Chemistry | ||
+ | | Gel | 14.0v - 14.3v | 14.2v | | ||
+ | | AGM | 14.2v - 14.5v | 14.4v | | ||
+ | | Flooded | ||
+ | | LiFePO4 | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | * flooded lead acid typically *requires* >14.6v and gel typically *requires* <14.3v so those two won't play well together. | ||
+ | 1. they remain connected when charging stops -- the split relay is there to stop that from happening | ||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
+ | |||
==== myth: you have to charge Li to 100% ==== | ==== myth: you have to charge Li to 100% ==== | ||
Lead batteries require fully charging to 100% state of charge (SoC) but lithium batteries do not. Charging them fully at higher voltages can cause cells to become further out of balance. | Lead batteries require fully charging to 100% state of charge (SoC) but lithium batteries do not. Charging them fully at higher voltages can cause cells to become further out of balance. | ||
+ | |||
+ | [[https:// | ||
+ | |||
+ | > | ||
Having said that, there are valid reasons for charging to 100%: | Having said that, there are valid reasons for charging to 100%: | ||
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+ | ==== myth: if you don't charge to 14.4v the cells won't balance ==== | ||
+ | |||
+ | Charging at higher voltages (and higher rates) //causes// cell imbalance, which the (usually comically-undersized) balancer attempts to correct. | ||
+ | |||
+ | This occurs because the cells hit the high-voltage " | ||
+ | |||
+ | * in cyclic use (like offgrid) ~13.8v (3.45Vpc) is sufficient to reach 100% with some absorption, without antagonizing cell balance. | ||
+ | * when on shore power (like on a power pedestal) voltages as low as 13.4v will slowly bring the bank up to 100% SoC. | ||
+ | |||
+ | 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' | ||
+ | |||
+ | |||
+ | Lithium doesn' | ||
+ | |||
+ | Most charts and tables showing voltage v. SoC assume moderate rates of charge like 0.2[[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. | ||
+ | Further reading: | ||
==== 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, | + | 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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- 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. |
- | * <13.4v will allow the bank to settle | + | * <13.4v will allow the bank to settle below 100% |
- | * 13.4v will hold the bank near whatever SoC it was charged to. If in doubt, this is a good default. | + | * 13.4v will hold the bank near whatever SoC it was charged to. If in doubt, this is a good default |
* >13.4v will continue to charge the bank beyond the SoC it was charged to during Absorption. | * >13.4v will continue to charge the bank beyond the SoC it was charged to during Absorption. | ||
+ | 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 both the battery, the alternator, 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. | ||
They do recommend [[electrical: | They do recommend [[electrical: | ||
+ | |||
=== why an isolator? === | === why an isolator? === | ||
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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. | + | * 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: | ||
=== testing your isolator with Li === | === testing your isolator with Li === | ||
- | Here an order of operations one might use to assess whether | + | see [[electrical: |
+ | |||
+ | ==== but that Victron video ==== | ||
+ | |||
+ | Why would a manufacturer | ||
+ | |||
+ | The setup: | ||
+ | |||
+ | * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https:// | ||
+ | * [[https:// | ||
+ | * " | ||
+ | * Balmar alternator ([[https:// | ||
+ | * dedicated negative return (" | ||
+ | |||
+ | The results: | ||
+ | |||
+ | Keep in mind that alternator RPM is typically 3x engine RPM. | ||
+ | |||
+ | * " | ||
+ | * 1.500rpm((~500 engine RPM)) - 65.1A. | ||
+ | * 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. | ||
+ | * Balmar | ||
+ | * 2, | ||
+ | * 3, | ||
+ | |||
+ | Their conclusion: | ||
+ | |||
+ | > charging lithium batteries at low RPM results in the altenator overheating.((3: | ||
+ | |||
+ | Yes, a **300Ah** LFP bank //can// smoke a ≤**90A** alternator **at idle**. | ||
+ | |||
+ | They go on to list the workarounds: | ||
+ | |||
+ | - install a high output alternator that can handle demand at idle ($hundreds) | ||
+ | - fit an externally-regulated alternator with temp sensor, as shown in the video (~$850) | ||
+ | - or (surprise!), | ||
+ | - {not mentioned: | ||
+ | |||
+ | |||
+ | { 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 | ||
+ | |||
+ | > 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. | ||
- | - Read and understand your Li battery manufacturer' | ||
- | - Read and understand your alternator' | ||
- | - Read and understand your isolator' | ||
- | - observe your vehicle' | ||
- | - decide whether this will work for your alternator, your isolator, and your Li battery | ||
- | - install [[electrical: | ||
- | - 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 that works test it with longer drives and/or with the Li at lower states of charge. | ||
- | **Caveats**: | ||
- | * Only alternator charge while driving (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: | ||
- | * You may want a manual disconnect or [[electrical: | ||
=== further reading === | === further reading === | ||
- | [[https:// | + | |
+ | * [[https:// | ||
+ | * [[https:// | ||
+ | * [[https:// | ||
+ | * [[electrical: | ||
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===== BMS functions ===== | ===== BMS functions ===== | ||
- | Lithium cells can hurt themselves if left unsupervised. | + | Lithium cells can hurt themselves if left unsupervised. |
- | Typical | + | Drop-in Lithium batteries all have a BMS integrated inside of them, so there is typically less to worry about. |
- | ==== charging | + | Typical BMS protections may include: |
+ | |||
+ | ==== Charging | ||
Charging is disabled for a few different reasons: | Charging is disabled for a few different reasons: | ||
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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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* cell 2 = 3.400v | * cell 2 = 3.400v | ||
* cell 3 = 3.400v | * cell 3 = 3.400v | ||
- | * cell 4 = 3.**500v** <-- balancer will try to slow this one down | + | * cell 4 = 3.**500v** < |
In both cases the overall battery voltage is 13.6v, but in the unbalanced battery cell #1 is lagging (reducing capacity) and cell #4 is too high. The balancer will attempt to rein in #4 but the effect is tiny. Using a typical balancing current of 50mA, if you are charging at 20A that means the cells are receiving 5A except cell #4 which gets only 4.95A, about a 1% difference. | In both cases the overall battery voltage is 13.6v, but in the unbalanced battery cell #1 is lagging (reducing capacity) and cell #4 is too high. The balancer will attempt to rein in #4 but the effect is tiny. Using a typical balancing current of 50mA, if you are charging at 20A that means the cells are receiving 5A except cell #4 which gets only 4.95A, about a 1% difference. | ||
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* premium - Battle Born | * premium - Battle Born | ||
* moderate - SOK | * moderate - SOK | ||
- | * inexpensive - Chins (no cutoff) or Weize (cold cutoff) | + | * inexpensive - Chins and Ampere Time (no cutoff) or Weize (cold cutoff) |
Charge/ | Charge/ | ||
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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 ==== | ||
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Absorption 14.2-14.6v, C/5 charging recommended, | Absorption 14.2-14.6v, C/5 charging recommended, | ||
+ | |||
+ | An after-sale email from Chins to an Amazon buyer((forwarded by personal correspondence to secessus)) said: | ||
+ | |||
+ | > | ||
+ | >Over Voltage Disconnect Voltage: 14.6V | ||
+ | >Over Voltage Reconnect Voltage: 13.8V | ||
+ | >Float Charging Voltage: 13.8V | ||
+ | >Low Voltage Disconnect Voltage: 11.6V | ||
+ | >Low Voltage Reconnect Voltage: 12.4V | ||
+ | >Under Voltage Warning Voltage: 12.8V | ||
+ | |||
+ | |||
* [[https:// | * [[https:// | ||
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There have been [[https:// | There have been [[https:// | ||
+ | According to Amazon answers((bao peng on https:// | ||
==== batteries with troubling reports ==== | ==== batteries with troubling reports ==== | ||
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===== further reading ===== | ===== further reading ===== | ||
+ | * [[https:// | ||
+ | * [[https:// | ||
* [[https:// | * [[https:// | ||
* [[https:// | * [[https:// |