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electrical:12v:drop-in_lifepo4
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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 [2023/04/01 14:50] frater_secessus [Why are manufacturer-recommended charging voltages so high?] added walkback |
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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 | ||
| Line 97: | Line 97: | ||
| ==== 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: | + | 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 " | ||
| Line 106: | Line 106: | ||
| * 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 cause cell imbalance** and behavior that worries new users, like premature disconnect of charging and apparent battery voltage spikes.((" | ||
| + | |||
| + | 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: | ||
| + | |||
| + | |||
| Line 208: | Line 218: | ||
| - 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)) | ||
| Line 253: | Line 263: | ||
| * 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: | ||
| Line 262: | Line 272: | ||
| 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: | ||
| Line 270: | Line 280: | ||
| * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https:// | * Victron 12v 300Ah Smart LiFePO4, no BMS. ([[https:// | ||
| * [[https:// | * [[https:// | ||
| - | * " | + | * " |
| * Balmar alternator ([[https:// | * Balmar alternator ([[https:// | ||
electrical/12v/drop-in_lifepo4.txt · Last modified: 2024/06/19 19:36 by frater_secessus
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