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electrical:12v:directcharginglfp [2023/12/17 17:02] frater_secessus [assessing your own setup for direct alternator charging] |
electrical:12v:directcharginglfp [2024/03/20 12:07] frater_secessus [assessing your own setup for direct alternator charging] |
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- | Let's assume battery resting voltage is 13.0 and alternator voltage is 14.0 and circuit resistance is 20mR. | + | Let's assume battery resting voltage is 13.0 and alternator voltage is 14.0 and circuit resistance is 20mR (.020R). |
- | * I=V/R = (14v-13v)/ | + | * I=V/R = (14v-13v)/ |
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Let's add 5m Ohm of resistance: | Let's add 5m Ohm of resistance: | ||
- | * I=V/R = (14v-13v)/ | + | * I=V/R = (14v-13v)/ |
===== tweaking current with voltage ===== | ===== tweaking current with voltage ===== | ||
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If the SoC was very low (near cutoff) the combiner would slightly faster, ~7.5 minutes. | If the SoC was very low (near cutoff) the combiner would slightly faster, ~7.5 minutes. | ||
- | ===== assessing your own setup for direct | + | ===== reasons NOT to attempt |
- | + | ||
- | There are good reasons //not// to attempt direct charging: | + | |
- | For example, if | ||
* you have [[electrical: | * you have [[electrical: | ||
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* In the van-relevant examples above LFP banks typically pull 0.33C, or 33A per 100Ah of capacity, so it might be acceptable to size them to 0.5C (noncritical). | * In the van-relevant examples above LFP banks typically pull 0.33C, or 33A per 100Ah of capacity, so it might be acceptable to size them to 0.5C (noncritical). | ||
* a set of heavy jumper cables and a clamp-on monitor might help assess max current draw before buying any wiring. | * a set of heavy jumper cables and a clamp-on monitor might help assess max current draw before buying any wiring. | ||
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+ | ===== assessing your own setup for direct alternator charging ===== | ||
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+ | [Note: | ||
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If you are still interested, here is one approach to assessing your setup for direct charging lithium. | If you are still interested, here is one approach to assessing your setup for direct charging lithium. | ||
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- test it with a drive. | - 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 state of charge you expect to recharge from alternator. | - repeat the last two steps with the Li bank at lower and lower states of charge, down to the lowest state of charge you expect to recharge from alternator. | ||
- | - disconnect the isolator with **a switch** when you come to the desired SoC, when charge rate exceeds your preferences, | + | - celebrate |
**Caveats**: | **Caveats**: | ||
* Only alternator charge while driving ([[rv: | * Only alternator charge while driving ([[rv: | ||
- | * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical: | + | * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical: |
- | * Fuse the wiring from the chassis so the bank cannot pull more than you specify | + | * if current is excessive but you want to direct-charge, |
- | * if current is higher than you want consider adding resistance | + | |
===== the parts list ===== | ===== the parts list ===== |