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electrical:12v:drop-in_lifepo4 [2022/09/14 15:24] frater_secessus [myth: you must use DC-DC for alternator charging Li] |
electrical:12v:drop-in_lifepo4 [2022/11/05 12:11] frater_secessus [myth: you must use DC-DC for alternator charging Li] daisy chain |
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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' | ||
+ | |||
+ | 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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* 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 === | ||
- | Here an order of operations one might use to assess whether or not isolator charging will work in a given install: | + | see [[electrical: |
- | + | ||
- | - 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// | + | |
- | - Read and understand your Li battery manufacturer' | + | |
- | - Read and understand your alternator' | + | |
- | - Read and understand your isolator' | + | |
- | - observe your vehicle' | + | |
- | - make a first approximation about the ability of alternator, your isolator, and your Li battery to cooperate | + | |
- | - install | + | |
- | - 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.)) | + | |
- | - 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. | + | |
- | + | ||
- | + | ||
- | **Caveats**: | + | |
- | + | ||
- | * 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: | + | |
- | * You may want a manual disconnect or [[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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- | 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 < |