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electrical:12v:alternator [2024/03/30 15:28]
frater_secessus [sizing an isolator] |
electrical:12v:alternator [2024/04/26 17:11] (current)
frater_secessus [sizing the wire] |
| * In many situations, it is possible to use a simple/inexpensive battery [[electrical:12v:alternator#combiners|combiner]] or [[electrical:12v:alternator#proper_isolators|isolator]] between the house batteries and the vehicle battery. These will allow the house battery to charge when the vehicle is running, but will prevent the vehicle battery from being drained when the engine is off. | * In many situations, it is possible to use a simple/inexpensive battery [[electrical:12v:alternator#combiners|combiner]] or [[electrical:12v:alternator#proper_isolators|isolator]] between the house batteries and the vehicle battery. These will allow the house battery to charge when the vehicle is running, but will prevent the vehicle battery from being drained when the engine is off. |
| * Some situations may benefit from or [[electrical:12v:mandatory_dcdc|require DC-DC chargers]] in between the vehicle batteries and the house batteries. | * Some situations may benefit from or [[electrical:12v:mandatory_dcdc|require DC-DC chargers]] in between the vehicle batteries and the house batteries. |
| | * charging is //triggered// by a 12v signal(("D+", "IGN", "ACC")) and/or by voltage-sensing((monitoring of the actual voltage coming from the chassis)) |
| * Idling the engine while parked for long periods of time just to recharge the batteries is possible, but generally a bad idea. | * Idling the engine while parked for long periods of time just to recharge the batteries is possible, but generally a bad idea. |
| * Pulling a lot of power from the alternator causes it to generate a lot of heat. When the vehicle is moving there's enough airflow to keep the alternator cool, but when parked the heat will build up and can damage the alternator. | * Pulling a lot of power from the alternator causes it to generate a lot of heat. When the vehicle is moving there's enough airflow to keep the alternator cool, but when parked the heat will build up and can damage the alternator. |
| * they have **no way to limit current** other than hitting their max rating and failing or tripping.((diode-based isolators will reduce current somewhat due to forward-voltage losses)) This might mean the battery can pull more current than is good for itself or for the alternator, necessitating the use of [[electrical:12v:b2b|a DC-DC charger]]. This typically is an issue only with oversized banks or small alternators. | * they have **no way to limit current** other than hitting their max rating and failing or tripping.((diode-based isolators will reduce current somewhat due to forward-voltage losses)) This might mean the battery can pull more current than is good for itself or for the alternator, necessitating the use of [[electrical:12v:b2b|a DC-DC charger]]. This typically is an issue only with oversized banks or small alternators. |
| * they **can't boost voltage**((diode isolators will reduce voltage)) like DC-DC. They are not "smart" and have no charging stages -- the house bank will be charged at alternator voltage while the engine is running. Compare your alternator's voltage output to the battery manufacturer's Absorption charging voltage [[electrical:solar:charge_controller_setpoints|setpoint]] before going this route. | * they **can't boost voltage**((diode isolators will reduce voltage)) like DC-DC. They are not "smart" and have no charging stages -- the house bank will be charged at alternator voltage while the engine is running. Compare your alternator's voltage output to the battery manufacturer's Absorption charging voltage [[electrical:solar:charge_controller_setpoints|setpoint]] before going this route. |
| * the charge acceptance rate (Amps) will decrease as bank voltage rises; this is called the //current taper//. | * the charge acceptance rate (Amps) will decrease as bank voltage rises; this is called the //current taper//. Because of the taper if you want to get maximal harvest for your engine's gasoline consumption it would be better to charge when the bank is low than if the bank is nearly full. |
| * vehicles with //smart// (variable voltage) alternators are usually not suitable for charging with normal combiners.((https://www.redarc.com.au/how-do-i-know-if-i-have-a-variable-voltage-smart-alternator)) See [[electrical:12v:alternator#smart_alternators|below]] | * vehicles with //smart// (variable voltage) alternators are usually not suitable for charging with normal combiners.((https://www.redarc.com.au/how-do-i-know-if-i-have-a-variable-voltage-smart-alternator)) See [[electrical:12v:alternator#smart_alternators|below]] |
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| See [[electrical:12v:alternator_details#heat|this sub-article]] on alternators and heat | See [[electrical:12v:alternator_details#heat|this sub-article]] on alternators and heat |
| ==== charging current patterns ==== | |
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| | ==== alternator current rating ==== |
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| | In general, vehicles with higher-rated alternators (150A, for example) will handle a given load better than vehicles with lower-rated alternators (60A, for example). The rating in Amps will be listed on the window sticker, often on the alternator housing itself, or can be looked up using a VIN decoder for your automaker. |
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| | see [[electrical:12v:alternator_details#current|this related article]] on assessing how much current you can safely take from the alternator |
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| | ==== fuel consumption ==== |
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| | Fuel consumption for power generation will be greatest when the vehicle is idled. When charging loads are imposed on a vehicle that is already driving the added cost can be minimal. |
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| | Using the 3.6L [[rv:ram_promaster|Promaster]] with a 40A [[electrical:12v:b2b|DC-DC charger]] as an example, ObvB estimates: |
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| | >> In terms of cost, an average USA price of gas at $3.36, **idling** for 2 hours to produce 1kWh with a 40A DC-DC charger would burn 2 * (2/3 + 0.074) gal = 1.48 gal = **$4.97 / kWh**. If you were going to be **driving** anyway, then the additional cost of turning on a DC-DC charger (using my assumptions) would be about **50c/kWh**.((https://www.promasterforum.com/threads/fuel-consumption-at-idle.103939/post-841876)) |
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| | ===== charging current patterns ===== |
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| * charging lead chemistries directly from the alternator tends toward | * charging lead chemistries directly from the alternator tends toward |
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| ''23A x 20 minutes / 60 minutes in an hour = 7.666666667Ah'' | ''23A x 20 minutes / 60 minutes in an hour = 7.666666667Ah'' |
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| ==== alternator current rating ==== | |
| |
| In general, vehicles with higher-rated alternators (150A, for example) will handle a given load better than vehicles with lower-rated alternators (60A, for example). The rating in Amps will be listed on the window sticker, often on the alternator housing itself, or can be looked up using a VIN decoder for your automaker. | |
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| see [[electrical:12v:alternator_details#current|this related article]] on assessing how much current you can safely take from the alternator | |
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| ===== fuel consumption ===== | |
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| Fuel consumption for power generation will be greatest when the vehicle is idled. When charging loads are imposed on a vehicle that is already driving the added cost can be minimal. | |
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| Using the 3.6L [[rv:ram_promaster|Promaster]] with a 40A [[electrical:12v:b2b|DC-DC charger]] as an example, ObvB estimates: | |
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| >> In terms of cost, an average USA price of gas at $3.36, **idling** for 2 hours to produce 1kWh with a 40A DC-DC charger would burn 2 * (2/3 + 0.074) gal = 1.48 gal = **$4.97 / kWh**. If you were going to be **driving** anyway, then the additional cost of turning on a DC-DC charger (using my assumptions) would be about **50c/kWh**.((https://www.promasterforum.com/threads/fuel-consumption-at-idle.103939/post-841876)) | |
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| * direct charging results in //tapering// charge current, decreasing as battery bank voltage / SoC increases.((among other factors)). So over an hour the current might go from 30A to 10A, an average of 20A. 20A x 1 hour = **20Ah replaced**. Pro: your bank gets more charging when it needs it most. Con: charge rates are less predictable until you learn how your system works. | * direct charging results in //tapering// charge current, decreasing as battery bank voltage / SoC increases.((among other factors)). So over an hour the current might go from 30A to 10A, an average of 20A. 20A x 1 hour = **20Ah replaced**. Pro: your bank gets more charging when it needs it most. Con: charge rates are less predictable until you learn how your system works. |
| * [[:b2b|DC-DC charging]] generally make its rated output (20A, for example) for the majority of the charging cycle. Pro: highly predictable charging (20A x 1 hour = **20Ah replaced**). Con: charging current is the ~same regardless of bank SoC | * [[electrical:12v:b2b|DC-DC charging]] generally make its rated output (20A, for example) for the majority of the charging cycle. Pro: highly predictable charging (20A x 1 hour = **20Ah replaced**). Con: charging current is the ~same regardless of bank SoC |
| * in this artificial example both charging setups will replace 20Ah in an hour of charging but they do it differently. In reality which charges "better" depends on your specific use case, bank chemistry & capacity, alternator voltage and rating, DC-DC rating, etc. Do your research and pick your poison. | * in this artificial example both charging setups will replace 20Ah in an hour of charging but they do it differently. In reality which charges "better" depends on your specific use case, bank chemistry & capacity, alternator voltage and rating, DC-DC rating, etc. Do your research and pick your poison. |
| ==== flooded lead-acid ==== | ==== flooded lead-acid ==== |
| * LiFePO4 resting voltages are high enough they may hold the circuit closed on VSRs designed for lead chemistries. Workaround: [[electrical:12v:alternator#disabling_alternator_charging|disable alternator charging]] (at least momentarily) after driving or install DC-DC. Or just let it work that way. | * LiFePO4 resting voltages are high enough they may hold the circuit closed on VSRs designed for lead chemistries. Workaround: [[electrical:12v:alternator#disabling_alternator_charging|disable alternator charging]] (at least momentarily) after driving or install DC-DC. Or just let it work that way. |
| * Voltage-sensing relays can be unintentionally triggered((dVSR)) or "held closed"((both VSR and dVSR)) [[http://bdp.mousetrap.net/index.php/2018/10/27/side-effect-of-solar-alternator-charging/|by voltage from the solar-charged side]] in some scenarios. Workaround: address with HVD as below if desired, or with a [[electrical:12v:b2b|DC-DC charger]], or by adding a switch to disable the VSR.((a momentary-off switch would kill the connection, although an ON/OFF switch might be useful for other purposes)) | * Voltage-sensing relays can be unintentionally triggered((dVSR)) or "held closed"((both VSR and dVSR)) [[http://bdp.mousetrap.net/index.php/2018/10/27/side-effect-of-solar-alternator-charging/|by voltage from the solar-charged side]] in some scenarios. Workaround: address with HVD as below if desired, or with a [[electrical:12v:b2b|DC-DC charger]], or by adding a switch to disable the VSR.((a momentary-off switch would kill the connection, although an ON/OFF switch might be useful for other purposes)) |
| * In early morning or other times when house battery voltage is lowest, **a plain solenoid may unintentionally allow depleted batteries to pull down the starter battery**. Workarounds: use a VSR, a DC delay timer, a DC-DC charger, or start the vehicle immediately after inserting the key((ie, do not leave in the Accessory position which would drain the starter battery)). | * On ignition-triggered((IGN, D+)) setups **if the key is turned to ACC but the engine not started a depleted house battery can pull down the starter battery**. Workarounds: use a VSR, a DC delay timer, a DC-DC charger, or start the vehicle immediately after inserting the key((ie, do not leave in the Accessory position which would drain the starter battery)). |
| * Solar charging while the engine is running may [[opinion:frater_secessus:alternatorSolarStall|get "stuck" at alternator voltage]]. Workaround: higher solar wattage, DC-DC charger, or diode/FET-based isolator, or a switch to disconnect isolator after alternator voltage is reached. The [[https://amzn.to/3h5iMUd|Victron Cyrix-ct isolator]] could be useful here, as it appears to disconnect >13.8v.((https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-ct-120A-230A-EN.pdf)) | * Solar charging while the engine is running may [[opinion:frater_secessus:alternatorSolarStall|get "stuck" at alternator voltage]]. Workaround: higher solar wattage, DC-DC charger, or diode/FET-based isolator, or a switch to disconnect isolator after alternator voltage is reached. The [[https://amzn.to/3h5iMUd|Victron Cyrix-ct isolator]] could be useful here, as it appears to disconnect >13.8v.((https://www.victronenergy.com/upload/documents/Datasheet-Cyrix-ct-120A-230A-EN.pdf)) |
| * Alternator charging may bring some battery chemistries (like bare lithium cells with no BMS) to **unsuitably high voltages**. Workarounds: A [[electrical:12v:hvd|high voltage disconnect]] can [[electrical:12v:alternator charging hvd|restrict alternator charging to lower voltages]]. [[electrical:12v:b2b|DC-DC chargers]] can also regulate voltage provided to the house battery. | * Alternator charging may bring some battery chemistries (like bare lithium cells with no BMS) to **unsuitably high voltages**. Workarounds: A [[electrical:12v:hvd|high voltage disconnect]] can [[electrical:12v:alternator charging hvd|restrict alternator charging to lower voltages]]. And [[electrical:12v:b2b|DC-DC chargers]] can also regulate voltage provided to the house battery. |
| * It is possible for a plain combiner to "mask" the symptoms of a failing starter battery since the house bank would be assisting with the start. | * It is possible for a plain combiner to "mask" the symptoms of a failing starter battery since the house bank would be assisting with the start. It is also possible for powerful solar to mask symptoms of a dying alternator because in that case the solar is helping run the chassis electricals. |
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| ===== disabling alternator charging ===== | ===== disabling alternator charging ===== |
| It may be desirable to disable alternator charging on-the-fly when stopped in traffic, on hot days, to avoid charging frozen Li cells,((using a temperature controller)) stop charging at a given voltage,((using a [[electrical:12v:alternator_charging_hvd|High Voltage Disconnect]])) or neutralize [[electrical:12v:alternator#gotchas|gotchas]], etc. The method of disabling will vary depending on the gear: | It may be desirable to disable alternator charging on-the-fly when stopped in traffic, on hot days, to avoid charging frozen Li cells,((using a temperature controller)) stop charging at a given voltage,((using a [[electrical:12v:alternator_charging_hvd|High Voltage Disconnect]])) or neutralize [[electrical:12v:alternator#gotchas|gotchas]], etc. The method of disabling will vary depending on the gear: |
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| * relays and DC-DC that are triggered solely by D+ can be disabled by a switch on the D+ wire | * relays and DC-DC that are triggered solely by D+ can be disabled by a switch on the D+ wire. [[https://www.reddit.com/r/VanLife/comments/1c4vjl0/is_this_renogy_a_good_dcdc_option_for_a_200ah/kzuc78v/|Additional control could be introduced]] with a relay and or delay ([[https://amzn.to/3TUEbmu|example]]) |
| * VSR triggered by voltage can can be disabled by a switch on the thin ground wire on the VSR itself.((the VSR requires a ground to make a complete circuit to run internal electronics. Breaking this circuit turns off the VSR)) | * VSR triggered by voltage can can be disabled by a switch on the thin ground wire on the VSR itself.((the VSR requires a ground to make a complete circuit to run internal electronics. Breaking this circuit turns off the VSR)) |
| * some DC-DC can be //derated// by providing a 12v signal to the CURRENT LIMIT terminal ([[electrical:12v:b2b#renogy1|Renogy DC1212 series]], [[electrical:12v:b2b#leaptrend|Leaptrend]]) | * some DC-DC can be //derated// by providing a 12v signal to the CURRENT LIMIT terminal ([[electrical:12v:b2b#renogy1|Renogy DC1212 series]], [[electrical:12v:b2b#leaptrend|Leaptrend]]) |
| - use [[electrical:12v:b2b|a DC-DC charger]] to get at least the correct charging voltage | - use [[electrical:12v:b2b|a DC-DC charger]] to get at least the correct charging voltage |
| - if charging by relay only, use Crtical size wire to get the most voltage and current to the lead house battery | - if charging by relay only, use Crtical size wire to get the most voltage and current to the lead house battery |
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| | ==== triggering ==== |
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| | The setup needs to be //triggered// (told when to start/stop) so that it isn't connected all the time. There are two main methods: |
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| | - use of an ON/OFF 12v trigger signal ("D+", "IGN", "ACC"). When the 12v signal is present the charging circuit is operational. Caveat: in this kind of setup leaving the key in the ACC position without starting the engine can drain the starter battery. |
| | - voltage-sensing - 12v is always being provided to the charger. The batteries are connected when the chassis voltage is above a voltage setpoint (often ≥13.4v) and disconnected when the chassis side measures below a setpoing (often ≤13.2v). |
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| | In some cases both are combined for particular installs. Ex. smart alternators. |
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| ===== alternator hacks ===== | ===== alternator hacks ===== |
