| Both sides previous revision
Previous revision
Next revision
|
Previous revision
Next revision
Both sides next revision
|
electrical:12v:alternator [2024/04/05 11:08]
frater_secessus [gotchas] |
electrical:12v:alternator [2024/04/09 14:41]
frater_secessus [limitations] timing |
| * 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]] |
| |
| * 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)). | * 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. |
| |
| ===== disabling alternator charging ===== | ===== disabling alternator charging ===== |
