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electrical:12v:directcharginglfp [2024/03/20 12:04]
frater_secessus [assessing your own setup for direct alternator charging] 		electrical:12v:directcharginglfp [2024/06/04 14:37] (current)
frater_secessus [testing phase]
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   * you have a **small or already-overloaded alternator**   * you have a **small or already-overloaded alternator**
   * you **already own a DC-DC**    * you **already own a DC-DC** 
 +  * your BMS has no low temp charging disconnect and you have no desire to work around that((to be fair, this also rules out DC-DC that lack low-temp disconnect))
   * you **want predictable charging rates**, like 40A over the next hour.  DC-DC will provide this((barring interference from big chassis loads, BMS protections, high ambients, etc));  isolator charging starts out high and drops as battery voltage rises.  You might learn its behavior over time, but it will never be as easy as "40A for 1.5 hours = 60Ah".    * you **want predictable charging rates**, like 40A over the next hour.  DC-DC will provide this((barring interference from big chassis loads, BMS protections, high ambients, etc));  isolator charging starts out high and drops as battery voltage rises.  You might learn its behavior over time, but it will never be as easy as "40A for 1.5 hours = 60Ah". 
   * you want **stable charging rates** regardless of state of charge((acceptance will taper in Absorption if present))     * you want **stable charging rates** regardless of state of charge((acceptance will taper in Absorption if present))  
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 [Note:  this section errs on the side of methodical plodding in the spirit of "don't eat this mattress" or "do not juggle chainsaws on the top step of this ladder".  For existing setups it can be as simple as starting the engine briefly to see how much current is drawn and going from there.  The existing fuse would intervene if the current is harmfully large.] [Note:  this section errs on the side of methodical plodding in the spirit of "don't eat this mattress" or "do not juggle chainsaws on the top step of this ladder".  For existing setups it can be as simple as starting the engine briefly to see how much current is drawn and going from there.  The existing fuse would intervene if the current is harmfully large.]
  
 +==== assessment phase ====
  
- 
-If you are still interested, here is one approach to assessing your setup for direct charging lithium.   
  
   - pay attention to the **chassis' normal voltage** while idling and cruising - this is a benchmark for how the vehicle behaves without aux charging.    - pay attention to the **chassis' normal voltage** while idling and cruising - this is a benchmark for how the vehicle behaves without aux charging. 
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   - now make a **sanity check** about the ability of alternator, your isolator, and your Li battery to cooperate.  Refer to the actual reports in the spreadsheet to see if any approximate your setup.  If you can measure the total resistance do so and work the formula.     - now make a **sanity check** about the ability of alternator, your isolator, and your Li battery to cooperate.  Refer to the actual reports in the spreadsheet to see if any approximate your setup.  If you can measure the total resistance do so and work the formula.  
   - ensure the **fuse** between your chassis and battery bank is sized so //you cannot draw more than the alternator and wiring can handle//   - 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.))  Start the engine and see if the charging current and voltage is acceptable.  See if chassis voltage remains stable.  Turn off the engine. 
-  - 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. 
-  - celebrate 
  
-**Caveats**:  +==== testing phase ==== 
 + 
 +  - make the first test run a brief one and with the Li well-charged.((higher states of charge will reduce current demand))  Start the engine and see if the charging current((per the BMS, [[electrical:12v:battery_monitor|battery monitor]], or [[https://amzn.to/3Vt8Jhh|clamp meter]])) and voltage is acceptable.  Check to see chassis voltage and engine RPM remain stable((do not drop precipitously anything longer than a moment while alternator output adjusts)) and belts do not squeal.  Turn off the engine. 
 +  - if solar or other charging source is present, disconnect those chargers and repeat #1.((other chargers will push up apparent bank voltage, which would decrease current demanded of the alternator)) 
 +  - repeat steps above with the Li bank at lower and lower states of charge, down to the lowest state of charge you expect to recharge from alternator. 
 + 
 + 
 +==== caveats ==== 
  
   * Only alternator charge while driving ([[rv:idling|no idling]] except for brief preliminary test).     * Only alternator charge while driving ([[rv:idling|no idling]] except for brief preliminary test).  
-  * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical:depth_of_discharge|states of charge]]. You may want a manual disconnect or [[electrical:12v:alternator_charging_hvd|HVD]] to shut off alternator charging due to excess voltage or if the bank is already charged.  These can be added on the D+ wire (ignition triggered) or electronics ground wire (VSR, solenoid, or voltage-triggered DC-DC) +  * Pay attention while charging from alternator to keep from overcharging the Li or holding for long periods at high [[electrical:depth_of_discharge|states of charge]]. You may want [[electrical:12v:alternator#disabling_alternator_charging|a manual disconnect]] or [[electrical:12v:alternator_charging_hvd|HVD]] to shut off alternator charging due to excess voltage or if the bank is already charged.  These can be added on the D+ wire (ignition triggered) or electronics ground wire (VSR, solenoid, or voltage-triggered DC-DC) 
-  * 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, you can tweak acceptance with resistance or voltage as seen elsewhere in this article
-  * if current is higher than you want consider adding resistance to the circuit+
  
 ===== the parts list ===== ===== the parts list =====
electrical/12v/directcharginglfp.1710950645.txt.gz · Last modified: 2024/03/20 12:04 by frater_secessus

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