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--- electrical:12v:alternator_details [2023/09/24 16:27]
frater_secessus [current]
+++ electrical:12v:alternator_details [2025/06/18 20:13] (current)
frater_secessus [load dumps]
@@ Line 52: / Line 52: @@
 **Externally-regulated alternators** are alternators where the regulation function is physically separated from the alternator.  There may be a stand-alone external regulator or the engine ECU may assume those duties.
-In a camper/RV context //an externally-regulated alternator// typically means an **aftermarket regulator**, like Balmar - voltage often provides [[electrical:12v:charging|multistage (smart) charging]], temperature-based derating, etc.  Read on.
+see [[electrical:12v:alternator_details#external_regulation|External Regulation]] below
-A separate alternator (see below) is not required to use external regulation but that is a common scenario.  If one externally regulates the vehicle's sole alternator the chassis could be exposed to higher or lower voltages than it was designed for.
-Common external regulators include:
-  * Balmar ARS-5 (no external voltage sensing)
-  * Balmar MC-614 (external voltage sensing)
-  * Xantrex Xar (no external voltage sensing)
-  * Wakespeed WS500 (CANBUS)
 === tricking the regulator ===
@@ Line 131: / Line 122: @@
-=== heat ===
+==== heat ====
 Heat in the alternator comes from
-  * the engine block (radiation)
+  * the engine block (radiation and conduction)
+  * the radiator (radiation)
   * ambient temperatures
   * the alternator itself - alternators are most efficient (produced the least heat per watt) at normal vehicle cruising speeds.  At low RPM and high RPM more heat will be generated:
@@ Line 177: / Line 169: @@
 === thermal switches ===
-In [[https://www.youtube.com/watch?v=bjeHJd6OO2Y&lc=Ugyusa6wH9p3jNMKbmh4AaABAg.9m5OeSgBRtB9m5UO1ANIfF|a comment]] on [[https://www.youtube.com/watch?v=bjeHJd6OO2Y|an excellent video about charging lithium from the alternator]] WorkingOnExploring talks about adding overtemp protection with:
+In [[https://www.youtube.com/watch?v=bjeHJd6OO2Y&lc=Ugyusa6wH9p3jNMKbmh4AaABAg.9m5OeSgBRtB9m5UO1ANIfF|a comment]] on [[https://www.youtube.com/watch?v=bjeHJd6OO2Y|an excellent video about charging lithium from the alternator]] WorkingOnExploring talks about adding overtemp protection with a thermal switch (a small bimetallic switch):((see [[https://www.youtube.com/watch?v=kF4Yxo9C9DM|this teardown and demo video]]  on youtube))
 >>  [[https://amzn.to/3luTwwx|a KSD9700 120C]], normally closed thermal switch epoxied to your alternator case. That way, if some abnormal event occurred and the alternator overheated, it could deactivate the [combiner] till the alternator cooled. It would likely cost less than $20 to install this thermal safety.
@@ Line 183: / Line 176: @@
 The idea here is to run the relay's control circuit((manual or D+ wire, //not// the charging wire)) through the **N**ormally-**C**losed((ie,circuit completed)) thermal switch.  When the switch hits the defined temperature the circuit opens((breaks)) and power to the combiner is cut off;  house bank charging from the alternator is stopped. The switch will typically reset when temperature drops by ~25%; read the datasheet for your switch for specific details.
-The thermal switch is a tiny bimetallic device.  See [[https://www.youtube.com/watch?v=kF4Yxo9C9DM|this teardown and demo video]] (youtube).
+If one had a DC with a current-limiting function ([[electrical:12v:b2b#renogy1|renogy's 20-40-60A models]], for example) or DC-DC in parallel one could use two different-spec switches to achieve staged charging.  Using placeholder temps:
+  - run an aggressive charging setup full blast
+  - at 90C engage current limiting
+  - at 120C disable charging completely
 Note:  120C = 248F.  Other temps like 90C (194F) and 100C (212C) are available and may be gentler on the alternator. Because the alternator is mounted to the block the alternator case may be at the ~same temp as the block.  Check case temps when engine has been running to get a feel for how hot the case should be, preferably at the location the diodes are heat-sinked to the alternator case.((https://forums.sailboatowners.com/threads/alternator-temperature.1249925187/post-1644191))
@@ Line 223: / Line 223: @@
 >> We have 500ah of lithium that can be charged at 3C, a theoretical 1,500 ampere charge rate. We have the Nations 280 amp second alternator. We control the Nations alternator with a DIY regulator that allows us to pretty much set the charge level anywhere we please. We'd be pleased to set it to 200+ amps, but that turns out to be impractical. The reality is, **if we set the charge rate to 125 amperes, we cannot continuously charge at this rate while standing still unless the outside air temperature is 55 degrees or below**. **When driving at highway speeds (which cools the alternator), we can run a continuous 150 ampere charge rate** at virtually any outside air temperature. While we have not tested this further, we suspect that should we desire to 'up the ante' much beyond our current 150 (sometimes 175) amperes, we would again find ourselves temperature limited even while driving. - [[https://www.promasterforum.com/threads/idea-help-wanted-alternator-charging-house-batteries-only.96415/post-766319|winston]]
+==== load dumps ====
+The alternator's voltage regulator responds to demand, increasing and decreasing field strength (and therefore output) as required to hold a given voltage setpoint.
+  * when **loads are added** chassis voltage will drop briefly while the regulator responds.
+  * when **loads are removed** chassis voltage will spike briefly while the regulator responds.
+  * if **large loads disappear suddenly** and nothing is available to absorb the spike that excess voltage can damage the alternator and/or other electrics.
+In typical installs there //are// places for the power in the alternator to go, chiefly the lead starter battery:
+> [lead] batteries have about 1000F ( farad ) [capacitance] per 150Ah of capacity so they act as very substantial capacitors.  Hence they have enormous ability to absorb spike energy.((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-7.html#post3533042)),((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-8.html#post3533143))
+The real problem is secondary alternators dedicated to LFP charging;  if the BMS disconnects charging there is no starter battery on that separate circuit to absorb the energy.
+For a typical install the  question is:  how much charging current are we talking about, and does the alternator already handle that level of sudden disconnect under normal operation? Secessus provides this example:
+> my van's radiator cooling fans are rated at 65A((https://www.promasterforum.com/threads/180-amp-alternator-with-amp-clamp-on-output.99118/post-792681)) and turn on/off frequently via relay.((see below))  My Li charging current is less than that.
+In addition, the speed of the disconnect plays a part:
+> there is a massive difference in the voltage spike from a 5 uS relay disconnect and a 10mS mosfet disconnect [as found in the BMS]((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-7.html#post3532864))
+When an alternator is outputting Big Power and the demand for that power vanishes the alternator (and other chassis electricals) can be damaged:
+> When the rotor current is stoked up to create a large rotor magnetic field for high alternator output and there is a sudden drop off in alternator load, the stored rotor energy takes some time to dissipate. This causes a voltage spike in output of the alternator if there is suddenly little to no load on alternator... the voltage spike can be up to several hundred volts when loading suddenly drops off. This can damage alternator diodes by exceeding their maximum voltage breakdown rating as well as any electronic equipment powered on the alternator output DC bus.((https://diysolarforum.com/threads/alternator-dc-dc-charger-compared-to-buc-converter-whats-the-difference.103819/post-1448377))
+=== approaches ===
+  * use the lead starter batt in the circuit to absorb the spike
+  * charge the bank in a manner unlikely to cause BMS disconnect in the first place
+  * for LFP-dedicated alternator setups
+    * consider a system that uses CANBUS or other networking protocol to inform the alternator's regulator prior to actual BMS shutdown.  The alt shuts down before the BMS so there are no spikes.
+    * install a possibly-sacrificial protection device.  They are typically mounted between the alernator's B+ and B- terminals and short to ground when voltage spikes above a certain level.
+      * The  [[https://amzn.to/45ofEh4|Balmar APM-12]]   apparently uses "A TVS (avalanche diode), Littlefuse brand, unipolar, 15kW peak pulse capability, with a stand-off voltage around 20 or 22 Volts"((https://www.cruisersforum.com/forums/f14/balmar-alternator-protection-module-apm-260911-post3607461.html#post3607461))
+      * the [[https://amzn.to/4ectIwD|Balmar TSP-12 spike protector]] may be the equivalent of the APM-12 without the LED and audio indicators.
+      * the Zap-Stop apparently uses a Motorola #MR2535L TVS diode((the original post called it a Zener but [[https://www.alldatasheet.com/datasheet-pdf/view/5199/MOTOROLA/MR2535L.html|the datasheet for the MR2535L]] says it's TVS)) to short the alternator output((https://www.cruisersforum.com/forums/f14/zap-stop-fact-or-fiction-29442.html#post315900))
+      * Sterling APD12 internals not documented
+      * mikecol recommends a "IN6277A [[https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode|TVS diode]] in series with 5A ATC fuse. The fuse characteristics with the diode clamp makes the full circuit. I don't have data to show it works well, but worth the cheap cost for me. Fuse and diode might not survive after hit, so good to be able to check condition (I have fuse end to alt+ so can measure with voltmeter [easily]"((https://sprinter-source.com/forums/index.php?threads/85448/post-918529))
 ===== common modifications =====
 ==== external regulation ====
-External regulation can provide overtemperature protection (see section on Heat above), and can also cause the alternator to behave like a smart charger with [[electrical:12v:charging|multistage charging]].
+External regulation can provide overtemperature protection (see section on Heat above), current limiting, and can also cause the alternator to behave like a smart charger with [[electrical:12v:charging|multistage charging]].
+In a camper/RV context //an externally-regulated alternator// typically means an **aftermarket external regulator** controlling a **dedicated secondary alternator**.((on boats there is typically one externally-regulated alternator that runs the electrics and charges the house bank.  Modern land vehicles are likely less tolerant of the alternator doing things the ECU did not command.))  Depending on the implementation external regulation might provide:
+  * configurable current levels and/or voltage setpoints
+  * [[electrical:12v:charging|multistage (smart) charging]]
+  * temperature monitoring so maximal current can be extracted without overheating
+  * RPM-based output limits
+  * slowly ramping up current to avoid belt slippage/damage
+  * shutoff when commanded by BMS
+  * CANBUS and other communication
+  * etc
+External regulators include:
+  * Balmar ARS-5 (no external voltage sensing)
+  * Balmar MC-614 (external voltage sensing)
+  * Xantrex Xar (no external voltage sensing)
+  * Wakespeed WS500 (CANBUS)
+  * [[https://theyachtrigger.com/arco-zeus-alternator-regulator/|Arco Zeus]] - new to market
+  * [[https://www.mastervolt.com/products/alpha-pro-mb-charge-regulator1/alpha-pro-iii/|Mastervolt]], more often seen in marine installs
+  * [[https://sterling-power.com/collections/alternator-regulators|Sterling]]
@@ Line 256: / Line 320: @@
 [[https://www.nationsstarteralternator.com/|Nations]] and similar alternator builders make alternators for specialty uses.
-Note that increasing alternator output may require upgrading stock chassis wiring:
+=== big three ===
+Note that increasing alternator output may require upgrading stock chassis wiring.  Often called "the Big Three":
+  - POS from alternator to starter battery
+  - NEG from starter battery to chassis
+  - NEG from chassis to engine block
 >> To run a [high output] alternator, ALL of your engine's factory high current cabling will need to be [sized] to support it, including engine and starting battery grounds, and alternator positive. -- MechEngrSGH((https://www.irv2.com/forums/f87/alternator-burn-out-from-lithium-batteries-558284-8.html#post6428559))
+In addition, the wiring from the starter batt or alternator to the house battery bank may require upsizing to actually get that current where you want it to go.
 ==== Idle optimized ====
@@ Line 303: / Line 379: @@
 [[https://youtu.be/uwrG3gUdDT8?t=725|This behavior surprised Mortons on the Move]], thwarting their alternator-charging plans.
+Known configurations:
   * 397A = 220A + 157A
@@ Line 317: / Line 394: @@
+== GM ==
+Information is limited, but GM factory dual alt setups appear to run the way one would expect in the first place, with load shared between them:
+> The two alternators are controlled over a common circuit from the ECM so they cannot be controlled independently. The ECM cannot shut one down and let the other one run. It is both or neither.((https://www.duramaxforum.com/threads/dual-alternator.934098/post-11906770))
+[[https://www.duramaxforum.com/threads/dual-alternator.934098/post-11906642|This upfitters guide excerpt]] contains additional information.
 ==== DUVAC ====
@@ Line 328: / Line 411: @@
 {As far as I can tell this was a workaround from when many isolators were diode-based so the alternator could not "see" aux battery voltage on the combined circuit((https://www.foreforums.com/index.php?PHPSESSID=bs0n0psbr6rrvd240rv4ijvg1p&topic=33250.msg300875#msg300875)) -- secessus}  See [[https://www.dixie-electric.com/tsb/TSB_704.pdf|this TSB]]. (PDF)
-===== sudden load disconnect =====
-The alternator's voltage regulator responds to demand, increasing and descreasing field strength (and therefore output) as required to hold a given voltage setpoint.
-  * when **large loads are suddenly added** chassis voltage will drop briefly while the regulator responds.
-  * when **large loads are suddenly removed** chassis voltage will spike briefly while the regulator responds.  If the chassis cannot absorb this spike the excess power can be dissipated within the alternator itself and cause damage
-**In theory** if the BMS disconnects charging the resulting spike could damage the alternator.  Team Karst explains it colloquially:
->> Alternator is chugging along, delivering 50 Amps. Suddenly, the output is disconnected. Since the regulator has a time constant, plus the field current can’t collapse instantly, plus stator windings, being coils, therefore inductive, they hold energy, there becomes a high positive voltage at the B+ port to keep the current flowing for a time. This transient energy may manifest itself in switch arcs, and other undesirable voltage excursions.((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-6.html#post3532355))
-This is called a //load dump//; the load is dumped (demand reduced to 0A) and there is nowhere for power in the alternator to go.  As we will see, in normal installs there //are// places for the power in the alternator to go.
-**In practice**:
-  * [a wise user will not be bouncing off the BMS in the first place -- Secessus]
-  * the vast majority of lithium banks charged by alternator do so in combination with the starter battery.  The lead battery will help absorb spikes from the alternator. "Batteries have about 1000F ( farad ) [capacitance] per 150Ah of capacity so they act as very substantial capacitors.  Hence they have enormous ability to absorb spike energy."((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-7.html#post3533042)),((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-8.html#post3533143))
-  * modern alternators have avalanche diodes and fast-acting regulators that can adjust within 100ms.((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292.html#post3527179))
-  * if BMS disconnect  caused alternator damage [[electrical:12v:alternator#lithium-specific_vsr|the Li-Bim]] recommended by Battle Born would quickly eat alts.  It disconnects the bank from alternator every 35 minutes.((15min on, 20mins off))
-The question for the user is:  how much charging current are we talking about, and does the alternator already handle that level of sudden disconnect under normal operation? Secessus provides this example:
-> my van's radiator cooling fans are rated at 65A((https://www.promasterforum.com/threads/180-amp-alternator-with-amp-clamp-on-output.99118/post-792681)) and turn on/off frequently.  My Li charging current is less than that.
-In addition, the speed of the disconnect plays a part:
-> there is a massive difference in the voltage spike from a 5 uS relay disconnect and a 10mS mosfet disconnect((https://www.cruisersforum.com/forums/f166/myth-of-alternator-damage-cause-by-bms-disconnect-258292-7.html#post3532864))
-==== exception:  dedicated secondary alternators ====
-Secondary alternators dedicated to Li charging will not have a starter battery or other loads inline to absorb spikes.  In this case the owner might:
-  * use a CANBUS or similar setup where the BMS can notify the alternator regulator of imminent shutdown ahead of time to allow orderly reduction of power; or
-  * use a protection device, like [[https://www.sterling-power-usa.com
-/SterlingPower12voltalternatorprotectiondevice.aspx|the Sterling Alternator Protection Device]]; ([[https://www.sterling-power-usa.com/library/Sterling%20Power%20Alternator%20Protection%20Device.pdf|manual]]), [[https://balmar.net/product/apm-12/|Balmar APM]], etc.
-  * some maintain a small lead battery in parallel with the Li bank
-Note that the Sterling device uses "a small resistive load" (milliAmps) to control the spike.

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