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--- electrical:12v:alternator_charging_hvd [2017/10/11 21:24]
frater_secessus [solenoids and relays] took out isolator sectoin
+++ electrical:12v:alternator_charging_hvd [2022/07/31 04:33] (current)
frater_secessus [solid state isolators]
@@ Line 1: / Line 1: @@
 ====== Disconnecting alternator charging at a voltage setpoint ======
-There are scenarios where one might want to prevent an isolator from combining the house and chassis 12v systems:
+There are scenarios where one might want to prevent a [[electrical:12v:alternator|battery isolator]] from combining the house and chassis 12v systems:
-  - the house battery needs less voltage than lead-acid (lithium, for example)
+  - the house battery might be a chemistry that could get overcharged by the alternator (lithium, for example)
+  - the house battery might have a resting voltage high enough to trigger the house side of a dual-sensing relay (LiFePO4)
   - the combined circuit can feed higher-than-optimal voltages back from solar charge controller to the chassis' electronics.
+  - a [[electrical:12v:b2b|b2b charger]] in parallel with an [[electrical:12v:alternator|isolator]] could have the same backfeeding result
@@ Line 11: / Line 13: @@
 [[electrical:12v:alternator|Isolator/relays/solenoids]], etc, use mechanical or electrical means to combine the chassis and house 12v systems.   These mechanical or electrical means will require a small amount power to operate.((latching relays excepted))
-If the device's own power source is disconnected it will turn off and 12v systems will be separate again.((again, latching relays excepted))  Using a High Voltage Disconnect to kill power to the device will stop the alternator from charging the house battery at a given voltage setpoint.
+If the device's own power source is disconnected it will turn off and 12v systems will be separate again.((again, latching relays excepted))  Using a [[electrical:12v:hvd|High Voltage Disconnect]] to kill power to the device will stop the alternator from charging the house battery at a given voltage setpoint.
 Shutting down the device will require different approaches, depending on where it gets the power to operate itself.
@@ Line 30: / Line 32: @@
 ===== solid state isolators =====
-Some solid state isolators have a trigger or exciter input;  drive with HVD as with solenoids and relays.
+It is unlikely you will need an HVD with a diode-based isolators because:
+   - the isolator can't backfeed voltage back to the starter battery, and
+   - voltage drops up to 1v in the diodes when passing alternator --> isolator --> house bank
+But it is theoretically possible alternator voltage is so high that even with the drop you might want an HVD.  Some solid state isolators have a trigger or exciter input;  control with HVD as with solenoids and relays.
 Three lug isolators without exciter input might not be usable with HVD.

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