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--- electrical:12v:alternator_charging_hvd [2019/04/10 15:12]
frater_secessus [how it works]
+++ electrical:12v:alternator_charging_hvd [2022/07/31 00:33] (current)
frater_secessus [solid state isolators]
@@ Line 3: / Line 3: @@
 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 could get overcharged by higher voltages 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 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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