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--- electrical:12v:b2b [2021/06/18 18:47]
frater_secessus [limitations]
+++ electrical:12v:b2b [2021/06/18 18:57]
frater_secessus [gotchas]
@@ Line 179: / Line 179: @@
 [[http://www.bogartengineering.com/products/solar-charger.html|Bogart's SC-2030]] can work as a DC-DC charger as well as a PWM charge controller.
+===== gotchas =====
+Observe voltage input maximums on units with built-in solar charge controllers.
+Voltage-sensing units((triggered by elevated chassis voltage)) can misbehave when an undersized starter battery charger/maintainer is attached.  For this example we assume a 10A maintainer and a 20A DC-DC charger.
+  - starter battery voltage rises from 10A maintainer charging...
+  - triggering the DC-DC charger...
+  - which begins pulling up to 20A from the chassis
+  - pulling down the starter battery since the 10A maintainer cannot keep up
+  - starter battery voltage drops far enough the DC-DC turns off
+  - repeat forever
+The workaround is to either charge the house battery first or to buy a big enough starter battery maintainer to support both the starter battery and DC-DC charger loads.
 ===== further reading =====
 [[https://diysolarforum.com/threads/dc-dc-charger-b2b-options-and-general-discussion.17211/|DC-DC charger (B2B) options and general discussion]] on DIY Solar Power Forum.

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