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Voltage sensing relay and solar charging set up

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#1 Neil


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Posted 18 April 2019 - 07:21 AM

This might be a dumb question and maybe I’m missing something but I have a query around battery bank set up.


Imagine the following:


A house bank and a cranking battery connected with a BEP Digital Voltage Sensing Relay which whenever it senses a charging voltage on EITHER side will operate and parallel up the two banks so as both receive charge. Thus, in normal operation when engine is off (no charging voltage) the two banks are isolated. However, start the engine and a charging voltage from the alternator comes on and the relay operates thus charge is a applied to both banks. All good so far.   


Now imagine the same scenario as above but add into it a solar panel (with regulator) which is connected to the house bank. With the engine off and the sun shining the solar panel is applying a charging voltage to the house bank and as the DVSR works when sensing a charging voltage on EITHER bank it becomes operational, parallels up the two banks and charge is applied to both. Still all good I think.


Now the question: In the second scenario (solar charging, relay applying charge to both banks) what happens if we put a large load on the house bank (ie. drawing a greater current than the solar panel/regulator is charging with)?  



  1. The voltage reading drop on the house bank and the relay go off thus isolating the cranking battery or
  2. Will the load drain both house and cranking battery due to relay operating based on solar charging voltage?


I feel as though I should really know the answer here but I’m a tad confused?

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#2 mattm


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Posted 18 April 2019 - 07:52 AM

The DVSR turns on at 13.2 and off again at 12.7. If you turn something on that draws more than the solar output, it will draw from both batteries until the voltage drops to 12.7. Depending on the size of the banks, the size of the load and the health of you batteries, that could be seconds or hours. The start battery when cut off at 12.7 will still have plenty left.
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