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Voltage Difference

Schtevie

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Nov 17, 2020
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I have a Victron SmartSolar MPPT 100V 30 amp charge controller running at 12 volts hooked to two 4S LifePo4 battery banks wired in parallel. When I take the voltage at the point where the two LifePo4 batteries are tied together for the parallel connection, the voltage is 14.1. If I then take a voltage reading on the battery input connectors on the charge controller, it's shows 14.5. Any ideas why this is happening?
 
Losing 0.4v at reasonable current levels seems like a corroded connection, so trace down what connection is doing this.
It's unlikely that four connections are losing 0.1v each.
 
Losing 0.4v at reasonable current levels seems like a corroded connection, so trace down what connection is doing this.
It's unlikely that four connections are losing 0.1v each.
Thanks for the idea, but I'm not exactly sure where to look for a corroded connection? Both of my 4S battery banks tie together at a metal point for their positive and negative. If I take a voltage reading at that metal point, the reading is 14.1. From that metal point, there is a positive and negative wire running directly to the charge controller. The voltage at the controller is 14.5. The battery voltage is actually going up between the metal parallel connection point and the controller. From 14.1 to 14.5.
 
Is your charge controller charging? If so it would show higher voltage.
Are you charging at 14.6 volts?
 
Is your charge controller charging? If so it would show higher voltage.
Are you charging at 14.6 volts?
Yes, it is charging. When this voltage discrepancy happens, it's in the 'absorption' state trying to hit or maintain 14.6.
 
use a multi-meter across the connections while current is moving. Compare voltage readings, that is voltage drop. Current should flow from controller to the battery. Voltage should be higher at the controller and then voltage drop has it lower at the battery. bad connections, long cables, too small of cables lots and lots of reasons
 
use a multi-meter across the connections while current is moving. Compare voltage readings, that is voltage drop. Current should flow from controller to the battery. Voltage should be higher at the controller and then voltage drop has it lower at the battery. bad connections, long cables, too small of cables lots and lots of reasons
Makes sense. Thanks so much!
 
You have a 3.5% loss between the SCC and battery.

I have a .4% loss on a 6’ one way run using 6 AWG from my SCC to battery busbar.

The set screws in the SCC can loosen around the wires over time. It may be as simple as that. It could also be your using 14 AWG wire and could go thicker.
 
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