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Is it possible to connect my solar charge controller (MPPT) to my load distribution bus? This would mean that the cables from the bus to the battery would transfer both the load current and the charge current. Anything to consider if possible?

It is a 12 volt system with appropiately sized cables. I am trying to avoid a double cable run for two meters.

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  • \$\begingroup\$ Can you draw a diagram to make sure we understand correctly? If I understand what you are asking, it should be fine. If anything, it will just reduce the current in the cables, since the charge current and load current travel in opposite directions. \$\endgroup\$ – mkeith Jul 15 '17 at 20:50
  • \$\begingroup\$ Are you trying to save $10 in wire or make the system most economical and optimal efficiency for power transfer. Or just figure out how to connect a MPPT in series when you on short cable. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jul 16 '17 at 0:24
  • \$\begingroup\$ Short on cable, will wait til monday when the stores open as per Kevin Reids warnings. \$\endgroup\$ – user156009 Jul 16 '17 at 14:05
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Risks of this configuration:

  • An open circuit on the the bus between the battery and charge controller will leave the charge controller connected to the loads directly with no battery. What happens then depends on the loads and the behavior of the charge controller; hopefully the controller is smart enough to decide the battery is missing/unsafe to charge.

  • The loads on the bus between the battery and charge controller will experience whatever variations in voltage, or noise, results from the charge controller's behavior and the voltage drop, capacitance, and inductance of the wiring.

Disadvantages of this configuration:

  • If the charge controller has a low-voltage cutout function for its load terminals (for when the load is being supplied from the battery, not the solar panels), that will not function.

  • The charge controller's charging current limit will be applied to current to the load as well as to the battery, so a load that exceeds that current will cause the battery to discharge even if plenty of solar power is available.

To summarize, none of this is guaranteed to be a problem. But saving a bit of copper and possibly overall voltage drop doesn't seem worth it.

(Disclaimer: This answer is theoretical. I have only very little experience in solar power systems and none big enough to observe these effects.)

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  • \$\begingroup\$ Thanks for a thourough answer! Good to know for the future. The chandler sold me a 4m roll of cable with only 3.2m on, hence my dilemma. I'll just wait til monday and get the right length. \$\endgroup\$ – user156009 Jul 15 '17 at 21:20

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