Orion XS at Argofet

DIY
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9

I’ve thought about this setup since it is nearly identical to mine (in my case, the AGM charger was turned off). I believe I have narrowed down the issue that causes the voltage spikes. I have not tested this reasoning, but it is the only explanation that makes sense to me—both for my setup and for yours. Feel free to disagree or point out errors in my reasoning; I would appreciate it. See also: What is wrong with this Agrofet and Orion-Tr Smart installation?

Your setup is likely to cause voltage spikes at the alternator and the batteries. An Agrofet should not be used with an Orion charger when the damping battery is behind an Agrofet output. Here’s why:

Remember that the Agrofet will close (allow current to flow) when the voltage at the input is slightly higher than the voltage at an output. The sequence that causes spikes is as follows (example in a 24V system):

  • The alternator is turned on and generates a steady 28V. This is higher than the output voltage at both the battery and the Orion. The Agrofet allows current to flow to both outputs.
  • The battery voltage rises to 28V as expected.
  • After a while—depending on your Orion configuration—the Orion starts charging. This causes an immediate drop in voltage that can be measured at the alternator.
  • The battery is slower to lower its voltage (it’s a battery!), so for a brief moment the output side of the Agrofet (to the battery) has a higher voltage than the input of the Agrofet. The Agrofet opens this circuit and disconnects the battery completely.
  • Now the damping battery is no longer connected to the running alternator. This causes the voltage to fluctuate. The Orion, if it is cycling on and off, compounds the problem (for example, due to voltage lock).
  • When the alternator voltage rises above the battery voltage (say it spikes to 30V), the Agrofet allows current to flow to the battery. This raises the battery voltage, stabilizes the alternator at 28V, and then immediately disconnects the battery again (since the battery is now sitting around 30V, higher than the alternator’s stable voltage).
  • This cycle—lasting only a few milliseconds—repeats over and over. In my case, I observed brief voltages as high as 40V.