PV/Inverter Simultaneity Note

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PV/Inverter Simultaneity Note

Post by RealityRipple »

The Outback Integration Guide from SimpliPhi mentions the possibility of overcharging if both PV and Inverter charging occur at the same time on a smaller battery bank (bottom of Page 11), and I thought it'd be nice to have some clarity on this point.

If I recall correctly from the documentation, the FLEXmax charge controllers can kind of notice if the batteries are being charged from another input, so they should automatically snooze if grid or generator input starts charging, correct? Lithium voltages make the detectable changes more subtle, so I'm a bit concerned about the possibility.

Does the warning only apply to less "intelligent" (and possibly third-party) charge controllers and users who set more complicated rulesets or force controller states manually, or is there reason for concern with standard setups? Is it a good idea to disable the charge controllers manually when starting the generator when you know there's PV input?
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Re: PV/Inverter Simultaneity Note

Post by raysun »

The Charge Controllers are essentially autonomous units that are triggered by battery voltage and their programmed set points. Past that, the individual controllers are only aware of their individual contribution to battery charging, and cannot sense other sources.

The "failsafe" in the chargers is to manually set their Maximum Current outputs such that all sources running at full capacity do not exceed the charging current limit of the battery. I'm not sure the MX series does that.

Four MX60 controllers have a theoretical maximum charging current of 240A, so in certain conditions can overcharge a small battery.

Manually disabling the charge controllers while charging on generator is one approach that could work. It does present a built-in operational risk of course.

The later FM charge controllers, paired with a Mate and FNDC provide automatic, dynamic charge current limiting. It works well in the scenario described.

Note that the SimpliPhi warranty has fairly stringent language regarding battery sizing vis-a-vis charger and inverter ratings.
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