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helmut51 asked

RS Smart Solar: Shut-down and restart behavior

I am planning an (completely) off-grid solar EV charger for my garage. I am new in solar systems, but I have a background in electrical engineering. Just a few questions concerning the shut-down and restart of the RS Smart Solar (and in general solar inverters):

  1. Shut-down due to DC input voltage below low battery shutdown level in practical terms means that it shuts down during night? [4.4.2. in the manual]
  2. Could it happen that on a bad rainy day the inverter is constantly switching on and off, because DC input is always somewhere between shutdown and restart level?
  3. What is actually meant by "shut-down", as the MPPT is still working and loading the battery, if possible?
  4. If the battery is full and the inverter is shut-down (during night) I could not supply any AC load?
  5. The inverter restarts based on the charge detect level, but also on the (re)start voltage (as implied by the paragraph on external MPPTs)? [in the technical specification the charge detect level is not mentioned, and the restart voltage is called start-up voltage (if that is the same)]

Sorry for the multiple questions, but I feel they cover the same topic.

smart solar set-up helpshutdown
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2 Answers
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Mike Dorsett answered ·

Based on what I know about how Victron MPPT's work -

1) the MPPT will shut down if the input voltage is <1V above the battery voltage - whatever the battery voltage currently is.

2) No. Even on a very dark day,the open circuit voltage of the panels will be high enough to keep the MPPT in operating area. Thus if it's very dim, the output voltage will be at least 80% of the VOc, but the current drawn by the MPPT will be reduced considerably.

3) The MPPT goes to sleep when the input voltage is <1v above battery, and wakes when the voltage is >5V above battery. In sleep mode, the step down converter is off, and current draw is minimal - just the ADC's for battery voltage and PV voltage.

4) The MPPT charger and the AC inverter functions are separate. The AC inverter will operate as long as the battery voltage is sufficient.

I think that 5 is covered by the above.

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helmut51 answered ·

Thank you very much, this makes more sense to me than the manual..;-)

The problem starts with the fact, that the Smart Solar is called inverter, but it has three main components, MPPT, charger, and inverter. Also, there are two adjustable thresholds, the low battery shutdown voltage (default 37.2 V), and the low battery restart voltage (default 43.6 V). They also speak of charge level being a voltage. I assume this is the restart voltage.

Then, there are two different scenarios (which I did not get). For both the shutdown voltage is used. a) if DC input below shutdown, then the MPPT is shut, but the manual says "inverter" b) if the battery is below shutdown, then the inverter is shut, so no more AC output, but MPPT is running. Both makes sense to me now.

In both cases the restart voltage determines restart of MPPT a) or inverter b). The only thing I still do not understand is the start-up voltage of the MPPT (120 V), which seems to be another (re)start threshold.


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