question

ralf-ct avatar image
ralf-ct asked

48V 3kVA MPII briefly switching to inverter while on AC - South Africa

Lately we have been experiencing the following:

  • Inverter buzzing with hairdryer on when on AC, even on low setting; sometimes also intermittently when the fridge is running;
  • While on AC the inverter briefly switches to DC for +-6s before switching back to AC. There is no AC failure as stove clock and prepaid meter remain on. It happened 3-4 times the past week.

What would cause the above? An inverter or incoming power issue?

Many thanks in advance.


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2 Answers
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ejrossouw answered ·

@Ralf_CT If you search the forum for hairdryer, you will find some insightful posts. As for briefly switching to inverter, it could be a grid voltage dip, however VRM may not capture it given the min 1min logging interval. I would not discount the possibility of a bad connection (loose) either.

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ralf-ct avatar image ralf-ct commented ·
Would the 2,200W hairdryer (HD) damage the inverter? The inverter also buzzes with the HD on the lowest setting. At the time of using the HD our loads are roughly 450W, so we aren't exceeding the inverter's limit. I haven't checked if the inverter buzzes if the HD is on full load, or if set to cold. We only use the HD (my wife does, I no longer need one) while getting power from the grid.
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nickdb avatar image nickdb ♦♦ ralf-ct commented ·
The issue tends to appear (hairdryers) on lower settings, not full power, and it is caused by pulling the power it needs through a partial cycle. Pulling 1000W for example, though a whole cycle is fine for a low frequency inverter, but when you try pull that power through part of the cycle is is more than the inverter can provide.

This is unrelated to the inverter dropping grid - it would trigger overloads and the inverter sounds like it wants to leap off the wall, it does way more than just buzz, so you're mixing two unrelated events.

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ralf-ct avatar image ralf-ct nickdb ♦♦ commented ·
I did a test and found the following: the inverter will buzz if the hairdryer is running on speeds 1 and 2, but not on 3, or if I press 'cold'. I suspect it may be due to circuitry reducing the power fed to the element at low fan speeds (to prevent it from overheating and triggering the thermal cut-out).
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nickdb answered ·

Brief grid rejection is fairly normal in SA, related to grid quality. You might see the cause logged in the NS protection log if you connect via a mk3 to the inverter.


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