question

steve-atwell avatar image
steve-atwell asked

MultiPlus II disconnects from generator on high inrush

I'm running into an issue with my MultiPlus II 48V 3000VA 120V where it disconnects from my small inverter generator when using a high-inrush device.

Configuration

This is off-grid, and I've got a small inverter generator (2kW peak, 1600W constant) that I use intermittently to keep the batteries charged. AC input current limit set to 13.3A (1600W) and charge current limit set to 23A (~1300W). Dynamic current limiter is enabled. UPS function is enabled. Power Assisst is enabled with default boost factor 2. Works great for most stuff.

I have a professional photography studio strobe power pack that I want to run off the MultiPlus II. This is basically a big capacitor. Take a picture and it dumps the power from the capacitor into the strobes and then recharges the capacitor for 1 to 2 seconds. So it's got high in-rush current on each recycle. It's nominally a 15A device, although it might spike higher. Works great on just the inverter when the generator is off. The generator by itself can also power the strobe power pack mostly okay. (There is voltage sag on recycle, but it never trips the generator overload protect.)

The Problem

I get frequent AC input disconnects when running the generator for battery charging while also using the strobe. The generator overload protection never trips, but the MultiPlus II disconnects from AC input. I'm pretty sure the generator voltage is dropping below min threshold due to sudden demand. After disconnect, voltage comes back up and the MultiPlus II syncs again. So I don't have to do anything and I never lose output AC. But it's an annoyance that I'd like to correct if possible.

A bigger generator isn't really feasible. I considered trying a soft start device for the power pack, but I don't think it will work. (The power pack has a baseline 300-400W power draw even when not recycling, because it's also powering modeling lights that are on constantly. My understanding is that this would prevent the soft start from being effective.)

The Question

Are there settings on the MultiPlus II that I could try? Would adjusting the boost factor make power assist more responsive to these large demand spikes? What would be a safe range of boost factor values to try?

I may also try turning down the input current limit and/or the battery charge current a bit to leave more generator power headroom. But I don't want to significantly increase the generator time needed to recharge my batteries.

Multiplus-IIGeneratorpowerassist
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3 Answers
netrange avatar image
netrange answered ·

Try the Option "Weak AC input" in the "Charger Menu.

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steve-atwell avatar image steve-atwell commented ·
I'll give this a try the next opportunity I get to test. Although it sounds like this is more about dealing with a distorted waveform that causes difficulty syncing, which I suspect is not a problem with an inverter generator. The MultiPlus Generator FAQ makes it sound like it may sync faster after disconnect, but possibly at the expense of worse charge efficiency.
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Kevin Windrem avatar image
Kevin Windrem answered ·

Try also turning UPS off. This slows the transition to inverter so you may see more of a drop in output voltage.

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steve-atwell avatar image steve-atwell commented ·
I should have mentioned, I did try turning UPS off, and it didn't resolve the disconnect issue. And low voltage threshold was already at the minimum value of 90V.
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klim8skeptic avatar image
klim8skeptic answered ·

Are you sure that the multi is disconnecting from the genset?

I have a tiny inverter genset for charging and when the fridge cuts in, the multi takes over the surge load via power assist. The genset is unloaded and revs up a bit, buts takes over loads/charging within 5-10 seconds.

Cut your ac in limit to 10a and try again?


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steve-atwell avatar image steve-atwell commented ·
I am sure it's disconnecting. The mains light goes out, the generator slows down to idle, and I can see the resync progress in VictronConnect.
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