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frankvw avatar image
frankvw asked

Why does my Multiplus switch to battery at a slight undervoltage?

I have just bought a Multiplus 24|800|16 charger/inverter. It works like a dream, except for one thing I don't understand.

Our mains voltage is between 230 and235V (varying depending on the time of day). During long power outages I run on a 2.2kVA generator that produces 230V to light loads, but when I add two fridge/freezers (about 300W each) the generator voltage drops to between 225 and 226V RMS. Which is normal.

However, at 225V the Multiplus appears to switch to inverter operation rather than continue to supply loads from the main voltage. There's a relay click and the LED changes from "Charger" (yellow) to "Inverter" (green). The output voltage supplied to the load is 230V at that point. The alarm LED remains off at all times.

However, according to the specs that came with the unit the input voltage range should be 180-265V. So why does the unit switch to inverter operation at 225V?

I am using the unit with the default factory settings (DIP switches are all off) and I don't have a VE bus interface or remote; the unit has been installed straight out-of-the-box without any programming or setting-up whatsoever.

All voltages have been measured with a Fluke true RMS meter which I have consistently found to be reliable.

What's going on here? Any ideas? All feedback would be appreciated!

Generator
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3 Answers
kevgermany avatar image
kevgermany answered ·

It's working as designed.

Are the extra loads on the generator or the multi? Might be best to have them on the output side of the multi.

The best solution is to adjust the AC input settings, but I don't think you can do that with what you have

Cheapest way is to get a mk3 to USB adapter and install VE Config or Victron connect on your pc. Use the cable and software to configure.

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Alexandra avatar image Alexandra ♦ commented ·

Likely it is not voltage but frequency related.


Generators usually have fluctuation or instability, unless they have really good regulation. Can be lower or higher than 50hz depends on tuning as well.

Ultimately to know what is going on a GX or an mk3.

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frankvw avatar image frankvw Alexandra ♦ commented ·

> It's working as designed.

I'm not saying it isn't, I'm just trying to understand what's happening. :-)

Indeed, I am unable to adjust the input voltage settings without getting a VE-bus to USB adaptor. But since according to the specs the acceptable voltage range starts at 180V I'm not sure that would solve the problem anyway since the input voltage is 225V when the Multiplus switches to inverter mode.

However, Alexandra's comment that it is most likely frequency related is a good point. I had not considered that. I just checked the specs and the acceptable frequency range is 45-65Hz, presumably divided in 45-55Hz and 55-65Hz when the Multiplus is set to 50 or 60Hz operation, respectively. And that's a much narrower range.

I'm going to break out the old frequency counter and have a look, but I'm fairly sure Alexandra nailed it.

Tnx!!

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Trevor Bird avatar image
Trevor Bird answered ·

@frankvw the voltage is one factor to be taken into account but the frequency and distortion of the generator output is another. If the generator frequency drops too far or the distortion is too great the MP will switch to inverter mode to try to maintain an output frequency and purity which is within spec for the inverter. Your fluke meter may be able to tell you the frequency of the generator while under load which may shine some light on the issue.

The "UPS" function should be disabled if the generator is causing the unit to switch to inverter.

I am not sure quite how to do that without access to VE Configure software. Maybe it can done via the dipswitches but I have not done that before.

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frankvw avatar image frankvw commented ·
I'm digging out my frequency counter (my Fluke is a model doesn't do frequency) to have a look but I'm pretty sure it's frequency related (as Alexandra already commented). I was considering voltage only. My bad. :-)


Distortion shouldn't be much of an issue at this load, but you never know so I'll hook up an oscilloscope at some point to see what's really going on there.


Tnx!


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JohnC avatar image
JohnC answered ·

Hi @frankvw

Check this link.. https://www.victronenergy.com/live/multiplus_faq

There's many things that may impinge. And some are dynamic, like a spike from a switching load that may not even show on your test kit. Small gensets (especially cheap ones) often need adjustments to the Multi's settings to enable them. You may need to invest in a MK3 adaptor to fix this.

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