High idle current with Multiplus 12/3000/120-50 in charger mode

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timnarramore asked Dec 4, '20

High idle current with Multiplus 12/3000/120-50 in charger mode

I have a pair of Multiplus inverter chargers 12/3000/120-50 operating in parallel. When I am connected to shore power, the AC loads are isolated, the DC breakers are isolated, and only the batteries are connected in float charging mode, I still see a 230VAC current reading of 1.1A on my shore power ammeter.

This looks like 260W of input power with nothing taking power out. My BMV700 battery monitors say that the batteries are taking less than 0.1A at 13V.

I would expect that a lightly loaded charger would take maybe 10 or 20W of idle power, but the readings suggest that 260W is going somewhere. Both Multiplus chargers are running cold, so I don’t think they are really taking 260W and turning it into heat.
Could something be fooling the ammeter into misreading? Maybe crest factor or power factor?

MultiPlus Quattro Inverter Charger

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Trina commented · Dec 06, 2020 at 12:32 AM

Three logical answers

1. Victron has mistated loads-off draws on those inverters

2. Victron hasn't -and your units have an issue (or something downstream)

3. You have a short somewhere drawing significant amps

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Answer 1 · 2020-12-05T06:48:07Z

Paul B answered · Dec 05, 2020 at 06:48 AM

If you look at the specs for the units you will see that they always have a power overhead of about 20watts each in normal mode and if in search mode then around 10 watts . 260 watts is high.

you may have a Isolation transformer connected in the boats input line and this will have a overhead. so check what else is between the input point and the inverters.

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Answer 2 · 2020-12-05T08:28:05Z

timnarramore answered · Dec 05, 2020 at 08:28 AM

Hi, thanks for that idea. The shore power input goes to the mains input switch (shore power or generator), with a voltmeter and ammeter, then straight to the inverters through a circuit breaker.

The ammeter does correctly read for resistive loads on the inverter output such as kettle, toaster, but my suspicion is that the ammeter is misreading the inverters idle loads. If each inverter was really taking 130W continuously, they would be getting very warm, and they are not.

I ran the power input and output cabling myself, so I know for sure I have isolated all loads when I see the 1.1A reading...

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Trina commented · Dec 06, 2020 at 12:12 AM

Oh lord! The hidden drains on a boat!

I personally would unplug every single circuit until you find that drain or short. It is significant so if you are methodical and work slowly it should not take too long

On a side note if you have.any way of killing all power OUT of your system to loads start there. I once had a bad (corroded) starter solenoid relay that had developed a ground and slowly drained things because it had just enough condensation in it to cause a drain but not enough to turn the motor! The darn thing would work just fine once I engaged the key and gave it full amps! Took forever to find as I never suspected it could be there.

Condensation might be your culprit somewhere in the most odd unexpected areas. Also check any radios or nav gear etc.

...or that tiny bilge pump just out of hearing range... keeping the boat afloat because your prop shaft leaks!

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Answer 3 · 2020-12-05T08:31:59Z

timnarramore answered · Dec 05, 2020 at 08:31 AM

One further data point, if I measure the idle load in inverter mode from the 12V battery bank, it is almost exactly 20W per inverter as per the spec sheet.

This high power reading is when the inverter is operating in charger mode, either forced to charger mode, or automatic with mains input.

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Answer 4 · 2020-12-06T15:52:32Z

timnarramore answered · Dec 06, 2020 at 03:52 PM

Ok, finally I understand the problem.

The inverter actually starts from first mains application with a sensible current of about 0.1A per inverter. After a few seconds you hear the clunk of a big relay or contactor in each inverter, and the current jumps up to 0.55er inverter at 235V.

Measuring the current with a true rms meter actually shows a more reasonable power level of 25-30W per inverter. So the problem is a power factor phase shift at low loads, probably caused by the big inductor which is the contactor coil inside each inverter.

The shore power ammeter in the boat panel is just an ammeter with no idea of phase shift, so reports what looks like 130W of power per inverter!

The good news here is that my shore power metering is true RMS, so I am only paying for the much lower real power consumption, not the apparent power consumption.

Thanks

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Daniël Boekel (Victron Energy Staff) ♦♦ commented · Dec 06, 2020 at 11:37 PM

Hi @Timnarramore

I think the source of that is the transformers in the units.

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timnarramore Daniël Boekel (Victron Energy Staff) ♦♦ commented · Dec 07, 2020 at 05:59 AM

Thank you, yes those are even bigger inductors!

Several bits of good news :

1) The inverters are not faulty

2) I’m only paying for the real power consumption

3) I can stop investigating current ‘losses’ and go sailing!

Thanks again,

Tim

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