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muddy1 avatar image
muddy1 asked

Multiplus II - DC current is wrong.

I have a Multiplus II 48v 5KVA. When running but with the output isolated, Venus reports 53.53v and -0.7a, giving 37.47W standby power.

Clearly greater than the specified 21w standby power.

The reported current is incorrect, a clip on meter gives 397mA which would give the correct 21W standby power. It is disappointing to find such a large discrepancy on a quality product.

This causes problems with negative DC currents which have been discussed on numerous posts.

Is there any way to zero the current meter in this unit ?

Multiplus-II
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3 Answers
wkirby avatar image
wkirby answered ·

Remember that the ADC in this device is expected to measure over 180A (9KW peak). It's probably a 10bit ADC, so it has a resolution of about 175mA. All ADC's, despite filtering and smoothing have an ammount of jitter and an error of 1 or 2 bits on a scale of 0 to 1024 is quite acceptable.
You are measuring right down in the noise floor and observing an error of less than 0.1% over the entire range up to 180A. This device which is primarily designed to convert vast ammounts of power (which inherently generates a lot of electrical noise) isn't doing too bad at measuring current.
A unit of this size is normally measuring tens of Amps so the resolution of a few hudred milliamps is in the noise and perfectly reasonable for its intended use.

Think of it like a car speedometer which goes from 0 to 200Km/h. It can't really measure a speed of 0.1Km/h and increments of 0.1Km/h are indiscernable and not required either.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

The measurement electronic inside the MultiPlus is not designed to be super accurate.

There is not much you can do about it.

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lex2k0 avatar image
lex2k0 answered ·

Thanks a lot for that answer, that the Multiplus can't be that accurate in low usage situation. However, is there maybe a chance to somehow use an external DC sensor to make it more accurate? Maybe to use a single Shunt somehow for the Multiplus? In my situation it is a Quattro II.

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