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Forum Index : Electronics : Inverter negative input current

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davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 02:08pm 25 Sep 2017
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I have a measurement shunt between the battery and the inverter. At standby levels, ie about 1Amp (26 Volt system) the rather distorted waveform shows that current apparently is flowing back into the battery over about 1/4 of the overall time.

As soon as I put on a small load, ie 2-3Amps the waveform shifts upwards to be completely positive.

As the measurement system only handles positive currents I get a source of error at low loads and of course that is where the system sits for the largest percentage of the time!

Does this sound normal?

Edited by davef 2017-09-27
 
Gizmo

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Joined: 05/06/2004
Location: Australia
Posts: 5078
Posted: 02:20pm 25 Sep 2017
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Could be. Circuits designed to measure 100 or so amps can struggle to give a accurate reading at the bottom of the scale.

Glenn
The best time to plant a tree was twenty years ago, the second best time is right now.
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davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 04:27pm 25 Sep 2017
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15bits of effective ADC resolution and low level DC loads are measured accurately. The ADC can only measure positive currents, the new model will be able to measure currents in both directions.
 
Madness

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Joined: 08/10/2011
Location: Australia
Posts: 2498
Posted: 05:54pm 25 Sep 2017
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There are Hall Effect Current Sensors that are bidirectional and are ideal for this application.
There are only 10 types of people in the world: those who understand binary, and those who don't.
 
davef
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Joined: 14/05/2006
Location: New Zealand
Posts: 499
Posted: 08:11pm 25 Sep 2017
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Thanks for suggested enhancement. It is an existing product that has software so realistically no opportunity to modify.

If some current flowing back into the battery is normal I will give up trying to incorporate this measurement error into my datalogging.
 
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