question

paul-berberian avatar image
paul-berberian asked

Autotransformer imbalance of amps between L1 and L2 post new Cerbo install

I have two stacked 8kw Quattros feeding a 100A autotransformer which then feeds my panel. My system is monitored with a Cerbo GX. My Cerbo GX failed and I needed to replace it. After the replacement I noticed a difference in output in the AT between L1 and L2. I'm noticing a 10 amp difference between legs. This was not the case before the failure.

Is the difference between legs normal and it is just how my panel is balanced or is there a configuration issue that was missed on the Cerbo replacement - there seems to be no ability to control the AT from the Cerbo. Does the AT balance L1 and L2 evenly or is 10 amps difference permissible?

The issue persists through the Quattros as well - if I limit the grid current to 40 amps the Quattros will pull 46A on one leg and 37A on the other. It all feels related.

cerbo gxAutotransformer
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Mike Dorsett avatar image
Mike Dorsett answered ·

1) There is nothing to 'control' for an auto transformer, thus there is no ability to control it from the Cerbo.

2) a 10% curent imbalance between the legs of an autotransformer is quite ok, you could in fact draw the 100A from 1 leg and no current on the other. Balancing is entirely down to your panel loading.

A sketch of your system ac connection would be useful in determining if any 'balancing' is done by the transformer.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·
A further detail to Mike's post, it is normal for the Autotransformer to not be completely balanced in voltage due to variations the tap wiring, which will also lead to variations in current.


All normal and nothing to worry about (nor is there anything that can be done about it).

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