Honda eu2000i 12v outlet for fan?

road-runner wrote:
This explanation is not correct. The DC output is driven from its own winding on the eu2000i's stator and has no electrical interaction with the windings that drive the 120 volt inverter.

Not withstanding the readings you have from the scope... the above statement is tough to make.

Certainly (as shown in the Honda schematic) the DC output is derived from a separate sub-winding.
Being separate that they are doesn't mean that one winding has no influence over the other. Actually there are four windings. . . counting the WYE connected setup for the 120 VAC as one winding.

Overload on either 12VDC or 120VAC will set off an alarm.

Warning light (red) will come on and about 4 sec the green warning light will go off but engine will keep running.
This interaction is not shown in details for end user to analyze the dynamics involved and the parameters associated how these two interact. It's all in the spark electronic module.
Unless a person has the training/skill in tracing how the various electronic components function in relation to each other.

Also, the excitation winding and other windings are in the same ferro-resonant core where the output before the bridge rectifier is connected. Nuances in the magnetic flux in the core (caused by overload) is sensed in the exciter winding and is then reflected in the DC winding.

I agree that the DC is unregulated and its output is much higher not beneficial to the fan. It will run the fan OK but in a short life span. Filtering an already high voltage will not help a bit--in fact with the wrong capacitance will even increase the output.

The DC output is meant to be higher by design to push electrons to the discharged battery.
Running at par or lower voltage will cause the charger winding to act like a load thereby making the battery condition worse.